American heart journal
-
This study was performed to evaluate the impact of beta blockers on QT adaptation to heart rate during the exercise and recovery phases of exercise testing in long QT syndrome. ⋯ Beta blockers reduce QT hysteresis in patients with long QT syndrome to values seen in normal patients. This improved QT adaptation to changes in heart rate may explain the clinical benefit of beta blockers in long QT syndrome.
-
American heart journal · Mar 2002
A noninvasive measure of baroreflex sensitivity without blood pressure measurement.
Baroreflex sensitivity (BRS) and heart rate variability (HRV) are attenuated in cardiovascular disease and can give important prognostic information. Conventional measures of BRS require expensive or invasive equipment for the beat-to-beat measure of blood pressure (BP). We examined the possibility of developing a simple protocol that would provide a relatively standardized BP stimulus, which might obviate the need to measure BP beat-by-beat. ⋯ During 0.1-Hz breathing, the marked difference in BRS between patients with CHF and age-matched control subjects is the result of smaller R-R interval oscillations. In young patients with diabetes, these R-R interval oscillations are significantly smaller than age-matched control subjects, even when some measures of spontaneous HRV are not different between groups. Breathing at 0.1 Hz provides a standard BP stimulus and concentrates spectral power of heart rate at one frequency, enabling simple evaluation of BRS even when BP measurement is not available.