Chapter 12

Cardiac arrhythmias are due to abnormalities in the heart rhythm or conduction that can range in clinical significance from benign to life threatening. The frequency with which these occur varies with age and comorbid conditions, and true cardiac arrhythmias are rare in young people. It is important for the clinician to identify the arrhythmia and determine whether further evaluation or treatment is required. In general, the principle of treatment in this population is to minimize or alleviate symptoms, reduce associated risks (ie, cardiac dysfunction), prevent hemodynamic compromise, and/or prevent mortality.

Proper identification of cardiac arrhythmias in the young requires a clear understanding of the normal physiologic changes in heart rate that occur with age and activity. It is also important to understand the average expected resting heart rate for a given age (Table 12-1).1,2 Identification of clinically relevant arrhythmias requires assessment of the patient's heart rate, a basic understanding of electrocardiogram interpretation in the context of the patient's age, a focused clinical history, and awareness of the patient's current hemodynamic state. This provides a framework for appropriate evaluation and management.

Table 12-1. Normal Heart Rate Range Based on Age

This chapter will outline basic pediatric arrhythmias and focus on several important cardiac conditions that may result in malignant arrhythmias or syncope. Each cardiac arrhythmia will be described based on electrocardiographic findings, causes, clinical features, and management options.2-6

#### Definition

A slow heart rate that is below the lower limits of normal for age but regular and originating from the sinus node. This is characterized by (1) a P wave preceding every QRS complex with a normal PR interval and (2) a normal P-wave morphology and axis (upright/positive in leads I and aVF).

#### Causes

Sinus bradycardia can be due to increased parasympathetic (vagal) tone as seen in well-conditioned athletes; withdrawal of sympathetic tone as seen during sleep and obstructive sleep apnea; drugs such as sedatives, parasympathomimetics, sympatholytics, and many antiarrhythmics agents; increased intracranial pressure; hypothyroidism; hypothermia; prolonged hypoxia; or sinus node dysfunction.

#### Clinical Features

Most patients with sinus bradycardia are asymptomatic. However, symptoms of bradycardia include lightheadedness, dizziness, fatigue, exercise intolerance, presyncope, or syncope.

#### Management

Generally, no therapy is required, but in symptomatic ...

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