Ramon V. Canent

The effect of corrective surgery on left heart volume and mass in children with ventricular septal defect

Abstract Quantitation of left ventricular and left atrial volume, left ventricular ejection fraction and muscle mass was performed in 23 patients an average of 2 years after successful closure of a ventricular septal defect. The results were contrasted with both preoperative and normal values. Left ventricular end-diastolic volume averaged 84 ± 3 cc/m 2 ( X ± SEM ) postoperatively and was significantly decreased (P

Pulsatile aortopulmonary pressure-flow dynamics of patent ductus arteriosus in patients with various hemodynamic states.

This paper considers the pulsatile pressure-flow relationships in patients with a patent ductus arteriosus (PDA). The emphasis is on the patterns that occurred with variable hemodynamic states, extending from the continuous left-to-right (L→R) PDA shunt with low pulmonary vascular resistance to the opposite extreme where the systemic circulation depended entirely on the right-to-left (R→L) PDA flow. Pressure gradients were determined from pressures measured simultaneously with matched catheter systems, and flow was evaluated by biplane cineangiography. In all of the hemodynamic states there was flow from the aorta to the pulmonary artery during diastole, even with aortic atresia. With bidirectional shunts, the R→L pressure gradient and flow occurred during the initial systolic rise of the pulse pressure in association with an earlier rise of the pulmonary artery pressure than the aortic pressure at the PDA site. With bidirectional shunts the L→R diastolic flow across the PDA originated preferentially from backflow in the descending thoracic aorta distal to the PDA. Because the aortic backflow appeared to be considerable and occurred over large distances in some patients, we suggest that this may result in a “diastolic steal” of blood from the abdominal organs to the pulmonary artery. The diastolic steal raises questions about a potential interaction of this steal and necrotizing enterocolitis in infants with a large PDA. Since the patterns found could not be explained using the concept of vascular resistance, especially the marked L→R PDA diastolic flow in aortic atresia, we relate the preferential L→R diastolic flow from the descending aorta to existing analyses of the effects of geometry on the impedance of the systemic arterial system.

Paroxysmal familial ventricular fibrillation

Several syndromes have been described which include paroxysmal ventricular fibrillation during the early years of life. In the family presented here, three siblings had syncopal episodes and sudden death; a fourth had syncopal episodes and proved paroxysmal ventricular fibrillation. Important characteristics of the ECG were short P-R interval and prominent U wave. The episodes of fibrillation were induced by stressful emotional stimuli and could not be produced by exercise. Possible electrophysiologic mechanisms and an outline for approach to patients with this problem are presented. The patient has been successfully maintained without recurrent symptoms for years with propanolol therapy.

Use of Externally Recorded Radioisotope- Dilution Curves for Quantitation of Left to Right Shunts*

Abstract This study evaluated the use of radioisotope-dilution curves as a method for estimating the magnitude of left to right shunts. Following injection of radiohippuran into the proximal right pulmonary artery, curves were recorded during monitoring over the right lung. The curves were analyzed by comparing area ratios which were derived following extrapolation of the initial exponential disappearance slope. Statistical analysis indicated a good correlation between estimation of the magnitude of left to right shunts by the radioisotope as compared to the Fick method. Additionally, it was shown that (1) an improved correlation was obtained with the use of the quadratic regression equation as compared to linear regression; (2) an improved regression coefficient and decrease in the standard error of estimate was obtained by separating individual defects (ventricular defect, atrial defect and patent ductus) into separate groups as compared to the total group; and (3) estimation of the left to right shunt was obtained equally well in infants as compared to older children.

RADIOISOTOPE-DILUTION CURVES AS AN ADJUNCT TO CARDIAC CATHETERIZATION.

Abstract A method of recordin externally monitored radioisotope-dilution curves at cardiac catheterization has been described. It was found to be reliable and had marked practical value as a routine procedure in the detection and localization of the site of left to right shunts. The geometry of the detection system was defined and correlated with the anatomic structures viewed by the heart and lung probes. Standards for normal curves were established in a series of patients without shunts. Radioisotope curves were compared with arterial dye-dilution curves and blood oxygen data for the detection and localization of the site of left to right shunts. All three methods detected shunts which comprised greater than 25 per cent of total pulmonary blood flow. The isotope and dye methods were found to be equally sensitive in the detection of small shunts if the indicator was injected into the pulmonary artery. All shunts detected by arterial dye-dilution curves were also detected by radioisotope-dilution curves. The reliability of the method was established and its practical usefulness shown. The major advantages of the radioisotope technic without blood sampling were found in severely ill young infants in whom the technic provided a quick and reliable method for the detection and localization of the site of the shunt.

Cardiac potentials in pulmonary disease. Overdistension of the lung versus cor pulmonale (right ventricular hypertrophy).

Abstract These studies demonstrated the distribution of cardiac potentials on the body surface in children with clinical evidence of overdistension of the lungs without right ventricular hypertrophy. The effect of the overdistended lung was shown to alter body surface events during ventricular activation by causing an inferior shift of potential maxima and minima during the middle third of the QRS. Roentgenographic studies demonstrated an associated inferior shift of the heart in relation to the anterior chest surface. Further shown was the associated diminished values of potentials over the left lateral chest during this interval in the patients with cystic fibrosis, as compared to normal children. The results of surface-mapping and x-ray studies indicated that leads placed in the fourth interspace monitor different body surface events during the middle of QRS in the cystic fibrosis children as compared to normal children due, in large part, to the inferior shift of potential maxima and minima. In the presence of cor pulmonale with marked right ventricular hypertrophy the potential distribution over the body was quite different in normal subjects and in those with cystic fibrosis. Right ventricular hypertrophy produced a migration of the anterior maximum in a rightward direction during the latter part of the QRS. Its terminal position was located beneath the right clavicle. These events differed from those in normal subjects and those with cystic fibrosis who showed a leftward migration of the maximum with a terminal distribution characterized by anterior minimum and posterior maximum.

Unusual observations during pacemaker therapy for complete heart block

Abstract During the course of management of spontaneously occurring complete heart block with Stokes-Adams syndrome in a 10 year old boy, rare clinical, therapeutic and physiologic observations were made. Initially, cardiac rate was controlled via a catheter electrode. The effect of ventricular rate on right atrial pressure was shown. There was a progressive fall in right atrial pressure as the ventricular rate was increased from 36 to 100/min. A Chardack pacemaker was implanted permanently, and cardiac rate was controlled with a 9-volt stimulus. During steroid therapy, retrograde atrial conduction and normal sinus rhythm developed. Unusual cardiac arrhythmias allowed electrocardiographic data to be obtained concerning the “vulnerable period” of the cardiac cycle in man. During alternating periods of normal sinus rhythm and pacemaker-controlled rate, ventricular premature beats resulted only when stimuli fell in a period of less than 30 msec, preceding the apex and during the descending portion of the T wave. Additionally, it was shown that stimuli in the “vulnerable period” of the cardiac cycle resulted in premature beats with QRS complexes of “multiform” shape. Although a single stimulus (considerably above the premature beat threshold value) placed in the vulnerable period can initiate ventricular fibrillation, a 9-volt stimulus was insufficient to reach ventricular fibrillation threshold in our patient. Steroid therapy was discontinued with subsequent loss of atrioventricular conduction. Pacemaker failure (due to breakage of a resistor wire) occurred 12 months postoperatively. Successful substitution of the abdominal wall pacemaker was made. At the time of pacemaker substitution, the threshold voltage required to control ventricular rate was 4.6 volts indicating that there had been no significant increase in myocardial resistance after one year.

Evaluation of Left Ventricular Contractile State in Children With a Chronic Left Heart Pressure Overload

Recent animal investigations have indicated that myocardial hypertrophy may be accompanied by a depression of muscle function as analyzed in terms of length-tension and force-velocity relationships. Myocardial function was evaluated in these terms in 14 children with left ventricular hypertrophy (LVH) secondary to aortic stenosis or coarctation of the aorta and 10 children with normal left hearts who were undergoing diagnostic cardiac catherization. Serial left ventricular volumes were calculated from biplane cineanangiocardiograms exposed at 60/frames sec, and left ventricular pressure was recorded simultaneously using a catheter tip transducer. Left ventricular circurrferential stress (LVS), LV circumference at the equator (LVC), and LV contractile element velocity (VCE) were calculated. Mean values for VCE at isostress points during isovolumic contraction were not different from normal in 9 patients with moderate LVH (LV Mass 115±13 vs. normal 82±10 g/M2). In 5 patients with more severe LVH and LV Mass averaging 156±31 g/M2, VCE was significantly depressed from normal during isovolumic systole indicating a depressed force-velocity relationship. In addition 4 of the 5 patients with severe LVH had depressions of LV stress at isocircumference points at end-systole when compared with normal children suggesting a depressed length-tension relationship. These date indicate that severe left ventricular hypertrophy in children may be accompanied by impaired muscle function when expressed in terms of basic muscle mechanics.

90 VIABLE ATRIAL BAFFLE FOR HEMODYNAMIC CORRECTION OF TRANSPOSITION OF THE GREAT VESSELS

Since Mustard reported pericardial baffling for correction of transposition of the great vessels, this has became the procedure of choice. Caval and pulmonary venous obstructions, tricuspid regurgitation, encroachment of atrial chambers and sudden death have occurred following this surgical technique.The purpose of this report is to present a modified baffling procedure which uses the viable atrial wall to prevent late baffle contracture and its dreaded obstruction. A flap of pericardium preferably pedicled is used to close and form the anterior atrial wall providing a large chamber to accomodate pulmonary venous return.The procedure was performed in 5 infants 11 to 15 months old. Except for one patient who died suddenly 16 hours post-op, 4 surviving patients had smooth post-surgical courses. One patient who had an associated VSD closed, developed complete heart block but continues to maintain a ventricular rate of 68 to 72/minute.Cardiac catheterization was performed in 3 patients 6 to 8 months after their surgery. Pulmonary capillary wedge, vena caval, atrial chambers and pulmonary venous pressures showed no obstruction. The atrial pressures tended to be slightly higher than normal. Selective right and left pulmonary arteriograms were filmed and demonstrated well the unobstructive pulmonary venous return.Atrial wall baffle has the advantage that viable tissue is used and unlikely to constrict systemic and pulmonary drainage.

RIGHT VENTRICULAR MYOCARDIAL BIOPSIES IN TETRALOGY OF FALLOT

Full thickness RV myocardial biopsies were taken during surgery in 21 patients with Tetralogy. Specimens stained with Trichrome and Verhoff VonGieson were analyzed. Grade I: Endocardial fibroelastosis with perivascular fibrous and collagen invasion. Grade II: Subendocardial collagen and fibroblast invasion with myocardial hypertrophy. Grade III: Myocardial cell disruption plus intimal thickening of intramural coronary arteries. Quantitative anglographic RV function was correlated with RV myocardial histology.Grade III changes were found in older age group which showed markedly depressed RV ejection fraction. Grade I and II changes characterized the myocardium of patients below 2 yrs. Between 2 and 4 yrs. some patients showed Grade I and II changes with moderately depressed RV functions. Of 10 patients with mild changes, 6 showed RV ejection fraction in the low normal range; 3 had ejection fraction below 0.55 and only 1 had RV ejection below 0.50. 11 patients over 2 yrs. showed Grade III changes and markedly depressed RV ejection, 7 below 0.50.Summary: RV myocardial changes correlated with the degree of RV function depression as well as the pts. age. Grade III myocardial changes accompanied severe RV function depression in Tetralogy pts. over 4 years of age; between 2 and 4 yrs. some pts. with marked RV depression showed only Grade I and II changes and pts. below 2 yrs. showed only Grade I and II changes with milder RV function depression. This study lends support to early corrective surgery for Tetralogy before marked myocardial changes accompanies deterioration of right heart function.