Heart rhythm : the official journal of the Heart Rhythm Society
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Mexiletine may protect patients with long QT syndrome (LQTS) type 3 from arrhythmias. However, we found an unusual in utero presentation of intermittent atrioventricular block and ventricular tachycardia (spontaneous or lidocaine-induced) in a fetus and his sibling with LQTS. ⋯ We identified a novel hERG/F627L mutation that results in LQTS with fetal onset of atrioventricular block and ventricular tachycardia. A coexisting SCN5A/R43Q variant, although it per se does not prolong repolarization, contributes to the development of ventricular tachyarrhythmias after lidocaine. Patients with such latent lidocaine-induced phenotype who are given lidocaine or mexiletine may be at risk.
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Knowledge of the shock potential gradient (nablaV) and postshock activation is limited to internal defibrillation of short-duration ventricular fibrillation (SDVF). ⋯ Compared with previous studies of internal defibrillation, during external defibrillation much less of the shock voltage appears across the heart and the shock field is much more even; however, the minimum nablaV is similar. Compared with external defibrillation of SDVF, the biphasic external DFT for LDVF is not increased; however, time to earliest postshock activation triples. Refibrillation is common after LDVF but not after SDVF in these normal hearts, indicating that LDVF by itself can cause refibrillation without requiring preexisting heart disease.
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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.