Study - no effect of fish oil on life-threatening cardiac arrhythmia

In patients with an increased risk of heart rhythm problems, cardiac arrest or arrhythmia, eating fish oil did little to reduce that risk.

This is the conclusion of a European multi-centre study reported by Brouwer and colleagues of the Wageningen Centre for Food Sciences (WCFS) at the European Society of Cardiology meeting in Stockholm.

The findings of this trial do not support strong anti-arrhythmic effects that have been attributed to fish oil in the past.

The Study on Omega-3 Fatty acids and ventricular Arrhythmia (SOFA) investigated the effect of taking fish oil capsules on life-threatening cardiac arrhythmia in 546 patients with an Implantable Cardioverter Defibrillator (ICD).

An ICD device is typically implanted into the chest of patients who survived serious cardiac arrhythmia or a cardiac arrest. It monitors the heart rate of the patient and automatically treats serious rhythm problems by shocking or pacing.

The ICD contains a memory chip that registers and stores all cardiac arrhythmias and the provided therapy; that is shocking or pacing. Patients with an ICD visit the hospital regularly, usually once per three or four months, to have their memory chip read out.

The cardiologist can read out the memory chip from outside the body, and see and record cardiac arrhythmias that occurred in the preceding period. Thus, the ICD enables continuous monitoring of serious heart rhythm disturbances in these patients. This patient group is therefore very suitable for testing a possible anti-arrhythmic effect of fish oil.

Very long-chain n-3 polyunsaturated fatty acids primarily occur in the diet in fish. They are also named n-3 PUFA or omega-3 fatty acids. Evidence from earlier studies indicates that intake of these n-3 PUFA as present in fish oil reduces the risk of sudden death. Sudden deaths are an important cause of death in the Western world. Approximately 50% of all deaths due to cardiovascular disease are sudden deaths and these are usually caused by arrhythmias. Sudden death is often the first manifestation of cardiovascular disease; thus, people suddenly die without even knowing that they were suffering from heart disease. Fish oil may protect against sudden death by preventing cardiac arrhythmias, but present evidence is contradictory.

Therefore, the Wageningen Centre for Food Sciences (WCFS) initiated and funded the SOFA trial. WCFS is a research alliance of the Dutch government, food industry and research organizations. It performs long-term strategic and fundamental research in the area of food sciences. The main aim of WCFS is to gain fundamental knowledge to develop new and improved foods and production methods with specific attention to health aspects. The SOFA trial also received a grant from the European Union (integrated project SEAFOODplus).

SOFA was designed to answer the question whether or not intake of n-3 PUFA from fish -a regular food ingredient- could reduce the incidence of life-threatening cardiac arrhythmia. If true, increasing the intake of n 3 PUFA would be an easy, effective and safe measure to prevent fatal arrhythmia in the general population.

The SOFA trial took place in 546 patients in 26 cardiology centres in eight European countries. Patients with an ICD were randomly given either daily 2g of fish oil (n=273) or placebo oil (n=273) for a period of up to 12 months. The trial was double-blind; neither the patients nor the investigators knew who received fish oil and who received placebo oil. Patients received the capsules on top of the usual patient care. The ICD monitored the occurrence of life-threatening cardiac arrhythmia during the entire study. At 12 months, 30% of the patients in the fish oil group had experienced either life-threatening arrhythmia or death compared to 33% of the patients in the placebo group. There was no clear difference between the two groups (P=0.24) in how long it took before a first life-threatening arrhythmia occurred or patients died after starting treatment. Among the subgroup of 342 patients who previously had a myocardial infarction (MI) there was a trend towards a beneficial effect of fish oil (p=0.086, log-rank). In this subgroup, 28% of the patients on fish oil experienced either life-threatening arrhythmia or death compared to 35% of the patients on placebo oil.

According to Brouwer, "The SOFA trial does not indicate a strong beneficial effect of n-3 PUFA from fish on life-threatening cardiac arrhythmia. However, patients with a previous myocardial infarction might still benefit from fish oil. In any case, we found no indications that fish oil would harm patients".