The systolic murmur associated with interventricular septal defect presents a number of variations which have been related to the location and size of the defect, the pulmonary vascular resistance, and to the pressure gradient between the ventricles. The purpose of this investigation was to study the relation of the pressure gradient in interventricular septal defect to the time-intensity characteristics of the murmur. This was accomplished by simultaneously ?ecording pressure pulses in both ventricles together with continuous pressure differences between the ventricles, and phonocardiograms.
SUBJECTS AND METHODSTwenty patients with isolated interventricular septal defect were studied. Left-to-right shunts of varying size and location with and without pulmonary hypertension were encountered. The diagnoses were supported by right heart catheterization and by left ventricular angiocardiography, and in one patient (L.R.) by operation. Ages ranged from 1 to 18 years. The following parameters were recorded simultaneously and with no significant parallax error on an Electronics for Medicine oscilloscopic recorder: equisensitive right and left ventricular pressure pulses and continuous pressure differences between the two ventricles by electronic subtraction; lead II of the electrocardiogram; phonocardiograms recorded from the point on the chest where the murmur was loudest, usually with both high and low frequency filtration.Right heart catheterization was performed by standard techniques. Left heart catheterization was done by arteriotomy of either the brachial or femoral artery (usually the former) and retrograde passage of a specially designed NIH catheter with a J-shaped tip, size 6F or 7F, into the left ventricle. Angiocardiograms from the left ventricle were obtained in all patients at the end of the procedure and established the diagnosis of interventricular septal defect as well as the location of the defect in each case. The classification of Baron et al. (1963) was used in defining the anatomy of the lesions (Fig. 1).Pressures were recorded by means of Statham P23G transducers. The microphone was of a ceramic crystal displacement type with flat frequency response from 30 to 1000 cycles per second (Electronics for Medicine). By means of branched plugs the output was fed through two separate pass band filters in the ranges of 25 to 250 cps (low frequency) and 250-2500 cps (high frequency). The murmur was usually best recorded in the high frequency range. Recordings were made at both 50 and 150 mm./sec. paper speed with time lines at 0-04 and 0-02 sec. The zero point for pressure was at the mid-thoracic level.Morphine and scopolamine premedication was given, and in the younger patients this was supplemented by intravenous or rectal pentothal sodium. One patient with a muscular defect was given phenylephrine intravenously to observe the effect on the murmur and on the pressure difference curve.
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