The effects of ventricular end‐diastolic and systolic pressures on action potential and duration in anaesthetized dogs.

Abstract

SUMMARY1. Although it is known that mechanical events in the heart influence the duration of the cardiac action potential, there is no quantitative information on the effects of independent changes in ventricular end-diastolic and systolic pressures.2. Experiments were carried out on open-chest anaesthetized dogs in which the autonomic nervous influences on the heart were prevented and monophasic action potentials were recorded from the epicardial surface of the left ventricle. The duration of these action potentials was taken as the interval from the upstroke to the point of 90 % repolarization.3. Elevation of left ventricular peak systolic pressure, at constant end-diastolic pressure, significantly shortened the monophasic action potential.4. Elevation of end-diastolic pressure at constant peak systolic pressure significantly lengthened the monophasic action potential.5. Responses were not dependent on release of noradrenaline from sympathetic nerve terminals because they persisted after administration of bretylium tosylate. They were also not due to myocardial ischaemia because they persisted when coronary perfusion pressure was maintained at a constant high level.6. Simultaneous recordings of changes in myocardial segment length showed the expected responses to changes in ventricular pressures: increases in shortening in response to increases in diastolic pressure and no consistent effect from changes in systolic pressure.7. These investigations demonstrate the independent effects of changes in systolic and end-diastolic pressures on cardiac action potential duration. This effect is likely to be an effect of the mechanical events, i.e. contraction-excitation feedback. This response may be mediated through changes in myocardial fibre tension, the consequent changes in fibre shortening, or both.

Effects of Psychologic Stress on Repolarization and Relationship to Autonomic and Hemodynamic Factors

“…It is possible that mental stress affected TWA in part through mechanoelectrical feedback, as changes in afterload can alter ventricular refractoriness. 44 While ischemia invokes TWA in animals, 45 as well as humans during coronary angioplasty, 45,46 in this study no ECG changes were seen, and a recent study 13 showed no correlation between stress-induced TWA changes and ischemia on SPECT. This suggests that mental stress-induced TWA is not ischemically mediated.…”

“…TWA changes also correlated strongly with increases in systolic BP. It is possible that mental stress affected TWA in part through mechanoelectrical feedback, as changes in afterload can alter ventricular refractoriness 44 …”

Restricted N‐terminal truncation of cardiac troponin T: a novel mechanism for functional adaptation to energetic crisis

“…The duration of the cardiac action potential is influenced by the mechanical loading conditions of the heart, a process termed ‘contraction–excitation feedback’ (Laboratory, 1982). Elevation of left ventricular peak systolic pressure was found to shorten the monophasic action potential in the heart (Coulshed et al 1992). Therefore, this mechanism is worth further investigation for its role in the production of cTnT‐ND in the responses of both ventricles to one sided pressure overload.…”

Cardiac loading conditions modify the ventricular repolarization in conscious dogs with heart failure

“…These effects have been studied in several in vitro and in vivo experimental studies. In contrast, after autonomic denervation in anesthetized dogs, the elevation in end diastolic pressure has been reported to increase the left ventricular MAP duration [8]. These apparently conflicting results may be due to the experimental protocol used and to the complex regulation of the mechanoelectric feedback mechanism.…”