INFLUENCE OF INTIMAL THICKENING ON CORONARY BLOOD-FLOW RESPONSES IN ORTHOTOPIC HEART-TRANSPLANT RECIPIENTS - A COMBINED INTRAVASCULAR DOPPLER AND ULTRASOUND IMAGING STUDY

Background Intravascular ultrasound imaging detects epicardial intimal thickening in the majority of heart transplant recipients with angiog raphically normal epicardial coronary arteries. Although coronary arte ry vasoreactivity is abnormal after cardiac transplantation, intimal t hickening does not appear to affect conduit vessel responses. However, the effect of intimal thickening on both conduit and resistance vesse l responses, as measured by changes in volumetric coronary blood flow (CBF), is unknown. Methods and Results Epicardial coronary artery cond uctance and microvascular resistance vessel responses were studied aft er intracoronary adenosine and nitroglycerin administration in 36 orth otopic heart transplant recipients 1 month to 7 years after transplant ation. Sequentially measured coronary flow average peak velocity ([APV , cm/s] 0.018 in Doppler guide wire) and epicardial luminal cross-sect ional area ([CSA, mm(2)] 4.3F 30-MHz ultrasound catheter) data were ob tained at baseline and during peak hyperemia after administration of 1 2 to 18 mu g IC adenosine and 150 to 200 mu g IC nitroglycerin. Volume tric CBF (mL/min) was calculated as CBF=APV (cm/s) x CSA (mm(2)) x 60 seconds/1 min x 1 cm(2)/100 mm(2) x 0.5. Measurements were made from a discrete position in the proximal left anterior descending (LAD) arte ry (n=22), mid-LAD artery (n=7), proximal circumflex artery (n=6), and proximal right coronary artery (n=1). Intimal thickening was present in 19 of 32 patients (60%). Both adenosine and nitroglycerin increased APV (from 18.9+/-4.9 to 56.0+/-11.5 cm/s for adenosine and from 20.2/-5.3 to 49.1+/-11.5 cm/s for nitroglycerin; both P<.05). Coronary flo w velocity reserve was significantly higher for adenosine compared wit h nitroglycerin (3.1+/-0.6 versus 2.5+/-0.7, respectively; P<.001). Ep icardial luminal CSA was unchanged during adenosine hyperemia compared with baseline (17.4+/-3.8 versus 17.3+/-4.0 mm(2), respectively; P=NS ) but was significantly greater during nitroglycerin hyperemia compare d with baseline (18.7+/-3.8 versus 17.3+/-4.0 mm(2), 6.2+/-3.6% change ; P<.05). Baseline CBF was similar before drug administration. Hyperem ic adenosine and nitroglycerin CBF responses (297+/-99 and 276+/-87 mL /min, respectively; P=NS) and CBF reserve (3.0+/-0.7 and 2.7+/-0.7, re spectively; P=NS) were not significantly different. Importantly, intim al thickening did not diminish resting or hyperemic APV, coronary flow velocity reserve, luminal CSA, CBF, or CBF reserve responses. Conclus ions In this study of angiographically normal heart transplant recipie nts, epicardial intimal thickening does not diminish conduit and resis tance vessel responses during endothelial-independent vasodilator admi nistration.