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Bradyarrhythmias occur when the heart rate is <60 beats per minute (bpm); can be physiologic, such as in young individuals and in well-trained athletes, or pathologic and symptomatic. Typically, symptoms occur when the heart rate is <40 beats per minute.


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Location of Disease Name of Disorder ECG Findings
SA nodal disease Sinus pause Transient absence of sinus P wave
AV nodal disease First-degree AV block Prolonged PR interval (>200 ms)
Mobitz Type I second-degree AV block (Wenckebach phenomenon) PR interval prolongs until a nonconducted P wave is seen; (Figure 9-1)
Third-degree (complete) block with narrow escape rhythm P's and QRS's are dissociated; QRS complexes are narrow (Figure 9-2)
Infranodal disease Mobitz Type II second-degree AV block PR interval constant and see intermittent nonconducted P waves
Third-degree (complete) block with wide escape rhythm P's and QRS's are dissociated; QRS complexes are wide

Abbreviations: AV node, atrioventricular node; SA node, sinoatrial node.


Mobitz Type I second-degree AV block, also known as Wenckebach phenomenon.


Complete heart block with a narrow escape.


  • In the setting of a reversible cause, the only treatment indicated is to avoid the inciting cause.

  • Indications for permanent pacing include evidence of infranodal disease or symptomatic bradycardia at any level (SA node, AV node, or infranodal) that is spontaneous or secondary to the need for advancement of medical therapy (β-blocker, calcium channel blocker, etc); symptoms include dizziness, fatigue, syncope, poor exercise tolerance, and so on.


Tachyarrhythmias occur when the heart rate is >100 beats per minute and are divided into narrow QRS complex and wide QRS complex tachyarrhythmias.


This can be further divided into supraventricular tachyarrhythmias (SVT), atrial fibrillation (AF), and atrial flutter.

Supraventricular Tachyarrhythmias

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Supraventricular Tachycardia ECG Findings
Sinus tachycardia Sinus P waves at a rate >100 bpm
AVNRT Narrow-complex tachycardia with no obvious P waves; short RP interval (Figure 9-3)
ORT Narrow-complex tachycardia; P waves often not visible, but if visible, then mid-RP interval
Atrial tachycardia Narrow-complex tachycardia with long RP interval
PJRT Narrow-complex tachycardia with long RP interval

Abbreviations: AVNRT, AV nodal reentrant tachycardia; ORT, orthodromic reciprocating tachycardia; PJRT, persistent junctional reciprocating tachycardia.


The figure demonstrates the relationship of the intervals that can be used to distinguish the different SVTs.


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