The electrophysiological effects of L 9394 (benzoyl-indolizine), a substance chemically related to amiodarone, but devoid of iodine atoms, were investigated by programmed electrical stimulation of the heart in 12 patients with various forms of tachycardia. Four subjects had electrocardiographic evidence of the WPW syndrome and episodes of circus movement tachycardia. Paroxysmal supraventricular tachycardia, confined to the atrioventricular (AV) node, was found in 3 patients. In 2 cases, where a short PR interval was present, the main complaint was the occurrence of paroxysmal atrial fibrillation. In the remaining 3 instances, the arrhythmia consisted of slow ventricular tachycardia (1 case), supraventricular tachycardia of the focal type (1 case), and episodes of primary ventricular fibrillation, not related to acute myocardial ischaemia (1 case). L 9394 injected intravenously was seen to lengthen the transnodal conduction time as well as the effective and functional refractory periods of the node. Similar effects were found on the retrograde VA pathway. The drug had no action on the infra-Hisian conduction system, on the refractory periods of ventricular muscle, or on the refractory periods of accessory bypasses. The drug was injected during an episode of tachycardia in 6 cases with reproducible supraventricular re-entrant tachycardia. Three had a tachycardia circuit confined to the node. In those instances, the drug had beneficial effects (slowing and interruption of tachycardia, decrease or abolition of echo zone; loss of ability to induce tachycardia). In the other 3 cases, an accessory pathway was incorporated in the circuit. L 9394 interrupted the tachycardia in 2 instances (by anterograde AV block), but failed to protect all 3 patients against reinitiation of tachycardia by premature stimuli. It is concluded that L9394 does not share all the pharmacological properties of amiodarone and will not replace it in all its indications.

BelgiumTwo cases are described in which, during investigation of rhythm disturbances, it was shown that, by delivering atrial stimuli of increasing prematurity, a point was reached where the artificial stimulus failed to induce an atrial response. However, with even more premature stimulations, atrial responses were again observed. These observations are best explained by a gap phenomenon in which very early stimuli delivered during the effective refractory period of the atria were delayed long enough in the exit area around the pacing electrode to allow atrial recovery.The phenomenon of 'gap' in atrioventricular conduction was first described by Moe et al. (1965). During experiments on dogs, they observed a zone in the cardiac cycle when atrial premature beats were not transmitted to the ventricles whereas atrial beats of greater or lesser prematurity were normally conducted to the ventricles. The atrioventricular gap phenomenon occurs when the effective refractory period of a distal site (for example, the His-Purkinje system) is longer than the functional refractory period of a proximal site (for example the AV node), and when closely coupled stimuli are delayed long enough at the proximal site to allow recovery at the distal end (Wu et al., 1974).At present, at least 6 types of gap phenomenon in atrioventricular conduction have been recognised; they differ from one another in the sites of proximal delay and distal block (Damato et al., 1976).In this paper, we report on two patients in whom the electrophysiological findings strongly suggested an unusual gap phenomenon where the exit area around a pacing electrode was the site of proximal delay and the atria the distal site with relatively long effective refractory period. using a bipolar electrode catheter introduced percutaneously into the femoral vein. Two other bipolar electrode catheters were employed, the first to stimulate the high lateral wall of the right atrium and the second to record the high right atrial electrogram.The His bundle electrogram, high right atrial electrogram, and 2 surface leads were recorded simultaneously on a 4-channel Elema Mingograf 81 at a paper speed of 100 mm/s. The stimuli were 2 ms square waves approximately equal to twice diastolic threshold and were delivered using a JS-U2 multipurpose programmable stimulator.During programmed stimulation, the test stimuli were given after each eighth driving stimulus or spontaneous beat, the coupling interval being decreased by decrements of 5 ms. Results CASE 1The patient was a 56-year-old man who had had an acute anterolateral myocardial infarct in September 1975. He was admitted in January 1976 for treatment of cardiac failure with digitalis and diuretics. Investigations at that time showed a large parietal left ventricular aneurysm, a totally occluded left anterior descending artery with poor distal perfusion, and significantly stenosed left circumflex and right coronary arteries. He had recurrent episodes of ventricular tachycardia for which an electrophysiological study was underta...

No abstract

No abstract

No abstract