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Experimental animal data have indicated that the site of ventricular tachycardia origin and, hence, the degree of asynchronous contraction, may influence the hemodynamic tolerance during sustained ventricular tachycardia. However, data in man are scarce. We studied patients with preserved left ventricular function and absence of significant coronary artery disease. Ventricular tachycardia was simulated with rapid pacing (at 120 and 150 beats/min), performed randomly, from the right ventricular apex or the right ventricular outflow tract. Following pacing from one site, it was repeated from the alternate site. Compared to outflow tract pacing, QRS duration was significantly longer during rapid pacing from the apex. Left ventricular pressure was recorded using a micromanometer-tipped catheter. During sinus rhythm, peak systolic pressure was 142 +/- 14 mmHg; at 120 beats/min, it decreased to 109 +/- 12 mmHg during pacing from the apex and to 127 +/- 21 mmHg during pacing from the outflow tract (P = 0.008). This difference diminished at 150 beats/min (101 +/- 16 mmHg vs 112 +/- 16 mmHg, respectively, P = 0.21). During sinus rhythm end-diastolic pressure was 13 +/- 1 mmHg, which did not change significantly during pacing at 120 beats/min. During pacing at 150 beats/min, end-diastolic pressure increased to 21 +/- 3 mmHg during pacing from the apex and to 16 +/- 2 mmHg during pacing from the outflow tract (P = 0.005). Changes in first derivative of pressure and in isovolumic relaxation time constant were comparable during pacing from the two sites. Thus, it seems that tachycardias originating from the right ventricular outflow tract result in more favorable left ventricular hemodynamics, compared to those from the right ventricular apex.

This study examined the effects of different atrioventricular (AV) intervals, during AV sequential pacing, on hemodynamics and coronary blood flow in individuals with normal hearts. Left anterior descending artery blood flow velocity was measured, using intracoronary Doppler, in 17 normal individuals. Five pacing tests were applied in random order for 5 min, at 15 beats/min above the sinus rate. Four tests using AV sequential pacing with AV intervals of 175, 150, 100, and 50 ms, and one using atrial pacing were applied. Mean flow velocity was 21 ± 9 cm/s, 20 ± 9 cm/s, 17 ± 7 cm/s, 17 ± 7 cm/s, and 22±10 cm/s, respectively (F = 8.87, p = .00001). The hemodynamic effects of these 5 pacing tests were assessed in 8 different normal subjects. Isovolumic relaxation time constant and left ventricular systolic pressure decreased, whereas right atrial pressure increased during AV sequential pacing with short AV intervals. Thus, during short-term AV sequential pacing at rest, coronary blood flow in a normal left anterior descending artery decreases with short AV intervals.

Heart rate changes to hypotensive stimuli (baroreceptor sensitivity [BRS]) and forearm blood flow (FBF) reduction during head-up tilt are mediated by arterial and cardiopulmonary baroreceptors. Regarding baroreflexes in neurocardiogenic syncope (NCS), an apparent variation exists in findings reported in the literature. This may be due to the existence of different types of response. This study included 39 patients with NCS and positive tilt test and 26 normal subjects with negative test. Patients were grouped according to the type of tilt test response (mixed, cardioinhibitory, vasodepressor). BRS was noninvasively assessed in the supine position as an estimate of arterial baroreceptor sensitivity. As an estimate of cardiopulmonary baroreceptor reactivity, FBF was measured by venous occlusion plethysmography in the supine position and every 2.5 minutes during the first 15 minutes of tilt. BRS was related to percent of FBF changes. BRS was impaired in syncopal patients relative to controls (7.2 +/- 0.9 vs 10.4 +/- 0.3 ms/mmHg, P = 0.01), especially in vasodepressive type (4.9 +/- 1.0 ms/mmHg, P = 0.0001). FBF changes during tilt were subnormal in NCS, ascribed to two different patterns: one, characterized by impaired vasoconstriction (FBF during tilt showing < 10% mean reduction relative to baseline, especially in vasodepressive type) and another, characterized by a great variability across time (unstable response, especially in cardioinhibitory type). In controls, BRS was related to the percent of FBF changes after 2.5, 5, and 10 minutes of tilt (P values 0.0001, 0.004, and 0.008). In patients, BRS was uncoupled from FBF changes. In conclusion, baroreflexes in NCS are impaired, unstable, and disorganized. Impairment predominates in the vasodepressive type and instability in the cardioinhibitory. The results of this study are indicative of more than one baroreflex-mediated response types.

ObjectivesWe sought to assess the relative therapeutic efficacy of propranolol, nadolol and placebo in recurrent vasovagal syncope (VVS).BackgroundCentral and peripheral mechanisms have been implicated in the pathogenesis of VVS. Propranolol, nadolol and placebo have different sites of action on central and/or peripheral mechanisms. It has not yet been clarified whether one of the aforementioned treatments is more efficient than the others in reducing clinical episodes and exerting a beneficial effect on patients’ well-being.MethodsWe studied 30 consecutive patients with recurrent VVS and a positive head-up tilt test. All were serially and randomly assigned to propranolol, nadolol or placebo. Therapy with each drug lasted three months. On the day of drug crossover, patients reported the total number of syncopal and presyncopal attacks during the previous period. They also gave a general assessment of their quality of life, taking into account: 1) symptom recurrence; 2) drug side effects; and 3) their personal well-being during therapy (scale 0 to 4: 0 = very bad/discontinuation; 1 = bad; 2 = good; 3 = very good; 4 = excellent). At the end of the nine-month follow-up period, they reported whether they preferred a specific treatment over the others.ResultsSpontaneous syncopal and presyncopal episode recurrence during each three-month follow-up period was reduced by all drugs tested (analysis of variance [ANOVA]: chi-square = 67.4, p < 0.0001 for syncopal attacks; chi-square = 60.1, p < 0.0001 for presyncopal attacks) No differences were observed in the recurrence of syncope and presyncope among the three drugs. All drugs improved the patients’ well-being (ANOVA: chi-square = 61.9, p < 0.0001).ConclusionsPropranolol, nadolol and placebo are equally effective treatments in VVS, as demonstrated by a reduction in the recurrence of syncope and presyncope, as well as an improvement in the patients’ well-being.