Heart Conditions
There are many types of heart conditions that may contribute to the development of an arrhythmia.
- High Blood Pressure (Hypertension): High blood pressure causes the heart chambers to pump and work harder, creating stress and strain on the heart muscle. In response to the increase stress and work, the main heart chamber, the left ventricle, over a period of time, becomes thickened, called hypertrophy. High blood pressure, even when treated, is a risk factor for developing for developing an abnormal heart rhythm of the upper chambers called atrial fibrillation. In addition, high blood pressure remains one of the most important factors in determining the risk of stroke in atrial fibrillation (see section on CHADS2 score). High blood pressure is also a risk factor for developing coronary artery disease.
- Heart Attack (Myocardial Infarction): According to the 2010 American Heart Association report, 785, 000 Americans will experience a coronary attack each year*. A coronary attack occurs when the heart muscle does not receive enough blood to the cells and the heart cells die. During a heart attack some patients may develop serious rhythms called ventricular tachycardias and ventricular fibrillation. In the area where the heart cells die, as the heart tissue heals, a scar forms. It is felt that the scar itself does not cause ventricular tachycardia. In the region of the heart in which scar tissue is interspersed with normal tissue there is a delay in the conduction of electrical signals that may cause a circuit of electrical signals called reentry that may produce ventricular tachycardia.
*Heart Disease and Stroke Statistics_2010 Update. A Report From the American Heart Association. Circulation. 2010 Feb 23;121(7):948-54.
- Cardiomyopathy: Cardiomyopathy is a condition when the heart muscle is weakened and/or enlarged. Causes of cardiomyopathy include a heart attack (lack of oxygen to the heart muscle), a viral infection that invades the heart muscle, a genetic condition that one inherits from other family members (familial), excessive alcohol or drug use, post pregnancy, an auto-immune disorder and/or for an unknown reason, called idiopathic.
- Dilated: Dilated cardiomyopathy is the most common type of cardiomyopathy. It is a condition when the heart is enlarged and weakened. The lower chambers of the heart enlarge, especially the left ventricle, and do not pump as effectively. Arrhythmias of the upper chamber and lower chamber are more likely to occur in weakened, enlarged and overstretched hearts.
Figure http://www.genedx.com/images/dcm_fig1.jpg
Dilated cardiomyopathy can be categorized into two types:
- Ischemic – Ischemic dilated cardiomyopathy occurs due to a heart attack, which results from a blood clot or blockage in the arteries to the heart. Scar forms over the area of cell damage and arrhythmias can come from the scarred area. It can happen soon after a heart attack or many years later.
- Non-ischemic – Non-ischemic cardiomyopathy occurs when the heart muscle is damaged by other reasons than lack of blood flow to the heart muscle itself. The heart cells are damaged and scar tissue or fibrosis occurs, which may cause arrhythmias.
- Arrhythmogenic right ventricular dysplasia/cardiomyopathy is a genetic condition that is characterized by fibro-fatty tissue replacing healthy heart tissue in the right ventricle. The electrical conduction system in the heart can be abnormal due to the scarred and fatty areas of the heart. Ventricular arrhythmias such as ventricular tachycardia are common with this condition. (see section on Arrhythmogenic right ventricular dysplasia/cardiomyopathy)
- Hypertrophic cardiomyopathy is a genetic condition in which the walls of the left ventricle become thickened. The condition is due to genetic differences in proteins of the heart muscle. In the population, it occurs in 1 out of 500 people.* (see section on Hypertrophy Cardiomyopathy)
*Maron, BJ Circulation. 1995;92:785–789.
- Restrictive cardiomyopathy is a condition where the walls of the left ventricle becomes stiff and rigid, causing improper filling of the heart chamber(s). The stiffened heart can cause an abnormal heart rhythms in the upper and lower chambers. There are a number of underlying causes of restrictive cardiomyopathy.
- .Valvular Disease: The heart has four valves, namely, the tricuspid, pulmonic, mitral and aortic.
The valves open and close quickly and efficiently to direct blood flow in the proper direction. The heart valves may no longer close properly and may permit blood to flow backward into the heart chamber(s). Blood flowing backward in the heart chamber is called regurgitation. Regurgitation of the aortic and mitral valves may lead to shortness of breath and enlargement of the left ventricle, the main pumping chamber. Regurgitation is usually scored from mild 1+ to severe 4+. Mild regurgitation usually does not have a significant in the overall heart pumping function called hemodynamics. In some cases 3+ or more regurgitation may lead to the need for heart valve surgery. The timing of surgery usually depends on the development of symptoms felt to be due to the regurgitation, decreasing function of the left ventricle which may be reflected in a decreased Ejection Fraction, or enlargement of the left ventricle. There also may be leakiness of the right sided heart valves, the tricuspid valve and the pulmonic valve. Regurgitation may also lead to enlargement of the upper chambers, the atria, and may result in the development of atrial fibrillation.
Heart valves can also have difficulty opening fully, a condition called stenosis. Stenosis of the aortic valve and the mitral valve are most likely to result in symptoms. Stenosis of the aortic valve results in a significant thickening of the left ventricular walls. The two most common causes of aortic stenosis include congenital absence of one of the 3 leaflets that make up the aortic valve called a bicuspid aortic valve and the acquired thickening of the aortic valve with age. Aortic valve replacement is usually performed when patients develop symptoms such as shortness of breath or dizziness or loss of consciousness. Patients with aortic stenosis may develop atrial fibrillation.
- Sleep Apnea: Sleep apnea is a condition where the patient oxygen levels are low due to an impaired airflow during sleep. There are three types: obstructive (OSA), central and hypoventilation/hypoxic syndrome. Sleep disordered breathing can cause stress on the heart and has been independently linked to high blood pressure, coronary disease and arrhythmias. Arrhythmias can occur in both the upper or lower chamber of the heart.
- Congenital: Some patients are born with structural heart disease and the way the heart is structured can cause heart arrhythmias. The congenital defects ranges from mild to complex and some patients require surgery to repair the defects in the heart. Patients who undergo surgery to correct the abnormalities may develop scarring from the surgical site which can also cause arrhythmias over time. Tetralology of Fallot is an example of a congenital heart condition that may result in the serious heart rhythm problem called ventricular tachycardia.