Stroke risk in paroxysmal and persistent AF
FLORENCE, ITALY. The risk of a thromboembolic event (ischemic stroke, transient ischemic attack [TIA] or systemic embolism) is elevated in atrial fibrillation (AF) patients with one or more risk factors for stroke. The degree of risk is commonly expressed in form of the CHADS2 score which assigns 1 point each for the presence of heart failure, hypertension, age over 75 years, and diabetes and 2 points for prior ischemic stroke or TIA. A score of 0 is considered low risk, a score of 1 is associated with moderate risk, and a score of 2 or more is considered high risk. Atrial fibrillation is classified as paroxysmal if lasting less than 7 days and as persistent if lasting more than 7 days but amenable to termination with cardioversion.

A group of Italian researchers (GISSI-AF investigators) now report that the risk of a thromboembolic (TE) event is low in both paroxysmal and persistent AF with moderate stroke risk. Their study involved 1234 participants in the GISSI-AF trial originally designed to evaluate the efficacy of the angiotensin II receptor blocker valsartan (Diovan) in preventing AF recurrence in patients with hypertension[1,2].

The average age of the participants was 67 years, 40% were women (46% in the paroxysmal group), 62% had paroxysmal and 38% had persistent AF. The majority (85%) had hypertension, 4% had coronary artery disease, 8% had heart failure or reduced left ventricular ejection fraction, and 6% had suffered a prior TE event. Heart failure was significantly more common among persistent afibbers than among paroxysmal ones (14% vs 4%). The average CHADS2 score for the total patient population was 1.41.

During a 1-year intensive follow-up period, 12 patients (0.97%) died, 12 patients (0.97%) suffered a TE event, and 10 patients (0.81%) suffered a major bleeding event (intracranial hemorrhage or major bleed requiring blood transfusion or hospitalization). There was no statistically significant difference in the incidence of TE events, major bleeding events or mortality between the paroxysmal group and the persistent group. However, the rate of TE events was significantly higher in women than in men. The incidence of TE and major bleeding events in untreated patients and in those treated with warfarin or antiplatelet agents is shown below.
Warfarin therapy was significantly more common among persistent afibbers (87% were treated with warfarin) than among paroxysmal afibbers (25% were treated with warfarin). Warfarin therapy was underprescribed in patients with a CHADS2 score of 2 or greater and overprescribed for those with a CHADS2 score of 0. Thirty-five percent of patients with a zero score were still on warfarin at the end of the study period.

The GISSI investigators conclude that the incidence of TE and bleeding events was remarkably low in both paroxysmal and persistent AF despite a significant degree of over- or under-treatment with warfarin.
Disertori, M, et al. Thromboembolic event rate in paroxysmal and persistent atrial fibrillation. BMC Cardiovascular Disorders, Vol. 13, 2013, pp. 28-37
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Editor's comment: This study adds to accumulating evidence that warfarin is often overprescribed and is not terribly effective except in the case of patients having suffered a previous stroke or TIA. It is also clear that the net benefit of warfarin therapy leaves much to be desired and is inappropriate in the case of lone afibbers with no risk factors for stroke[3,4].
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