SAO PAULO, BRAZIL. A catheter ablation for atrial fibrillation creates a significant amount of scar tissue. An important question is, "Does this scar tissue impair the function of the left atrium?" Although the function of the left atrium is mainly to act as a reservoir for the left ventricle, it does contribute some pumping action on its own and a significant reduction in this action may have undesirable consequences. The most important parameters in evaluating the pumping action of the left atrium are the left atrial emptying fraction (EF) and the flow velocity (FV) through the mitral valve (the valve between the left atrium and the left ventricle). The EF is defined as the maximal minus the minimal left atrial volume divided by the maximal volume. The FV is obtained from echocardiographic measurements.
Electrophysiologists at the University of Sao Paulo now report that left atrial function is indeed impaired immediately following an ablation, but then improves over time. Their study involved a control group of 28 age- and gender-matched healthy individuals without afib and 28 paroxysmal afibbers. All the AF patients had normal left ventricular ejection fractions and no significant structural heart disease. However, 39% did have hypertension and 18% had undergone a previous ablation. At baseline (prior to ablation) members of the control group had a significantly shorter left atrial diameter (average 36 mm vs. 41 mm), a significantly higher average EF (53% vs. 47%), and a greater FV (average 10.2 cm/s vs. 8.2 cm/s) than members of the afib group.
The paroxysmal afibbers underwent a standard pulmonary vein isolation (PVI) procedure and then had their EF and FV measured 24 hours and an average of 8 months following the procedure (minimum 6 months post-procedure). Sixty-one percent of ablatees were in normal sinus rhythm at both the 24-hour and 8-month evaluations. The researchers found that the average EF in the PVI group decreased from the baseline 47% to 40% 24 hours after the ablation. However, at the 8-month check-up it had recovered to 43%. Similarly, the FV decreased from an average 8.2 cm/s at baseline to 6.9 cm/s at the 24-hour mark, but then increased to 7.7 cm/s over the following 8 months.
The researchers conclude that a PVI causes a significant drop in left atrium performance immediately after the procedure, but that the performance improves with time. They did not observe any decrease in left atrial diameter or volume after the procedure, but speculate that this could, at least partially, be due to the fact that 39% of the group were still experiencing afib episodes following their ablation.
Rodrigues, ACT, et al. Left atrial function after ablation for paroxysmal atrial fibrillation. American Journal of Cardiology, Vol. 103, 2009, pp. 395-98