Isovolumetric contraction

Isovolumetric Contraction is a phase in the cardiac cycle during which the ventricles contract with no change in volume. This phase occurs immediately after the closure of the mitral valve and before the opening of the aortic valve. During isovolumetric contraction, the pressure within the ventricles increases rapidly, but because both the mitral and aortic valves are closed, there is no change in the volume of blood within the ventricles. This phase is crucial for building the pressure necessary to eject blood into the aorta and pulmonary artery during the subsequent phases of the cardiac cycle.

Physiology

The cardiac cycle comprises several phases, including ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation. Isovolumetric contraction is the second phase of the cardiac cycle and occurs after the atria have contracted to complete ventricular filling. The term "isovolumetric" refers to the constant volume within the ventricles during this phase, as the ventricles are completely closed chambers with the mitral and aortic valves shut.

During isovolumetric contraction, the cardiac muscle fibers of the ventricles begin to contract in response to electrical stimulation from the cardiac conduction system. This contraction increases the pressure within the ventricles rapidly. However, since the ventricles are closed chambers at this point, the blood volume within them remains unchanged. The pressure continues to rise until it exceeds the pressure in the aorta and pulmonary artery, leading to the opening of the aortic and pulmonary valves, marking the end of isovolumetric contraction and the beginning of the ventricular ejection phase.

Clinical Significance

The duration and intensity of isovolumetric contraction can be affected by various factors, including myocardial contractility, preload, and afterload. Changes in these factors can be indicative of cardiac diseases or conditions. For example, increased afterload, as seen in hypertension, can prolong isovolumetric contraction, while enhanced myocardial contractility, as seen with inotropic drugs, can shorten it.

Isovolumetric contraction time (IVCT) is an important parameter in echocardiography and cardiac diagnostics. It provides insights into ventricular function and can be used to assess cardiac performance. Abnormalities in IVCT can indicate underlying cardiac conditions such as heart failure or valvular heart disease.

Measurement

Isovolumetric contraction time can be measured using various cardiac imaging techniques, including echocardiography. In echocardiography, Doppler imaging can be used to assess the timing of valve movements and blood flow, allowing for the calculation of IVCT. This measurement, along with other echocardiographic parameters, can help in the diagnosis and management of various cardiac conditions.

See Also

• Cardiac cycle
• Ventricular ejection
• Isovolumetric relaxation
• Cardiac conduction system