Two unusual cases of intra-atrial gap.

Abstract

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...

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“…This is measured from the earliest point of stria I activation (surface ECG or intracardiac electrogram) to the low right atrial (LRA) electrogram recorded by the His bundle catheter. Intra-atrial conduction time cannot be reliably measured by the stimulus-LRA interval because this measurement may include stimulus latency (Waleffe et al, 1977). The right atrium is a complex geometric structure and there is no single pathway of impulse conduction from the point of stimulation to the low right atrial recording site.…”

“…"Gaps" in the propagation of a response may occur at ~ny level in the A-V conduction system (Agha et al, 1973;Camm et al, 1978;Gallagher et al, 1973;Moe et al, 1965;Waleffe et al, 1977;Wu et al, 1974). Unrecognised gaps in propagation due to proximal block may lead to an overestimation of refractoriness.…”

“…Unrecognised gaps in propagation due to proximal block may lead to an overestimation of refractoriness. For example, an undetected intra-atrial gap (Akhtar et al, 1978;Waleffe et al, 1977) may lead to an overestimation of the ERP of the atrium. The entire cardiac cycle must therefore be scanned carefully to avoid false conclusions.…”

Pharmacokinetic study of three cardiovascular drugs by high-performance liquid chromatography using pre-column derivatization with 9,10-anthraquinone-2-sulfonyl chloride

“…When their concentrations in plasma exceeded the therapeutic window, serious side effects can occur [2,3]. It is thus important to monitor their concentrations in plasma.…”