Think of the EKG tracings for Lead I and III as someone looking at you, holding out their thumbs with their right thumb as Lead I and their left thumb as Lead III.
Lead I (Right) is upright. Lead III (left) is upright.
Lead I (Right) is upright. Lead III (left) is down. Consult Lead II, if it is also down, then it is an anterior hemiblock.
Lead I (Right) is down. Lead III (left) is up. Most likely a posterior hemiblock.
Lead I (Right) is down. Lead III (left) is down. This indicates a possible bifasicular block.
Keep the rate up, may give Dobutamine
March Cardio Review
Cardiac ReviewA&P, EKG, MI, Other Cardiac Emergencies
What is ACS?• ACS is coronary disease that is causing an acute illness, inclusive of: – Ischemia/unstable angina (UA or USA) – Non-ST Elevation MI (NSTEMI) – ST Elevation MI (STEMI)• STEMI and NSTEMI are relatively new terms; “NQMI” and similar terms are no longer used• The term “AMI” is still used and is usually synonymous with STEMI
Epidemiology of ACS• AMI most common 6am to noon due to elevated bp, catacholamines and platelet aggregability• AMI more common in winter• >1 million infarcts/500k US deaths per year• Leading cause of mortality in US• Annual cost >$120 billion per year
STEMI• Acute phase is <6 hrs from onset• Immediate transfer to interventional cardiac cath lab is most effective treatment!• Fibrinolytics is also definitive treatment
Layers of the Heart• 1. Endocardium-inner• 2. Myocardium- middle• 3. Epicardium-outer• 4. Pericardium-sac around heart
Blood Flow through Heart • Blood flows from VC to the R atria. • It crosses the tricuspid valve into the R ventricle. • It goes past the pulmonic valve into the pulmonary artery and the lungs.
Blood Flow cont. • Blood comes from the lungs via the pulm. veins into the L atria. • It crosses the mitral valve into the L vent. • It goes past the aortic valve into the aorta and the systemic and coronary circulation.
Heart Valves **Valve order T-P-M-A**• Two types: atrioventricular and semilunar.• AV: Open as the result of lower ventricular pressure – Tricuspid and Mitral valves• Semilunar: Located between the ventricles and great arteries – Pulmonic and Aortic
Coronary Circulation• Right and Left coronary arteries originating at the coronary ostia at the base of the aorta. – Left Coronary Artery • Left Anterior Descending – Anterior, 2/3 of the septum, partial lateral wall • Left Circumflex – Primary Lateral Wall circulation – Right Coronary Artery • Right atrium, right ventricle, inferior & posterior wall of left ventricle.
Properties of Cardiac Cells• Automaticity• Excitability• Conductivity• Contractility
• Polarization: No electrical activity. Inside of cell negative.• Depolarization: Na+ rapidly rushes in and causes inside to become positive.• Repolarization: Na+ stops and K+ leaks out as cell returns to resting levels.
SA Node • Initiates electrical impulses at a rate of 60- 100 bpm. • Reaches threshold and depolarizes more rapidly than other cardiac cell. • Blood supply from SA node artery (from RCA in 55% of hearts).
Atrioventricular Junction • AV node and Bundle of His • Electrical link between atria and ventricle
AV Node• Supplied by RCA in 90% of hearts and LCx in 10%.• Delays conduction to allow atria to empty
Bundle of His• Dual blood supply from LAD and PDA• Intrinsic pacemaker rate of 40-60 bpm• Normally is the only electrical connection between the atria and the ventricles.
Right and Left Bundle Branch • RBB innervates RV • LBB innervates the septum and LV • LBB has 3 divisions: – Anterior fascicle – Posterior fascicle – Septal fascicle
Purkinje Fibers• Spread from the septum into the papillary muscles and downward into the apex of the heart• Penetrates 1/3 of the way into the ventricle muscle mass• Intrinsic rate of 20-40 bpm
Electrophysiology• Depolarization – Complete depolarization normally results in muscle contraction• Threshold – minimal stimulus required to produce excitation of myocardial cells
Electrophysiology• Repolarization – Process of returning to resting potential state • Sodium influx stops and potassium leaves cell • Sodium pumped to outside the cell – Relative refractory period • cell will respond to a second action potential but the action potential must be stronger than usual – Absolute refractory period • cell will not respond to a repeated action potential regardless of how strong it is
Electrophysiology Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+Myocardial cells are POLARIZED. They have more positive chargesoutside than inside.
Electrophysiology Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+Stimulation of cell opens “fast” channels in cell membrane. Na+ rapidlyenters cell. Now there are more positive charges inside than outside.The cell is DEPOLARIZED.
Electrophysiology• Depolarization causes Ca2+ to be released from storage sites in cell.• Ca2+ release causes contraction. Calcium couples the electrical event of depolarization to the mechanical event of
Electrophysiology Na+ Na+ Na+ Na+ K+ Na+ Na+ Na+ Na+ Na+ K+ K+ Na+ Na+ K+ Na+ Na+ Na+ Na+ Na+ K+ Na+ Na+Cell then REPOLARIZES by pumping out K+ then Na+ to restorenormal charge balance.
Electrophysiology Na+ Na+ Na+ Na+ K+ Na+ Na+ Na+ Na+ Na+ K+ K+ Na+ Na+ K+ Na+ Na+ Na+ Na+ Na+ K+ Na+ Na+Finally, the Na+-K+ pump in the cell membrane restores the properbalance of sodium and potassiuim.
Cardiac Conduction CyclePhase 0 = rapid Na influxPhase 1 = stop Na influx, K efflux, Cl influxPhase 2 = Ca influx, K influx Sarcomere:Phase 3 = stop Ca influx, minimal K efflux, Na Fast Sodiumefflux ChannelsPhase 4 = resting membrane potential state
What is an electrocardiogram?• Picture of the electrical activity of the heart• Used to evaluate/monitor heart rate, effects of disease, meds, or injury, pacemaker function, electrolytes, conduction disturbances, mass of muscle, orientation of heart in chest or presence of ischemic damage.
Leads• Record of electrical activity between two electrodes.• Averages the current flow at a specific time in a portion of the heart.• 3 types: standard limb leads, augmented leads and precordial (chest) leads.• Each has positive and negative pole.• The positive electrode is like an “eye”.
Leads (cont.)• If the impulse is moving toward the positive electrode the waveform goes up.• If away, the waveform goes down.• If perpendicular, it will either be biphasic or a straight line.• No electrical activity is called the baseline or isoelectric line.
Standard Limb Leads• Leads I, II, III• Einthoven’s triangle• The voltage of I + III = II
Lead I • Shows lateral surface of the left ventricle • Normally is upright because the impulse is moving toward the positive electrode.
Lead II • Views inferior surface of the left ventricle • Normally positive • Commonly used for monitoring
Lead III • Views inferior surface of the left ventricle • Usually the QRS is positive but the P may be +, - or biphasic
Augmented Limb Leads• Letters stand for “augmented voltage ___”• Only consist of one electrode on the body surface• Negative point is the center
aVR • Views heart from right shoulder • Does not view the walls of the heart, only the base and great vessels • Normally negative
aVL • Views heart from the left shoulder • Views high lateral wall of the left ventricle • Usually biphasic because depolarization is perpendicular to the electrode
aVF • Views the heart from the left leg • Views the inferior wall of the left ventricle • Should be positive
Precordial (Chest) Leads• View the heart in the horizontal plane• Each electrode is positive
V leads cont.• V1: 4th ics to right of sternum, septum, negative• V2: 4th ics to left of sternum, septum, biphasic• V3: midway between V2 & V4, anterior, biphasic• V4: 5th ics midclavicular line, anterior, biphasic• V5: between V4 & V6 @ 5th ics, lateral, positive• V6: midaxillary line in 5th ics, lateral, positive
12 Lead EKG Technique• Effective contact between electrode and skin is essential• Try to exclude artifact – Internal (larger patients) – External (60hz noise)• Precise placement of precordial electrodes• Correct patient position
Technically Accurate EKG Tracing• Remember Einthoven’s triangle • Lead I + Lead III = Lead II • P waves positive in lead II and negative in aVR• R waves in V1-V6 should gradually progress from negative to upright• Check standardization box before interpreting the EKG tracing
Interpretation of the 12-Lead ECG• In the limb leads – P wave is typically upright in leads I, II, aVL and aVF – P wave is often biphasic in lead III and is negatively deflected in lead aVR• In precordial leads – P wave is typically upright in leads V5 and V6 – Lead V1 is biphasic, and leads V2 and V4 are variable
Interpretation of the 12-Lead ECG• Septal depolarization is not always seen on the ECG. When it is, there will be a small Q wave in leads I, aVL, V5, and V6.• The T wave will usually be recorded in a positive deflection in the same leads that record a positive deflection in the R wave.
Systematic Approaches• Use the same method of analysis each time to ensure consistent interpretation.• Questions to consider when looking for arrhythmias – Is the rhythm fast or slow? – Is the rhythm regular or irregular? – Are there any P waves? – Are all P waves the same?
Systematic Approaches• Questions to consider (continued) – Does each QRS complex have a P wave? – Is the PR interval constant? – Are the P waves and QRS complexes associated with each other? – Are the QRS complexes narrow or wide? – Are the QRS complexes grouped or not? – Are there any dropped beats?
Hemiblock• Block of one of the two fascicles of the left bundle branch system• Marked axis deviation often indicates hemiblock
Trifascicular System• Part of the electrical conduction system – Right bundle branch – Left bundle branch • Branches into two separate fascicles • Left anterior hemifascicle (fascicle) • Left posterior hemifascicle (fascicle)
Trifascicular System• Electrical impulse can travel to the ventricles in three ways: – Right bundle branch – Left anterior hemifascicle • Blood supply from LAD – Left posterior hemifascicle – Blood supply from RCA and circumflex
Left Anterior Hemiblock• Anterior hemifascicle of left bundle branch blocked – Ischemia, necrosis• ECG finds: – Pathological left-axis deviation – Small Q wave in LI – Small R wave in LIII – Narrow QRS possible
Left Anterior HemiblockBledsoe/Benner, Critical Care Paramedic
Left Posterior Hemiblock• Posterior fascicle of left bundle branch blocked• ECG finds: – Pathological right-axis deviation – Small R waves in LI – Small Q waves in LIII – Right ventricular hypertrophy• Clinically more significant than left anterior block
Clinical Significance of Hemiblock• Mortality rate for patients with AMIs with hemiblocks four times greater than those without• Risk factor for complete heart block – Patient considered high risk if AV block presents with hemiblock• In AMI setting, can indicate proximal artery occlusion
Axis• Definition: axis is the average vector (direction) of the cardiac electrical impulse in the vertical plane.• We are concerned with the QRS axis, which is the direction of the ventricular depolarization impulse.
Axis• What does this mean? – The electrical impulse that depolarizes the heart travels a certain route thru the heart – The vertical plane is the one that runs head to toe when the patient is facing forward – The average direction the impulse travels in this plane is the axis – Simple, right?!
Axis• Measured in degrees – 0° is at 3 o’clock – 180° is at 9 o’clock – Degrees are positive from 3 o’clock to 9 o’clock in clockwise direction – Degrees are negative from 3 o’clock to 9 o’clock in counterclockwise direction
Axis Quadrants• The axis circle is divided into four quadrants – Normal= 0° to +90° – RAD= +90° to ±180° – LAD= 0° to -90° – Indeterminate axis= -90° to ±180°• This makes sense as the normal impulse travels from SA node to ventricles in a SW direction!• All quadrants besides normal are “deviated”
Rapid Axis and Hemiblock Determination• See “Rapid Axis and Hemiblock Chart” on the next slide. – Designed to help clinicians quickly determine presence of axis deviation and hemiblock• Two ways to use chart – When cardiac monitor does not provide axis angle: • Assess LI, II, and III on ECG • Determine if QRS complex is deflected more positively or negatively in each lead • Compare finds to “Rapid Axis and Hemiblock Chart” – When cardiac monistor provides axis angle: • Compare monitor readout (don’t trust machine)
Significance of Axis Deviation• Shifts away from infarcted tissue• Left Deviation – Left Hypertrophy, WPW, Septal defects, Hyperkalemia• Right Deviation – Right Hypertrophy, Left Posterior Hemiblock, PE, Atrial defects, Chronic lung disease• Extreme Right – V-Tach, Paced, Anterolateral Infarct
Bundle Branch Blocks• Definition – Block to the left or right bundle branch system • Left bundle branch block more clinically significant – Higher mortality – Results in wide QRS ∀ >120 ms• Etiology – Myocardial ischemia, infarction – Congenital defects
Bundle Branch Blocks “Turn Signal Criteria”• MCL-1, any of the precordial leads can be used• QRS must be >120 ms
Bundle Branch Blocks “Turn Signal Criteria”• Technique • View the QRS of V1 (or MCL-1) • Lies immediately over the right ventricle and provides the best view of the superior aspect of the interventricular septum • Identify the J point of the QRS • Draw a horizontal line from the J point either to an intersecting line of the QRS or to the beginning of the QRS • Will produce a triangle pointing upward or downward • When pointing upward, triangle indicates a right bundle branch block • When you push a vehicle’s turn signal upward, the signal lights indicate a right turn • When pointing downward, triangle indicates left bundle branch block • When you pull a vehicle’s turn signal downward, the signal lights indicate a left turn
Rate-Dependent Bundle Branch Blocks• Easy to misidentify as VT – VT therapy could result in rapid hemodynamic compromise• MCL-1 useful for differentiating tachycardia with BBB from VT – RSR’ complex >120 ms = RBBB, not VT – QRS >120 ms = LBBB, not VT
Coronary Plaques• Have the consistency of toothpaste• Cells within plaque synthesize and secrete proteins that promote clot formation• Prone to rupture if they are large and have a soft lipid core
Coronary Artery Obstruction• If the clot partially occludes the artery: – Acute coronary syndrome or unstable angina• If the clot fully occludes the artery: – Myocardial infarction
Angina• Stable – Onset with physical exertion or stress. Lasts 1 – 5 minutes and is relieved by stress.• Unstable – Change in Stable angina frequency, quality, duration, or intensity. Lasts >10 minutes despite rest and/or NTG.• Variable – Spontaneous noted at rest (sleeping); relieved by NTG• Silent – Asymptomatic with evidence of ischemia• Mixed – Combination of the above
Types of Infarctions• Divided into Transmural and non-transmural MIs.• Transmural: Extends through full thickness of the myocardium and includes the endocardium and epicardium.• Subendocardial: Damage is limited to the subendocardial surface.
Ischemia, Injury and Infarction – 12 Leads• Changes usually begin early and progress• May take more than an hour for changes to show• 20-30% of infarcts do not change the 12-lead EKG -must base diagnosis on labs and clinical presentation
Hyperacute T Waves• The T wave can become tall and narrow because of ischemia.• The first change that might appear is an upward slanting of the ST segment and a subtle enlargement of the T wave.• The hyperacute T waves are localized to the area of ischemia and infarction.
ST-Segment Elevation• Caused by changes that affect ventricular depolarization and repolarization• Non-MI changes can also cause this condition – Left BBB – Ventricular rhythms – LVH – Pericarditis – Early repolarization
ST-Segment Elevation• A persistent ST-segment elevation may indicate a ventricular aneurysm.• In benign J-point elevation, the T wave is clearly distinguished as a separate wave.• With myocardial disease, the elevated J point bows upward and merges with the T wave.
J-PointPoint where QRS ends and ST segment begins
Ischemia• Lack of blood may be due to a decreased supply or an increased demand – Causes a delay in repolarization• ST segment is depressed if it is more than 1 mm below the isoelectric line at .04 sec past the J-point• Inverted T waves are always normal in aVR and may be normal in III and V1
Injury• Injured tissue does not depolarize completely and remains more positive than other tissue• ST segment is elevated more than 1mm above the baseline at 0.04 sec after the J-point in 2 or more related leads
Infarction• Q waves must be wider the 0.04 sec &/or greater than 25% of the height of the R wave• Q waves may be normal in III and aVR• Small Q waves in I, aVL, V5 and V6 are not infarction but are septal depolarization• Q waves in the V leads is also known as poor R wave progression
Reciprocal Changes• Mirror image that occurs when two electrodes view the AMI from opposite angles – Tall, upright T waves – ST seg depression – Taller R waves• May or may not be present and may indicate more severe damage
Inferior MI• Bradycardia• Atrial fib• AV Blocks: – 1st degree, 2nd degree type I, 3rd degree with junctional escape mechanism• Hypotension (treat with fluids)• Possible NTG, Morphine intolerance• Hiccoughs, Vomiting, JVD• Will Have clear lungs• Possible RV failure (RCA involved)
Anterior MI• Left ventricle• Involves the LAD• Indicative changes: V1-4
Anterior MI• Sinus tachycardia• AV blocks – 2nd degree II, 3rd degree with ventricular escape mechanism• Bundle Branch Blocks – Beware if RBBB b/c septal arteries are high in LAD and a lot of muscle has probable been damaged• LV failure• Pulmonary edema• Hypotension is bad sign
Lateral Wall MI• Left Ventricle• Involves the LCx• Indicative changes: I, aVL, V5-6• Reciprocal changes: II, III, aVF
Lateral Wall• Bradycardia• Possible junctional rhythms• Possibly AV Blocks – 1st degree – 2nd degree, type I – 3rd degree, junctional escape mechanism
Posterior Wall• Back of LV• Generally involves the LCx but may be PDA coming off RCA• Indicative changes: V7-9 (if you do posterior leads)• Reciprocal changes: (look for these as your best clues) – Tall R waves in V1-2 – ST depression in V1-2• Frequently paired with inferior MI
Non-Q wave MI• Subendocardial MI• 30% of all MI’s• Non-specific ST-T wave changes without Q wave formation• Usually hemodynamically stable• Risk of “extension” is significant
Serum Cardiac Markers• CK-MB subfomes for Dx within 6 hrs of MI onset• cTnI and cTnT efficient for late Dx of MI• CK-MB subform plus cardiac-specific Troponin best combination• Do not rely solely on Troponins because they remain elevated for 7-14 days and compromise ability to diagnose recurrent infarction
MI Management and Treatment• Nitrates to improve coronary blood flow; venous pooling reduces cardiac output, O2 use, and decreased preload.• Morphine vasodilates and decreases preload and afterload. Decreases sympathetic tone causing a decreased HR and O2 consumption.• Beta-blockers decrease HR and contractility and increase diastolic filling time.• Calcium Channel Blockers produce dilation of the coronary arteries and collateral vessels, decreasing contractility and conduction.
Thrombolytics• Indications – New onset ST segment elevation MI• Contraindications – Relative: HTN, recent trauma, pregnancy – Absolute: Active internal bleeding, suspected aortic dissection, intracranial neoplasm, prior hemorrhagic CVA or any CVA <1 yr old.
Angioplasty• Best outcome if <90 minutes from onset• Treat chest pain• Inhibit clotting• Watch for bleeding and reocclusion post procedure. – Leg kept straight – Head of bed < 30 degrees elevation
Pericarditis• Inflammation of the pericardium, the membrane that surrounds the heart – May cause ST-segment elevation and T-wave flattening or inversion – ST-segment and T-wave changes tend to be throughout all leads of the ECG. – The T wave usually does not invert until the ST segment has returned to baseline.
Pericarditis• Diagnostics – Help determine etiology of pericarditis – White blood cells • Elevated in infection – ESR • Elevated in infection – EKG • Diffuse ST segment changes • PR segment depression • Inverted T waves
Pericardial Effusion• Pathophysiology – Abnormal buildup of fluid in the pericardial sac – Secondary to: • Pericarditis • Trauma – Places pressure on heart, decreases diastolic filling pressures
Cardiomyopathies• Cardiac disorders whose dominant feature is pathologic change to the myocardium• Include: – Primary cardiomyopathies • No underlying cause identified – Secondary cardiomyopathies • Have demonstrable underlying cause• Three major categories – Dilated cardiomyopathies – Hypertrophic cardiomyopathies – Restrictive cardiomyopathies
Dilated Cardiomyopathy• Pathophysiology – Myocardium enlarged, dilated – All four chambers can be involved – Often idiopathic – Toxic, metabolic, infectious factors may be involved – Decreased SV, EF = Increased end systolic volume – Increased end systolic volume = Increased end systolic pressure = Dilated chambers
Dilated Cardiomyopathy• Clinical manifestations – Fatigue, weakness – Progressive signs and symptoms of CHF – Right and left side – S3, S4 summation gallop – Mitral/tricuspid regurgitation murmurs
Aortic Stenosis• Pathophysiology – Opening of aortic valve is narrowed and obstructs forward blood flow into aorta – Left ventricle attempts to increase SV and CO – Results in left ventricular hypertrophy• Clinical manifestations – Typically presents with triad of: • Angina, Exertional syncope, Dyspnea on exertion – Left Axis Deviation, Left Hypertrophy• Treatment includes nitrates, diuretics, digitalis, IABP as bridge to surgery
Aortic Regurgitation / Insufficiency• Pathophysiology – Leaking aortic valve – Rising left ventricular pressures result in: • Left ventricular dilation, Left ventricular hypertrophy, Left heart failure• Presentation – CHF, Hypotension, Angina, Wide Pulse Pressure, Corrigan’s Pulse• Treatment – surgical repair
Mitral Stenosis• Stenotic valve obstructs forward blood flow from the left atrium into the left ventricle• Results in elevated left atrial pressure• Pulmonary hypertension – Right ventricle can fail• Rheumatic fever most common cause• Clinical presentation – Exertional dyspnea, orthopnea, fatigue, malaise, palpable diastolic thrill
Mitral Stenosis• Management – Treat symptoms of congestive heart failure – Use diuretics – Give nitrates – Treat atrial fibrillation – Conduct digitalis – Complete anticoagulation for new-onset atrial fibrillation – Intervene surgically
Hypokalemia• Decreased level of potassium• Diagnostic criteria – ST-segment depression – Slightly decreased amplitude of the T waves – Minimal prolongation of the QRS interval – U wave is usually small and follows the T wave.
Hypercalcemia• Elevated levels of calcium (normal 8.5 – 10.5 mg/dl)• Diagnostic criteria – Shortening of the ST-segment, which, in turn, shortens the QT interval – PR interval may be prolonged – QRS may lengthen – T waves may become flat or invert
Hypocalcemia• Reduced levels of calcium• Diagnostic criteria – A prolongation of the ST segment that produces a lengthening of the QT interval
Coronary Artery Spasm• Variant or Prinzmetal’s angina• May occur spontaneously or: – Exposure to cold – Emotional stress – Vasoconstricting meds – Cocaine – Smoking• Mimics MI