External counterpulsation of a systemic-to-pulmonary artery shunt increases coronary blood flow in neonatal piglets.

BACKGROUND

Systemic-to-pulmonary artery shunt (SPS) palliation reduces coronary blood flow (CBF), which may precipitate myocardial ischemia postoperatively.

HYPOTHESIS

Counterpulsation (CP) of SPS augments CBF.

METHODS

Seven neonatal piglets (4.3 ± 0.23 kg) underwent sternotomy and ductus ligation. With a 5-mm polytetrafluoroethylene graft, SPS was created from innominate to pulmonary artery. A rigid shell holding a 9.5-mm diameter balloon was placed around the graft for CP. Using electrocardiographic signal, CP was initiated to trigger balloon inflation/deflation during the diastolic/systolic intervals, respectively. Instantaneous proximal and distal pulmonary artery and mid-anterior descending coronary artery flow rates were measured using transit time flow probes. Blood pressure and flow rates were recorded during three states: shunt closed, shunt open, and shunt open with CP.

STATISTICAL COMPARISON

Friedman's test and repeated measures analysis of variance.

RESULTS

Diastolic pressure decreased significantly with the shunt open (39 ± 8.4 to 28 ± 4.5 mm Hg, P = .05), then increased with CP (33 ± 2.3 mm Hg, P = .03). Median ratio of pulmonary to systemic flow (Qp/Qs) was 1.19, 1.9, and 1.53 with shunt closed, open, and open with CP, respectively. With CP, both diastolic coronary flow per minute (P = .018) and average diastolic flow rate per diastolic interval (P = .03) increased as well as total coronary flow per minute (P = .066; 19.6% ± 11.7%, 25.2% ± 17.0%, and 15.4% ± 13.9% change from shunt open, respectively). The percentage increase in average diastolic flow rate per diastolic interval correlated strongly with Qp/Qs (R (2) = .838).

CONCLUSIONS

In this model of SPS, CP increased diastolic blood pressure and CBF while maintaining significant augmentation of pulmonary blood flow (Qp/Qs). Shunt CP may aid in early postoperative management of palliative congenital heart disease.