Electrocardiogram changes, myocardium

NS (general population) Cardiovascular Degenerative changes in myocardium, electrocardiogram abnormalities in children 6-20 Silver and Rodriguez-Torres 1968... 

The effects of coenzyme Q10 on coronary artery disease and chronic stable angina are modest but appear promising. A theoretical basis for such benefit could be metabolic protection of the ischemic myocardium. Double-blind, placebo-controlled trials have demonstrated that coenzyme Q10 supplementation improved a number of clinical measures in patients with a history of acute myocardial infarction (AMI). Improvements have been observed in lipoprotein a, high-density lipoprotein cholesterol, exercise tolerance, and time to development of ischemic changes on the electrocardiogram during stress tests. In addition, very small reductions in cardiac deaths and rate of reinfarction in patients with previous AMI have been reported (absolute risk reduction 1.5%). 

The cardiac cycle is tightly controlled by the cardiac conducting system, which initiates electrical impulses and carries them, via a specialized conducting system, to the myocardium. The surface electrocardiogram (EGG) records changes in potential and is a graphic tracing of the variations in electrical potential caused by the excitation of the heart muscle and detected at the body surface. Clinically, the EGG is used to identify (1) anatomic, (2) metabolic, (3)... 

Electrical activity in the heart can be picked up by electrodes placed on the skin and recorded as the familiar electrocardiogram (ECG). The ECG is a record of the sum of all action potentials in the heart as it contracts. Action potentials are generated by depolarization followed by repolarization of the cardiac muscle cell membrane. Depolarization is initiated by an influx of sodium ions into the cardiac muscle cells, followed by an influx of calcium ions. Repolarization is brought about by efflux of potassium ions. The phases of a cardiac action potential are shown in Eigure 4.3 where the depolarization is the change in resting membrane potential of cardiac muscle cells from —90 mV to 4-20 mV. This is due to influx of sodium ions followed by influx of calcium ions. Contraction of the myocardium follows depolarization. The refractory period is the time interval when a second contraction cannot occur and repolarization is the recovery of the resting potential due to efflux of potassium ions. After this the cycle repeats itself. 

Houchin and Smith have described death in vitamin E deficient rabbits as being due to myocardial failure. They have also described an increased uptake of oxygen by the cardiac muscle of vitamin E deficient hamsters. It had previously been reported by Freire that vitamin E deficient rats showed foci of hyaline necrosis in the myocardium. Freire and Magahas confirmed this result and found accompanying changes in the electrocardiogram. Subsequently Mason and EmmeP described necrosis of the myocardium and fibrous replacement of the damaged tissue. 

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