How much of the intraaortic balloon volume is displaced toward the coronary circulation?

Abstract

Objective: During intraaortic balloon inflation, blood volume is displaced toward the heart (V(tip)), traveling retrograde in the descending aorta, passing by the arch vessels, reaching the aortic root (V(root)), and eventually perfusing the coronary circulation (V(cor)). V(cor) leads to coronary flow augmentation, one of the main benefits of the intraaortic balloon pump. The aim of this study was to assess V(root) and V(cor) in vivo and in vitro, respectively.

Methods: During intraaortic balloon inflation, V(root) was obtained by integrating over time the aortic root flow signals measured in 10 patients with intraaortic balloon assistance frequencies of 1:1 and 1:2. In a mock circulation system, flow measurements were recorded simultaneously upstream of the intraaortic balloon tip and at each of the arch and coronary branches of a silicone aorta during 1:1 and 1:2 intraaortic balloon support. Integration over time of the flow signals during inflation yielded V(cor) and the distribution of V(tip).

Results: In patients, V(root) was 6.4% +/- 4.8% of the intraaortic balloon volume during 1:1 assistance and 10.0% +/- 5.0% during 1:2 assistance. In vitro and with an artificial heart simulating the native heart, V(cor) was smaller, 3.7% and 3.8%, respectively. The distribution of V(tip) in vitro varied, with less volume displaced toward the arch and coronary branches and more volume stored in the compliant aortic wall when the artificial heart was not operating.

Conclusion: The blood volume displaced toward the coronary circulation as the result of intraaortic balloon inflation is a small percentage of the nominal intraaortic balloon volume. Although small, this percentage is still a significant fraction of baseline coronary flow.

Figure 1

Hemodynamic waveforms in vivo during 1:2 IABP support for a control (top) and an assisted (bottom) beat in 2 different patients (A, B). P_ao, aortic pressure (solid black); Q_ao, aortic flow (filled grey). In cases of correctly timed inflation (A), V_root was derived by subtracting the intrinsic backflow of the control beat from the backflow of the assisted beat (both areas shaded in dark grey). In cases of late inflation (B), V_root was derived directly from the assisted beat by integrating the area shaded in dark grey.

Figure 2

Pressure (P_tip, solid black) and flow (Q_tip, filled grey) in vitro during 1:2 IABP assistance. The onset of inflation and deflation (indicated by the arrows). A, No artificial heart is connected to the system. B, IABP is synchronized to the artificial heart. V_tip was derived by integrating the area shaded in dark grey in each case.

Figure 3

Percent distribution of the total volume displaced upstream and downstream of a 25-mL IAB during inflation at 1:2 assistance without (A) and with (B) the artificial heart connected to the in vitro setup. L, Left; R, right.

Figure 4

Upper portion of the artificial aorta showing the tip of the IAB and the approximate locations where flow was measured in the coronary and arch branches. The fluid volume that passed through each branch in vitro because of the inflation of the 40-mL IAB at 1:1 frequency is noted both for the cases with and without artificial heart connected to the system. L, Left; R, right; IAB, intraaortic balloon.