ECG Review: When to Pace Sick Sinus?
By Ken Grauer, MD, Professor, Assistant Director, Family Practice Residency Program, University of Florida, and Associate Editor, Internal Medicine Alert.
Figure. Non-consecutive lead II rhythm strips obtained from a 76-year-old woman. Does she have sick sinus syndrome?
Clinical Scenario: The non-continuous lead II rhythm strips shown in the Figure were obtained from an asymptomatic 76-year-old woman. Are these rhythms diagnostic (or at least consistent) with sick sinus syndrome (SSS)? Is permanent pacemaker implantation indicated? On what does your answer depend?
Answer: The QRS complex is narrow and the rhythm is irregularly irregular. No P waves are seen. The rhythm is therefore atrial fibrillation. Although the overall ventricular response is controlled (if not moderately rapid), a pause of slightly more than 2 seconds is seen in each tracing.
A variety of rhythms may be seen with sick sinus syndrome (SSS). Among these are sinus bradycardia, sinus arrhythmia, sinus pauses, SA (sino-atrial) node exit block, and/or sinus arrest, which may then result in atrial fibrillation or an AV (atrio-ventricular) nodal escape rhythm. Because conduction system disease generally affects not only the SA node, but also the AV node, the ventricular response to either atrial fibrillation or AV nodal escape rhythms is typically slow. In addition to bradyarrhythmias, a "tachy-brady" syndrome is often seen in which brief episodes of tachyarrhythmias (most commonly rapid atrial fibrillation) are followed by relative pauses. This is the situation here, where the two rhythm strips shown in the Figure manifest relatively rapid atrial fibrillation with two brief pauses.
Essential to the diagnosis of SSS is the ruling out of other potential causes of bradycardia, such as medication effect from rate-slowing drugs (ie, digoxin, beta-blockers, verapamil/diltiazem), hypothyroidism, and/or recent myocardial infarction. It is important to appreciate that the two principle indications for permanent pacing of SSS are: i) symptomatic bradycardia (not symptomatic tachycardia); and ii) tachycardia for which rate-slowing medication is needed that then produces symptomatic bradycardia. In general, pauses are not of concern until they exceed 3 seconds in duration. Thus, while the 76-year-old woman in this case may indeed have SSS, permanent pacing is not yet indicated because her pauses are brief and she is still asymptomatic.
The non-continuous lead II rhythm strips shown in the Figure were obtained from an asymptomatic 76-year-old woman. Are these rhythms diagnostic (or at least consistent) with sick sinus syndrome? Is permanent pacemaker implantation indicated? On what does your answer depend?
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