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The Cardiac Cycle


Left ventricular pressure

Aortic pressure

Left atrial pressure

Figure 1. Cardiac bicycle of the left next of the heart. The EKG listed below the diagram reflects the corresponding waves through each step of the cardiac cycle. The bottom line represents the first and 2nd heart sounds.

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The cardiac cycle to represent the hemodynamic and also electric changes that occur in systole and also diastole. It has many phases.

Phases that the Cardiac Cycle:

Isovolumetric ventricular convulsion (a-b): This step marks the start of systole and also starts v the appearance of the QRS complex on the EKG and the closure the the AV valves at allude (a). V all valves closed, the ventricle generates optimistic pressure without any adjust in that volume (isovolumetric) to get over the semilunar valves resistance that open up at point b. This phase typically lasts because that 6% the the cardiac cycle.Rapid ejection (b-c): as the semilunar valves open up at allude (b), over there is a quick ejection of blood because of increased ventricular contractility. The arterial pressure rises until getting to it maximum at suggest (c). This phase usually lasts for 13% the the cardiac cycle.Reduced ejection (c-d): This step marks the start of ventricular repolarization as depicted by the start of the T tide on the EKG. Repolarization leader to a rapid decline in ventricular pressures and also hence the reduced rate the ejection. However, part forward circulation of blood continues an additional to remnant kinetic energy from the vault phase. This phase normally lasts for 15% that the cardiac cycle.Isovolumetric be safe (d-e): once the ventricular pressures drop listed below the diastolic aortic and also pulmonary pressures (80 mmHg and also 10 mmHg respectively), the aortic and pulmonary valves close developing the 2nd heart sound (point d). This marks the beginning of diastole. The ventricles generate an unfavorable pressure without an altering their volume (isovolumetric) so that the ventricular pressure becomes reduced than the atrial pressure. This phase generally lasts for 8% the the cardiac cycle.Ventricular filling (e-a): together the AV valves open at point (e), ventricular filling starts. The initial quick filling is greatly augmented by ventricular suction which outcomes from ventricular untwisting and the return of every ventricular muscle fiber come its slack length. The ventricular pressure gradually increases till it equates to the atrial pressure and the AV valves near (point a). This phase usually lasts because that 44% the the cardiac cycle.Atrial contraction: Finally, close to the end of ventricular diastole, the atrial contraction contributes about 10% that the ventricular pour it until it is full volume. This is stood for by the P tide on the EKG of the following cycle. This phase typically lasts because that 14% that the cardiac cycle.

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Content ©2017. Some rights Reserved.Date last modified: July 7, 2017.Ashraf Aly and also Soham DusguptaDept. That PediatricsUniversity of Texas clinical Branch.