Causes of CHF
Blood Flow Through the Heart
CHF is not a specific diagnosis, but is a result of another underlying condition. Finding the underlying condition is important because the treatment often depends on what that condition is. Many conditions can lead to CHF:
- High blood pressure (hypertension) increases the work of the heart. The heart has to pump blood against higher resistance and must therefore generate more force. The added strain on the heart muscle can cause failure. This is one of the most common causes of CHF in the United States.
- Coronary artery disease causes ischemia, inadequate oxygen supply to the heart muscle, which can damage or destroy heart muscle tissue, leading to failure. Coronary artery disease is the other most common cause of CHF in the United States.
- Valvular heart disease causes improper blood flow through the heart, which increases the heart's workload. There are three main types of faulty heart valves:
- Narrow (stenotic) valves restrict the flow of blood. To generate enough pressure to pump blood through a narrow valve, the heart has to work much harder.
- Leaky (regurgitant) valves allow blood to flow back through after it has been pumped out. The heart must pump more blood with each heartbeat (the blood coming in normally plus blood leaking back), greatly increasing its workload.
- Endocarditis is an infection of the heart valves that can damage them.
- Abnormal heart rhythms (arrhythmias) interrupt the normal filling and pumping cycle. If the heart beats too slow (bradycardia), then not enough blood gets pumped out. If the heart beats too fast (tachycardia), then there is not enough time for the heart to fill with blood. In either case, cardiac output is reduced causing the heart to fail.
- Overactive thyroid gland (hyperthyroidism) increases the overall rate of metabolism in the body. The heart must circulate blood more frequently so that the body's tissues get an adequate amount of oxygen. This increased work can cause the heart to fail.
- A severe decrease in red blood cells (anemia) reduces the supply of oxygen in circulated blood (blood cells carry oxygen). To provide adequate amounts of oxygen to bodily tissues, the heart must circulate blood more frequently. This extra work can cause the heart to fail.
- Diseases that affect the heart muscle itself (cardiomyopathy) result in inadequate contraction of the heart. This decreases the cardiac output, which leads to CHF. Technically, cardiomyopathy only means diseases that originate and primarily affect the myocardium. However, many physicians also use the term in "ischemic cardiomyopathy," a condition resulting from the scarring caused by coronary artery disease. Diseases that cause cardiomyopathy include:
- Infections (viral, bacterial, AIDS, Lyme disease, rheumatic fever, etc.)
- Toxins (alcohol, cocaine, radiation, chemotherapy, etc.)
- Nutritional deficiencies (thiamine deficiency causing beri-beri)
- Connective tissue disorders (lupus, rheumatoid arthritis, etc.)
- Neuromuscular diseases (muscular dystrophy)
- Infiltrative (amyloidosis, sarcoidosis, cancer)
- Idiopathic (unknown)
- Peripartum cardiomyopathy
- Diseases that affect the pericardium (the sac surrounding the heart) restrict the ability of the heart to stretch when it fills. The filling is reduced, thereby diminishing cardiac output. A thickened or scarred sac (constrictive pericarditis) or fluid within the sac (pericardial tamponade) both reduce the ability of the heart to fill.
- Birth defects in the formation of the heart (congenital heart disease) produce an additional workload on the heart eventually causing it to fail. These defects involve abnormal formation of the walls between different chambers of the heart (hole in the heart), abnormal formation of the heart valves, or abnormal positions of the blood vessels that bring blood to or from the heart.