9. Inappropriate Sinus Bradycardia
Chronotropic Incompetence
• HR<60 that doesn’t increase appropriately with
exercise
• Usually defined as failure to attain 80% of
maximal age predicted HR (MAHR) on exercise
testing
• MAHR = 220 – Age
• e.g. failure to reach a HR of 120 in a 70 year old
patient
18. Tachycardia-Bradycardia Syndrome
• Bradycardia/sinus pauses interspersed with
atrial arrhythmias (AFL, A fib, A tach)
• Sinus arrest manifests after termination of
atrial arrhythmia (spontaneously or after DCCV)
• Sinus Node Recovery Time (SNRT) uses the
above observation to assess SA node function
in EP studies
20. Indications for pacing in SND
• Class I (recommended)
– SND with documented symptoms
– SND due to irreversible factors or due to essential
drug therapy
– Chronotropic incompetence
• Class III (NOT recommended)
– Asymptomatic
21. Bradycardias
• SA node dysfunction or
Sick Sinus Syndrome
– Inappropriate sinus
bradycardia
– Sinoatrial exit Block
– Sinus Pause/Arrest
– Tachycarda/Bradycardia
syndrome
– Persistent Atrial Standstill
• AV Blocks
– First Degree
– Second Degree
• Mobitz I
• Mobitz II
• 2:1 Block
– Third Degree
– High Grade AV Block
22. AV Blocks
• First Degree
• Second Degree
– Mobitz I
– 2:1 Block
– Mobitz II
• Third Degree
• High Grade AV Block
23. First Degree AV Block
• PR interval > 200msec
• If QRS is normal, block is usually at the level of
the AV node
• If QRS shows bundle branch block, block
maybe in His-Purkinje System
26. Second Degree Heart Block
Mobitz I or Wenchebach
• Progressive Prolongation of the PR interval
and shortening of the RR interval until a P
wave is blocked
• RR interval containing the non conducted P
wave is less than two PP intervals
• PR interval longer after the non conducted P
wave
• Grouped beating
28. Causes
• Normal
• Athletes
• Medications
• Myocardial Infarction
(inferior wall)
• Acute rheumatic fever
• Myocarditis
Features
• Usually asymptomatic
• Usually narrow QRS complex
block at AV node
• The presence of bundle branch
block suggests the possibility
of block below the AV node in
His Purkinje system
30. Second Degree – Mobitz II
• Constant PR interval with intermittent
nonconducted P wave and no evidence for PACs
• RR interval between non conducted P waves is
equal to two PP intervals
• Each QRS is preceded by multiple P waves
• 3:1, 4:1 also called high grade AV block
• Other variations include 3:2
• 2:1 block maybe Mobitz I or Mobitz II
33. Management
• Usually require permanent pacing especially if
symptomatic due to high likelihood of
progression to high grade AV block and third
degree AV block
34. Differentiating mechanism of 2:1 block
Feature Mobitz I Mobitz II
QRS duration Narrow Wide
Response to increasing
HR & AV conduction i.e.
exercise, atropine
Improves Worsens
Response to decreasing
HR & AV conduction i.e.
carotid sinus massage
Worsens Improves
Acute MI Inferior Anterior
35. Third Degree AV block
• Atrial impulses consistently fail to reach the
ventricles, resulting in atrial and ventricular
rhythms that are independent of each other
• PR interval varies
• PP and RR intervals are constant
• Ventriculophasic sinus arrhythmia
– PP interval containing QRS is shorter than PP
interval without a QRS complex
45. P P P P P P P P P P P
3rd
degree AV block, junctional escape
46. P P P P P P P P P P
3rd
degree AV block, junctional escape
or high grade AV block
47. Problem
• 50 year old female with no PMH presents with
acute onset of shortness of breath on exertion
of 4 days duration
• HR 50/min, BP 140/80
• Initial ECG sinus bradycardia
• TropI 1.2
HR 46/min
Put her on a treadmill reached HR of 137/min
3.4 and 4.8 second pauses
Patient had acute coronary syndrome with lesion in proximal RCA involving the branch to the SA node, placed a dual chamber pacemaker
ACC/AHA guidelines
Prolongation of of the PR interval &gt; 200ms, 1:1 conduction, P before every QRS complex, both P and QRS are normal
Progressive prolongation of the PR interval terminated in a non conducted P wave
