The diagnosis of the syndrome is easily obtained by electrocardiography as long as the patient presents the typical electrocardiographic pattern (picture 1) and there is a history of aborted sudden death or syncopes caused by a polymorphic ventricular tachycardia. It is difficult to forget such a typical electrocardiogram. The ST segment elevation in V1 to V3 with the right bundle branch block pattern is characteristic. The ST changes are different from the ones observed in acute septal ischemia, pericarditis, ventricular aneurysm and in some normal variants like early repolarization. There are though, electrocardiograms which are not as characteristic (picture 6), and they are only recognized by a physician who is thinking of the syndrome. There are also many patients with a normal electrocardiogram in whom the syndrome can only be recognized a posteriori when the typical pattern appears in a follow-up electrocardiogram or after the administration of ajmaline, procainamide or flecainide (picture 7).
Six precordial leads showing spontaneous changes of the electrocardiogram in five different days. Note that the panel in the right shows a less typical electrocardiogram. This pattern has been called saddle-back by the Japanese investigators.
It is possible that the electrocardiographic patterns are different depending on the genetic abnormality. This is the case in other genetic diseases like the long QT syndrome. The mutations that have been discovered in two families give proof of this fact: their electrocardiograms are similar, but not identical (picture 8). Even though in both cases the affected gene was the same, the exact mutation was different. It will be necessary to identify more mutations and make close genotype-phenotype correlation to establish the links. However, we cannot forget the great variability of the electrocardiogram in this syndrome, something which will certainly not facilitate analysis.
12-lead ECG during administration of ajmaline (50 mg in 5 min). Note the progressive appearance of the ST elevation in V1-V3.
Additional diagnostic problems are caused by the changes in the electrocardiogram induced by the autonomous system and by antiarrhythmic drugs. The study by Miyazaki et al was the first one to show the variability of the electrocardiographic pattern in the syndrome. Despite the fact that the syndrome was initially described as a persistent electrocardiographic pattern, it was soon recognized that the electrocardiogram is variable over time, depending on the autonomic interaction and the administration of antiarrhythmic drugs. Adrenergic stimulation decreases the ST segment elevation, while vagal stimulation worsens it. The administration of class Ia, Ic and III drugs increases the ST segment elevation, and also fever. Exercise decreases ST segment elevation in some patients but increases it in others (after exercise when the body temperature has risen). The changes in heart rate induced by atrial pacing are accompanied by changes in the degree of ST segment elevation. When the heart rate decreases, the ST segment elevation increases and when the heart rate increases the ST segment elevation decreases. However, the contrary can also be observed.
Leads V1 to V3 are shown from two patients with two
different mutations in the sodium channel. It is possible
that the electrocardiogram varies depending upon the type of mutation.
Patients with syncope of unknown cause must be challenged with antiarrhythmic drugs in order to exclude the possibility of this syndrome as a cause of ventricular arrhythmias and syncope.
|Clinical Manifestations||Origin of the Electrocardiogram and Ventricular Arrhythmias|