Everest study: One in three had cardiac arrhythmias

South side of Mount Everest, Khumbu Icefall on the lower left
South side of Mount Everest

If you attempt Mount Everest, you should be aware that you are risking your life. You can get caught in an avalanche, fall into a crevasse, be hit by falling rocks, fall off, freeze to death, die of exhaustion, high altitude cerebral or pulmonary edema. With their “SUMMIT” study, Nepalese and Swiss scientists have now drawn attention to another potential danger that can also be fatal in extreme cases: Cardiac arrhythmias during the ascent from Everest Base Camp at 5,300 meters to the summit at 8,849 meters.

Very strong test group

Tents on the Everest South Col (in 2013)
Everest South Col

In the spring season of 2023, they examined 41 mountaineers who made their way to the highest point on earth. To make it clear right away: The test subjects were not Everest aspirants who lacked experience on the mountain and at high altitude. More than 80 percent of them were Sherpas. One in four already had more than ten eight-thousander ascents under their belt.

Taking danger seriously

The test subjects were fitted with ECG patches that recorded every heartbeat. The result of the “SUMMIT” study: cardiac arrhythmias were detected in 13 of the 34 climbers who were on their way above the base camp – in other words, more than one in three was affected. In 43 of the 45 cases of arrhythmia, the hearts were beating far too slowly (bradycardia), and in two cases far too quickly (ventricular tachycardia). The results should not be taken lightly, warns Thomas Pilgrim. The professor at Inselspital, the university hospital in the Swiss capital Bern, led the study together with his Nepalese colleague Kunjang Sherpa, who works as a cardiologist at Bir Hospital in Kathmandu.

Underestimated danger?

Some mountaineers have been found to have “high-grade AV blockages and ventricular tachycardia”, which “generally lead to clinical symptoms”, says Pilgrim. For example, dizziness or fainting, which can lead to falls that quickly end fatally on Everest. An AV block is when the electrical conduction in the heart is disturbed. The stronger this disruption is, the slower the heart beats. In ventricular tachycardia, on the other hand, the ventricles beat much too fast. As a result, the ventricles no longer fill with enough blood and no longer empty properly.

It is “crucial to identify individuals who are prone to developing dangerous arrhythmias (such as ventricular tachycardia) that can lead to loss of consciousness and even death,” Pilgrim tells me. “Future studies must examine the possible effects of the observed arrhythmias in more detail in order to gain a better understanding of whether cardiac arrhythmias represent an additional, previously underestimated risk in high-altitude mountaineering.”

The 46-year-old cardiologist is a mountaineer himself. In 2016, Pilgrim scaled the eight-thousander Cho Oyu with bottled oxygen. In spring 2023, he also made a summit attempt on Everest – with a breathing mask – but turned back at the South Col due to bad weather.

Out of breath

Myself sleeping at Everest Advanced Base Camp on the Central Rongbuk Glacier in 2005
Restless sleep at high altitude – myself at Everest Advanced Base Camp on the Central Rongbuk Glacier in 2005

The aim of the study was to determine, as a first step, how frequently cardiac arrhythmias occur in healthy Everest climbers. But what causes the heart to lose its rhythm? Further studies must show this. “The cardiac arrhythmias are most likely the result of characteristic breathing patterns during sleep and disturbances in the salt balance due to hyperventilation,” explains the scientist.

The body reacts to the thin air at high altitude with accelerated breathing. You hyperventilate. During sleep, the depth of breathing changes at regular intervals (high-altitude periodic breathing), and short pauses in breathing can also occur.

Bottled oxygen apparently reduces the risk

The majority of cardiac arrhythmias occurred between Everest Base Camp and Camp 3 at 7,300 meters, “at altitudes where no additional bottled oxygen was used,” says Pilgrim. In the summit zone, above the South Col, where all test subjects wore breathing masks, the number of arrhythmias was lower. “Our data suggest that the use of additional bottled oxygen reduces the risk of cardiac arrhythmia,” the cardiologist answers my question as to how mountaineers can prevent the danger.

Pilgrim also advises that they should have an ECG done at home before the start of the expedition to check whether they are susceptible to cardiac arrhythmia. As with all other dangers on Everest, the same applies here: Caution helps – although the risk can never be completely ruled out.

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