Heart rhythm : the official journal of the Heart Rhythm Society
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Nonrheumatic atrial fibrillation (AF) is a common cause of embolic stroke. Warfarin therapy can reduce stroke risk by two-thirds in patients with AF, but therapy may not always be used or always be used optimally. ⋯ Warfarin remains underused within the outpatient setting. Nontherapeutic INR levels are associated with increased risk of stroke, bleeding, and thromboembolism compared with therapeutic INR levels.
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Accurately measured and properly heart-rate corrected QTc intervals show little daytime variability.
Circadian QTc changes have been reported, with conflicting results. Spontaneous QTc variability is important for pharmaceutical cardiac safety studies. ⋯ Previously reported large QTc variability largely results from methodologic imprecision. Little QTc variability is present in daytime recordings of healthy subjects. Consequently, QT-related pharmaceutical cardiac safety studies can be made smaller without decreasing their power.