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Coronary Bloodflow Reversal and Other Flow Alterations with Aortopulmonary Shunting in Neonates
F. W. Tsai, H. Munro, D. Felix, J. Bailey, B. Freud, C. Smith, W. DeCampli. Arnold Palmer Hospital, Orlando, FL,
BACKGROUND:
Theoretical calculations and indirect clinical evidence suggest that coronary blood flow (CBF) is altered with aortopulmonary shunting. This could potentially affect survival in high-risk patients, especially those with single ventricles.
METHODS:
Sixteen infant piglets underwent midline placement of a 3.0-4.0mm polytetrafluoroethylene graft between the innominate artery and pulmonary artery bifurcation. Doppler transit-time microprobes were used to directly measure flow in the aorta (AOF), pulmonary artery (PAF) and anterior descending artery (CBF). Data were recorded continuously with alternate opening and closing of the shunt. Measurements were obtained either with no epinephrine (EPI) or with an epinephrine infusion titrated to increase the heart rate by 35-50%. No other pharmacological support was used.
RESULTS:
With the shunt closed, the mean AOF was 0.65 L/min and CBF was 1.89 mL/min. Opening the shunt increased the mean AOF to 1.22 L/min (p < 0.001) and the mean ratio of pulmonary to systemic flow (Qp/Qs) to 1.88 ± 0.49 (range: 1.2-2.6). Diastolic blood pressure decreased an average of 12 mmHg (no EPI) and 25 mmHg (EPI) (p < 0.001). Piglets not receiving epinephrine had no significant change in CBF with shunt opening. However, with epinephrine, CBF decreased significantly from 2.26 mL/min by 0.49 ± 0.68 mL/min (p < 0.05). In some subjects, we observed significant coronary flow disturbance and possible flow reversal during part of the cardiac cycle. Coronary vascular resistance indexed to body surface area (CVRI) decreased from 145 mmHg•m2•min/mL by 26 ± 36.6 mmHgm2•min/mL (p < 0.001). This change was significant with and without epinephrine. An index of myocardial supply versus demand, [CBF/(MAPxAOF)], decreased significantly (p < 0.001) as well, with and without epinephrine. With the shunt closed, this myocardial index was 1.98 ± 0.45 times that with the shunt open.
CONCLUSIONS:
In this model, aortopulmonary shunting significantly decreases diastolic blood pressure, CBF, and CVRI. These effects are significantly heightened with the addition of an epinephrine infusion. With or without epinephrine, shunting also adversely affects myocardial supply versus demand, mainly due to increased cardiac output demand without a proportionate increase in CBF. These findings may suggest alternate pharmacological, surgical or mechanical means to improve coronary blood flow, especially after single ventricle palliation.
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