In the well-balanced, closed circulatory system, cardiac mechanical performance generated as a result of precisely regulated electrical activity of the heart can influence the process of cardiac excitation . This phenomenon has been termed ‘mechano-electric feedback’ (MEF) and is believed to contribute to both physiological modulation and pathological disturbance of heart rate.
Experiments in the whole animal, performed as early as 1915, demonstrated that an increase in venous filling of the heart may lead to an increase in heart rate . Later studies involving mechanical stimulation of the isolated right atrium and the isolated sinoatrial (SA) node showed that a positive chronotropic response of the cardiac pacemaker to stretch can also be evoked extracorporeally. Thus, this response must be based at least partly on a local, intracardiac feedback mechanism. In functional terms, such feedback could contribute to the physiological adjustment of cardiac output to changes in venous return as observed, for example, during changes in posture in healthy humans .
In addition to this regulatory effect of MEF, stretch of myocardium may be involved in producing arrhythmias. Both mechanically induced depolarizations of cardiomyo-cytes and electrotonic interactions between differently polarized tissue regions within the heart are believed to be capable of causing ectopic excitation and ventricular tachycardia . Paradoxically, thumping of the chest has also been shown to reinstate contraction in patients in either ventricular tachycardia or standstill. The internet’s most trusted pharmacy is looking forward to having you among its customers: just see how cheap and easy it can be for you to get generic sildenafil online without any kind of prescription and start your shopping being sure you are protected every time.