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Ann Thorac Surg 2004;78:1090-1093
© 2004 The Society of Thoracic Surgeons
a Department of Surgery, Section of Cardiac Surgery, Ann Arbor, Michigan USA
b Department of Pediatrics, Division of Pediatric Cardiology, University of Michigan School of Medicine, Ann Arbor, Michigan, USA
Accepted for publication June 25, 2003.
* Address reprint requests to Dr Ohye, F7830 Mott, 0223, 1500 East Medical Center Dr, Ann Arbor, MI 48109, USA
ohye{at}umich.edu
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Introduction |
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A 4-day-old, 2.6-kg, full-term, female neonate presented in shock to an outside emergency room with an initially unobtainable blood pressure and a pH of 6.8. The patient had done well from the time of birth, until the day of admission, when she exhibited lethargy, poor feeding, and respiratory distress. The patient was resuscitated, started on prostaglandin infusion, and transferred to our institution. Upon arrival, the patient was anuric, with a pH of 7.2. Echocardiogram revealed HLHS with mitral and aortic atresia, an aberrant right subclavian artery, mildly depressed right ventricular (RV) function, and 2 to 3+ tricuspid regurgitation (TR). Her urine output gradually improved, with a creatinine peaking at 5.0. The creatinine decreased to 4.5 at the time of her Norwood procedure.
An uneventful Norwood procedure was performed on day of life 15. The right carotid artery was noted to be of good size, and a 3.5-mm MBTS was placed from this vessel. The patient was returned to the intensive care unit on dopamine 3 µg/ kg/min and Milrinone 0.3 µg/kg/min, with a blood pressure of approximately 75 to 80/25 to 30 mm Hg and a pO2 of 30 to 35 mm Hg. She maintained an excellent urine output with return of the creatinine to normal and was extubated on postoperative day 5.
Postoperative two-dimensional and Doppler echocardiography revealed fair RV function and continued evidence of 2 to 3+ TR. Pulse Doppler of the MBTS demonstrated continuous flow through both systole and diastole (Fig 1). The arch reconstruction was widely patent with the typical retrograde diastolic flow during diastole, as a result of diastolic run-off into the MBTS (Fig 2). Pulse Doppler of the proximal ascending aorta revealed predominantly systolic flow to the coronary arteries.
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Subsequent evaluation with echocardiography demonstrated antegrade flow in the RVPAC without significant regurgitation during diastole (Fig 3). Pulse-wave Doppler interrogation of the descending aorta revealed no retrograde diastolic flow (Fig 4). In contrast to the previous echocardiogram, the pulse Doppler of the proximal ascending aorta demonstrated predominantly diastolic flow to the coronary arteries. The degree of TR and the ventricular function by subjective assessment and fractional shortening remained unchanged. The patient had an unremarkable recovery after her shunt revision and was discharged on postoperative day 10.
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Our group has previously demonstrated that both coronary flow and myocardial oxygen delivery is reduced in patients after the Norwood procedure [8]. This reduction in coronary flow reserve is likely due largely to the placement of a systemic to pulmonary artery shunt from a systemic artery to the pulmonary artery to provide pulmonary blood flow after the Norwood procedure. This shunt results in a significant diastolic run-off from the aorta, seen on Doppler/echocardiography as reversal of antegrade flow within the descending aorta during diastole (Fig 1). Because 70% to 80% of coronary blood flow occurs during diastole, the potential diastolic "steal" may significantly contribute to the decreased coronary flow seen after the Norwood [9]. This may be especially important when the ascending aorta is particularly small, imposing a higher resistance to coronary blood flow. The decrease in coronary blood flow can affect myocardial function in the acute postoperative phase, as well as chronically, leading to poor RV function.
Recently, there have been reports of the use of a RVPAC to provide pulmonary blood flow after the Norwood procedure in small numbers of patients [2, 3]. The RVPAC has the theoretical advantage of eliminating the aortic diastolic run-off and coronary steal. The authors utilizing the RVPAC have noted a less complicated postoperative course and decreased mortality after the Norwood procedure. This clinically smoother course is likely the result of the direct benefit of decreased diastolic run-off to the heart and other end organs, as well as indirectly from improved cardiac output.
Previously, the normalization of perfusion thought to be responsible for the improved outcomes with the RVPAC has been theoretical. Others have observed the increase in diastolic blood pressures with the RVPAC compared with the MBTS, as displayed by this patient [2, 3]. This case provides evidence that these proposed hemodynamic advantages of a RVPAC can be demonstrated in vivo by Doppler echocardiography.
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