Terrence Dillon

Noninvasive pulsed Doppler determination of cardiac output in neonates and children

Mean blood flow velocity (VAo) in the ascending aorta was measured noninvasively in 33 children, ages 3 days to 17 years, by pulsed Doppler technique at the time of cardiac catheterization. Measurements were made from a suprasternal approach with a portable, range-gated device. The ascending aortic diameter was determined echocardiographically and aortic cross sectional area calculated (A = pi d2/4 cm2). Aortic flow (QAo) was computed from Doppler recordings: QAo (ml/minute) = VAo (cm/second) X A (cm2) X 60 (second/minute). Values were compared with cardiac outputs determined according to the Fick principle, using measured oxygen consumption calculated oxygen capacity, and oxygen saturation. Subjects with aortic valve abnormalities or left ventricular outflow tract obstruction were excluded from study. Agreement between the two methods was excellent (linear regression r = 0.98, slope = 1.07, y-intercept = -4.5 ml, range 403 to 5.540 ml/minute). The Doppler technique is a quick, noninvasive, and accurate method of determining ascending aortic blood flow in neonates and children.

Effects of Digoxin in Infants with a Congested Circulatory State Due to a Ventricular Septal Defect

Digoxin alone was used to treat a congested circulatory state in 21 infants (mean age, 2.7 months; mean weight, 3.8 kg) with a ventricular septal defect. The dose was adjusted on the basis of pharmacokinetics to achieve a mean steady-state concentration of 1.6 +/- 0.3 ng of digoxin per milliliter of serum. The mean red-cell level of sodium-potassium ATPase fell from 23.1 +/- 7.0 to 12.6 +/- 5.2 nmol per milligram per minute with treatment. Only 6 of the 21 patients had an inotropic response, as reflected by echocardiographic measurements, but the drug was of clinical benefit to 12 infants (including these 6). These results show that not all infants with a congested circulatory state due to a ventricular septal defect benefit from digoxin therapy. Furthermore, in some subjects clinical improvement occurs in the absence of a measurable inotropic response.

Vasodilator therapy for congestive heart failure

Six patients with severe congestive heart failure were treated with nitroprusside intravenously. Four of the six patients showed salutary responses and were successfully weaned from the NP with marked resolution of symptoms. No adverse side effects were observed. These four patients and one additional child (who did not receive NP) were treated with prazosin by mouth in addition to digoxin and diuretics daily. Two of these patients are entirely symptom free, and additional child is moderately improved, and the fourth patient has shown minimal symptomatic improvement. Despite the severity of their pretherapy symptoms, only one patient has died while receiving oral vasodilator therapy. This preliminary study suggests that afterload reduction may be life-saving in children who are virtually moribund because of congestive heart failure. This improvement can be maintained with oral vasodilator therapy and continuation of classic anticongestive therapy. However, afterload reduction has no effect on the underlying disease. Confirmatory studies are essential before this experimental mode of therapy is accepted for routine use in infants and children.

Management of infective endocarditis using echocardiography

Serial echocardiograms of five children who had infective endocarditis were analyzed and correlated with the clinical course. Vegetations were visualized initially on M-mode in four and on two-dimensional echocardiograms in all patients. The appearance of the vegetation was unexpected in one. More accurate anatomic localization of the vegetation was possible using two-dimensional echography. Four of the five patients died despite vigorous medical treatment and valve replacement in two. Complete resolution of the vegetation was documented for the first time in a child following medical therapy. This study suggests that echocardiography plays an important role in the diagnosis of endocarditis, allows objective follow-up of the size of the vegetations and their effects on valve function, and, therefore, may prove helpful in the management of these patients.

NON-INVASIVE ESTIMATION OF LEFT TO RIGHT SHUNTS USING ECHOCARDIOGRAMS AND RADIONUCLIDE ANGIOCARDIOGRAPHY

Echocardtography (echo) has been used in children with ventricular septal defects (VSD) to estimate the magnitude of left to right shunt (Qp/Qs) and has been correlated with Qp/Qs measured by Fick method using assumed oxygen consumption (VO2). The purpose of this study was to compare echo determined left atrial to aortic root ratio (LA/Ao) and radionuclide angiocardiography (RN) in assessing QP/Qs.Twenty three patients were studied with echo. Nine also had RN and area-ratio analysis of the radioisotope pulmonary dilution curve. These were then compared to Fick Qp/Qs using measured VO2We found the LA/Ao to be poorly correlated with the Qp/Qs regardless of shunt size (r=0.51). However, the RN area ratios significantly correlated to Fick Qp/Qs (r=0.93).Thus we conclude that the LA/Ao is not accurate for estimation of magnitude of left to right shunt whereas RN aren ratios provide a better method for estimating Qp/Qs.

THE UNNATURAL HISTORY OF AORTIC STENOSIS

We report on the clinical course and serial hemodynamic studies of three patients with severe valvar aortic stenosis diagnosed in the neonatal period. None of the subjects was symptomatic in the first year of life. In each case, a conservative initial management approach was adopted. Between the time of initial study (mean age 1.8 months) and the follow up at 12-27 months of age (mean 14.3 months), mean left ventricular systolic pressure fell from 151 to 135 mmHg, the mean peak systolic pressure gradient across the aortic valve fell from 54 to 42 mraHg, and the mean calculated aortic valve area index increased from 0.20 to 0.39 cm2/meter2. One of the patients was operated on for symptoms which appeared at 14 months of age. The patient followed longest is now 5 years old, is growing well, has a normal electrocardiogram and an echo-predicted left ventricular systolic pressure of 128 mmHg. This experience suggests that not all asymptomatic neonates with severe valvar aortic stenosis require surgical intervention early in life. In some, the aortic valve orifice may increase in size with somatic growth and obviate the need for surgery in early childhood.

THE EFFECTS OF BACTERIAL SEPSIS ON MYOCARDIAL FUNCTION

We studied the effects of serum from children with bacterial sepsis and poor cardiac function on isolated myocardial muscle performance. We measured the force (Fmax -mg) and dF/dt (gm/sec) of isolated dog papillary muscle contraction. Control serum was obtained from 3 uninfected subjects and a normotensive child with S. aureus bacteremia. Our 4 study subjects had hypotension and bacteremia due to either H. influenza, N. meningitidis, Yersinia pestis or D. pneumoniae. All study subjects required mechanical ventilation and inotropic support - mean LV % fractional shortening = 21%(nl=28-40%), mean Doppler cardiac output = 3.2 L/min/M2 (nl=2.5-4.5) and mean systemic vascular resistance = 11.6 units (nl=18-28). Baseline Fmax and dF/dt were compared to values measured 10 minutes after the addition of 0.3-1.0 ml of serum to the 50ml muscle bath.Serum from study subjects caused significant reductions in Fmax and dF/dt. We conclude that children with bacteremia and depressed myocardial function have a serum myocardial depressant factor which may also reduce vascular tone. Definition of this factor may provide new directions for the early management of hemodynamic distress in these critically ill subjects.

LEFT VENTRICULAR (LV) END SYSTOLIC WALL STRESS SHORTENING RELATIONSHIPS IN PRETERM INFANTS AND INFANTS OF DIABETIC MOTHERS (IDM)

Preterm infants and those with hypertrophic cardiomyopathy (HC) are frequently described as having a hypercontractile LV. Relationships between the extent of LV shortening and the force opposing shortening (wall stress (g)) reflect intrinsic LV function. The method for determining LV end systolic (ES) meridional g was validated in 8 children with normal LV undergoing catheterization (GpI). We then evaluated ESg in 20 preterm infants (4.8days) without PDA (GpII), 23 preterm infants (4.8days) with PDA (GpIII) and 11 term IDM (2.1days) with HC (GpIV). ESg was calculated from echo measurements of ES LV dimension (DES) and wall thickness (hES) and intraarterial or Doppler blood pressures.Preterm infants and IDM have a disproportionately thick LV. Their enhanced LV ejection performance is related to the reduced ESg (afterload). Compared to GpII, GpIII infants have even better ejection indices at the same ESg suggesting an effect of the increased preload or augmented inotropy, the latter possibly due to increased sympathetic tone.

1246 EVALUATION OF BRONCHOPULMONARY DYSPLASIA BY CARDIAC CATHETERIZATION

Six infants, 10 mos.-2½yrs., were evaluated for bronchopulmonary dysplasia (BPD) by concurrent cardiac catheterization and echocardiography. Mean estimated gestational age=30wks; mean birth weight=1350gms. All infants required oxygen and diuretic therapy (mean FIO2 28%). Measurements in room air included oxygen consumption (VO2); oxygen capacity; oxygen saturations; pulmonary artery (PA) and wedge pressures; right ventricular dp/dt (RVdp/dt) and right sided systolic time intervals from a Millar catheter tracing; and derived pulmonary vascular resistance (PVR). Measurements were repeated in 40% and 88% oxygen. Ventricular function and systolic time intervals were measured concurrently by echocardiography. Pulmonary wedge angiograms were performed at the conclusion of study. Mean values in room air were mean PA pressure 32mmHg; RVdp/dt 515mmHg·sec−1; RPEP/RVET 0.271; VO2 132 m1 O2·M2−1 ·min−1; pulmonary flow index 3.4 L·min−1 ·M2−1; PVR 6.7 units; PO255 torr, PCO241 torr, pH 7.37. 2 of 6 children responded to O2 with a significant fall in PA pressure and PVR. The two children who responded had the highest mean PA pressures, PCO2s and PVRs of the group (means 46mmHg, 48 torr and 9.6 units). Echo measurements of RPEP/RVET correlated well with values from the Millar catheter, but neither measurement reflected PVR accurately. LV function studies and pulmonary wedge angiograms were normal. These studies suggest invasive studies may aid in management of children with BPD.