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Biomedical subjects

C C Gornick

Publications and source records attributed to C C Gornick.

29 records · Page 2Linked to original sources
PubMed1987

Potentiation of cardiac electrophysiologic effects of verapamil after autonomic blockade or cardiac transplantation.

Cardiac electrophysiologic effects of verapamil in vivo are the result of both direct and indirect actions on the heart (the latter due to augmentation of sympathetic neural tone, diminution of parasympathetic neural tone, and increased circulating catecholamines). In this study we assessed the interaction of verapamil's direct and indirect actions on electrophysiologic properties of the heart in awake, previously instrumented, unsedated dogs. After administration of intravenous verapamil (0.2 mg/kg), electrophysiologic effects were assessed serially over a 1 hr period in 10 awake dogs before (group 1 studies) and during pharmacologic autonomic blockade (group 2 studies), and in a subset of these dogs (n = 5) after orthotopic cardiac transplantation (group 3 studies). In group 1 dogs, sinus cycle length (SCL) initially shortened after verapamil (postverapamil 379 +/- 50 msec vs baseline of 494 +/- 72 msec, p less than .001) and subsequently gradually prolonged. In groups 2 and 3, transient SCL shortening was absent. SCL prolonged promptly after verapamil, and sinus arrest developed in two of 10 group 2 and two of five group 3 animals. Verapamil exerted a negative dromotropic effect on atrioventricular node conduction in all three experimental groups, as assessed by drug-induced changes in minimum cycle length with sustained 1:1 atrioventricular conduction and measurements of atrioventricular node effective and functional refractory period. However, compared with findings in group 1, this negative dromotropic effect occurred more rapidly and was markedly potentiated in groups 2 and 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Sensor-triggered, rate-variable cardiac pacing. Current technologies and clinical implications.

Conventional implantable dual-chamber cardiac pacemakers adjust heart rate and maintain normal atrial and ventricular contraction by tracking "native" atrial electrical activity and pacing the ventricles after a predetermined programmable atrioventricular delay. However, in patients with symptomatic bradyarrhythmias, optimal function of "atrial-tracking" devices may be limited by concomitant sinoatrial disease. Provision of chronotropic response during physical exertion or emotional stress may be achieved by using physiologic sensors to alter pacing rate independently of atrial activity. Additional systems using sensor technologies are being developed. Future pacing systems will have dual-chamber pacing capability and may use several sensors coupled synergistically in order to take advantage of particular strengths of each. Physiologic sensor technology may be of diagnostic value in both antitachycardia devices and implantable cardioverter and defibrillator systems.

Bradycardia↗
PubMed1986

Intracavitary electrode catheter cardioversion of atrial tachyarrhythmias in the dog.

This study examined factors determining efficacy of intracavitary cardioversion of atrial tachyarrhythmias in closed chest, anesthetized dogs with talc pericarditis. Electrode catheters were positioned transvenously with the cathode in the right atrial appendage. In Group 1 dogs (n = 6), three anode sites (superior and inferior venae cavae ostia and mid-right atrium) were tested with graded energy shocks to determine the lowest effective cardioversion energy at each anode position. In Group 2 dogs (n = 9), multiple cardioversion attempts with energy levels of 0.01 to 5.0 J were used to evaluate reproducibility of energy thresholds. In Group 3 dogs (n = 6) without talc-induced pericarditis, atrial pathologic study was done after five intracavitary shocks (0.5 or 5.0 J). In Group 1, cardioversion was achieved with 0.75 J or less with no significant difference in minimal effective cardioversion energies among the three anode positions tested. In Group 2, 98 (26%) of 372 cardioversion attempts were successful. Intra-animal minimal effective cardioversion energies varied widely, and timing of shocks relative to atrial electrograms did not influence efficacy. Complications were infrequent and included delayed sinus rhythm recovery, transient atrioventricular block and ventricular fibrillation. Ventricular fibrillation occurred in 9 (2.4%) of 372 shocks, and was associated with higher delivered energies (6 of 9 with greater than or equal to 1.0 J) and with shocks delivered 116 to 180 ms after onset of the QRS complex. In Group 3, two dogs had no histologic damage, three dogs had multiple small foci of subendocardial necrosis and in one dog these foci coalesced to involve half the atrial wall thickness. Thus, low energy cardioversion of atrial tachyarrhythmias is feasible using intracavitary electrodes. Synchronization of energy delivery to the QRS complex is important to minimize risk of ventricular fibrillation.

Animals↗
PubMed1986

Electrophysiologic effects of papillary muscle traction in the intact heart.

In this study we used transmural multipolar electrodes, sonomicrometers implanted within the left ventricular wall, and cardiac electrical stimulation techniques to examine the effect of transient mechanical posterior papillary muscle traction on local myocardial electrophysiologic characteristics. Nine open-chest dogs were atrially paced (cycle length 400 msec) followed by insertion of timed premature extrastimuli at left ventricular epicardial pacing sites either in the vicinity of (traction zone) or remote from (nontraction zone) the site of papillary muscle traction. Electrophysiologic recordings were made before and during periods of intermittent papillary muscle traction of predetermined timing, application rate (25 cm/sec), and duration (170 msec). Papillary muscle traction was applied in late diastole just before the last beat of each atrial drive train. In seven of nine dogs application of transient papillary muscle traction resulted in significantly earlier local ventricular activation (mean activation advancement 30 +/- 13 msec), altered QRS morphology of the last conducted atrial drive-train beat, and relative prolongation of ventricular functional refractory period in the traction zone. Conversely, in nontraction zones in these seven dogs, early activation did not occur and refractoriness remained unchanged as tested by a locally placed extrastimulus. In two of nine dogs traction failed to induce early activation and changes in refractoriness did not occur. Alterations in regional myocardial blood flow (assessed by radioactive microsphere technique) did not appear responsible for the observed changes, since there was no demonstrable traction-induced difference in regional blood flow between the traction and nontraction zones.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Electrophysiologic properties of the myocardial infarction border zone: effects of transient aortic occlusion.

This study used transmural multipolar electrodes, ventricular pressure monitoring, and cardiac electrical stimulation techniques to examine the effects of transient aortic occlusion on ventricular refractoriness in a canine model of recent myocardial infarction. Six previously instrumented resting awake dogs were atrially paced, followed by timed premature extrastimuli inserted at epicardial pacing sites adjacent to an apical left ventricular (LV) myocardial infarction or in an LV control zone remote from the myocardial infarction. Electrophysiologic and pressure recordings were obtained before and during periods of transient aortic occlusion. Aortic occlusion was applied before the last beat of an eight-beat atrial pacing sequence and resulted in increased peak LV pressure (92.8 +/- 27.7 mm Hg, p = 0.003). Aortic occlusion shortened LV effective refractory period (ERP) recorded from the myocardial infarction border zone in both the subepicardial (-17.0 +/- 11.8 msec, p = 0.019) and subendocardial (-17.7 +/- 10.9 msec, p = 0.011) regions, whereas LVERP of the control zone was unchanged. Conduction latency of premature beats at equivalent coupling intervals and maximum latency observed were unchanged by aortic occlusion. atrioventricular conduction interval shortened in association with aortic occlusion. Thus transient aortic occlusion reduced ventricular refractoriness in the border zone adjacent to the myocardial infarction while control zone refractoriness was minimally or not changed. Heterogeneity of ventricular myocardial refractoriness may result from mechanical dysfunction, potentially increasing susceptibility to arrhythmias.

Animals↗
PubMed1985

Electrophysiologic effects of flecainide acetate and its major metabolites in the canine heart.

Flecainide acetate, an investigational class 1 antiarrhythmic agent, undergoes biotransformation in man with production of 2 major metabolites: meta-O-dealkylated flecainide (S-24623) and the meta-O-dealkylated lactam of flecainide (S-26191). This study compared the effects of flecainide, S-24623 and S-26191 on cardiac electrophysiologic characteristics in the anesthetized dog. Each dog received 2 dose levels of 1 of the 3 test compounds after control measurements. Flecainide (2 and 4 mg/kg in 8 dogs), S-24623 (4 and 8 mg/kg in 8 dogs) and S-26191 (4 and 10 mg/kg in 7 dogs) were administered intravenously in dilute solution. Of the 3 compounds, only flecainide significantly prolonged sinus cycle length (p less than 0.01). However, both flecainide and S-24623 significantly prolonged minimum atrial paced cycle length with 1:1 atrioventricular conduction, atrioventricular nodal effective and functional refractory periods, and right ventricular effective refractory period. Metabolite S-26191 exhibited qualitatively similar but much weaker electrophysiologic actions. The maximal electrophysiologic effects of flecainide and S-24623 were approximately equivalent, but the metabolite was about one-half as potent on a milligram-permilligram basis, and lacked marked effects on infranodal (HV interval) conduction. S-26191 was less than one-tenth as potent as flecainide. Therefore, since both flecainide metabolites occur primarily in the conjugated form in plasma (i.e., free metabolite concentrations are low), it is unlikely that these compounds either potentiate flecainide's antiarrhythmic action or increase susceptibility to drug toxicity in the clinical setting.

Animals↗
PubMed1985

Electrophysiological effects of transient aortic occlusion in intact canine heart.

This study utilized sonomicrometers transmural multipolar electrodes and cardiac electrical stimulation techniques to examine the effect on myocardial electrophysiological characteristics of altering ventricular systolic mechanical properties by transient aortic occlusion. Nine anesthetized open-chest dogs were atrially paced, and timed extrastimuli were inserted during alternate drive-train sequences at right or left ventricular (RV, LV) epicardial sites to measure ventricular effective refractory period (ERP). Sonomicrometer measurements of LV systolic mechanical parameters and both RV and LV electrophysiological findings were determined prior to and during periods of transient aortic occlusion. Aortic occlusion was applied just prior to the last beat of each eight-beat atrial drive train and released immediately following the programmed ventricular extrastimulus. Aortic occlusion increased LV systolic pressure (+42 +/- 26.6 mmHg, P less than 0.01) and diminished segmental stroke shortening (0.100 +/- 0.059 mm, P less than 0.02), shortening fraction (0.086 +/- 0.048, P less than 0.001), mean velocity of stroke shortening (0.444 +/- 0.186 mm/s, P less than 0.001), and stroke work (P less than 0.001). LV epicardial and endocardial ERP were prolonged as a result of aortic occlusion (5 +/- 7.2 and 6 +/- 6.5 ms, respectively, P less than 0.05), whereas RV ERP was unchanged. Latency of premature beats at equivalent coupling intervals was unaltered. ERP prolongation correlated most strongly with reductions of segmental stroke shortening (r = 0.928, P less than 0.001), shortening fraction (r = 0.901, P less than 0.001), and mean shortening velocity (r = 0.819, P less than 0.01). Thus transient aortic occlusion prolonged LV refractoriness, and electrophysiological changes closely paralleled the severity of systolic mechanical disturbance.

Animals↗
PubMed1984

Atrial flutter, atrial fibrillation, and other primary atrial tachycardias.

Traditional classifications of atrial tachycardias include not only rhythm disturbances arising primarily within the atria, but also dysrhythmias in which it is now recognized that participation of both atrial and non-atrial tissue is required. We prefer to consider those arrhythmias in which the atria are the principal site of electrophysiologic disturbance as "primary" atrial tachyarrhythmias. The mechanisms, diagnosis, and treatment of these "primary" atrial tachycardias are the subject of this article.

Anti-Arrhythmia Agents↗
PubMed1981

Primary cutaneous Nocardia asteroides infection with dissemination.

In a 77 year old previously healthy man with mild adult-onset diabetes mellitus, a primary cutaneous Nocardia asteroides infection developed on the hand following inoculation of a traumatic injury. Initially untreated, the infection became locally invasive and resulted in dissemination to the lungs and normal skin. This represents the first known reported case of a N. asteroides actinomycetoma associated with dissemination.

Aged↗