Heart rate date normally used to date pregnancy in the medical community. The electrical depolarizations that trigger cardiac myocytes to contract arise spontaneously within the myocyte itself. The heartbeat is initiated in the pacemaker regions and spreads to the rest of the heart through a conduction pathway. Pacemaker cells develop in the primitive atrium and the sinus venosus to form the sinoatrial node and the atrioventricular node respectively. Conductive cells develop the bundle of His and carry the depolarization into the lower heart. The human heart begins beating at a rate near the mother’s, about 75–80 beats per minute (bpm). The embryonic
Contraction band necrosis Contraction band necrosis Contraction band necrosis is a type of uncontrolled cell death (necrosis) unique to cardiac myocytes and thought to arise in reperfusion from hypercontraction, which results in sarcolemmal rupture. It is a characteristic histologic finding of a recent myocardial infarction (heart attack) that was partially reperfused. The name of the histopathologic finding comes from the appearance under the microscope; contraction bands are thick intensely eosinophilic staining bands (typically 4-5 micrometres wide) that span the short axis of the myocyte. They can be thought of extra thick striae, typical of cardiac muscle and striated muscle. Contraction band necrosis is