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Tachyarrhythmias may appear in the presence or absence of structural heart disease; they are more serious in the former. Conditions that provoke arrhythmias include (1) myocardial ischemia, (2) heart failure, (3) hypoxemia, (4) hypercapnia, (5) hypotension, (6) electrolyte disturbances (e.g., hypokalemia and/or hypomagnesemia), (7) drug toxicity (digoxin, drugs that prolong the QT interval), (8) caffeine consumption, (9) ethanol consumption.


Examine ECG for evidence of ischemic changes (Chap. 113), prolonged or shortened QT interval, characteristics of Wolff-Parkinson-White (WPW) syndrome (see below), or ST elevation in leads V1–V3 typical of Brugada syndrome. See Table 125-1 for diagnosis of tachyarrhythmias; always identify atrial activity and relationship between P waves and QRS complexes. To aid the diagnosis:

  • Obtain long rhythm strip of lead II, aVF, or V1. P waves can be made more evident by intentionally doubling the ECG voltage.

  • Place accessory ECG leads (e.g., right-sided chest leads) to help identify P waves. Record ECG during carotid sinus massage (Table 125-1). Note: Do not massage both carotids simultaneously.

  • For intermittent symptoms, consider 24-h Holter monitor (if symptoms occur daily), a pt-activated or continuously recording event monitor over 2–4 weeks, or, if symptoms are very infrequent but severely symptomatic, an implanted loop monitor. A standard exercise test may be used to provoke arrhythmias for diagnostic purposes.

TABLE 125-1Clinical and Electrocardiographic Features of Common Arrhythmias

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