Biomedical subjects

A Addas

Publications and source records attributed to A Addas.

5 recordsLinked to original sources

PubMed1987

Effects of abrupt changes in cycle length on atrial refractory periods in man.

While the electrophysiologic effects of sudden changes in cycle length on the His-Purkinje System and ventricular myocardial refractoriness are better known, the behavior of atrial myocardium in this regard is poorly understood. The effects of an abrupt long to short cycle length change (11 patients: group A) and/or short to long cycle length alteration (18 patients: group B) on the atrial effective and functional refractory period were assessed during electrophysiologic studies. The values thus obtained were compared to those observed during the scanning of both constant long and constant short cycle lengths of the same duration. In group A the effective and functional refractory periods of the right atrium measured 250 +/- 38 msec and 296 +/- 31 msec during a constant long cycle length of 709 +/- 80 msec, whereas the same parameters had values of 228 +/- 30 msec and 260 +/- 32 msec, respectively, at a constant short cycle length of 436 +/- 81 msec. With an abrupt change in cycle length from long to short (a change of 273 +/- 75 msec), the effective and functional atrial refractory periods were 225 +/- 29 and 267 +/- 29 msec in that order, and these values closely approximated those seen with a constant short cycle length. Similarly, the two atrial refractory period parameters in group B measured 218 +/- 16 msec and 262 +/- 19 msec during a constant short cycle length of 414 +/- 68 msec and were 236 +/- 17 msec and 284 +/- 21 msec, respectively, at a constant long cycle length of 689 +/- 92 msec.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗

PubMed1986

Sex-specific criteria for interpretation of thallium-201 myocardial uptake and washout studies.

A study was undertaken to determine the effect of gender on criteria for the quantitative analysis of exercise-redistribution 201Tl myocardial scintigraphy. The studies of 26 normal females and 23 normal males were subjected to bilinear interpolative background subtraction and horizontal profile analysis. Significant sexual differences were found in both regional uptake ratios and washout rates. These differences primarily reflected a proportionately decreased anterior and upper septal uptake in females, and faster washout in females. Faster myocardial 201Tl washout rates in females could not be clearly ascribed to either a physiological or artifactual explanation. It is concluded that since important differences exist between males and females in the detected pattern of 201Tl myocardial uptake and washout, sex-specific criteria may enhance the predictive accuracy of exercise-redistribution 201Tl myocardial scintigraphy.

Adult↗

PubMed1985

Unidirectional retrograde atrioventricular nodal block in man: determinants of reversibility by vagal antagonism.

The mechanism of unidirectional retrograde atrioventricular (AV) nodal block remains largely unknown. In this study, factors determining the reversal of the unidirectional block by atropine were evaluated in 12 patients who had no demonstrable ventriculoatrial (VA) conduction during ventricular pacing. Six patients demonstrated 1:1 VA conduction after atropine (group I), while the remaining six patients continued to show VA block (group II). During the control study there was no significant difference in the sinus cycle length and AH interval between the two groups. The percent decrease in sinus cycle length after atropine was also similar in groups I and II (i.e., 23 +/- 12 and 26 +/- 6, respectively). The effect on antegrade AV nodal conduction (i.e., the percent decrease in AH interval), however, was significantly greater in group I (24 +/- 9) as compared to group II (9 +/- 5) (p less than 0.004). The onset of VA conduction appeared to correlate with the improvement of antegrade conduction. The ratio of these two effects of atropine (i.e., percent decrease in AH interval to percent decrease in sinus cycle length) was higher when VA conduction was first demonstrated in group I (2.3 +/- 1.1) than at the maximal effect of atropine (1.2 +/- 0.3), reflecting a relatively greater decrease in sinus cycle length. Three of six group I patients redeveloped VA block at maximal effect of atropine. The results suggest a functional and dynamic nature of the unidirectional AV nodal block, possibly caused by vagal influence exaggerating the well-known directional asymmetry of AV nodal conduction in man.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1985

Electrophysiology studies: precordial thumping patients paced into ventricular tachycardia.

The American Heart Association currently recommends the precordial thump as the initial maneuver in the treatment of ventricular tachycardia and monitored ventricular fibrillation. Advocates of the precordial thump maintain that it affords the advantage of immediate availability and might prove lifesaving in cases of ventricular tachycardia. A canine study and a prehospital study have argued that in the cardiac arrest model, thumping ventricular tachycardia causes ventricular fibrillation as often as reversion to a sinus rhythm. We therefore studied the effects of the precordial thump on patients undergoing electrophysiology studies who had been paced into ventricular tachycardia. A total of nine patients received precordial thumps for 11 separate episodes of electrically induced sustained ventricular tachycardia. Our thumps failed on all 11 attempts to convert any of our patients. All 11 were subsequently successfully restored to a supraventricular rhythm with overdrive pacing or countershock. There was no detrimental effect from thumping ventricular tachycardia as has been previously reported. Our results would indicate that countershock is more effective than precordial thumping for converting ventricular tachycardia to a supraventricular rhythm, but previously reported "detrimental effects" of thumping are not confirmed by this study.

Electric Countershock↗

PubMed1985

Linking: a dynamic electrophysiologic phenomenon in macroreentry circuits.

The term "linking" has been used specifically to describe the mechanism for perpetuation of functional anterograde bundle branch block: namely, repetitive transseptal retrograde concealed penetration by impulses propagating along the contralateral bundle. We present selected examples that demonstrate tht linking-type phenomena actually have a wide spectrum of expression in human macroreentry circuits, particularly those incorporating either the bundle branches and His bundle or the normal pathway and Kent bundle. The examples presented are as follows: (1) persistent retrograde functional conduction delays in the His-Purkinje system during right ventricular pacing, (2) anterograde Kent bundle condution at rapid rates, dependent on prior block in the normal pathway, (3) persistent anterograde functional infra-His block of atrial impulses during rapid ventricular pacing in the presence of a retrogradely conducting accessory pathway, and (4) transient advancement of His activation with ventricular fusion complexes during overdrive ventricular pacing of bundle branch reentrant tachycardia. Based on these examples, we characterize linking as a generalized electrophysiologic phenomenon in which each successive impulse entering a macroreentry circuit propagates preferentially along one limb because of functional block in the contralateral limb resulting from the effects of the prior impulse. It is proposed that such functional block may be dynamically maintained either by repetitive impulse interference, which perpetuates local refractoriness (examples No. 1 to 3), or by repetitive impulse collision (example No. 4). The general conceptual scheme outlined can be applied to specific electrophysiologic phenomena associated with a wide variety of reentry circuits in man.

Adult↗