a Cardiovascular Disease Service, Department of Medicine, Walter Reed National Military Medical Center, Bethesda, MD, United States b Pulmonary Disease and Critical Care Service, Department of Medicine, Walter Reed National Military Medical Center, Bethesda, MD, United States c Internal Medicine Service, Department of Medicine, Walter Reed National Military Medical Center, Bethesda, MD, United ...

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . doi:10.1093/ehjci/jet051 Online publish-ahead-of-pr...

A pacemaker is a medical device which uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart. The primary purpose of a pacemaker is to maintain an adequate heart rate, either because the heart's native pacemaker is not fast enough, or there is a block in the heart's electrical conduction system (Fig. 1,2a,2b,3) (McWilliam, JA. 2007.,...

THE RELATIONSHIP among cardiac pacemakers is characterized by the fact that usually one pacemaker is dominant and all the others are subsidiary. The sinoatrial node acts as the dominant pacemaker and all other pacemaker tissues are discharged by a conducted impulse before their diastolic depolarization can attain threshold. These pacemakers are called subsidiary to emphasize the fact that under...

• It is common knowledge that the heart possesses subsidiary pacemaker tissues capable of initiating effective heart action in the absence of normal sinoatrial node function.' When sinoatrial node pacemaker action is stopped by crushing or by quick inactivation, a heart beat originates in the atrioventricular conducting system or from another region of the myocardium but only after some delay, ...