Electrocardiographic Changes During Sustained Normobaric Hypoxia in Patients After Myocardial Infarction

Abstract

Abstract Background Whether physically fit patients who have recovered from myocardial infarction can safely stay and exercise at high altitude is unclear. Myocardial tissue hypoxia and pulmonary hypertension could affect cardiac function, electrophysiology and predispose to arrythmias. Methods We included four non-professional male athletes (57.8 ± 3.3 years). All were clinically stable 37 to 104 months after left ventricular ST-elevation myocardial infarction and subsequent drug-eluting stenting of single-vessel coronary artery disease. Oxygen was gradually decreased to a minimum of 11.8% followed by oxygen increase back to 20.9%. ECG, ergometry, and echocardiography were performed in normoxia and hypoxia. Results In hypoxia, ECG showed significant QTc interval prolongations using Bazett’s (402 ± 13 to 417 ± 25ms), Fridericia's (409 ± 12 to 419 ± 19ms), and Holzmann’s (103 ± 4 to 107 ± 6%) formula compared to normoxia. The response was partly reversed during recovery. Echocardiographic signs of pulmonary hypertension during normobaric hypoxia correlated significantly with altered QTc intervals (p < 0.001). Conclusions Even exceptionally healthy and fully revascularized patients post myocardial infarction may be susceptible to hypoxia-induced QTc prolongation and VES, particularly during physical exertion. Patients after myocardial infarction should be advised to seek consultation and examination by a cardiovascular specialist with expertise in high-altitude medicine prior to physical activities at high altitude.