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More on fish oils and arrhythmias

Are fish oils truly anti-arrhythmics, do they prevent sudden cardiac death and if so, how? These were among the questions addressed at a symposium during the recent British Cardiovascular Society (BCS) meeting in Manchester. Here we review some of the key messages from the meeting.

The symposium, The impact of Omega-3’s on cardiovascular disease, was chaired by Professor Julian Halcox from the University Hospital of Wales, who described how the many pleiotropic effects of Polyunsaturated fatty acids , PUFAs/fish oils  (table 1) may help to create an environment to “calm down” plaque and patient vulnerability.

fishy2b

Haemodynamic effects include reductions in systolic (-3-5 mmHg) and diastolic (- 2-3 mmHg) blood pressure, reducing systemic vascular resistance (↑ arterial wall compliance and vasodilatory responses but ↓ vasoconstrictive responses) while leaving cardiac output relatively unchanged. Similarly, high fish oil consuming populations have been shown to have lower heart rates (approx -2-3 beats/min) than other populations. PUFAs can also increase stroke volume (approx 4ml/beat) and improve early diastolic filling. The overall effects result in reduced levels of oxygen consumption while improving cardiac efficiency and reducing the likelihood of cardiac hypertrophy.

Other potentially beneficial pleiotropic effects include reduction of triglycerides, anti-inflammatory activity and effects at a platelet and endothelial level which, along with reducing risk of ischaemia-reperfusion injury, may, along with other metabolic and rheological factors, ‘protect’ against sudden cardiac death (SCD). Arguably, this has been observed in studies such as GISSI-Prevenzione, which showed a 44%  SCD reduction in patients randomized to daily consumption of 1g Omega-3 fish oil capsules.

Table 1. Potential coronary vascular effects of n-3 PUFA

  • Reduce triglycerides
  • Reduce platelet aggregation
  • Blood pressure reduction
  • Direct effects on endothelium
  • Anti-inflammatory

Clinical Outcomes:

  • Antiatherogenesis
  • Increases plaque stability
  • Reduces thrombosis

Professor John Camm, St George’s Hospital Medical School, London, said that  “ion channel trafficking can be fundamentally affected” by n-3 PUFAs, with dose-dependent inhibition of sodium and potassium channels, for example. Experimental evidence supports how PUFAs are anti-fibrillatory and reduce both the incidence and duration of arrhythmias. Their effects in humans is less clear, however and some studies have shown no benefits in  primary prevention or in prevention of atrial fibrillation (AF) after cardiac surgery. While sometimes considered a more benign arrhythmia, over one third on AF patients die from SCD, Professor Camm reminded. There are inconsistencies in trials (and in their meta-analysis) and fundamental problems in their design, we therefore need “large, prospective placebo-controlled trials to establish the value of PUFA treatment on arrhythmias” he proposed. “There is an antiarrhythmic effect but it is difficult to detect it with the type of trials so far”, Professor Camm concluded.

Professor Roberto Marchioli from the GISSI Group, suggested that the early benefits of n-3 PUFAs observed in the GISSI-P study, occurred without changes in the lipid pattern. Also, benefits on SCD were independent of beta blockers.  In the n-3’s trial in heart failure, GISSI-HF, modest risk reductions were seen in patients taking fish oils (but not statin) and this extended to those with depressed ejection fractions, but he said that because heart failure is a chronic disease and it is difficult to tease out any early effects of interventions when events (and event rates overall) are occurring chronically. He agreed more trials are needed. More trials are underway, eg FORWARD, OPERA, PROFI, which may help clarify what are the effects of fish oils in high risk cardiac patients, and perhaps allow for clearer guidelines on the use of n-3’s in heart failure patients. He concluded with some wisdom from Karl Popper (1902-1944), “the growth of knowledge depends entirely on disagreement”

The symposium was sponsored by Abbott Healthcare Products Ltd.

Published on: June 18, 2010

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ENDORSED BY

  • ArrhythmiaAlliance
  • Stars
  • Anticoagulation Europe
  • Atrial Fibrillation Association
 

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