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.
| 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 |
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 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 |
It is often difficult to diagnose the type of SVT based solely on surface ECG findings. Most often, electrophysiology (EP) study is required for definitive diagnosis. However, evaluating the RP interval (Figure 9-4) can be helpful; if the RP interval is short (less than one-half the R-R interval), then the rhythm is usually that of a typical AVNRT or atrioventricular reciprocating tachycardia (AVRT). If the RP interval is long (greater than one-half the R-R interval), then the rhythm is either atrial tachycardia or atypical AVNRT or PJRT.
Acute therapy involves vagal maneuvers and carotid sinus massage; adenosine can be used if vagal maneuvers fail. Cardioversion should also be considered in the setting of hemodynamic instability if the SVT fails to terminate with adenosine.
Definitive therapy consists of either antiarrhythmic medications or catheter ablation; all patients with SVT should be referred to electrophysiologists for consideration of an EP study and ablation. Catheter ablation is generally associated with a high cure rate and a very low complication rate.
Physicians are more likely to attribute symptoms of paroxysmal SVT in women specifically, as compared to men, to panic, anxiety, and stress rather than correctly diagnosing the arrhythmia. This often leads to delay in therapy and a higher likelihood of women not being treated for their arrhythmia.
Women are not referred for curative ablation as often as men. This is specifically problematic as SVT ablation is associated with a very high cure rate and many of the medications used to suppress SVT are highly toxic.
A cyclical variation of SVT occurs in women; those with a history of paroxysmal SVT have a higher incidence of episodes during the luteal phase of their menstrual cycle and this is likely secondary to increased progesterone, decreased estrogen, and increased sympathetic activity.1
Women have a 2-fold greater risk of AVNRT as compared to men. AVNRT is one of the most common types of SVT and has a very high cure rate with ablation.
| Rhythm | ECG Findings |
|---|---|
| Atrial flutter | Classic sawtooth pattern on ECG; (Figure 9-5), atrial flutter waves are generally regular and of consistent cycle length |
| Atrial fibrillation | No clear P waves with irregularly irregular rhythm (Figure 9-6) |
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