Pathophysiology
Systolic failure, the most common cause of CHF, results from an inability of the heart to pump blood. It is a defect in the ability of the ventricles to contract. The ventricle loses its ability to generate enough pressure to pump blood against the pressure of the lungs (right ventricle) or the aorta (left ventricle).
Diastolic failure is the inability of the ventricles to fill during diastole. The result is venous engorgement of the pulmonary and systemic vascular systems.
There are various precipitating causes of heart failure. This is not an inclusive list but it will give an idea of how the following can lead to heart failure. Understanding these processes will help you answer most questions people may ask you about heart failure.
Anemia decreases the oxygen carrying capacity of the blood. Cardiac Output increases to meet the demands of the tissues. Prolonged high demand causes the heart to resort to the following compensatory mechanisms (1) ventricular dilation, (2) ventricular hypertrophy, (3) increased sympathetic nervous system stimulation, and (4) neurohormonal responses. These compensatory mechanisms may or may not be seen in each of the precipitating causes.
Infection causes an increased oxygen demand in the tissues requiring a higher cardiac output.
Thyrotoxicosis causes a change in the rate of metabolism at the tissue level resulting in an increased heart rate and heart workload.
Hypothyroidism indirectly predisposes the arteries to increased atherosclerosis. Severe hypothyroidism decreases myocardial contractility.
Arrhythmias may decrease cardiac output and increase the heart workload and oxygen requirements of myocardial tissue.
Bacterial endocarditis follows two processes, (1) infection increases the oxygen demands of the tissues, and (2) valvular dysfunction results in stenosis and regurgitation.
Pulmonary embolism causes increased pulmonary pressure that exerts pressure on the right ventricle, leading to right ventricle hypertrophy and then failure.
Pulmonary disease causes increased pulmonary pressure that exerts pressure on the right ventricle, leading to right ventricle hypertrophy and then failure.
Paget’s disease is a skeletal bone disorder in which there is excessive bone resorption followed by replacement of normal marrow by vascular, fibrous connective tissue. This disorder increases the workload of the heart because of the rapid development of the vascular bed in the skeletal muscle.
Nutritional deficiencies May decrease cardiac function by decreasing myocardial muscle mass and myocardial contractility.
Hypervolemia increases preload and causes volume load on the right ventricle.
There are also many underlying diseases that can result in heart failure. Some causes are acute and may resolve to some extent, while others remain chronic, or result in permanent damage to the heart tissue.
The following table summarizes the underlying diseases that can result in heart failure.
Common Causes of Congestive Heart Failure
Early signs of heart failure
Regardless of the etiology, heart failure typically manifests itself as pulmonary edema. This is an acute, life-threatening condition in which the alveoli become filled with serosanguinous fluid. The most common cause of pulmonary edema is left ventricular failure due to coronary artery disease.
The clinical signs of pulmonary edema are unmistakable. The person may be agitated, pale, and possibly cyanotic. The skin is cold and clammy from vasoconstriction due to stimulation of the sympathetic nervous system. The person has severe dyspnea, as evidenced by the use of accessory muscles, and the respiratory rate is greater than 30 breaths per minute. There may be wheezing and coughing, and the production of blood-tinged sputum, indicating that red blood cells are crossing the alveolar membrane. The heart rate will be increased and the blood pressure may be elevated or decreased depending on the severity of the edema.
Watching for these signs will help you identify when the person requires additional medical attention. However, there are immediate interventions you can utilize to assist a person through this stressful and potentially fatal situation.
