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INTRODUCTION

We are often confronted by electrocardiographic (ECG) abnormalities that are discovered incidentally during screening or during the course of investigating an unrelated problem. These are more frequent in the elderly, reflecting to some degree an increasing prevalence of subclinical heart disease. Appropriate advice to the patient requires balancing a knowledge of the natural history of the specific abnormality and potential favorable or harmful effects of a contemplated intervention. An intervention in an asymptomatic individual should be undertaken only with clear information supporting the potential benefit of further investigation and treatment over the natural history of the finding.

It is also obvious that virtually any cardiac abnormality can be reflected in some way in the ECG. For this reason, the scope of this brief section is to summarize the common abnormalities in the domain of the cardiac electrophysiologist. The section is focused to answer the following bottom-line question, namely: Do we leave it alone or do we need to move on to the next step, whether further diagnostic testing or treatment?

BRADYARRHYTHMIAS

Sinus Node Dysfunction

Sinus node dysfunction is said to be present when the ECG criteria of sick sinus syndrome (severe inappropriate bradycardia, sinus pause, chronic atrial fibrillation with a slow ventricular response, alternating tachycardia, and bradycardia) are present in the absence of symptoms.1 The diagnosis must be made with caution, because sinus bradycardia to 40/min or less and sinus pauses to 3 s or greater can be observed in normal individuals during sleep and at rest.2 There are no data to support the utility of permanent pacing in patients with asymptomatic sinus node dysfunction.3 Patients followed for asymptomatic sinus node dysfunction may of course ultimately develop symptoms requiring pacing or need other drug therapy potentially aggravating bradycardia but mortality is dependent on the presence and severity of coexistent disease.

The decision to pace becomes more complex in the patient with sinus node dysfunction who has vague or nonspecific symptoms (fatigue, personality change, memory impairment, dizzy spells), which could potentially be due to bradycardia. The relationship of these symptoms to bradycardia may be established by ambulatory monitoring or treadmill testing, but frequently the link is difficult to clarify and the decision to pace is guided by clinical judgment. A trial of pacing would be useful, especially if a more prolonged period of temporary pacing were possible.

Atrioventricular Block

The risk of syncope or death in patients with atrioventricular (AV) block depends both on the presence of concomitant heart disease and the site of block. In asymptomatic individuals, first-degree AV block and Mobitz type I second-degree AV block are relatively common,4 the latter usually reflecting vagal tone. Pacing is not indicated. The situation is more complex with Mobitz type II second-degree AV block. Knowledge of the site of the block is helpful, as AV nodal ...

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