Etiology, warning signs and therapy of torsade de pointes. A study of 10 patients

Torsade de pointes, also called atypical ventricular tachycardia (AVT), was diagnosed in 10 patients, nine on antiarrhythmic therapy and one with acute central nervous system damage. Four patients received quinidine and five disopyramide, either alone or in combination with amiodarone. AVT was dose-dependent in some, but in others, it started shortly after initiation of drug therapy (idiosyncrasy). All patients had QT prolongation longer than 0.60 second immediately before the onset of AVT. This measurement appeared to be a more sensitive predictor of the development of AVT than QTc prolongation or QRS widening. All patients also showed bradycardia before AVT onset. After therapy, the QT immediately decreased, while QTc and QRS remained prolonged for longer periods. Isoproterenol was effective in five of seven patients, but was contraindicated in two others. Ventricular pacing was used in four patients, including the two who did not respond to isoproterenol, and this abolished AVT promptly. Isoproterenol or pacing appear to be the therapy of choice for AVT, while the conventional drugs used to treat the usual form of ventricular tachycardia are not only ineffective, but even contraindicated.

Neonatal tachycardia

This paper presents two cases of neonatal paroxysmal atrial tachycardia originating in the same country area, and in fact, presenting to the same general practitioner within a month of each other. Both cases were complicated by cardiac failure, and various forms of treatment were employed with variable success.

[Studies of nodal conduction]

Nodal conduction has been studied in 44 normal subjects, 21 cases of 1st or 2nd degree AV block, 16 cases of LGL syndrome, and 19 patients with a distal infra-His AV block, by means of stimulation which was increased in regular steps of 5 beats per minute, and of extra-systolic stimulation. These two techniques demonstrate that the nodal response to an extrasystole or a regular tachycardia is not the same, and that different mechanisms are probably at play. With regular stimulation, the normal limits of 1/1 conduction lie between 140 and 200 per minute. A nodal block for a rate less than 130 per minute can be taken as indicative of a nodal defect. Delayed AH conduction is a much less precise criterion. It may reach a high level in normal subjects, and it is not certain that the finding of a PR interval of more than 200 msec. (AH of more than 140 msec.) at a normal rate is neccessarily indicative of nodal pathology. Cases of LGL syndrome are associated with short-circuits which are usually partial. The diverse responses observed in these different groups can be explained by modifications of structure within the A/V node itself.

His bundle recordings in bilateral bundle-branch block combined with Wolff-Parkinson-White Syndrome. Antegrade type II (Mobitz) block and 1:1 retrograde conduction through the anomalous bundle

An example of bilateral bundle-branch block (RBBB) in the presence of WPW syndrome in which diagnosis was established with the aid of His bundle recordings is presented. Complete RBBB and intermittent block of the superior and inferior divisions of the left bundle branch were coexistent for at least 2 years before complete heart block (trifascicular block) occurred. It was demonstrated that the preexcitation pathway conducted and blocked together with the normal pathways. It is suggested that the anomalous bundle in this case traveled with the normal pathways and that this close relationship is more common than has been suspected.

Retrograde V-A conduction at 1:1 ratio was present during electrical stimulation of the right ventricle and the anomalous bundle was used for retrograde spread of activation from the ventricles to the atria. The retrograde P waves, thus produced, conducted antegrade through the His bundle (reciprocation) but reached the ventricles only when they appeared near the end of the T waves of the preceding beats. The mechanism of supramaximal conductivity or excitability, therefore, appears to be a plausible explanation.