Association of Sick Sinus Syndrome with Hyperinsulinemia and Insulin Resistance in Patients with Non-Insulin-Dependent Diabetes Mellitus: Report of Four Cases

We report four non-insulin-dependent diabetic (NIDDM) patients accompanied by a unique combination of sick sinus syndrome (SSS) and hyperinsulinemia of unknown etiology. SSS of all four cases was due to sinus arrest in association with paroxysmal atrial fibrillation (Rubenstein-III). Of special interest is that one patient showed a high prevalence of SSS and NIDDM among her close relatives. Hyperinsulinemia of moderate degree was seen at fasting state or after carbohydrate ingestion in the absence of obesity. The resistance to the action of insulin on glucose metabolism which was evaluated in three patients by the euglycemic hyperinsulinemic clamp study was found to be comparable to the lowest quartile level for common NIDDM patients. Because insulin is a physiological regulator of cell-membrane Na+/K+-ATPase, we speculate that malfunction of the sinus node automaticity may be caused by chronic exposure to hyperinsulinemia secondary to insulin resistance in these NIDDM patients.