Elman G. Frantz

Anatomically sound, simplified approach to repair of “complete” atrioventricular septal defect

BACKGROUND There are few congenital anomalies of the heart that have benefited more from thorough anatomic analysis than the complex anomaly known as atrioventricular septal defect in the setting of common atrioventricular junction. Recent advances in understanding the anatomy of this lesion have led to alternative methods of repairing these defects. METHODS The medical records of 21 consecutive patients undergoing repair of complete atrioventricular septal defect have been reviewed. Nine of these patients had a standard one- or two-patch repair, and 12 had direct closure of the ventricular element of the defect. RESULTS Direct closure resulted in significantly shorter pump and cross-clamp times. Follow-up for an average of 34 months suggests that when direct closure can be performed, the results are comparable with those of the more standard technique. CONCLUSIONS Our initial success with this approach is encouraging; however, longer follow-up is required to establish whether it will be broadly applicable.

Induction of right ventricular hypertrophy with obstructing balloon catheter. Nonsurgical ventricular preparation for the arterial switch operation in simple transposition.

BackgroundRecently, a successful result with a rapid two-stage arterial switch operation (ASO) was reported for patients with transposition of the great arteries (TGA) with low left ventricular pressure. In this procedure, the interval between pulmonary arterial banding and ASO was approximately 1 week. This successful result indicates the possibility of a nonsurgical ventricular preparation procedure using an obstructing balloon catheter prior to ASO. Methods and ResultsA SF atrioseptostomy catheter was inserted directly into the main pulmonary artery in six lambs aged 20 to 38 days. After the chest was closed, the balloon was inflated twice a day for a period of 2 to 2.5 hours. This procedure was performed for 4 consecutive days. After the final inflation, the ratio of right ventricular weight to total ventricular weight was compared with that in an age-matched control group. After the final inflation, the peak systolic right ventricular pressure and the percentage of peak systolic right ventricular to peak systolic aortic pressure rose to 85.6±4.7 mm Hg (mean±1 SD) and 79.6±8.6%, respectively. The percentages of the right ventricular weight to the total ventricular weight were significantly higher after the balloon inflation than those in the control group in terms of wet heart weight (29.5±1.2% versus 23.0±1.0%o; P<.0001) and dry heart weight (27.0±2.0% versus 21.0±1.1%; P<.0001) ConclusionsThe myocardial mass in the right ventricle increased after 4 days of intermittently applied pressure overload. Nonsurgical preparation of the ventricle for ASO in TGA is feasible.

Characterization of Pulmonary Artery Blood Velocity Patterns in Lambs

Optimal management of patients with congenital heart disease often depends on the ability to assess pulmonary vascular impairment and monitor pulmonary hemodynamics. Need for improved techniques has prompted investigations of relationships between abnormal pulmonary circulations and pulmonary artery blood velocity patterns that can be observed noninvasively with pulsed Doppler ultrasound. Features commonly associated with pulmonary hypertension in humans (observed in the main pulmonary artery) are increased flow reversal [1,2], decreased rise time (time from onset of systole to peak velocity)[3–6] and a velocity waveform with a triangular or skewed shape, [7] as illustrated in Figure 1. Unfortunately, none of the techniques derived for estimating pulmonary pressure and flow solely from features of pulmonary velocity waveforms has been proven sufficiently reliable to be widely adopted in clinical practice. Failure has been attributed to individual variability and changing flow patterns in various parts of the pulmonary trunk [8,9]. Though studies examining the effects of acutely altered pulmonary hemodynamics on velocity patterns in animals have been reported, [10–12] surprisingly little work has been reported using animal models with chronically altered hemodynamics. Thus the goal of this report is to describe progress made in our laboratory in examining the velocity patterns in animal models of chronically elevated pulmonary blood pressure and flow, which are more analogous to the patient population of interest.

Blood Flow Velocity Profiles in Pulmonary Branch Arteries in Lambs

We studied the detailed profiles of blood flow in the right and left pulmonary arteries using 20 MHz pulsed Doppler ultrasound equipment in a lamb model. Fourteen lambs aged four to six weeks were selected. In six lambs, monocrotaline pyrrole was injected parenterally to create pulmonary hypertension (PH group). Eight other lambs served as unaltered controls (control group). The blood flow velocities were sampled in 1mm increments along the anterior-posterior axis of the branch arteries. The maximum velocity of the forward flow in the left pulmonary artery was higher than that in the right pulmonary artery in the control group (71.7 +/- 15.9 cm/s vs 60.2 +/- 13.5; p < 0.05). The fastest backward flow was located at the posterior position of the vessel in the right pulmonary artery in the control group (71.7 +/- 15.9 cm/s vs 60.2 +/- 13.5; p < 0.05). The fastest backward flow was located at the posterior position of the vessel in the right pulmonary artery in the control group. No significant bias in location was shown in the left pulmonary artery. Using indices of P90, acceleration time, P90*AcT, the velocity waveforms in the PH group were compared with those in the control group. In the left pulmonary artery, every index in the control group showed a significantly greater value that in the PH group. On the other hand, no significant differences were found between either group in the right pulmonary artery.

Pulmonary blood velocity patterns in lamb models of pulmonary vascular impairment

SummaryTo provide a comprehensive picture of the interaction between abnormal pulmonary hemodynamics and pulmonary blood velocity patterns in the young, we have developed infant animal models of pulmonary hypertension and/or elevated pulmonary blood flow. This report focuses on relationships between selected velocity waveform shape-dependent variables — i.e., the time between the onset of systole and peak velocity (rise time), the time during which velocity remains at >90% of that peak (90% time), and flow reversal patterns — and traditional hemodynamic indications of pulmonary vascular impairment, i.e., elevated pulmonary artery pressure and pulmonary vascular resistance. Studies were performed on 36 anesthetized, open-chest, one-month-old lambs with normal pulmonary circulations or with abnormal conditions that had been initiated during the first few days of life via (1) a central venous injection of monocrotaline pyrrole (hypertension) or (2) a side-to-side anastomosis between the common carotid artery and jugular vein (elevated flow). Animals with large shunts (shunt open cardiac output/shunt closed cardiac output >2.1) had both elevated pressures and flows. The tightest correlations (linear and log-linear) were found between unindexed pulmonary vascular resistance and waveform variables, the most reliable being 90% time (r = −0.838), 90% time + rise time (r = −0.838), and 90% time × rise time (r = −0.824). The best correlate to mean pulmonary artery pressure was 90% time + rise time (r = −0.713). Combined rise time and 90% time variables yielded results that exceeded 90% sensitivity and specificity levels in diagnosing elevated pulmonary vascular resistance (>700 dyne-sec/cm5). Absence of flow reversal in central and anterior regions was an indicator of markedly elevated pulmonary artery pressures (mean >28mmHg). The findings of this report (1) demonstrate the successful development of animal models that mimic a broad spectrum of relevant pulmonary hemodynamics in infants and children with compromised pulmonary circulations and (2) point to shape variables that should improve noninvasive assessment of elevated pulmonary vascular resistance.

Pulmonary input impedance spectra in models of chronically altered pulmonary hemodynamics

Pulmonary input impedance spectra were estimated in one-month-old lambs whose circulation had been altered during the first few days of life to mimic the pulmonary. hemodynamic states observed in infants and children with left-to-right shunts (high flow) and /or pulmonary vascular obstructive disease (high pressure). Spectral results obtained from the animal models were compared with those obtained from a computer simulation based on morphometric and hemorheologic data compiled for the 4 kg cat. Spectral features examined included the frequency of the first modulus minimum (indicative of the pulse wave reflection and/or pulse wave velocity) and characteristic impedance (average resistance to pulsatile flow). High flow (shunt-open/shunt-closed ratio>2.1) resulted in a slight spectral shift to the right with little change in characteristic impedance in both the lamb and the passive computer simulation models. High pressure (mean pulmonary artery pressure >28 mmHg) in the lamb model resulted in a marked shift to the right with a doubling of characteristic impedance.<<ETX>>

Pulse Wave Reflections In A Lamb Model Of Pulmonary Hypertension

The relationship between wave reflections and ventricular/vascular coupling of lambs with nmal pulmonary pressures (CONT) and pulmonary hypertension (PH) was examined. We compared reflection indexes quantitating changes in magnitude and timing of the positive reflected pressure wave. Results indicate that the reflected wave returns earlier in the PH group compared to the CONT goup (0.39 sec vs 0.62 sec; pd.005). In contrast to the CONT group, in the PH group the duration of the reflected wave is longer in systole (0.61 sec vs 0.38 sec) but shorter in diastole (0.26 sec vs 0.64 sec) (~~0.005). using a frequency domain averaging technique described previously [l]. Forward and reverse pressure and flow waveforms were calculated using the method described by Westerhof et al[21, based on characteristic impedance (2). Zc estimates were obtained by dividing the slope of the upstroke of the pressure wave at max (dPAP/dt) by the slope of the flow waveform at max (dPAQ/dt) [ 11. A global reflection coefficient (REF) was calculated as the ratio of the amplitude of reflected pressure wave to the amplitude of forward pressure wave. Wave reflection indexes quantitating changes in the timing of the positive reflected wave included the following ratios: the onset of the reflected wave/systolic interval (RBT); the duration of the reflected wave during systole/systolic interval (RST); and the duration of the reflected wave during diastole/diastolic interval (RDT).

Comparison of techniques for assessing pulmonary input impedance spectra

A six-element lumped parameter model of the pulmonary circulation was used to evaluate two signal-averaging techniques for calculating the pulmonary input impedance spectra of normal lambs. Pulmonary artery pressure and pulmonary artery flow data obtained simultaneously in the main pulmonary artery were subjected to time-domain averaging and frequency-domain averaging techniques. Input impedance was determined by a cross-power spectral method designed to retain the periodicity of the signals. Preliminary studies indicate that the impedance spectra determined from noise-free input flow data to the model closely approximated the model-derived impedance spectra for a wide range of heart rates. The addition of noise signals to the noise-free input data produced impedance spectra that were consistently in agreement with model spectra for the lower-order (1-3) harmonics but not for the higher-order terms.<<ETX>>