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Chapter 123: Tachyarrhythmias

INTRODUCTION

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, pharmacologic agents that prolong the QT interval), (8) caffeine consumption, (9) ethanol consumption.

Diagnosis

Examine ECG for evidence of ischemic changes (Chap. 111), 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 123-1 for diagnosis of tachyarrhythmias; always identify atrial activity and relationship between P waves and QRS complexes. To aid the diagnosis:

TABLE 123-1CLINICAL AND ELECTROCARDIOGRAPHIC FEATURES OF COMMON ARRHYTHMIAS
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TABLE 123-1CLINICAL AND ELECTROCARDIOGRAPHIC FEATURES OF COMMON ARRHYTHMIAS
Rhythm Atrial Rate Features Carotid Sinus Massage Precipitating Conditions Initial Treatment
Narrow QRS complex
Atrial premature beats — P wave abnormal; QRS width normal — Can be normal or due to anxiety, CHF, hypoxia, caffeine, abnormal electrolytes (↓K+ ↓Mg2+) Remove precipitating cause; if symptomatic: beta blocker
Sinus tachycardia 100–160 Normal P wave contour Rate gradually slows Fever, anxiety, dehydration, pain, CHF, hyperthyroidism, COPD Remove precipitating cause; if symptomatic: beta blocker
AV nodal tachycardia (reentrant) 120–250 Absent or retrograde P wave Abruptly converts to sinus rhythm (or no effect) Can occur in healthy individuals Vagal maneuvers; if unsuccessful: adenosine, verapamil, beta blocker, cardioversion (100–200 J). To prevent recurrence: beta blocker, verapamil, diltiazem, digoxin, class IC agent, or catheter ablation
Atrial tachycardia 130–200 P contour different from sinus P wave; AV block may occur; automatic form shows “warm-up” in rate in first several beats AV block may ↑ Digitalis toxicity; pulmonary disease; scars from prior cardiac surgery

If digitalis toxic: hold digoxin, correct [K+]

In absence of digoxin toxicity: slow rate with beta blocker, verapamil, or diltiazem; can attempt conversion with IV procainamide or amiodarone; if unsuccessful, proceed to cardioversion or catheter ablation

Atrial flutter

Atrial fibrillation

260–300

>350

“Sawtooth” flutter waves; 2:1, 4:1 block

No discrete P; irregularly spaced QRS

↑ AV block with ↓ventricular rate

↓ Ventricular rate

 Mitral valve disease, hypertension, pulmonary embolism, pericarditis, post–cardiac surgery, hyperthyroidism; obstructive lung disease, EtOH, idiopathic

  1. Slow the ventricular rate: beta blocker, verapamil, diltiazem, or digoxin

  2. Convert to NSR (after anticoagulation if chronic) electrically (50–100 J for atrial flutter, 100–200 J for atrial fibrillation) or chemically with IV ibutilide or oral class IC, III, or IAa agent

    Atrial flutter may respond to rapid atrial pacing, and radio frequency ablation highly effective to prevent recurrences; consider ablation for recurrences of atrial fibrillation
Multifocal atrial tachycardia 100–150 More than three different P wave shapes with varying PR intervals No effect Severe respiratory insufficiency Treat underlying lung disease; verapamil or diltiazem may be ...

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