Take this course for free. Electrocardiography is the making of graphic records of the variations in electrical potential caused by electrical activity of the heart muscle and detected at the body surface , as a method for studying the action of the heart muscle . Use the EKG library below. In the following graphic, Q is the bottom starting point, R the top point, and S the bottom end point of the QRS Complex.
Atrial contraction starts in the P-wave and continues throughout the PR interval.
The blood is pumped into the ventricles and the ventricular pressure rises. Ventricular contraction begins at R which corresponds to the peak of the QRS complex, and continues during the ST segment and T-wave. The mitral and bicuspid valves close due to increase in ventricular pressure. At R, the closing valves produce the heart sound. Between point R and S ventricular pressure increases greatly since the semilunar valves are still closed and there is no blood flow.