Altitude and the Heart: Is Going High Safe for Your Cardiac Patient?

From American Heart Journal
John P. Higgins, MD, MPhil; Troy Tuttle, MS; Johanna A. Higgins, MD
Posted: 02/22/2010; American Heart Journal © 2010

Abstract
Our aging population combined with the ease of travel and the interest in high altitude recreation pursuits exposes more patients to the acute physiologic effects of high altitude and lower oxygen availability.
Acute exposure high altitude is associated with significant alterations to the cardiovascular system. These may be important in patients with underlying cardiovascular disease who are not able to compensate to such physiologic changes. Exacerbating factors pertinent to patients with cardiovascular disease include acute hypoxia, increased myocardial work, increased epinephrine release, and increased pulmonary artery pressures.
This review summarizes the physiology and clinical evidence regarding acute altitude exposure on the cardiopulmonary system with practical recommendations to address the question: "Is it safe for me to ski in the Rockies or climb Mt. Kilimanjaro?"

Introduction
More than 100 million people travel to high altitudes annually, which place some at risk for complications involving the acute effects of hypobaric hypoxia.[1] High altitude trekking and recreational activities provide a unique physiologic challenge to the cardiopulmonary system.[2,3] Often, people are acutely exposed to high altitude for 4 to 6 hours for specific recreational activities, and thus, there is limited time for physiologic adaptations to occur.[4] Environmental changes when moving from sea level to altitude include reductions in atmospheric pressure, oxygen pressure, humidity, and temperature.[5] The exact altitude at which physiologic changes affect health and cardiopulmonary performance is not constant, but significant changes typically begin at > 2,500 m (8,200 ft).[6] At this moderate altitude, the partial pressure of oxygen in the arterial blood is about 60 mm Hg, compared with 98 mm Hg at sea level.[7] The degree to which changes occur depend on the change in elevation, degree of hypoxia, rate of ascent, level of acclimatization, exercise intensity, genetics, and age.[5,8,9] For the purpose of this review, low altitude is considered to range from sea-level to 1,500 m (4,950 ft), moderate altitude from 1,500-2,500 m (4,950-8,250 ft), and high altitude > 2500 m (8,250 ft).

Recommendations
On the basis of this review, we advocate the following recommendations for unacclimatized patients who are considering ascent to high altitude and/or exercise at elevation. To review, low: sea-level to 1,500 m (4,950 ft), moderate: 1,500-2,500 m (4,950-8,250 ft), high altitude: > 2,500 m (8,250 ft).

Recommendations for every patient:

At moderate or high altitude, limit activity to a lower maximal level than at sea level. Based on the available literature, limitation of exercise workload or exercise time to about 80% to 90% of what one can do at sea level.
Raise your sleeping altitude gradually by < 305 m (1,000 ft) per day each night > 3,050 m (10,000 ft), especially if a prolonged trek is planned "the sleeping rule."[27]
A moderate degree of physical conditioning is encouraged at sea level before exercise at altitude.[62]
Alcohol consumption should be minimized and proper hydration should be maintained to keep blood viscosity and volume within normal parameters.
If unsure of a patient's cardiac status, in any male or female > 40 years, consider performing an exercise treadmill stress test for the evaluation of heart disease before planned activity at high altitude.[40]
In addition to the above, recommendations specific for cardiac patients:

Patients with unstable angina, uncontrolled ventricular or supraventricular arrhythmias, uncompensated heart failure, myocardial infarction in prior 2 weeks, or revascularization or major thoracic surgery in prior 3 weeks should not exercise above low altitude.[62]
Patients with severe heart failure, severe angina, or severe valvular disease should not ascend to high altitude.[27]
Patients who have had coronary events within last 14 days should avoid traveling to altitude until a maximal stress test (treadmill, echocardiographic, or nuclear) rules out significant ischemia; for patients who have undergone revascularization in the mean time, a submaximal or pharmacologic stress test should be considered.[63]
Elderly people and/or those with significant structural but stable heart disease should limit their activity the first few days at moderate or high altitude.[34,38]
Patients with significant cardiovascular disease that is borderline compensated at sea level should limit their ascent to low or moderate altitude.[39]
Patients with CAD, arrhythmia, or congestive heart failure should be advised that they may become symptomatic at lower exercise workloads at altitude than at sea level.[35,36]
Individual activity limits should be based on peak heart rate or rate pressure product rather than workload because ischemia may occur at a lower workload at altitude.[6]
Patients with prior HAPE and known intracardiac shunts will likely experience an increase in right heart and pulmonary artery pressures, which may result in worsening of their condition, and therefore should be advised to avoid travel to high altitude.[56]
Patients with a history of HAPE or ascending rapidly to high altitude should be aware of the signs and symptoms of HAPE, with plans for immediate descent to lower altitude and oxygen administration as the first priority; also, prophylactic use of and emergency medical treatment consisting of calcium antagonists and phosphodiesterase inhibitors should be considered.[10]
Patients with pacemakers can be safely exposed to high altitudes with no impact on ventricular stimulation thresholds;[64] effects of altitude on implantable cardioverter-defibrillators are unknown at this time.