Autonomic and Cardiovascular Effects of Acute High Altitude Exposure After Myocardial Infarction and in Normal Volunteers

Abstract

Background: High sympathetic tone creates a significant risk for ventricular arrhythmias and sudden death, which can especially affect patients after a myocardial infarction (MI) when exercising in a hypoxic environment. Methods and Results: The 16 patients after MI and 10 normal volunteers (NV) underwent a 1-day trip from low altitude (540 m, Bern) to high altitude (3,564 m Jungfraujoch, Swiss Alps). Autonomic function under resting and mental stress conditions at low and high altitude was assessed. MI patients demonstrated a significantly lower stroke volume (P<0.05) at rest compared with the NV at low as well as high altitude. High altitude exposure was accompanied by higher low-frequency/high-frequency values in the MI patients compared with NV (P<0.01). Following mental stress, MI patients failed to show the normal return to resting values at high altitude, suggesting sustained sympathetic and diminished parasympathetic activation during post-stress recovery. Conclusions: Although all MI patients were either on β-blockers or AII inhibitors, they showed higher sympathetic activity during exposure to high altitude compared with NV. In addition, the respective parasympathetic tone was reduced, especially during recovery. This puts patients after MI at an increased risk for cardiac arrhythmias and they should be advised of this if going to high altitudes. (Circ J 2009; 73: 1485 -1491

Clinical recommendations for high altitude exposure of individuals with pre-existing cardiovascular conditions

“…Furthermore, Messerli-Burgy et al . 5 did not find any increased risk for cardiac arrhythmias in post-MI patients at 3546 m.…”

“…After a few hours, this is counter-balanced, however, by a generalized altitude-dependent increase in sympathetically mediated vasoconstriction, caused primarily by arterial hypoxaemia through afferent signalling to the cardiovascular control regions of the mid-brain via the arterial peripheral chemoreceptors located in the carotid bodies. 5 , 6 , 10S As a result, a significant and persistent arterial BP increase occurs shortly after the arrival at HA, proportional to the altitude reached and more evident at night. 7 This leads to a reduced degree of the physiological blood pressure fall during sleep, 8 which persists at least over the first 7 days of altitude exposure.…”

“… IIa C 28 After AMI/CABG Patients should wait at least 6 months after uncomplicated ACS episode as well as after revascularization before HA exposure. I C 5 , 12 , 30 After stenting Patients should wait at least 6–12 months after coronary stenting before HA exposure. IIa C 12 , 31 , 33 , 30S Low risk (CCS 0-I) May safely ascend to HA, up to 4200 m asl, and practice light-to-moderate physical exertion.…”

“…The increased sympathetic activity 5 and decreased SaO 2 characterizing HA exposure, in addition to the increase in right ventricular work and in cellular transmembrane shifts of potassium, might be a favourable substrate for arrhythmias. However, to date, an increase in malignant arrhythmias at HA has never been systematically demonstrated.…”

The effect of hypoxia on exercise tolerance in persons after acute coronary syndrome treated with angioplasty combined with coronary stent implantation – pilot studies

“…Information on the risks to those with CAD who ascend to altitudes above 5,000 m is lacking, although there are plenty of anecdotal examples of individuals with stable CAD performing well at these altitudes [4]. It should be remembered that if an individual suffering from coronary disease experiences any type of pain during the exercise test, then surely this pain is also expected to occur after reaching even low altitudes, which disqualifies the participant from activities in high-mountain environments [3,[9][10][11]. It should also be mentioned that this limitation should help the individual avoid visiting a moderate altitude just to enjoy scenery without significant physical activity [12,13].…”