Treatment

1. Treatment is not necessary. On occasion, AIVR may be the only functioning pacemaker, and suppression with lidocaine can lead to cardiac asystole.

2. If sustained AIVR produces symptoms secondary to a decrease in cardiac output, treatment with atrial pacing may be required.

VENTRICULAR TACHYCARDIA Ventricular tachycardia is the occurrence of three or more depoplarizations from a ventricular ectopic pacemaker at a rate greater than 100. The ECG characteristics of ventricular tachycardia are (1) wide QRS complexes; (2) rate greater than 100 (most commonly 150 to 200); (3) rhythm usually regular, although there may be some beat-to-beat variation; and (4) QRS axis usually constant ( Fig 2.4.-1.9). Uncommonly (about 5 percent of episodes), ventricular tachycardia may have a narrow (<120 ms) QRS complex. In these cases, ECG criteria usually suggest a ventricular origin (see " Ab§I[aOi,.v®rsMs.,.Ve.DÎricM!§[,.. Tachyarrhythmias," below). Ventricular tachycardia can occur in a nonsustained manner—usually short episodes, lasting seconds, with spontaneous termination—or in a sustained fashion—longer episodes that typically require treatment.

There are several variants of ventricular tachycardia. Ventricular flutter is the phrase used for a regular zigzag pattern without distinguishable QRS complexes or T

waves. In bidirectional ventricular tachycardia, the QRS complexes alternate polarity as recorded in a single lead. In alternating ventricular tachycardia, the QRS complexes alternate in height (but not polarity) in a single lead. (Both bidirectional and alternating ventricular tachycardia indicate serious myocardial disease and are often due to digitalis toxicity.) In polymorphous ventricular tachycardia, the QRS complexes have many different shapes in one lead. Atypical ventricular tachycardia

[torsade de pointes (TdP), or "twisting of the points"] is where the QRS axis swings from a positive to negative direction in a single lead ( Fig 24-20). This rhythm results from a triggered arrhythmic mechanism. TdP usually occurs in short runs of 5 to 15 s at a rate of 200 to 240. This form of ventricular tachycardia generally occurs in patients with serious myocardial disease who have a prolonged and uneven ventricular repolarization (prolonged QT interval) ( T§M§...24-3).

FIG. 24-20. Two examples of short runs of atypical ventricular tachycardia showing sinusoidal variation in amplitude and direction of the QRS complexes: "Le torsade de pointes" (twisting of the points). Note that the top example is initiated by a late-occurring PVC (lead II).

b • — — ■ ■ 9k IM ■ I km*— 11 i -J- ¡1 ki flu _JB JU . - ■ — - . ■

b • — — ■ ■ 9k IM ■ I km*— 11 i -J- ¡1 ki flu _JB JU . - ■ — - . ■

tVfl 1BK HniB Wliah ITPJii M 1 it ■.n-'il t"* iÊ"-i--*-

tVfl 1BK HniB Wliah ITPJii M 1 it ■.n-'il t"* iÊ"-i--*-

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