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PubMedDate not supplied

Enhanced arrhythmogenicity of Freon 113 by hypoxia in the perfused rat heart.

The interaction of Freon 113 (1,1,2-trichloro-1,2,2-trifluoroethane) and hypoxia on the heart conduction system was studied using electrocardiogram monitoring of isolated perfused rat hearts. Freon 113 (0.2 mM) alone elicited significant atrioventricular conduction delay (p less than 0.05) and heart rate decrease (p less than 0.01), which were significantly enhanced by hypoxia (75% oxygen decrease), for instance, resulting in 2:1 AV block. The data suggest that arrhythmogenicity of Freon 113 on the heart conduction system may be enhanced synergistically by hypoxia.

Animals↗
PubMed2001

Action potential characteristics and arrhythmogenic properties of the cardiac conduction system of the murine heart.

Studies have characterized conduction velocity in the right and left bundle branches (RBB, LBB) of normal and genetically engineered mice. However, no information is available on the action potential characteristics of the specialized conduction system (SCS). We have used microelectrode techniques to characterize action potential properties of the murine SCS, as well as epicardial and endocardial muscle preparations for comparison. In the RBB, action potential duration at 50%, 70%, and 90% repolarization (APD(50,70,90)) was 6+/-0.7, 35+/-6, and 90+/-7 ms, respectively. Maximum upstroke velocity (dV/dt(max)) was 153+/-14 V/s, and conduction velocity averaged 0.85+/-0.2 m/s. APD(90) was longer in the Purkinje network of fibers (web) than in the RBB (P<0.01). Web APD(50) was longer in the left than in the right ventricle (P<0.05). Yet, web APD(90) was longer in the right than in the left ventricle (P<0.001). APD(50,70) was significantly longer in the endocardial than in the epicardial (P<0.001; P<0.003). APD(90) in the epicardial and endocardial was shorter than in the RBB ( approximately 36 ms versus approximately 100 ms). Spontaneous electrical oscillations in phase 2 of the SCS occasionally resulted in early afterdepolarizations. These results demonstrate that APDs in the murine SCS are significantly ( approximately 2-fold) longer than in the myocardium and implicate the role of the murine SCS in arrhythmias. The differences should have important implications in the use of the mouse heart to study excitation, propagation, and arrhythmias.

Acetylthiocholine↗
PubMed1991

[The excitation-conduction system of the heart in primary mitral valve prolapse (electrophysiological study)].

Forty patients (mean age 40 yrs) with primary mitral valve prolapse (MVP) and 20 healthy controls were subjected to electrophysiologic investigation. The following measurements were performed: 1) intracardiac conduction time, 2) effective and functional refractory periods of the right atrium, a-v node and right ventricle, 3) Wenkebach point, 4) retrograde Wenkebach point. Disturbances of intracardiac conduction were detected in 13 (32.5%) patients with MVP (in 8 patients within proximal part of the conduction system, in 5 patients distally). Patients with MVP were more sensitive to ajmaline. Conduction time in the proximal part was significantly increased only in these patients. The incidence of retrograde conduction was more frequent in the patients with MVP than in the controls. In 12 (30%) patients with MVP, constant conduction time and high value of retrograde Wenkebach point were found. Mean values of effective and functional refractory periods of the right ventricle and effective refractory period of the a-v node were not significantly different in both groups. In patients with MVP, mean values of effective and functional refractory periods of the right atrium were significantly lower and functional refractory period of the a-v node significantly higher than in the controls. In 8 (20%) patients with MVP and in 2 (10%) controls, longitudinal division of the a-v node was found. Atrial hyperreactivity was detected in 14 (35%) patients and in 3 (15%) controls. In conclusion, MVP is often accompanied by electrophysiologic abnormalities, such as disturbed intracardiac conduction, retrograde preexcitation, shortening of atrial refractory periods, longitudinal division of the a-v node and atrial hyperreactivity.

Adolescent↗
PubMed1978

Myocardial conducting system dysfunctions from thoracic impact.

An analysis of electrocardiograms (ECG lead II) obtained following blunt thoracic impacts conducted on 12 anesthetized pigs indicated that all animals developed some degree of trauma to the heart conducting system: sino-atrial nodal disturbances, atrio-ventricular junctional dysfunction, intraventricular conduction defects (e.g., bundle branch blocks), or ventricular fibrillation. The induced ventricular fibrillation proceeded rapidly to the demise of four animals in this study. A comparison of the occurrence of ventricular fibrillation with measured biomechanical response parameters indicated a significant correlation of ventricular dysfunction with high levels of sternal acceleration (930 g) and impact velocity (10.7 m/s). The initiation of ventricular fibrillation did not correlate with typical biomechanical thoracic injury "indicators" (i.i., level of normalized thoracic deflection, cumulative AIS, peak spinal acceleration, or applied force). An injury severity classification (MCD) was subsequently developed for the evaluation of myocardial conducting system dysfunctions.

Animals↗
PubMed1997

[Morphological and functional aspects of the cardiovascular system related to aging: does "aging heart" exist?].

Elderly people are the most rapid growing segment of society, and heart disease is the most common cause of death in this population. The aging process is associated with anatomic and physiologic alterations in the cardiovascular system; consequently, the manifestations of disease in the geriatric population differ from those involving younger patients. To formulate diagnosis of "aging heart" in older patient may be difficult, because of atypical symptoms or of the acceptance of symptoms as manifestations of old age. Aging is, moreover, often associated with a decline in physical activity, which may result in cardiovascular "deconditioning". The treatment strategy is the same as in younger patients, but the higher incidence of adverse effects and complications demands special awareness. In this article we discuss about age-related structural and functional changes that occur in the cardiovascular system, including changes in the heart muscle, valves, conduction system and major arteries.

Adaptation, Physiological↗