Exercise Performance of Asymptomatic Subjects with Hereditary Hemochromatosis: The Increase in Abnormal Electrocardiographic Changes and Complex Arrhythmias

Abstract

Exercise performance and electrocardiogram (ECG) responses in hereditary hemochromatosis (HH) subjects who are New York Heart Association Functional Class I are unknown. Thus, we evaluated exercise performance and ECG responses in asymptomatic HH subjects. We recruited a total of 43 HH subjects and 21 normal control subjects through NHLBI-sponsored “Heart Study of Hemochromatosis.” They underwent metabolic stress testing using Bruce protocol and exercise performance and exercise ECG parameters were obtained. The overall exercise performance of HH subjects was comparable to control subjects. However, ischemic ECG changes were frequently seen in this group (42% vs 5%, P<0.05). Additional cardiac stress imaging demonstrated no evidence of significant ischemic heart disease in any subjects who had an abnormal test, indicating that they were likely false positive responses. The occurrence of supraventricular (SVT) and ventricular tachycardia (VT) was only observed in HH. The incidence of complex arrhythmias (couplet ventricular ectopics, SVT, and VT) was significantly higher in HH subjects (19% vs 0%, P<0.05). Induction phlebotomy treatment did not affect exercise performance and ischemic ECG changes (41%) in HH. In conclusion, asymptomatic HH subjects appear to have comparable exercise capacity to normal subjects. However, abnormal ischemic stress ECGs and complex arrhythmias are more frequently seen in HH. The significance of these findings warrants further investigation of electrocardiographic instability of HH subjects during exercise.