Which of the following is a complication of long-standing uncontrolled hyperthyroidism?

Long-standing uncontrolled hyperthyroidism can lead to several complications due to the profound metabolic effects of excess thyroid hormone. One significant complication is heart failure. In hyperthyroidism, the overproduction of thyroid hormones results in increased heart rate (tachycardia), elevated blood pressure, and heightened cardiac contractility. These effects increase the workload of the heart, leading to conditions such as atrial fibrillation and ultimately contributing to the risk of developing heart failure.

The heart may become unable to cope with the increased demand, which can lead to complications such as left ventricular hypertrophy and diastolic dysfunction. The consequent high-output heart failure can develop, particularly in older adults or those with pre-existing cardiovascular issues, reinforcing the connection between uncontrolled hyperthyroidism and heart failure.

The other options listed, while they may occur in different contexts or conditions, do not directly relate to the long-term effects of hyperthyroidism in the same manner as heart failure does. Myxedema coma is associated with severe hypothyroidism, diabetic ketoacidosis is primarily linked to uncontrolled diabetes mellitus, and while stroke can occur in various circumstances, it is not a direct or primary complication stemming specifically from uncontrolled hyperthyroidism.