BACKGROUND: Omega-3 polyunsaturated fatty acids in fish oils may have anti-fibrillatory effects. Their mechanism of action in humans is poorly understood.

OBJECTIVE: To investigate the effects of chronic fish oil supplementation on human atrial electrophysiology.

METHODS: Two groups of patients without clinical AF or structural heart disease and fish intake ≤ 1/week were prospectively recruited into a control group (n=30) and a fish oil group (n=31). The latter were prescribed 6g/day of fish oil for a ≥1 month prior to an electrophysiology (EP) study. The following were compared at time of EP: serum omega-3 levels, right atrial and coronary sinus effective refractory periods (ERPs), inter-atrial, intra-atrial, left atrial and coronary sinus conduction at baseline and the maximal conduction delay with the shortest propagated extra-stimulus, and inducibility of AF (10 inductions/patient).

RESULTS: The following significant differences were noted favoring the fish oil group at time of EP: (i) 2 fold higher total omega-3 levels (P<.001) (ii) lengthening of ERPs by 8-14% at all measured sites and pacing cycle lengths (P<.05) (iii) no effect on baseline inter-atrial, intra-atrial, left atrial and coronary sinus conduction but a significant attenuation of maximal conduction delay (P<.05) (iv) less inducible AF (AF ≥30 s: 24.2% vs. 7.9%, P<.001) (v) shorter mean duration of induced AF (P=.003) and (vi) prolongation of induced AF cycle length (P<.001).

CONCLUSIONS: Chronic fish oil supplementation in humans prolongs atrial refractoriness and reduces vulnerability to inducible AF. These electrophysiological changes may explain the anti-fibrillatory effect of chronic fish oil ingestion.