Direct effects of intraaortic balloon pumping on intramyocardial coronary flow velocity waveform and coronary arteriolar diameter Eiji Toyota* *Depart

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1 Direct effects of intraaortic balloon pumping on intramyocardial coronary flow velocity waveform and coronary arteriolar diameter Eiji Toyota* *Department of Medical Engineering and Syste ms Cardiology, Kawasaki Medical School 577 Matsushima, Kurashiki We aimed to evaluate the direct effects of intraaortic balloon pumping (IABP) on the phasic coronary flow velocity waveform into myocardium and coronary arteriolar diameter change under absence and presence of severe coronary artery stenosis. In anesthetized open chest dogs, flow velocity of septal artery was measured using 20-MHz Doppler flow velocimeter and diameters of epicardial coronary arterioles were observed using intravital videomicroscope during 2:1 model of IABP. The flow and diameters were compared between the coupled beats of IABP-on and IABP-off. Following control experiments without stenosis, a severe stenosis in the left main coronary artery was introduced by a snare occluder so as to reduce the post-stenotic pressure to about 50 mmhg. Without stenosis, IABP significantly enhanced the systolic retrograde flow, however, which was overcome by much more increased diastolic inflow. Moreover, IABP did enhance early diatolic inflow which is assumed to be beneficial for subendocardial perfusion. The diameters of coronary arterioles increased substantially during diastole by IABP. Under the presence of severe coronary stenosis, IABP failed to affect any flow variables or coronary arteriolar diameter. Thus, these results suggested that IABP has beneficial effects on both the systolic unloading and the diastolic coronary flow augmentation in the heart without stenosis, while the major effect of IABP on the heart with severe stenosis is derived from reduction of oxygen demand by the systolic unloading. Key words: intraaortic balloon pumping, coronary flow velocity waveform, coronary arteriole, coronary stenosis.

2 Fig. 1 Schematic drawing of animal preparation and measurements. Intraaortic balloon pumping was introduced in the thoracic aorta and needle-probe of the microscope was placed on the epicardial surface. Severe stenosis was introduced in the left main coronary artery with a snare occluder. Abbreviations; AoP=aortic pressure, DiP=distal coronary arterial pressure, LAD=left anterior descending artery, LVP=left ventricular pressure, max LV dp/dt=maximal increasing rate of LVP.

4 Table 1 Systemic and coronary hemodynamics during IABP. Data were expressed as mean value }SE. *; p<0.05 IABP-ON vs. IABP-OFF, t; Stenosis (+) with IABP-OFF vs. Stenosis (-) with IABP-OFF p<0.05. Abbreviations; AoP=aortic pressure, DiP=distal coronary arterial pressure, IABP=intraaoric balloon pumping, max LV dp/dt = maximal increasing rate of left ventricular pressure, Stenosis (-)=the absence of coronary stenosis, Stenosis (+)=the presence of coronary stenosis.

5 Fig. 2 Representative tracings of the septal arterial blood velocities with and without severe coronary stenosis. Left panel; Without stenosis, DA and early diastolic inflow increased during IABP. SR also increased. Right panel; With stenosis, DA and early diastolic inflow failed to increase during IABP. SR did not change. Abbreviations; DA =diastolic antegrade flow integral, ECG =electrocardiogram, SR =Systolic retrograde flow integral, Stenosis (-)=without coronary stenosis, Stenosis (+)=with coronary stenosis. Fig. 3 Effect of IABP on the septal arterial blood velocity waveform and LAD coronary blood flow. Upper panel; Without Stenosis, DA increased, while SR also increased. Thus, the slosh ratio (SR/DA) was augmented during IABP. The net coronary blood flow (LAD flow) was augmented during IABP. Lower panel; With Stenosis, neither DA nor SR were augmented by IABP. LAD flow did not increase during IABP.

6 Fig. 4 Effect of IABP on early diastolic coronary inflow with and without severe coronary stenosis. Early diastolic coronary inflow was defined as diastolic antegrade flow integral during the first half of the diastole (Refer to Fig. 2). IABP increased the early diastolic coronary inflow (p<0.05), however, this effect was significantly attenuated by severe coronary stenosis (p< 0.05). Percentile change of early diastolic inflow was calculated from [IABP-ON- IABP-OFF]/IABP-OFF. Fig. 5 Typical images of an epicardial coronary arteriole during IABP in the case with and without coronary artery stenosis. Without stenosis (upper panel, left; IABP-ON, right; IABP-OFF), IABP dilated the coronary arteriole by 21% during diastole. However, with stenosis (lower panel, left; IABP-ON, right; IABP-OFF), the vasodilatory effect of IABP was less acknowledged.

7 Fig. 6 Effects of IABP on epicardial coronary arteriolar diameters with and without severe coronary stenosis. Left panel; IABP significantly dilated coronary arterioles during diastole without stenosis (p<0.0001), while the vasodilatory effect of IABP was reduced under the presence of stenosis (p<0.0005). Right panel; IABP enhanced coronary arteriolar pulsation amplitude without stenosis (open circle, p<0.0005). However, under the presence of stenosis (closed circle), pulsation amplitude was not enhanced by IABP (NS). The effect of IABP on the coronary arteriolar pulsation amplitude was significantly attenuated by coronary stenosis (ANOVA, p<0.005). Percentile diameter change of coronary arterioles by IABP was calculated by the diastolic diameters of [IABP-ON-IABP-OFFPIABP-OFF, Percent pulsation amplitude of coronary arterioles by IABP was calculated by [diastolic diametersystolic diameter]/systolic diameter.

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