Review of Causes of Decreased Cardiac Output

Cardiac output (CO) is the amount of blood that is pumped by the heart in one minute and is an important indicator of cardiac health. A decrease in CO can lead to a variety of serious conditions, from heart failure to shock. It is therefore important to understand the potential causes of decreased cardiac output in order to effectively diagnose and treat this condition. This article will review the various pathophysiological causes of decreased cardiac output.

Preload

Preload refers to the amount of tension or stretch in the ventricle walls just before they contract. This tension is created by the filling of the ventricle with blood during diastole. It is the most important determinant of cardiac output and a decrease in preload will lead to a decrease in cardiac output.

The most common cause of decreased preload is dehydration, which can lead to a decrease in the amount of blood that reaches the ventricles. Other causes of decreased preload include hypovolemia, which is a decrease in the total blood volume, and increased venous tone, which is increased resistance to blood flow in the veins.

Afterload

Afterload is the tension or resistance that the ventricle must overcome in order to push the blood out of the ventricle. An increase in afterload will lead to a decrease in cardiac output as the ventricle is not able to push the blood out effectively.

The most common cause of increased afterload is hypertension, which is an increase in the systemic arterial blood pressure. Other causes of increased afterload include aortic stenosis, which is a narrowing of the aortic valve, and pulmonary hypertension, which is an increase in the pressure in the pulmonary arteries.

Contractility

Contractility refers to the strength of the heart muscle contraction and is an important determinant of cardiac output. A decrease in contractility will lead to a decrease in cardiac output as the heart is not able to effectively pump the blood out.

The most common cause of decreased contractility is myocardial ischemia, which is a decrease in the oxygen supply to the heart muscle. Other causes of decreased contractility include cardiomyopathies, which are diseases of the heart muscle, and electrolyte imbalances, which can affect the way the heart muscle contracts.

Heart Rate

Heart rate is the number of times the heart beats in one minute and is an important determinant of cardiac output. A decrease in heart rate will lead to a decrease in cardiac output as the heart is not able to pump as much blood in the same amount of time.

The most common cause of decreased heart rate is bradycardia, which is a decrease in the heart rate. Other causes of decreased heart rate include hypothyroidism, which is an underactive thyroid gland, and drug toxicity, which can affect the electrical conduction system of the heart.

Summary

In summary, decreased cardiac output can be caused by a variety of pathophysiological mechanisms, including decreased preload, increased afterload, decreased contractility, and decreased heart rate. It is important to recognize these potential causes in order to effectively diagnose and treat this condition.