Margaret A.WinkerMD, Senior EditorIndividualAuthorPhil B.FontanarosaMD, Senior EditorIndividualAuthor
To the Editor.—The SPAF III aspirin cohort study was intended to identify those who might safely avoid anticoagulation.1 A prior model of risk of stroke based on a set of pooled trial data (AFI), including data from SPAF I, identified patients with AF younger than 65 years with no risk factors as the group at low enough absolute risk to forgo anticoagulation.2 The main novel features of the SPAF III risk scheme were that older age in men (but not women) and a diagnosis of hypertension (but with an entry systolic BP <160 mm Hg) were not risk factors for stroke in patients with AF. One half of the SPAF III low-risk aspirin cohort carried a diagnosis of hypertension, and the rate of stroke among these patients was 3.6% per year, with the confidence interval reaching 5.2% per year. This is not low risk. For purposes of calibration, appreciate that the data monitoring committees of the Boston Area Anticoagulation Trial for AF and Veteran Affairs Stroke Prevention in nonrheumatic atrial fibrillation (SPIN-AF) trials stopped their respective studies when the risk in their control groups was 3% to 4% per year (vs <1% per year among warfarin-treated patients), concluding it was ethically imperative to offer warfarin to all control patients.3,4 The SPAF III cohort data also demonstrated that increasing age was, in fact, an independent risk factor, with a relative risk of 1.7 per decade, actually larger than the AFI estimate of 1.4 per decade. It appears that these novel features of the SPAF III risk scheme were not confirmed by the study's own data. Increasing age, regardless of sex, and a diagnosis of hypertension confer increased risk of stroke in patients with AF.
Singer DE. Patients With Atrial Fibrillation at Low Risk of Stroke. JAMA. 1998;280(10):882-883. doi:10-1001/pubs.JAMA-ISSN-0098-7484-280-10-jac80015