Ventricular late potentials in myotonic dystrophy

Article Abstract:

Myotonic dystrophy is an adult form of muscular dystrophy, and is characterized by weakness, loss of muscle bulk, and a slowing of the muscles' ability to relax. A number of heart abnormalities are associated with myotonic dystrophy, particularly abnormalities of the electrical system involving the control of heart rhythm. Up to 30 percent of persons with myotonic dystrophy will die suddenly from heart rhythm abnormalities. A new form of electrocardiogram has been developed in recent years known as the signal-averaged electrocardiogram. A sophisticated computer analysis of an individual's electrocardiogram is performed, and the results can predict those people who are at risk of certain heart rhythm abnormalities. A group of patients with known myotonic dystrophy underwent signal-averaged electrocardiography, and their results were compared with those of a group of normal volunteers and a group of people without myotonic dystrophy, but with pre-existing heart rhythm abnormalities. The signal-averaged results were most abnormal for those with known rhythm disturbances, significantly abnormal for those with myotonic dystrophy, and generally normal for the healthy volunteers. The likeliest explanation for this is that myotonic dystrophy produces the same abnormalities in heart muscle that it does in skeletal muscle, thus disrupting the rhythm system of the heart and producing electrocardiographic abnormalities. Interestingly, certain drugs that are used to treat heart rhythm abnormalities have been found to reduce the skeletal muscle symptoms of persons with myotonic dystrophy. Routine electrocardiograms may reveal abnormalities in persons with the genetic predisposition to develop myotonic dystrophy well in advance of the appearance of muscle symptoms. Signal-averaged electrocardiography may serve as an effective predictor of those who are likely to develop the lethal rhythm abnormalities observed in some persons with myotonic dystrophy. (Consumer Summary produced by Reliance Medical Information, Inc.)

Causes of, Complications and side effects, Arrhythmia, Myotonic dystrophy

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Left ventricular hypertrophy in men with normal blood pressure: relation to exaggerated blood pressure response to exercise

Article Abstract:

The relation between abnormal increases in blood pressure during exercise and hypertrophy, or enlargement, of the left ventricle of the heart was assessed in 39 men with normal blood pressure. (The right side of the heart pumps blood to the lungs where it is oxygenated. The left atrium receives the freshly oxygenated blood, which then fills the left ventricle. The main function of the left ventricle is to pump freshly oxygenated blood into the circulation.) Twenty-two of the men had abnormal increases in blood pressure during exercise, and fourteen of these men had left ventricle hypertrophy. Only one of 17 men with low blood pressure during exercise was found to have left ventricle hypertrophy. The mass or size of the left ventricle correlated with maximum blood pressure during exercise. Left ventricular hypertrophy was mild in 50 percent of the men who experienced elevated blood pressure during exercise, but more severe in the remaining cases. The presence of enlargement of the left ventricle was not associated with better physical training, but was accompanied by increased size of the left atrium, suggesting impaired filling of the left ventricle during the heart cycle. The findings indicate that even in patients with normal blood pressure during regular activity, blood pressure increases during exercise may be associated with left ventricular hypertrophy, a possible sign of hypertension. (Consumer Summary produced by Reliance Medical Information, Inc.)

Measurement, Blood pressure, Heart enlargement, Heart hypertrophy, Blood pressure measurement

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Impaired exercise tolerance in hypertensive patients

Article Abstract:

Exercise performance in patients with high blood pressure may be a valuable tool in evaluating disease progression and the beneficial effects of medication. Researchers reviewed the current literature and summarized findings in relation to exercise testing on stationary bicycles and treadmills and high blood pressure. A study of 2,000 healthy middle-aged men over a period of 16 years found an association (16.1%) between elevated blood pressure after 6 minutes of exercise and risk for death from heart disease. Another study of 541 male patients with a history of chest pain or heart attack found that 86% of the patients with high blood pressure also had heart disease. Calcium channel blockers and medication containing both alpha- and beta-blockers seem to improve exercise tolerance in patients with high blood pressure. Other variables contributing to exercise performance in patients with high blood pressure may include impaired lung and nerve function.

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