[Long-term electrocardiography in the idiopathic QT syndrome].

The value of long-term electrocardiographic (ECG) monitoring was assessed in 14 patients (8 males, 6 females; mean age 21 [17-30] years) with the idiopathic long QT syndrome (LQTS), 14 healthy subjects of the same age serving as controls. Twelve patients had the typical history of syncopes or sudden cardiac death among family members; seven patients had a history of syncope, while four patients had been successfully resuscitated. None had associated cardiac disease. Among the group with LQTS the rate-corrected QT interval at rest was 498 + 56 ms, in the control group 412 +/- 30 ms (P < 0.005). Resting and maximal heart rates on exercise were similar in the two groups. The rate-corrected QT interval on exercise was significantly longer in the LQTS patients (P < 0.001). In the control group the maximal heart rate in the long-term ECG was significantly higher (144 +/- 28/min) than in the LQTS patients (128 +/- 17/min; P < 0.01). The long-term ECG recorded abnormal findings in five patients: torsade-de-pointes tachycardia in two, T-wave alternans in two, and bradycardia resulting from intermittent sinoatrial block in one. No abnormal findings were recorded in the control group (P < 0.03).