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CLINICAL STUDY

Pause-dependent torsade de pointes following acute myocardial infarction

A variant of the acquired long QT syndrome

^a Department of Cardiology, Tel Aviv-Sourasky Medical Center, and the Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel

Manuscript received February 23, 2001; revised manuscript received May 21, 2001, accepted June 11, 2001.

Reprint requests and correspondence: Dr. Sami Viskin, Department of Cardiology, Tel Aviv Medical Center, Weizman St. 6, Tel Aviv 64239, Israel
viskin_s{at}netvision.net.il

OBJECTIVES

We report on a previously unrecognized form of the long QT syndrome (QT interval prolongation and pause-dependent polymorphic ventricular tachycardia [VT]) entirely related to myocardial infarction (MI).

BACKGROUND

Polymorphic VT in the setting of acute MI generally occurs during the hyperacute phase, is related to ischemia, and is not associated with QT prolongation. Although QT prolongation after MI is well described, typical pause-dependent polymorphic VT (torsade de pointes) secondary to uncomplicated MI was previously unknown.

METHODS

Of 434 consecutive admissions for acute MI, 8 patients had progressive QT prolongation that led to typical torsade de pointes. None of these patients had active ischemia or other known causes of QT prolongation. These patients were compared with 100 consecutive patients with uncomplicated MI who served as controls.

RESULTS

The incidence of torsade de pointes following MI was 1.8% (95% confidence interval 0.8% to 3.6%). The QTc intervals of patients and controls were similar on admission. The QTc lengthened by day 2 in both groups, but more so in patients with torsade de pointes (from 470 ± 46 to 492 ± 57 ms [p < 0.05] and from 445 ± 58 to 558 ± 84 ms, respectively [p < 0.01]). Maximal QT prolongation and torsade de pointes occurred 3 to 11 days after infarction. Therapy included defibrillation, magnesium, lidocaine and beta-blockers. Three patients required rapid cardiac pacing. The long-term course was uneventful.

CONCLUSIONS

Infarct-related torsade de pointes is uncommon but potentially lethal. An acquired long QT syndrome should be considered in patients recovering from MI who experience polymorphic VT as specific therapeutic measures are mandatory.

Abbreviations and Acronyms   EAD = early after depolarization   ECG = electrocardiogram/electrocardiographic   LAD = left anterior descending   LQTS = long QT syndrome   MI = myocardial infarction   VF = ventricular fibrillation   VT = ventricular tachycardia

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