Omega-3 fatty acids in post-MI patients lowers heart rate and recovery after exercise

April 11, 2006

Kansas City, MO - A new study designed to explore the possible mechanisms in which fish oil protects against the risk of sudden death has shown that supplementation with omega-3 fatty acids significantly decreases heart rate at rest as well as accelerates a return to a normal heart rate after exercise [1].

"The dose we gave, about 800 mg per day, did not have any effect on serum lipids, blood pressure, inflammatory markers, or arterial compliance, but it did have a pretty consistent and profound effect on heart rate," senior investigator Dr William Harris (Mid America Heart Institute, Kansas City, MO) told heart wire . "This decrease in heart rate could help explain the decreased risk in sudden death with omega-3 fatty acids, because there is a relationship between resting heart rate and the risk of sudden death. The higher the rate, the higher the risk."

The results of the study are published in the April 2006 issue of the American Journal of Cardiology.

Restoring autonomic balance

Several mechanisms have recently been proposed to explain the benefits of omega-3 fatty acids, including reductions in blood pressure, lipids, platelet aggregation, and inflammation, said Harris. Most of these mechanisms, however, are observed at much higher doses, approximately 3 to 5 g/day, and do not account for the decreased risk of fatal coronary heart disease seen with lower doses, he noted.

"The American Heart Association has made a recommendation of approximately 1 g/day for people with known coronary disease," said Harris. "This is based on the GISSI prevention study, where post-MI men taking 800 to 900 mg of omega-3 fatty acids had less death and less sudden death. So the reason for doing our study was to take that patient population, give them the same dose of omega-3s, and observe what changes. What are the changes that would explain why they have less sudden death?"

In this double-blind, placebo-controlled crossover study, 18 men with a history of myocardial infarction and ejection fractions <40% were randomized to placebo or omega-3 fatty-acid supplements (585 mg of docosahexaenoic and 225 mg of eicosapentaenoic acid) for two four-month periods. At the end of each period, heart rate, heart-rate variability, and rate of recovery after exercise were determined, as were the effects on arterial compliance, blood pressure, cardiac function, and fasting serum levels of lipids and inflammatory markers.

Resting heart rate, averaged from the supine, standing, and sitting position, significantly decreased with omega-3 fatty-acid supplementation, decreasing from 73 beats per minute after receiving placebo to 68 beats per minute after treatment with omega-3 fatty acids. There was no effect of treatment on peak exercise heart rate or test duration, but among 14 subjects who completed the two stress tests, the decrease in heart rate at one minute after exercise was 19% greater after omega-3 fatty-acid treatment (p<0.01).

Heart-rate variability in the high-frequency band increased, indicative of improved parasympathetic activity, but no change was observed in overall heart-rate variability. There were no significant effects on blood pressure, arterial compliance, lipids, or inflammatory markers.

The results of the study are in line with a previous study that pooled data from 30 clinical trials and showed that fish-oil consumption reduced heart rate by 1.6 beats per minute, with greater reductions seen in studies of longer duration [2]. According to Harris, the results suggest that omega-3 fatty acids at low doses exert their influence by improving autonomic balance, leading to a decreased risk of fatal dysrhythmia. However, low-dose fatty acids also appear to have a direct effect on cardiac physiology, he said.

"The omega-3s, in these low doses, at the AHA-recommended doses, really do seem to have a beneficial effect on the heart," said Harris. "Reducing how much the heart is beating is a sign of a much healthier heart."


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