Although differences in patient sex in heart rate and QT interval have been well characterized, sexual differences in other cardiac electrophysiological properties have not been well defined. The study population consisted of 354 consecutive patients without structural heart disease or preexcitation who underwent clinically indicated electrophysiological testing in the drug-free state. Atrial, AV nodal, and ventricular effective refractory periods (AERP, AVNERP, VERP) were determined at a pacing cycle length of 500 ms using an 8-beat drive train and 3-second intertrain pause. There were 124 men and 230 women with a mean age of 45 +/- 19 and 47 +/- 18 years, respectively. The sinus cycle length (SCL) was longer in men than in women (864 +/- 186 and 824 +/- 172 ms, respectively, P < 0.05). The QRS duration was significantly longer in men (90 +/- 12 ms) than women (86 +/- 13 ms) (P < 0.005). The HV interval was 48 +/- 9 ms in men and 45 +/- 8 ms in women (P < 0.05). The sinus node recovery time (SNRT) was significantly longer in men than in women (1215 +/- 297 ms and 1135 +/- 214 ms, respectively, P < 0.05). AERP and VERP were similar in both sexes. Aging did not influence sexual differences in cardiac electrophysiological properties, although, it independently prolonged the SCL, PR, and QT intervals, AH and HV intervals, SNRT, AVNERP, and the AV Wenckebach cycle length. The SCL, QRS duration, HV interval, and SNRT were significantly longer in men than in women. Aging prolonged cardiac conduction and increased the SCL but the effects were similar in both sexes. AERP and VERP were unaffected by aging or sex.
ST height and QTc varied among the three phases of the menstrual cycle, predominantly after double autonomic blockade. Female sex hormones that vary throughout the menstrual cycle may modulate measures of repolarization.
Cardiac electrical alternans have been associated with spontaneous ventricular arrhythmias during myocardial ischemia. The study aims were to use a new algorithm to measure depolarization and repolarization alternans from epicardial electrograms in an ischemia model and to evaluate which features are predictive of ventricular fibrillation (VF). The left anterior descending coronary artery was occluded in 21 dogs, of which 6 developed spontaneous VF. Four seconds of unipolar epicardial electrograms was recorded before and 5 min after occlusion from an 8 x 14-electrode plaque placed on the anterior left ventricle. Alternans amplitudes were estimated with a triangular wave-fitting algorithm and for each unipolar electrogram for various measurements of the QRS and ST-T wave amplitude. The root mean square error was computed for each fit. Receiver-operator characteristic curves were used to determine whether prevalence of alternans having estimated alternans amplitude-to-error ratio (A/E) above a given threshold could distinguish the dogs who had and did not have spontaneous VF. The prevalence of alternans after ischemia was highly predictive of VF when measured both during depolarization (sensitivity of 83% and specificity of 87%) and during repolarization (sensitivity of 100% and specificity of 73%). The optimal alternans A/E ranged from 1 to 4. There were no differences in the level of discordance or alternans amplitude between dogs who developed VF versus dogs who did not. The prevalence of alternans in the ventricles may be the key risk factor for developing VF during myocardial ischemia when short-term recordings are used.
Frequency characteristics of repeated episodes of VF induced in the same subjects show fair-to-good but not excellent reproducibility. Bipolar recordings were far more reproducible than unipolar recordings, but both bipolar configurations had similar reproducibility. These findings have implications for both the pathophysiology of induced VF and the design of VF detection algorithms.
VF induced in animals by T wave shock and AC current had different characteristics than VF induced by other methods. These findings may have implications for our understanding of VF pathophysiology.
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