Myocardial contractility

What is Myocardial Contractility?

Myocardial contractility is a measurement of the strength of the heart muscle's ability to squeeze and relax. It is used to describe the amount of force with which cardiac muscle fibers contract in response to an electrical stimulus.

The contractility of cardiac muscle fibers is regulated by their internal calcium content, which is in turn driven by the heart rate and the time interval between contractions (their diastolic time). The higher the heart rate, the higher the calcium content and the higher the force of contraction.

Contractility is, in turn, linked to the level of oxygenation the heart has at any given time. When oxygen is present, cardiac muscle cells are more efficient at generating force. When oxygen is absent, cardiac muscle cell contractility decreases.

Measuring Myocardial Contractility

Contractility can be assessed in a variety of ways, including invasive and noninvasive measurements. Commonly used parameters for measuring myocardial contractility include ejection fraction (EF), fractional shortening (FS), and systolic velocities (Vmax).

Ejection fraction (EF) is the ratio of stroke volume (the amount of blood ejected by the heart in one contraction) to end-diastolic volume (the amount of blood in the heart at the end of the diastole). A normal EF is 55% to 70%.

Fractional shortening (FS) is the ratio of end-diastolic diameter (the diameter of the heart at the end of diastole) to end systolic diameter (the diameter of the heart at the end of systole). A normal FS is 25-35%.

Systolic velocities (Vmax) measure the rate of velocity of contraction. This measurement is based on a Doppler ultrasound, which measures the velocity of red blood cells as they move through the heart. A normal Vmax is greater than 5 cm/s.

Treatment of Decreased Cardiac Contractility

Treatment of decreased cardiac contractility can involve pharmacologic and lifestyle interventions. Drugs such as beta-blockers and calcium-channel blockers can decrease heart rate and improve contractility. Lifestyle interventions such as diet and exercise can also help improve cardiac contractility.

Other treatments may include surgical intervention, such as a coronary artery bypass graft (CABG) or valve replacement.

Conclusion

Myocardial contractility is an important measure of the heart's ability to generate adequate force with each contraction. Myocardial contractility can be assessed through a variety of invasive and noninvasive methods, and treatments can range from lifestyle interventions to surgical intervention. It is important for patients to understand their individual risk factors and consider all options for treatment.