Effects of Nitroglycerin and Dipyridamole on Myocardial Perfusion during Total and Graded Partial Coronary Occlusion in Open Chest Dogs

BACKGROUND: To investigate the effects of nitroglycerin(NTG) and dipyridamoie(DIP) on the perfusion of ischemic myocardium during total occlusion of one coronary vessel and with 3 graded partial occlusion of its collateral supplying vessel, myocardial contrast echocardiography(MC-Echo) was performed on seven pentobarbital anesthetized open chest dogs. METHODS: After a left thoracotomy was done, the left anterior descending coronary artery(LAD) was dissected for ligation to produce total LAD occlusion and left circumflex coronary artery(LCX) was separated to place an electromagnetic flow probe and, distally, screw occluder to restrict LCX flow by 50% and 90% of the preocclusion value. MC-Echo images were made by bolus injections of a 5ml of two-syringe-agitated mixture of sodium meglumine ioxaglate(Hexabrix) and normal saline(2 : 3 by volume) into the aortic root, and then the echocontrast defect area(EDA) with planimeter, peak echocontrast intensity(PEI) and the echocontrast washout halftime(WHT) with videodensitometer were measured. A 100microg of NTG was administered by bolus injection in the aortic root and was followed by 5mg of DIP after the hemodynamic effect of the NTG has been abolished. MC-Echo images were obtained after each infusion of NTG and DIP, first 60 minutes after total LAD occlusion with intact LCX flow, next with a 50% restriction of LCX flow, and third with a 90% restriction of LCX flow. RESULTS: 1) During total LAD occlusion with intact LCX flow : The EDA measured 60 minutes postocclusiom(PO) of LAD(14.2%) was smaller than that 3 minutes PO(20.5%, p<0.01). After NTG, systolic and diastolic blood pressure(BP) was decreased(p<0.01, p<0.05, respectively) and heart rate(HR) was not changed. The mean EDA(15.1%) was not changed, but an increase in EDA occurred in cases of which the diastolic BP fell by more than 20mmHg, and/or the systolic BP was less than 80mmHG after NTG, After DIP, BP and HR were unchanged. The PEI was increased and WHT was shortened in the nonischemic area, reflecting an increase in myocardial perfusion to a normal zone. However, the EDA(17.0%) was increased(p<0.05). The increase in EDA was more prominent in cases with good collaterals. This finding indicates that DIP cases coronary steal from the ischemic myocardium to the normal myocardium through the collaterals. 2) During total LAD occlusion with a 50% restriction of LCX flow : BP and HR were not altered. EDA, PEI and WHT were the same as those taken during intact LCX flow. After NTG, BP was decreased(p<0.01), but HR were not different from baseline values, After DIP, BP and HR remaince unchanged and EDA(16.2%) was increased(p<0.05). PEI was decreased(p<0.05) and WHT was delayed(p=0.054), indicating that DIP impaired any further increase of perfusion in ischemic myocardium. 3) During total LAD occlusion with a 90% restriction of LCX flow : Systolic and diastolic BP were decreased(p<0.05), but HR was unchanged. EDA(20.2%) was increased as compared to those during intact LCX flow(p<0.01). NTG decreased the EDA(17.6%, p<0.05) despite decrease in BP(p<0.01), while DIP did not alter the hemodynamics or EDA(20.7%). The PEI and WHT after infusion of both NTG and DIP were not different from baseline values. CONCLUSION: 1) Dipyridamole causes coronary steal from ischemic myocardium when the flow of collateral supplying vessel is intact or restricted by 50%, but not during 90% restriction of flow, suggesting the degree of stenosis of collateral supplying vessels is a determinant of coronary steal. 2) The beneficial effect of nitroglycerin to ischemic myocardium was largely determined by the extent of collateral flow and its effect on hemodynamics.

The Pattern of Pulmonary Venous Flow in Various Heart Disease

To evaluate the influencing factors on pulmonary venous flow(PVF) pattern, we studied the relationship between PVF and left ventricular ejection fracton(EF), mitral annulus motion(MAM) and transmitral flow using pulsed doppler echocardiography in patients with dilated cardiomyopathy(DCMP), acute myocardioal infarction(AMI), left ventricular hypertrophy(LVH) and atrial fibrillation(AE). Ther results were as follows : 1) In the normal controls(13 cases), two forward flow during ventricular systole(VS) and diastole(VD) and one retrograde flow during atrial systole(AS) were observed. The peak velocity of VS, VD and AS flow was 45.9cm/s, 42.8cm/s and -18.3cm/sec, respectively. The peak VS/VD ratio was 1.1. 2) In patients with DCMP(11 cases), (a) compared to the noraml subjects, the peak velocity of VS flow and VS/VD ratio were were significantly reduced(p<0.005 and p<0.001, respectively) and were positively correlated with ejection fraction(r=0.8 and r=0.7, respectively) (b) in 2 DCMP cases with severe mitral regurgitation, systolic retrograde flow was observed in the pulmonary vein instead of forward VS flow. 3) In 12 AMI cases and 7 LVH cases with normal or slightly diminished left ventricular systolic function but with abnormal diastolic function. (a) the peak velocity of VS flow and peak VS/VD ratio were significantly increased(r<0.005 and p<0.01, respectively). (b) the peak velocity of VD flow is positively correlated with transmitral E/A ratio(r=0.8) and the peak VS/VD ratio was positively correlated with transmitral pressure half time(r=0.8). (c) the peak velocity of retrograde AS flow was significantly increased(p<0.001). (d) there was no correlation between doppler parameters of PVF and left ventricular ejection fraction. 4) In patients with atrial fibrillation(10 cases), VS flow was markedly diminished or absent and only VD flow was observed. Also, retrograde AS flow was not observed. These findings suggest that the pattern of PVF is influnced by LVEF, MAM, transmitral inflow and atrial contraction. However, main contributary factors in determining the pattern of PVF in each disease are diverse according to its main pathophysiology.

Relation between the Efficacy of Amiodarone on Chronic Atrial Fibrillation and Left Atrial Size and Fibrillatory Wave Form

To assess the efficacy of amiodarone on chronic atral fibrillation(AF) and to evaluate the relation between the ability to convert AF to sinus rhythm (SR) with amiodarone therapy and left atrial(LA) size and atrial fibrillatory wave forms, 22 patients with AF, aged 40 to 60 years(mean 47.5 years), were studied. Nine patients(40.9%) had mitral valvaular heart disease, 6(27.3%) hypertension, 5(18.2%) lone AF and 2 (9.1%) cadiomyopathy. Amiodarone therapy with either 600mg for 1 week, 200mg for 4 weeks in 5 consecutive patients, or 800mg for 1 week, 400mg for 4 weeks and 200mg for 6 weeks in 17 patients, converted AF to SR in 9(40.9%) patients 3 to 6 weeks after amiodarone was started on. In either group, patients who achieved conversion had smaller LA size(mean 43.7mm) than those who failed conversion(mean50.2mm)(P<0.05). Those who had LA size less than 45mm achieved conversion of AF to SR in 70%, comparing to 16.7% in patients with LA size more than 46mm(P<0.05). Among patients who achieved conversion, LA size was less than 46mm in 77.8% comparing to 23.1% in patients who failed conversion on Amiodarone. Those with coarse AF(46.2mm), althogh the difference was not significant statistically. There was no converstion in patients with LA size greater then 58mm and in patients with coarse AF who concomittantly had MVD. These findings suggest that the efficacy of amiodarone was related to LA size, and to the atrial fibrillation wave form in patients with mitral valvular heart disease.