B. Hypothyroidism (Myxedema)
1. Cardiovascular Manifestations
The heart may become dilated and the heart rate is often reduced to less than 50 beats per minute. The heart muscle is partially replaced by interstitial fibrosis with weakening of the cardiac muscles resulting in heart failure. There is a marked increase in serum cholesterol and angina or myo-cardial infarction occurs prematurely. Electrocardiogram shows sinus bradycardia, elongation of the QT interval, and low voltage.
2. Management
These cardiac complications are rarely seen because of more efficient diagnosis and treatment. Administration of L-thyroxine in adequate doses usually produces beneficial results after 3–6 months of therapy.

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