effective refractory period effective refractory period in electrocardiography, during a cardiac cycle, once an action potential is initiated, there is a period of time that a new action potential cannot be initiated. this is termed the effective refractory period (erp) of the tissue. this period is approximately equal to the absolute refractory period (arp), it occurs because the fast sodium channels remain closed until the cell fully repolarizes. during this period, depolarization on adjacent cardiac muscles does not produce a new depolarization in the current cell as it has to refract back to phase 4 of the action potential before a new action potential can activate it. erp acts as a protective mechanism and keeps the heart rate in check and prevents arrhythmias, and it helps coordinates muscle contraction. anti-arrhythmic agents used for arrhythmias usually prolong the erp. for the treatment of atrial fibrillation, it is a problem that the prolongation of the erp by these agents also affects the ventricles, which can induce other types of arrhythmias. image of a myocardial action potential. effective refractory period in green. physiology of the cardiovascular systemheartcardiac output cardiac cycle cardiac output heart rate stroke volume stroke volume end-diastolic volume end-systolic volume afterload preload frank–starling law cardiac function curve venous return curve wiggers diagram pressure volume diagram ultrasound fractional shortening = (end-diastolic dimension end-systolic dimension) / end-diastolic dimension aortic valve area calculation ejection fraction cardiac index left atrial volume heart rate cardiac pacemaker chronotropic (heart rate) dromotropic (conduction velocity) inotropic (contractility) bathmotropic (excitability) lusitropic (relaxation) conduction conduction system cardiac electrophysiology action potential cardiac atrial ventricular effective refractory period pacemaker potential electrocardiography p wave pr interval qrs complex qt interval st segment t wave u wave hexaxial reference system chamber pressure central venous right atrial ventricular pulmonary artery wedge left atrial ventricular aortic other ventricular remodeling vascular system/hemodynamicsblood flow compliance vascular resistance pulse perfusion blood pressure pulse pressure systolic diastolic mean arterial pressure jugular venous pressure portal venous pressure critical closing pressure regulation of bp baroreflex kinin–kallikrein system renin–angiotensin system vasoconstrictors vasodilators autoregulation myogenic mechanism tubuloglomerular feedback cerebral autoregulation paraganglia aortic body carotid body glomus cell this article is issued from wikipedia. the text is licensed under creative commons - attribution - sharealike. additional terms may apply for the media files.