Journal of the American College of Cardiology
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J. Am. Coll. Cardiol. · May 1992
Randomized Controlled Trial Comparative Study Clinical TrialInfluence of histamine receptors on basal left ventricular contractile tone in humans: assessment using the H2 receptor antagonist famotidine and the beta-adrenoceptor antagonist esmolol as pharmacologic probes.
Histamine has a positive inotropic action in humans. Recent controversial data have suggested that histamine2 (H2) receptor blockade depresses overall left ventricular systolic performance in healthy volunteers. To explore the possibility that H2 receptors positively influence basal left ventricular contractile tone, 10 normal subjects were studied by using imaging and Doppler echocardiography and calibrated subclavian pulse data in a blinded, randomized, two-period crossover trial with measurements obtained at the end of each 7-day period. ⋯ Famotidine did not alter blood pressure, left ventricular percent fractional shortening, circumferential end-systolic wall stress, stroke volume index, cardiac index, total vascular resistance or ventricular contractile state in comparison with placebo but did decrease heart rate by 3 beats/min (p less than 0.05). With beta-adrenergic blockade, no differences in contractility were evident between esmolol alone and famotidine plus esmolol. Thus, H2 receptor blockade with famotidine does not alter myocardial mechanics or cardiac sympathetic tone, suggesting that in humans basal left ventricular contractile state is not physiologically dependent on the H2-mediated effects of histamine.
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J. Am. Coll. Cardiol. · May 1992
Comparative StudyValue and limitations of transesophageal echocardiography in determination of left ventricular volumes and ejection fraction.
Several formulas exist for estimating left ventricular volumes and ejection fraction using conventional two-dimensional echocardiography from transthoracic views. Transesophageal imaging provides superior resolution of endocardial borders but employs slightly different scan planes. The estimation of left ventricular volumes by transesophageal echocardiography has not been validated in human patients. ⋯ Measurements of left ventricular length by transesophageal echocardiography were smaller for systole (mean 5.7 +/- 1.6 cm) and diastole (mean 7.7 +/- 1.2 cm) than values by ventriculography (mean 9.2 +/- 1.4 and 8.1 +/- 1.6 cm, respectively; p less than 0.0001), suggesting that underestimation of the ventricular length is a major factor contributing to the smaller volumes obtained by transesophageal echocardiography. In conclusion, currently existing formulas can be applied to transesophageal images for predicting left ventricular volumes and ejection fraction. However, volumes obtained by these models are significantly smaller than those obtained with angiography, possibly because of foreshortening in the transesophageal four-chamber view.