Electrophysiologic Study

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Electrophysiologic Study

  1. 1. Electrophysiologic Study Pacing Methods & EP Testing1
  2. 2. Pacing Methods: Programmed Electrical Stimulation (PES) PES is a pacing technique using an intermittent or continuous introduction of an electrical current to the intracardiac surface through an electrode catheter. Cells near the electrodes depolarize and begin a wave of depolarization that propagates throughout the heart. This facilitates the evaluation of cardiac refractory periods, conduction dynamics, automaticity and arrhythmic mechanisms.2
  3. 3. Unipolar versus Bipolar Pacing Thresholds Pacing Threshold Strength-Interval curve Unipolar Cathodal _ Unipolar Anodal + Bipolar3 + _
  4. 4. Programmed Electrical Stimulation  PES consists of three types of pacing: – Incremental (burst) – Decremental (ramp) – Extrastimulus  PES is used to measure and evaluate …. – Refractory periods – Conduction properties – Pattern of myocardial activation – Tachycardia Characteristics  Initiation  Termination  Differentiation4
  5. 5. Definitions and Types of PES  Pacing Drive Train – a series of 6-10 fixed paced stimuli at a constant rate that are separated by a pause. Referred to as “S1s” (stimulus cycle length #1) . Sensed S1 S1 S1 S1 S1 S1 S1 S1S2 S3 S4 DRIVETRAIN5
  6. 6. Definitions and Types of PES Incremental Pacing - is pacing the heart at a fixed rate. The rate is increased (pacing interval decreased) with each set of beats. S1-S1 = 400 S1-S1 = 390 S1-S1 = 380 S1-S1 = 3706
  7. 7. Definitions and Types of PES Decremental Pacing – pacing at a progressively increasing heart rate by decreasing the amount of time between each paced beat. Used primarily to induce or terminate tachycardias. It is also called “ramp” pacing. Click to start Sns Sns Sns Sns S 1 S 1 S 1 S 1 S 1 Sns Sns Sns7 TACHY.SENSE RAMP
  8. 8. Definitions and Types of PES  Exrastimulus Pacing Sensed S1 S1 S1 S1 S1 S1 S1 S1S2For the standard EP studyto test the refractoryperiods, one extrastimulus Single extras(S2) will be used. If asecond extrastimulus is DRIVETRAINused, it is usually forarrhythmia induction and is Sensed S1 S1 S1 S1 S1 S1 S1 S1S2 S 3called “S3”. Up to 3 (S4)extrastimuli (S2, S3, S4)can be given in a standard Double extrasEPS. Any more than 3extrastimuli would induce a DRIVETRAINnon-clinical arrhythmia.That is, it could induce an Sensed S1 S1 S1 S1 S1 S1 S1 S1S2 S3 S4arrhythmia in a normalsubject. Triple extras DRIVETRAIN 8
  9. 9. Common Extrastimulus Induction Protocol Type of Basic Single extrastimuli Double extrastimuli (ms) Triple extrastimuli (ms)arrhythmia cycle (ms) length (ms) S1-S1 S1-S1 S1-S2 S1-S1 S1-S2 S2-S3 S1-S1 S1-S2 S2-S3 S3-S4 Atrial 600, 400 600, 400 600- 200 or 600, 400 600-200 or 600-200 or 600, 400 600-200 or 600-200 or 600-200 or ERP in ERP in ERP in ERP in ERP in ERP in 10ms 10ms 10ms 10ms 10ms 10ms decrements decrements decrements decrements decrements decrementsVentricular 600, 400 600, 400 ERP + 60- 600, 400 ERP + 60- ERP + 60- 600, 400 ERP + 60- ERP + 60- ERP + 60- 200 or ERP 200 or ERP 200 or ERP 200 or ERP 200 or ERP 200 or ERP in 10ms in 10ms in 10ms in 10ms in 10ms in 10ms decrements decrements decrements decrements decrements decrementsFor triple extrastimuli (S4), the S1-S2 and S2-S3 may be reduced with either the S1-S2 being long and the S2-S3 being short or vice versa. They can also bedecreased simultaneously. Some arrhythmias are often easily induced by a short (S1-S2) - long (S2-S3) configuration. 9
  10. 10. Pacing Protocols in EPS  Typical Pacing Protocols – Right Atrial Straight (Incremental) Pacing – Decremental Atrial Pacing – Programmed Atrial Stimuli with Atrial Extrastimuli – Right Ventricular Straight (Incremental) Pacing – Decremental Ventricular Pacing – Programmed Ventricular Pacing with Single, Double and Triple Extrastimuli10
  11. 11. Refractory Periods General Overview11
  12. 12. Absolute and Relative Refractory PeriodsAbsolute (Effective) refractory period - no matter how strongthe stimulus is, the cell can not depolarize.Relative refractory period - if the stimulus is strong enough(PAC, PVC or high pacing output) the cell may depolarize12
  13. 13. Absolute and Relative Refractory PeriodsThe ventricular relative refractory period (RRP) falls around themiddle of the “T wave”, and this is called the vulnerable period.The same occurs for the atrium. If a stimulus or PVC in theventricle or PAC in the atrium falls in this period, it may induceeither atrial fibrillation (if in the atrial RRP), or ventriculartachycardia or ventricular fibrillation (if in the ventricular RRP).13
  14. 14. Refractory PeriodsPremature impulses are used to measure refractory periods of cardiac tissue. They are the: • Effective refractory period (ERP) – Phase 2 - longest coupling interval that a premature impulse fails to propagate through cardiac tissue = absolute refractory period • Cardiac cells cannot be depolarized during the ERP • Coupling interval – time between the last paced impulse and premature impulse. • Relative refractory period (RRP) – time from the end of the ERP to the beginning of Phase 4 (Phases 3 & 4) – longest coupling interval that a premature impulse results in slow conduction. Time when cells can be depolarized again with a strong enough stimulus. • If a cardiac cell is stimulated during the RRP, the resulting action potential has a slower Phase 0 slope and the impulse propagates at a slower conduction velocity. • Functional refractory period (FRP) – shortest time between 2 successive conducted impulses (time when cells can be depolarized again - usually used 14 describe AV node function). The shortest output of any given input. to
  15. 15. AV Nodal Conduction Curves15
  16. 16. AV Node Conduction (Refractory) Curves There are 2 main plots used to show the conduction properties obtained during programmed stimulation: – A1-A2 versus H1-H2 and V1-V2.  This gives an assessment of the FRP of the AV conduction system. – A1-A2 versus A2-H2 and H2-V2 .  Allows to actually determine conduction times through the AV conduction system. rd16 Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3 Edition), Lippincott, Williams and Wilkins, 2002, pp.47.
  17. 17. AV Node Conduction (Refractory) Curves A1-A2 versus H1-H2 and V1-V2The doctor will pace to determine the conduction properties of the AVN. Theconduction curve will look as below. V1-V2 H1-H2 (msec) 700 A 600 C Line of Identity 500 FRP 400 B 300 400 500 600 700 A1-A2 ERP (msec)17
  18. 18. Responses to Atrial Extrastimuli There are 3 main patterns of the response to atrial stimuli: – Type I – Most common and involves the impulse propagation meeting a progressively greater delay in the AV node without any change in the infranodal (His- Purkinje) conduction. Thus, the AH interval prolongs, but the HV interval does not. Block will occur in the AV node or the atrium. – Type II – Delay is initially noted in the AV node, but at shorter coupling intervals (S1-S2), delay is noted in the His-Purkinje system. However, block still usually occurs in the AV node first, but may occur in the atrium or occasionally in the His-Purkinje system. – Type III – Least common and initially conduction slows in the AV node, but at a critical S1-S2, a sudden and marked prolongation occurs in the HV interval (His-Purkinje system). Block first occurs in the His-Purkinje system. rd18 Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3 Edition), Lippincott, Williams and Wilkins, 2002, pp.46-47.
  19. 19. AV Node Conduction (Refractory) Curves A1-A2 versus A2-H2 and H2-V2 – Type I ResponseThe doctor will pace to determine the conduction properties of the AVN. Theconduction curve will look as below. 400 A2-H2 H2-V2 300 (msec) 700 200 100 200 300 400 500 600 ERP A1-A219 (msec)
  20. 20. AV Node Conduction (Refractory) Curves A1-A2 versus A2-H2 and H2-V2 – Type II ResponseThe doctor will pace to determine the conduction properties of the AVN. Theconduction curve will look as below. 400 A2-H2 H2-V2 300 (msec) 700 200 100 200 300 400 500 600 ERP A1-A220 (msec)
  21. 21. AV Node Conduction (Refractory) Curves A1-A2 versus A2-H2 and H2-V2 – Type III ResponseThe doctor will pace to determine the conduction properties of the AVN. Theconduction curve will look as below. 400 A2-H2 H2-V2 300 (msec) 700 200 100 200 300 400 500 600 ERP A1-A221 (msec)
  22. 22. Types of Conduction Properties Decremental Conduction – Normal nodal tissue exhibits decremental conduction. – A propagated impulse at a progressively decreasing interval causes a progressive increase in the impulse conduction delay. (i.e. The increasing prematurity of the impulse = Slower impulse conduction)Non-Decremental Conduction – Atrial and ventricular myocardium and most accessory pathways (Kent) exhibit non-decremental conduction. – There is no delay in the propagation of an impulse through the tissue despite an increasing prematurity of an impulse.22 (i.e All or none conduction)
  23. 23. Conduction Properties – AV Decremental ConductionWith the AV decremental properties, as the pacing rate is increased,eventually the rate of conduction will progressively slow, as seen byprogressively longer and longer AH intervals as the S1-S2 or S1-S1 pacinginterval is increased. This prolongation indicates the pacing has entered therelative refractory period. S1-S2 AH interval prolongs 23
  24. 24. AV Node Conduction Curve – AV WenckebachDuring incremental pacing Wenckebach occurs due to progressivelyentering the relative refractory period (RRP) until a beat drops. The ERPalso prolongs as each stimulus enters deeper into the RRP.Phase 0 Dropped beat No “H” and “V” S1 24 S1 S1 S1 S1
  25. 25. AV Node Conduction Curve – AV Wenckebach AV Wenckebach is associated with:  Group beating  Progressively prolonging AH intervals Prolonging AH Grouped beats Dropped beats intervals25
  26. 26. AV Node Conduction Curve – AV Wenckebach AH Intervals Dropped beatWith Wenckebach there are grouped beats with gradual prolongation of the AH intervaluntil conduction to the ventricle eventually drops. Therefore only an occasional “A”wave will not conduct to produce a “V” (see the dropped “V” above). This occurs aspacing is hitting far into the relative refractory period. 26
  27. 27. Drugs Used in EP Studies27
  28. 28. Autonomic Nervous System  Increases in sympathetic tone increases conduction velocity and decreases refractory periods.  Increases in parasympathetic tone decreases conduction velocity and increases refractory periods.28
  29. 29. Determining Refractory Periods in an EPS29
  30. 30. Relative Refractory Period The relative refractory period (RRP) is the period of time when only a stimulus greater than normal results in an action potential. The RRP is the longest S1-S2 coupling interval (premature impulse) that causes prolonged conduction of the S2 relative to the basic cycle length (S1-S1). The start of the RRP is just after the end of the full recovery period where the conduction of the S2 and S1 is the same (i.e. the RRP will have slower conduction for S2 than for S1).30
  31. 31. Relative Refractory Period V1 V2 S1-S2 = 320ms A1-A2 = 320msS1 H1 S2 H2 A1 A2 A A2-H2 = 50ms S1-A1 = 5ms S2-A2 = 5ms V1 V2 S1-S2 = 310ms H2 A1-A2 = 310msS1 H1 S2 A1 A2 A A2-H2 = 50ms S1-A1 = 5ms S2-A2 = 5ms V1 V2 S1-S2 = 300ms H2 A1-A2 = 310msS1 H1 S2 A1 A2 A A2-H2 = 80ms S1-A1 = 5ms S2-A2 = 10ms31
  32. 32. Refractory Periods: RRP Physiology of the Heart, Katz, Ch.14; p. 248. RRPRelative, (phase 3,4) (RRP).• Time when cells can be depolarized again with a strong enough stimulus. The longest premature coupling interval at which delay in conduction (prolongation of conduction) occurs.32
  33. 33. Relative Refractory PeriodsIf a stimulus falls in the relative refractory period, and if it is strongenough the cell will depolarize. However, depolarization (slope ofphase 0) will become slower and slower the closer you approach theERP. For the AV node this is expressed as a progressivelylengthening AH interval as you pace closer and closer to the ERP.33
  34. 34. Determination of the Relative Refractory Period34
  35. 35. Relative Refractory Period: AntegradeAntegrade Relative Refractory Periods:Atrial RRP or ARRP:• The longest S1 - S2 interval at which the S2-A2 interval exceeds the S1-A1. This is called latency. (-ms)Atrioventricular Nodal RRP or AVNRRP:• The longest A1 - A2 at which the A2-H2 interval exceeds the A1-H1. (-ms)His Purkinje System RRP or HPRRP:• The longest H1 - H2 at which the H2-V2 interval exceeds the H1-V1 or results in an aberrant QRS complex. (-ms) rd35 Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3 Edition), Lippincott, Williams and Wilkins, 2002, pp.39.
  36. 36. Atrial Relative Refractory Period S1-S2 = 310ms V1 V2 A1-A2 = 310ms A2-H2 = 50ms S1-A1 = 5msS1 H1 S2 H2 A1 A2 A S2-A2 = 5ms H2-V2 = 30ms V1 V2 S1-S2 = 290ms A1-A2 = 300ms AVNRRP A2-H2 = 80ms ARRPS1 S2 H2 S1-A1 = 5ms H1 A1 A2 A S2-A2 = 10ms H2-V2 = 30ms V2 V1 S1-S2 = 270ms HPRRP A1-A2 = 285ms H2 A2-H2 = 110msS1 H1 S2 A S1-A1 = 5ms A1 A2 S2-A2 = 15ms H2-V2 = 40ms36
  37. 37. Latency (ARRP)Latency is defined as the time difference (delay)between the initiation of a stimulus and the observedresponse to that stimulus. As an extra stimulus isintroduced with shorter coupling intervals, the abilityof the targeted tissue to accept and conduct thisimpulse becomes more compromised. Increasing therate of pacing results in less time for recovery of tissue(shortening of the action potential). This is especiallytrue of AV nodal cells.37
  38. 38. Latency con’t. S1-A1 S1-A1 S2-A2 HIS 3-438
  39. 39. Relative Refractory Period: Retrograde Retrograde Relative Refractory Periods:Ventriculoatrial RRP or VARRP:• The longest S1 - S2 interval at which the S2-A2 interval exceeds the S1-A1. (-ms)Ventricular RRP or VRRP:• The longest S1 - S2 interval at which the S2-V2 interval exceeds the S1-V1. This is called latency. (-ms) Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),39 Lippincott, Williams and Wilkins, 2002, pp.39.
  40. 40. Ventriculoatrial Relative Refractory Period V1 V2 S1-S2 = 290ms V1-V2 = 300ms H1-A1 = 60ms H2 H2-A2 = 60ms S1 H1 S2 A1 A2 S2-V2 = 10ms S1-A1 = 180ms S2-A2 = 140ms V1 V2 VRRP S1-S2 = 270ms V1-V2 = 285ms H2 H1-A1 = 60ms S1 H1 S2 VARRP A1 A2 H2-A2 = 90ms S2-V2 = 15ms S1-A1 = 180ms S2-A2 = 140ms V1 V2 H2 S1-S2 = 250ms S1 H1 S2 V1-V2 = 280ms A1 A2 H1-A1 = 60ms H2-A2 = 140ms S2-V2 = 30ms40
  41. 41. Determination of the Functional Refractory Period41
  42. 42. Functional Refractory Period (FRP) The minimum interval between two consecutively conducted impulses through the cardiac tissue. The FRP of the AV node can vary, but it tends to decrease with decreasing cycle lengths. For atrial and ventricular tissue it tells you how fast that tissue can conduct on a beat to beat basis.42
  43. 43. Functional Refractory Period FRP S1 S243
  44. 44. Functional Refractory Period: AntegradeAntegrade Functional Refractory Periods:Atrial FRP or AFRP The shortest A1 - A2 in response to any S1- S2.Atrioventricular Nodal FRP or AVNFRP The shortest H1- H2 in response to any A1-A2 (320-680ms).Atrioventricular Conduction System FRP or AVFRP The shortest V1 - V2 in response to any S1- S2. Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),44 Lippincott, Williams and Wilkins, 2002, pp.39.
  45. 45. Atrioventricular Functional Conduction System Refractory Period S1-S2 = 220ms S1-A1 = 5ms S2-A2 = 25ms A1-A2 = 240ms A1-H1 = 50msS1 H1 S2 H2 A2-H2 = 60ms A1 A2 A H1-H2 = 250ms H1-V1 = 25ms H2-V2 = 30 ms V1-V1 = 255ms V1 V2 S1-S2 = 200ms S1-A1 = 5ms AVNFRP S2-A2 = 25ms A1-A2 = 225ms A1-H1 = 50msS1 H1 S2 H2 A2-H2 = 60ms A1 A2 A H1-H2 = 240ms H1-V1 = 25ms H2-V2 = 35 ms V1-V1 = 255ms V1 AFRP V2 S1-S2 = 180ms AVFRP S1-A1 =5ms S2-A2 = 35ms A1-A2 = 230msS1 H1 S2 H2 A1-H1 = 50ms A1 A2 A A2-H2 = 100ms H1-H2 = 260ms H1-V1 = 30ms H2-V2 = 40 ms V1-V1 = 265ms45
  46. 46. Functional Refractory Period: RetrogradeRetrograde Functional Refractory Periods:Retrograde Atrioventricular Nodal FRP or AVNFRP The shortest A1- A2 in response to any S1-S2.Ventriculoatrial Conduction System FRP or VAFRP The shortest A1- A2 in response to any H1-H2.Ventricular FRP or VFRP The shortest V1-V2 in response to any S1-S2 orshortest V1-V2 as measured on the surface leads. Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),46 Lippincott, Williams and Wilkins, 2002, pp.39.
  47. 47. Retrograde AV Nodal Functional Refractory Period V1 V2 S1-S2 = 300ms A1-A2 = 440ms H1-A1 = 60ms S1 H2 H2-A2 = 200ms H1 S2 A1 A2 S2-H2 = 120ms S2-A2 = 240ms A1-A2 = 440ms V1 V2 A1-A2 = 435ms S1-S2 = 290ms H1-A1 = 60ms H2 H2-A2 = 205ms S1 H1 S2 Retrograde A1 A2 S2-H2 = 120ms AVNFRP S2-A2 = 245ms A1-A2 = 435ms V1 V2 A1-A2 = 445ms S1-S2 = 280ms H1-A1 = 60ms H2-A2 = 220ms S1 H1 S2 H2 A1 A2 S2-H2 = 120ms S2-A2 = 260ms A1-A2 = 440ms Retrograde Atrioventricular Nodal FRP or AVNFRP47 The shortest A1- A2 in response to any S1-S2
  48. 48. Ventricular Functional Refractory Period V1 V2 S1-S2 = 300ms V1-V2 = 355ms S1-V1 = 5ms S1 S2 H2 S2-V2 = 60ms H1 A1 A2 V1-V2 = 355ms V1 V2 S1-S2 = 290ms V1-V2 = 350ms S1-V1 = 5ms S2-V2 = 65ms S1 H1 S2 H2 A1 A2 VFRP V1-V2 = 350ms V1 V2 V1-V2 = 360ms S1-S2 = 280ms S1-V1 = 5ms S1 H1 S2 H2 S2-V2 = 75ms A1 A2 V1-V2 = 360ms Ventricular FRP or VFRP The shortest V1-V2 in response to any S1-S2 or shortest V1-V2 as48 measured on the surface leads.
  49. 49. Determination of the Effective Refractory Period49
  50. 50. Effective Refractory Period Effective or absolute, (phase 2) (ERP) is the longest amount of time when cells cannot be depolarized again. The longest input that fails to conduct.  Atria 200-270 msecs  Ventricles 200-270 msecs  AV node 280-450 msecs Ch 22 intracardiac Eectrophysiology. John Dimarco S1 S250 Physiology of the Heart, Katz, Ch.14; p. 248
  51. 51. Effective Refractory Period Measurement The ERP is measured using extrastimulus pacing with an early beat inserted following 8-10 beats at a fixed rate (pacing train). The pacing train allows the refractoriness to stabilize. This stabilization usually occurs after 3-4 beats. Also the current strength of the stimulus will influence the ERP. The greater the current strength, the shorter the ERP (in msec). The ERP will continue to shorten as the current increases, but eventually becomes fixed at further increases. Increasing the current strength to 10 mA usually results in shortening the ERP by 30 msec.51 •(Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition), Lippincott, Williams and Wilkins, 2002, pp.39-40.)
  52. 52. ERP: Effect of Current StrengthAtrial and ventricular ERPs decrease with the increased currentstrength of the impulse. Normal ERP measurements are taken at twicethe diastolic threshold, but if the current strength is increased up to10mA, the ERP will shorten on average by 30msec. The important thingis to be consistent with the method you use. 10 8 Current (mA) 6 4 2 0 180 200 220 240 VERP (msec)52Josephson, M. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition), Lippincott, Williams and Wilkins, 2002, pp. 39-40.
  53. 53. Affect of Pacing on the ERP ERP of atrial and ventricular tissue shortens with pacing, allowing introduction of premature beats. ERP of AV node lengthens with pacing, and results in blocking of conduction to the ventricles.53
  54. 54. ERP Response to Different Cycle LengthsThe ERPs of ventricular tissue and the His-Purkinje system differ in their response to different drivecycle lengths and extrastimuli (abrupt cycle length changes). Ventricular refractoriness demonstratesthe cumulative effect of the preceding cycle lengths (several beats of a drive cycle), whereas the His-Purkinje system is effected greatly by the immediately preceding cycle length. Thus a change from along to short cycle length will shorten both the His-Purkinje and ventricular ERPs, but a short to longcycle length will drastically prolong the His-Purkinje ERP, but will have only a slight effect if at all onthe ventricular ERP. This is even more exaggerated if only a single extrastimulus is used. Below showsthe effect on the His-Purkinje system. His-Purkinje System A. Constant CL 600 600 600 600 Cycle length (CL) Action Potential Duration 350 350 350 350 350 (APD) 250 250 250 250 Diastolic Interval B. Long to short 800 800 600 450 450 450 300 350 350 150 400 400 400 600 Effect on His- C. Short to Long Purkinje System, but not on the 250 250 250 250 400 VERP 150 150 150 350 54 Josephson, M. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition), Lippincott, Williams and Wilkins, 2002, pp. 40-44.
  55. 55. ERP Response to Multiple StimuliThe determinate factor of the ventricular ERP appears to be the diastolic interval. Theventricular refractory period (VERP) following one extrastimulus is shorter than thatfollowing two. In A, S2 hits making the diastolic interval only 40ms. Because it is short,it makes the resultant VERP shorter at 180ms. In B, the same thing occurs after S2,but when S3 is placed at the same cycle length as S1-S2 (260ms), because theVERP was only 180ms, the diastolic interval becomes 80ms. Since that is longer thanthe previous 40ms one, now the VERP is longer at 195ms. If this were the His-Purkinge system, the ERP both after the S2 and S3 would have been much moreprolonged. 40ms Diastolic Interval: 180ms 180ms VERP: 220ms 220ms 220ms 180ms Coupling Interval: 400ms 400ms 260ms A S1 S1 S1 S2 40ms 80ms Diastolic Interval: 180ms 180ms VERP: 220ms 220ms 220ms 180ms 195ms Coupling Interval: 400ms 400ms 260ms 260ms B S1 S1 S1 S2 S3 Josephson, M. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition), Lippincott, Williams and Wilkins, 2002, pp.44.55
  56. 56. Effective Refractory Periods: AntegradeAntegrade Effective Refractory Periods:Atrial ERP or AERP: The longest S1 - S2 that fails to capture the atrium (150-360ms)Atrioventricular Nodal ERP or AVNERP: The longest A1 - A2 measured from the His Bundleelectrogram that fails to conduct to the His (230-430ms)Atrioventricular conduction system (AVCS) ERP or AVERP: The longest S1 - S2 that fails to result in a ventricledepolarization Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),56 Lippincott, Williams and Wilkins, 2002, pp.39.
  57. 57. Atrial and AV Node Effective Refractory Periods V1 V2 S1-S2 = 290ms A1-A2 = 300msS1 H1 S2 H2 A1 A2 A2 A2-H2 = 60ms S2-A2 = 10ms V1 V S1-S2 = 270ms AVNERP A1-A2 = 285msS1 H1 S2 No H2 H A2-H2 = 90ms A1 A2 A S2-A2 = 15ms V1 V S1-S2 = 250ms A1-A2 = 280ms No A2 AERP H A2-H2 = NAS1 H1 S2 A1 A S2-A2 = NA Atrial ERP or AERP: The longest S1 - S2 that fails to capture the atrium (150- 360ms) Atrioventricular Nodal ERP or AVNERP: The longest A1 - A2 measured from the57 His Bundle electrogram that fails to conduct to the His (230-430ms)
  58. 58. AV Conduction system Effective Refractory Period V1 V2 S1-S2 = 310ms A1-A2 = 315msS1 H1 S2 H2 A2-H2 = 50ms A1 A2 A2 S2-A2 = 5ms V1 V Recovery of S1-S2 = 270ms AVERP sinus beat A1-A2 = 100msS1 H2 No V H A2-H2 = NA H1 S2 A1 A2 A S2-A2 = 15ms V1 V AVERP Recovery of S1-S2 = 270ms sinus beat A1-A2 = 285msS1 No H2 H A2-H2 = NA H1 S2 A1 A2 A S2-A2 = 15ms Atrioventricular conduction system (AVCS) ERP or AVERP: The longest S1 -58 S2 that fails to result in a ventricle depolarization
  59. 59. Effective Refractory Periods: RetrogradeRetrograde Effective Refractory Periods:Retrograde His Purkinje System ERP or Retrograde HPERP: The longest S1 - S2 or V1-V2 in which S2 or V2 block below thebundle of His. Can only measure if H2 is recorded before the retrogradeblock.Retrograde AV Node ERP or Retrograde AVNERP: The longest S1 - H2 or H1-H2 that H2 fails to conduct to the atriumVentriculoatrial Conduction System (VACS) ERP or VAERP: The longest S1 - S2 that fails to conduct to the atriumVentricular ERP or VERP: The longest S1 - S2 that fails to capture the ventricle (170-290ms) Josephson, ME. Clinical Cardiac Electrophysiology, Techniques and Interpretations (3rd Edition),59 Lippincott, Williams and Wilkins, 2002, pp.39.
  60. 60. Retrograde AV Node Effective Refractory Period V1 V2 S1-S2 = 290ms V1-V2 = 300ms S1 H2 H2-A2 = 60ms H1 S2 A1 A2 H1-H2 = 295ms S1-H2 = 340ms V1 V2 S1-S2 = 270ms V1-V2 = 285ms H2-A2 = 90ms S1 H1 S2 H2 A2 H1-H2 = 280ms A1 S1-H2 = 335ms V1 V2 S1-S2 = 250ms Retrograde AVNERP V1-V2 = 280ms H2-A2 = NA S1 H1 S2 H2 H1-H2 = 265ms A1 No A2 S1-H2 = 330ms Retrograde AV Node ERP or Retrograde AVNERP: The longest S1 - H2 or H1-60 H2 that H2 fails to conduct to the atrium
  61. 61. VA Conduction System (VACS) ERP: Block in the AV Node an His- Purkinje System V1 V2 S1-S2 = 290ms V1-V2 = 300ms S1 H1 S2 H2 H2-A2 = 60ms A1 A2 S2-V2 = 10ms V1 V2 S1-S2 = 250ms VAERP V1-V2 = 280ms S1 H1 S2 H2 A1 No A2 H2-A2 = NA S2-V2 = 30ms S1-S2 = 250ms V1 V2 V1-V2 = 280ms VAERP S1-V1 = 5ms S2-V2 = 20ms S1 H1 S2 No H2 S1-H1 = 40ms A1 No A2 S2-H2 = NA Ventriculoatrial Conduction System (VACS) ERP or VAERP: The longest S1 - S2 that fails to conduct to the atrium61 Ventricular ERP or VERP: The longest S1 - S2 that fails to capture the ventricle (170-290ms)
  62. 62. Ventricular Effective Refractory Period V1 V2 S1-S2 = 270ms V1-V2 = 285ms S1 H1 S2 H2 H2-A2 = 90ms A1 A2 S2-V2 = 15ms V1 V2 S1-S2 = 250ms V1-V2 = 280ms S1 H1 S2 H2 No A2 H2-A2 = NA A1 S2-V2 = 30ms V1 V S1-S2 = 230ms VERP V1-V2 = NA H H2-A2 = NA S1 H1 S2 No V2 A1 A S2-V2 = NA Ventricular ERP or VERP: The longest S1 - S2 that fails to capture the ventricle62 (170-290ms)
  63. 63. Performing a Basic EP Study Programmed Electrical Stimulation Baseline EGM Recordings Refractory Periods Sinus Node Recovery Time (SNRT) Sinoatrial Conduction Time (SACT) Basic EP Tasks63
  64. 64. What is an EP Study? Electrical stress test An invasive study to assess the heart’s electrical conduction system Patient under conscious sedation Often classified outpatient Done in EP lab, part of cardiac cath labs64
  65. 65. Why Conduct an EP Study?  To evaluate conduction system function  To confirm supraventricular tachycardia  To evaluate ventricular tachyarrhythmias  To classify the extent of bradycardia  To test efficacy of antiarrhythmic drugs  To test efficacy of implanted devices65
  66. 66. EP study Indications ACC/AHA Guidelines66
  67. 67. Which Type of EP Study? Clinical Presentation Recommended Study  Documented SVT or  Comprehensive EPS atrial flutter with ablation  Suspected SVT  Comprehensive EPS  Syncope  Tilt, Baseline EPS, or loop recorder  Nonsustained VT  Baseline EPS  Suspected brady  Baseline EPS only if VT suspected67
  68. 68. EP Study Outcomes EP Study Pharmacologic Device Device Surgical Catheter No Therapy Implant Ablation Therapy Therapy Therapy Therapy68
  69. 69. Basic Steps in an EP Study  Equipment in room and functional  Patient info in recording system  Check plan with physician  Gather sheaths, catheters, connectors  Patient in room and prepped  Prep sterile table, open products  Sedate patient  Catheters placed with acceptable thresholds  Baseline intervals and stimulation protocols  Ablate, wait, re-test  Pull and hold69
  70. 70. TESTING USED IN EPS70
  71. 71. Electrophysiology Study Measurement of baseline conduction intervals Atrial Pacing - Assessment of SA nodal automaticity and conductivity - Assessment of AV nodal conductivity and refractoriness - Assessment His-Purkinjie system conductivity and refractoriness - Assessment of atrial refractoriness71
  72. 72. Electrophysiology Study con t  Ventricular pacing – Access retrograde conduction – Access ventricular refractoriness  Arrhythmia Induction – Atrial extrastimulus testing – Atrial burst pacing – Ventricular extrastimulus testing – Ventricular burst pacing72
  73. 73. Catheters used in a Conduction System Study Quadripolar for HRA Evaluate sinus node function Evaluate antegrade AV node Quadripolar for HBE conduction Quadripolar for RVA Evaluate retrograde AV node conduction73
  74. 74. Catheters used in a EP Study Catheters used in standard EP studies: Quadripolar in the HRA (usually fixed curve) Quadri, hexa, octa, or decapolar at the HBE (fixed curve or steerable) Quadripolar in the RVA (usually fixed curve) Hex, octa, or decapolar in the CS (fixed curve or steerable)74
  75. 75. Catheters used in SVT and VT Studies Catheters used in SVT studies:  Quadripolar in the HRA (usually fixed curve)  Quadri, hexa, octa, or decapolar at the HBE (fixed curve or steerable)  Quadripolar in the RVA (usually fixed curve)  Hex, octa, or decapolar in the CS (fixed curve or steerable)  Steerable large tip (4mm) mapping catheter Catheters used in VT studies:  Quadripolar in the HRA (sometimes omitted)  Quadripolar (most common) at the HBE (fixed or steerable)  Quadripolar in the RVA (steerable is common so that it can be moved to the RVOT)  Steerable large tip (4mm) mapping catheter75
  76. 76. Standard Conduction System Study  Evaluate sinus node function  Sinus node recovery time (SNRT)  Sino-atrial conduction time (SACT)  Evaluate antegrade AV node conduction  AV Decremental Properties  AVNERP  AERP  AV Wenckebach cycle length (Incremental pacing only)  Evaluate retrograde AV node conduction (S1S2 and Incremental pacing)  VAERP  VERP  VA Wenckebach cycle length (Incremental pacing only)76
  77. 77. Standard EP Study Protocol Atrial Pacing Pacing spike A wave Atrial pacing is performed with the HRA catheter to determine the following: – AV decremental properties – AVNERP – AV Wenckebach cycle length77 – AERP
  78. 78. Standard Conduction System Study - Antegrade Stimulation For SA node evaluation two tests are performed – SNRT – SACT If just one of these tests are performed, the evaluation of the SA node may not be accurate, therefore it is recommended to perform both Since the autonomic nervous system can highly influence these tests, it is recommended to perform a pharmacological blockade to observe the true state of the SA node – Atropine to eliminate the parasympathetic influence – Propranolol to eliminate the sympathetic influence Depending on the results of these tests, a pacemaker may be implanted, so a correct evaluation should be made78
  79. 79. Standard Conduction System Study – Sinus Node Recovery Time (SNRT) Sinus node recovery time (SNRT) – time it takes for the SA node to recover from overdrive suppression of normal automaticity.  Test: To suppress SA nodal automaticity, overdrive pacing impulses are delivered via the HRA at a rate faster than the intrinsic sinus rate at a constant rate for at least 30 seconds; then abruptly stopped and the SNRT measured. The SNRT is the longest pause between the last paced beat and the first intrinsic beat after overdrive pacing ends. SNRT measurements are typically taken at 800, 700, 600, 500, 450, 400, 350 and possibly 300 ms intervals. The longest interval observed during recovery is the SNRT. An SNRT longer than 1,500 ms is considered abnormal.  Since the first cycles after the sinus node recovery are usually slightly longer than the BCL, either a corrected sinus node recovery time (CSNRT) or an SNRT:BCL ratio is used as below:  CSNRT = SNRT – BCL A CSNRT longer than 525 ms is considered abnormal.  SNRT / BCL x 100%. A ratio greater than 160% is considered abnormal. 79
  80. 80. Standard Conduction System Study – Sinus Node Recovery Time (SNRT) Sinus node recovery times (SNRTs) A A A1 A1 A1 A2 A3HRA SCL S1 S1 SNRT SNRT=A1A2 (NORMAL < 1500 MSEC)80 CSNRT=A1A2-SCL (NORMAL < 525 MSEC)
  81. 81. Standard Conduction System Study – Sinoatrial Conduction Time (SACT) SA Node (with pacemaker cells) Transitional cells Last pacing Conduction from the impulse atrium into the SA node Conduction from the SA node to the atrium  Sinoatrial conduction time (SACT) – time it takes for a sinus impulse to conduct through perinodal (surrounding) atrial tissue  When SA node disease (sick sinus syndrome) occurs, it is due to poor conduction in the transitional cells and not failure of the pacemaker cells firing  A prolonged SACT suggests sinus exit block.81
  82. 82. Standard Conduction System Study – Sinoatrial Conduction Time (SACT) SA Node (PAcells) Transitional cells Conduction from the Conduction from the SA node to atrium into the SA node the atrium A A First sinus A wave Last pacing spike Return cycle A SCL A Pace from the HRA catheter at a rate slightly above the sinus rate for 30 - 60 seconds and then stop abruptly and measure from the last pacing spike to the82 first sinus A wave
  83. 83. Standard Conduction System Study – Sinoatrial Conduction Time (SACT) SA Node (PAcells) Transitional cells A A Return cycle A SCL A SACT = the return cycle (last S1 to the first sinus A wave) minus the SCL and then divided by 2 (i.e. A + A) *SCL = A-A interval measured on the HRA catheter in sinus rhythm83 A = SACT (normal 50-125ms)
  84. 84. Standard Conduction System Study – Antegrade Extrastimulus Pacing  After completing the SA node evaluation, the doctor will use both extrastimulus pacing and incremental pacing  Both antegrade (atrial pacing) and retrograde (ventricular pacing) studies will be performed.84
  85. 85. Standard EP Study Protocol Antegrade Study Antegrade study – Extrastimulus pacing: The HRA catheter is used to deliver single extrastimulation (S2) following an 8-10 beat pacing train (S1) during sinus rhythm to assess the AV node and atrial conduction properties. This is often performed at 2 different cycle lengths (Ex. 600 and 500 ms) and up to 300bpm (200ms) or the AERP to assess the following:  AV Activation  AV Decremental Conduction  AVNERP  AERP – Incremental pacing: The HRA catheter is used to deliver incremental pacing with progressive increases in the rate by decreasing the pacing cycle length (S1-S1) by 10-20ms decrements to assess the following:  AV Activation  AV Decremental Conduction  AV Wenckebach cycle length  AVNERP85  AERP
  86. 86. Standard EP Study Protocol AV Decremental ConductionWith the AV decremental property, as the pacing rate is increased, eventually the rateof conduction will progressively slow, as seen by progressively longer and longer AHintervals as the S1-S2 or S1-S1 pacing interval is increased. This prolongationindicates the pacing has entered the releative refractory period. S1-S2 AH interval prolongs 86
  87. 87. Standard EP Study Protocol AV Wenckebach AH Intervals Dropped beatWith Wenckebach there are grouped beats with gradual prolongation of the AH intervaluntil conduction to the ventricle eventually drops. Therefore only an occasional “A”wave will not conduct to produce a “V” (see the dropped “V” above). This occurs aspacing is hitting far into the relative refractory period. 87
  88. 88. Standard EP Study Protocol AVNERP Pacing spike A V No His or “V” The ERP of the AV node is reached when conduction from the atrium to the ventricle is blocked due to reaching the refractory period of the AV nodal tissue. This would be evidenced by an “A” wave after the pacing spike not followed by a His potential or a “V” wave. AVNERP = 280 - 450 msecs88
  89. 89. Standard EP Study Protocol AVNERPTo identify the ERP of the AV Node a series of programmed stimulation trains are conducted tofind the longest A1-A2 interval that fails to conduct to the His. Identifying the ERP of othercardiac tissues is done in the same fashion:  Atrial ERP (AERP): The longest S1 - S2 that fails to capture the atrium  Ventricular ERP (VERP): The longest S1 - S2 that fails to capture the ventricle. ERP of the AV Node This is the longest A1-A2 that fails to conduct 89 This A1-A2 is longer but it DOES conduct 145
  90. 90. Standard EP Study Protocol AERP No local atrial Pacing “spike” electrogram AERP90 AERP = 200 - 270 msecs
  91. 91. Standard EP Study Protocol AVNERP and AERP AVNERP AERP91
  92. 92. Standard EP Study Protocol Effective Refractory Periods ERPs of the various cardiac tissue  Atria 200-270 msecs  Ventricles 200-270 msecs  AV node 280-450 msecs Ch 22 intracardiac Eectrophysiology. John Dimarco92
  93. 93. Standard EP Study Protocol AH Jump AH = 80msec AH = 90msec AH = 180msec This sequence is showing evidence of what?93
  94. 94. Standard Conduction System Study Retrograde Study Retrograde study – Extrastimulus pacing: The RVA catheter is used to deliver single extrastimulation (S2) following an 8-10 beat pacing train (S1) during sinus rhythm to assess the VA and ventricular conduction properties. This is often performed at 2 different cycle lengths (Ex. 600 and 500 ms) and up to 250bpm (240msec) or the VERP to assess the following:  VA Activation  VA Decremental Conduction  VAERP  VERP – Incremental pacing: The HRA catheter is used to deliver incremental pacing with progressive increases in the rate by decreasing the pacing cycle length (S1-S1) by 10-20ms decrements to assess the following:  VA Activation  VA Decremental Conduction  VA Wenckebach cycle length  VAERP  VERP 94
  95. 95. Standard EP Study Protocol Retrograde Conduction Study– Right Ventricular Straight Pacing  performed to  Check and set pacing thresholds  Check to see if the AV Node works backwards (retrograde conduction)  Check to see if there is an accessory pathway with retrograde conduction (if no conduction can go retrograde up the normal conduction system, yet you see retrograde conduction, then it means there is an accessory pathway)  Do “rescue” pacing  Terminate or induce tachycardias95
  96. 96. Standard EP Study Protocol Retrograde Conduction Study – Ventricular Pacing V A VAIn this example pacing is being performed from the rightventricular apex (RVA). Therefore you will first have a “V”wave. Conduction will then conduct up the conduction systemresulting in a His potential and then an “A” wave. This iscalled retrograde conduction. However, although it is anormal phenomenon, not everyone has retrograde96conduction.
  97. 97. Standard EP Study Protocol Retrograde Conduction Study – VA Block V A V A V A V V A V No “A” waveNote that on the 4th and 6th beats no “A” wave follows the“V” wave. This is called VA block.97
  98. 98. Standard EP Study Protocol Retrograde Conduction Study – VA Decremental Conduction V HA V H AJust as when you pace faster and faster from the atrium, when you pace at faster andfaster rates in the ventricle, you will have decremental conduction. That is, as youpace faster and faster, the VA or HA interval will progressively prolong the faster yougo. This is because as you begin to enter the relative refractory period (RRP) of theAV node, conduction begins to slow. The further into the RRP you pace, the slowerthe conduction. In the example above, you can see that the VA and HA (not easilyseen) widened with the shorter (faster) pacing interval.98
  99. 99. Standard EP Study Protocol Retrograde Conduction Study – VERPThe ventricular ERP(VERP) is reached whenyou pace at a rate faster VERPthan the absoluterefractory period of theventricular tissue. Thiswould be evidenced bya pacing spike not No local ventricular electrogramfollowed by a “V” wave.Consequently therewould be no Hispotential or “A” wave. Pacing “spike”99 VERP = 200 - 270 msecs
  100. 100. Arrhythmia Induction100
  101. 101. Standard EP Study Protocol Cont. – Arrhythmia Induction - SVT 1. 1 or 2 extrastimuli (S2 and S3) during SR from the RV apex 2. 1 or 2 extrastimuli (S2 and S3) during ventricular pacing (S1) at 100, 120 and 150 bpm (600, 500 and 400msec) from the apex 3. Incremental pacing from RV apex up to 250bpm (240msec) in 10-20msec decrements 4. 1 or 2 extrastimuli (S2 and S3) during SR from the HRA 5. 1 or 2 extrastimuli (S2 and S3) during atrial pacing (S1) at 100, 120, and 140 bpm (600,500,400msec) from the HRA 6. Incremental pacing from the HRA up to Wenckebach or 300 bpm (200msec), or until an arrhythmia is initiated in 10-20msec decrements 7. Repeat steps 4-6 from the CS or left atrium 8. If not inducible with above give an isoproterenol infusion at a rate of 1 to 6 µg/min to increase patients’ heart rate to at least 20% above the resting sinus rate or shorten the sinus CL to 450 msec and repeat steps 1-7101
  102. 102. Standard EP Study Protocol Arrhythmia Induction - VTAtrial Protocol1.1 extrastimuli (S2) during SR from the HRA2.1 extrastimuli (S2) during atrial pacing at 100, 120 and 150 bpm (600, 500 and 400msec) from the HRA3.Incremental pacing from the HRA up to the Wenckebach point, or 300 bpm (200msec), or initiation of SVT in 10-20msec decrementsVentricular Protocol 1.1 - 2 extrastimuli (S2 and S3) during SR from the RV apex 2.1 - 2 extrastimuli during ventricular pacing at 100, 120 and 150 bpm (600, 500 and 400msec) from the RV apex 3.Incremental pacing from RVA up to 250bpm (240msec) in 10-20msec decrements 4.3 extrastimuli (S2, S3 and S4) during SR from the RV apex 5.3 extrastimuli (S2, S3 and S4) during ventricular pacing at 100, 120 and 150 bpm (600, 500 and 400msec) from the RV apex 6.Repeat steps 1-5 from the right ventricular outflow tract 7.If not inducible with above give an isoproterenol infusion starting at a rate102 of 2.5µg/min to increase patients’ heart rate to at least 20% above the resting rate and repeat steps 1-6
  103. 103. Standard EP Study Protocol Cont. – Arrhythmia InductionIn an EP study various types of pacing are used to induce the arrhythmias so that itcan be evaluated for its type and origin. In the example above a single (S2)extrastimulus is used to induce the arrhythmia.103
  104. 104. Standard EP Study Protocol Cont. – Basic EP Tasks - SummaryEP Protocol:• Measure baseline conduction intervals (BCL, IACT, AH, HV, QRS and QT) in sinus rhythm• Ventricular extrastimulus testing (VAERP, VERP, and retrograde conduction)• Incremental ventricular pacing (VA conduction, VAERP, VERP, VA Wenckebach, FRP) - Pace at a rate slightly faster than the BCL and increase until VA block. Pacing is typically no faster than 240 ms.• PES in the ventricle (arrhythmia induction) - Drive train (S1) of 600, 500 and then 400 ms with extrastimuli until the VERP. • Ventricular burst pacing (fixed, incremental or decremental – arrhythmia induction).• Atrial extrastimulus testing to measure the AV nodal and atrial refractory periods.• Incremental atrial pacing to assess AV and atrial conduction (AVNERP, AV Wenckebach, AERP)- Pace at a rate slightly faster than the BCL and decrease until AV block, but not faster than 200 ms.• PES in the atrium (arrhythmia induction) - Drive train (S1) of 600, 500 and 400 ms with extrastimuli. • Atrial burst pacing (fixed, incremental or decremental-arrhythmia104 induction).
  105. 105. Induction of Reentrant Arrhythmias105
  106. 106. Reentry Requirements Reentry circuits consist of a fast pathway and slow pathway and reentry requires an area of “slow” This is a longer path to this point... conduction with a short refractory period – this could be caused by:  The AV Node;  An area of disease;  Or, simply a physically longer path (like this example). The fast pathway has fast conduction, but a long refractory period – This can be the:  Fast pathway of the AV node  Accessory Pathway  Atrial tissue  Or a shorter path (as in the example) Note how the wavefront cancels out in the longer path (slow pathway) …than this one 106
  107. 107. Requirements for Reentry “Sinus” “Reentry” http://rezidentiat.3x.ro/eng/tulbritmeng.htm  Two limbs joined at their ends The other conducts faster but has  One conducts more slowly but a longer refractory period107 has a shorter refractory period Unidirectional block in one limb
  108. 108. Reentry Requirements  Reentry requires an area of unidirectional block- – this also can come from the AV Node or disease, as well as normal variations in refractoriness in the presence of an abnormal structure (bypass tract).108
  109. 109. Reentry Requirements Reentry requires a complete circuit that has both an area of “slow” conduction and Unidirectional block in it.109
  110. 110. Terminating a Reentrant Circuit  Pacing  Pharmacological (Ex. Adenosine)  Ablation… – Eliminates the complete circuit.110
  111. 111. Reentrant Circuits and Pacing Maneuvers – Resetting and Advancing the Tachycardia “Resetting” or “Advancing” a tachycardia: If you can pace faster than the tachycardia and speed the tachycardia up to the pacing rate with one or more beats (entrainment) thus resetting or advancing the tachycardia, then the mechanism is reentry.111
  112. 112. Reentrant Circuits and Pacing Maneuvers – Resetting and Advancing the Tachycardia112
  113. 113. Reentrant Circuits and Pacing Maneuvers – Entrainment  Entrainment: – The placement of several pacing impulses into a tachycardia circuit that does not terminate it.  The intent of entrainment is to determine if the pacing site is in the tachycardia circuit…  If the pacing site is in the circuit, it might be an effective ablation site113
  114. 114. Reentrant Circuits and Pacing Maneuvers – Entrainment  Entrainment is continuous pacing during a tachycardia that accelerates the activation to the pacing cycle length and does not terminate the arrhythmia.  The ability to entrain a tachycardia supports reentry as the tachycardia mechanism.  Entrainment pacing can occur outside of or within the actual tachycardia circuit.  If it occurs outside the circuit, the ECG will be a combination of the tachycardia morphology and what the morphology would look like when pacing in normal sinus rhythm (fusion).  If entrainment occurs within the circuit, the ECG morphology remains constant (concealed entrainment).114
  115. 115. Reentrant Circuits and Pacing Maneuvers – Entrainment – Pacing with Fusion This is a demonstration of pacing with fusion.115
  116. 116. Reentrant Circuits and Pacing Maneuvers – Entrainment – Pacing with Concealed Entrainment This is a demonstration of pacing with concealed entrainment.116
  117. 117. Reentrant Circuits and Pacing Maneuvers – Entrainment – Post Pacing Interval This is known as the Return Cycle Length, or the Post Pacing Interval (PPI) and it is the time it takes for the tachycardia to resume after pacing is stopped. If the pacing occurred outside of the tachycardia circuit, the time it takes for the tachycardia to resume will be longer than if it were inside the circuit. = pacing site The reentry circuit = Tachycardia cycle length (TCL) PLUS Time from pacing site to the circuit PLUS Time from circuit to the pacing site =Return Cycle Length117 Return cycle length= (Time from pacing site)x2 +TCL
  118. 118. Reentrant Circuits and Pacing Maneuvers – Entrainment – Post Pacing Interval  If the pacing occurred inside of the tachycardia circuit, the time it takes for the tachycardia to resume will be the tachycardia cycle length only, since there is no distance outside of the circuit to add time. A PPI < 30 msec is considered in the tachycardia circuit. Return cycle length= (Time from pacing site)x2 +TCL The reentry circuit = Tachycardia cycle length (TCL) PLUS Time from pacing site to the circuit (in this case it’s 0) PLUS Time from circuit to the pacing site (also 0) =Return Cycle Length118
  119. 119. Reentrant Circuits and Pacing Maneuvers – Concealed Entrainment – Post Pacing Interval = TCL PPI :Post pacing interval FCL: Flutter cycle length 15. Lesh et al. JCE Vol.7,No 4, April 1996119

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