Intravenous Dipyridamole Research Articles

Intravenous dipyridamole-induced myocardial ischemia during percutaneous transluminal coronary angioplasty in humans

Percutaneous transluminal coronary angioplasty was used as a model of controlled myocardial ischemia to study the effect of intravenous dipyridamole on myocardial ischemia and coronary hemodynamics in 10 patients. All patients had 1-vessel coronary artery disease with visualized collaterals. Intravenous dipyridamole increased myocardial ischemia during inflations. ST elevation, as measured by intracoronary electrogram, increased significantly from the control inflation to the second inflation after dipyridamole injection (0.05 ± 0.23 vs 0.44 ± 0.43 mV, p < 0.03). Of the 10 patients, 8 developed new or more severe angina with subsequent inflations after dipyridamole. The pulmonary artery wedge pressure increased significantly from the control inflation to the fourth inflation (15 ± 8 vs 20 ± 9 mm Hg, p < 0.05). The coronary wedge pressure showed a decreasing trend with subsequent inflations after dipyridamole but did not reach statistical significance. The double product (heart rate X blood pressure) was not significantly altered by dipyridamole. The findings indicate that intravenous dipyridamole increases myocardial ischemia during balloon occlusion. The constancy of the double product and the trend toward a decrease in coronary wedge pressure suggest that dipyridamole may induce ischemia by reducing the amount of collateral flow through a coronary steal phenomenon.

Severe impairment of coronary reserve during rejection in patients with orthotopic heart transplant.

The present study analyzed coronary sinus blood flow alterations after dipyridamole induced coronary vasodilation in seven patients whose endomyocardial biopsies evidenced no sign of rejection (group 1) and in five patients with histologic signs of rejection (group 2) after orthotopic heart transplantation. All patients were treated with cyclosporine and prednisone and some with azathioprine and had normal coronary arteriograms. Coronary sinus blood flow and coronary resistance were measured before and after intravenous dipyridamole (0.18 mg/kg/min over 4 minutes). Basal values were similar in groups 1 and 2 for coronary sinus blood flow (166 +/- 34 compared with 181 +/- 39 ml/min, respectively), coronary resistance (0.62 +/- 10 compared with 0.52 +/- 13 mm Hg/ml/min, respectively), coronary sinus blood oxygen content (5.7 +/- 1.6 compared with 4.5 +/- 0.9 ml/100 ml, respectively) and arterial-coronary sinus blood oxygen difference (10.6 +/- 1.3 compared with 10.3 +/- 1.8 ml/100 ml, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of correlation after reperfusion between ventricular function and infarct size estimated by thallium single-photon emission computed tomography.

In 32 patients with acute myocardial infarction, who had undergone successful intracoronary thrombolysis, the results of regional wall motion measured from contrast cineangiograms 10 to 21 days after thrombolysis were related to the results of thallium single-photon emission computed tomography (SPECT) after intravenous dipyridamole. Wall motion was measured by means of the centerline method, and thallium defect size was estimated by comparing the patient's circumferential profile with that of 20 normals. No correlation was found between ejection fraction or regional wall motion and thallium defect size. The time from symptom onset to thrombolysis was inversely correlated with the degree of hypokinesis (r = -0.51) but not with thallium defect size. In patients treated within 3 hours, hypokinesis was significantly less than in patients treated later (-1.1 +/- 0.6 SD vs -2.2 +/- 0.8 SD, p less than 0.01) whereas thallium defect size was not significantly different in both groups. It is concluded that, in patients after thrombolysis, thallium defect size determined by SPECT does not reflect the degree of left ventricular dysfunction.

Doppler and two-dimensional echocardiographic assessment of left ventricular function before and after intravenous dipyridamole stress testing for detection of coronary artery

Thallium perfusion imaging following the intravenous infusion of dipyridamole, a potent coronary vasodilator, has been demonstrated to be useful in the evaluation of the functional significance of coronary artery disease (CAD). While recent studies have demonstrated that 2-dimensional echocardiographic monitoring of left ventricular (LV) function after intravenous dipyridamole has a sensitivity somewhat less than that of thallium perfusion imaging, none has examined the usefulness of Doppler evaluation of aortic blood flow in this setting. One hundred patients undergoing dipyridamolethallium imaging for clinical indications were studied. Technically adequate Doppler echocardiographic studies were obtained in 97 patients. LV ejection fraction, peak aortic velocity and acceleration, as well as segmental LV wall motion, were analyzed before and at peak dipyridamole effect. Thallium perfusion images were normal in 41 and abnormal in 53 patients studied. A statistically significant difference in percent change from baseline to peak dipyridamole effect in velocity, acceleration and ejection fraction was seen between the 2 groups (26 vs −2%, 51 vs −2% and 16 vs 4%, respectively, all p < 0.05). Comparison of 2-dimensional wall motion analysis to thallium yielded a sensitivity and specificity of 74 and 80%, respectively. In the group of patients who underwent cardiac catheterization, 2-dimensional wall motion analysis yielded a sensitivity of 64% in the detection of CAD. The combination of 2-dimensional and Doppler echocardiographic parameters increased the sensitivity in the detection of CAD to 85%. The combination of the 2 techniques was particularly sensitive in the detection of multivessel CAD with significant differences in percent change from baseline to peak dipyridamole effect in velocity, acceleration and ejection fraction observed between those with and without multivessel CAD. Thus, the addition of Doppler evaluation of aortic blood flow velocities to standard 2-dimensional echocardiographic imaging appears to add significantly to the sensitivity of this technique and is furthermore applicable in most patients studied. These data indicate that cardiac ultrasound examination before and after intravenous administration of dipyridamole may be a reasonable alternative to thallium perfusion imaging in clinical settings for detection and functional assessment of patients with CAD.

Dipyridamole-thallium 201 scintigraphy in the early post-infarction period. (Safety and accuracy in predicting the extent of coronary disease and future recurrence of angina in patients suffering from their first myocardial infarction).

To evaluate the safety and usefulness of myocardial thallium-201 scintigraphy after intravenous dipyridamole during the early post-infarction period, 35 patients under 60 years of age and with recent first transmural uncomplicated myocardial infarction (27 inferior, 8 anterior) were examined between the 5th and 13th day of hospitalization. Although four patients experienced angina and transient ischemic ST depression during the test, there were no serious complications. Patients were followed for a mean period of 11.4 +/- 6.3 months after hospital discharge. None of the patients experienced recurrent infarction and there were no cardiac deaths. In 11 patients there were reversible perfusion defects in areas different from those of myocardial infarction. Of these patients, seven (one with infarct vessel stenosis only and six with multivessel coronary disease) developed angina during the follow-up: five underwent coronary surgery because of severe angina refractory to full medical therapy. Out of the 24 patients without reversible perfusion defects, only two (with multivessel coronary disease) showed typical angina symptoms. The presence of redistribution on thallium scans was significantly more frequent in patients who developed a recurrence of angina over a period of 11.4 +/- 6.3 months of follow-up (P less than 0.0005). Thus dipyridamole-thallium 201 scintigraphy is a safe, non-invasive stress test which may be used early following uncomplicated myocardial infarction in order to identify patients at risk for the recurrence of angina.

Simultaneous low level treadmill exercise and intravenous dipyridamole stress thallium imaging

Intravenous dipyridamole-thallium imaging unmasks ischemia in patients unable to exercise adequately. However, some of these patients can perform limited exercise, which, if added, may provide useful information. Treadmill exercise combined with dipyridamole-thallium imaging was performed in 100 patients and results compared with those of 100 other blindly age- and sex-matched patients who received dipyridamole alone. Exercise began after completion of the dipyridamole infusion. Mean ±1 standard deviation peak heart rate (109 ± 19 vs 83 ± 12 beats/min, p < 0.0001) and peak systolic and diastolic blood pressure (146 ± 28/77 ± 14 vs 125 ± 24/68 ± 11 mm Hg, p < 0.0001) were higher in the exercise group compared with the nonexercise group. There was no difference in the occurrence of chest pain, but more patients in the exercise group developed ST-segment depression (26 vs 12%, p < 0.0001). The exercise group had fewer noncardiac side effects (4 vs 12%, p < 0.01) and a higher target (heart) to background (liver) count ratio (2.1 ± 0.7 vs 1.2 ± 0.3; p < 0.01), due to fewer liver counts. There were no deaths, myocardial infarctions or sustained arrhythmias in either group. Combined treadmill exercise and dipyridamole testing is safe, associated with fewer noncardiac side effects, a higher target to background ratio and a higher incidence of clinical electrocardiographic ischemia than dipyridamole alone. Therefore, it is recommended whenever possible.

Dipyridamole preserved platelets and reduced blood loss after cardiopulmonary bypass

Cardiopulmonary bypass activates and depletes platelets, which may contribute to postoperative bleeding. In addition, activated platelets may be deposited in the coronary vasculature after ischemia and cardioplegia, which may delay recovery of cardiac function and metabolism and may contribute to early bypass graft occlusion. The antiplatelet agent dipyridamole reduces platelet activation and depletion and may decrease postoperative bleeding and transfusion requirements. A prospective randomized trial was conducted in 58 patients undergoing elective coronary bypass operations to compare the effects of oral (19 patients) and intravenous (21 patients) dipyridamole to the results obtained in a control group (18 patients) who received no dipyridamole. Preoperative oral administration of dipyridamole resulted in lower plasma drug concentrations in the early postoperative period than perioperative intravenous administration (p = 0.0001 by analysis of variance). Postoperative arterial platelet counts were highest in the patients receiving intravenous dipyridamole, intermediate in those receiving oral dipyridamole, and lowest in the control group (p = 0.03 by analysis of variance). Postoperative blood loss and blood product transfusions were significantly reduced with both oral and intravenous dipyridamole (p = 0.04 by analysis of variance). Dipyridamole preserved platelets and reduced postoperative bleeding. Intravenous dipyridamole resulted in higher platelet counts than oral dipyridamole and may be required to reduce postoperative bleeding in high-risk patients.

Dipyridamole thallium testing: noncardiac side effects, cardiac effects, electrocardiographic changes and hemodynamic changes after dipyridamole infusion with and without exercise

Thallium-201 scintigraphy in combination with intravenous dipyridamole has been reported to be useful in patients who are unable to perform maximal exercise stress testing. Few reports have dealt with side effects in large numbers of patients. For that reason noncardiac side effects, cardiac effects, electrocardiographic changes, as well as hemodynamic changes were studied in 301 consecutive patients, examined by dipyridamole thallium-201 imaging because of suspected coronary artery disease. The patients were divided into two groups (A and B). Patients in group A (101 patients) received an infusion of 0.14 mg/kg per minute dipyridamole for four minutes. Patients in group B (200 patients) received the same dose of dipyridamole followed by low level exercise ( 60 rpm 30 Watts ) for three minutes to achieve maximal coronary blood flow and to diminish thallium-201 uptake in the gastrointestinal organs. The likelihood of having hemodynamically significant coronary artery disease was the same in both groups. Patients in group B experienced significantly less side effects than patients in group A (11% vs 43%, P < 0.05). In group B changes in systolic blood pressure ( P < 0.05), heart rate ( P < 0.05), and rate pressure product ( P < 0.05) were more distinct. The occurrence of angina was the same in both groups (47% vs 44%, NS), but ischemic ST segment changes were significantly more frequent in group B than in group A (25% vs 12%, P < 0.05). Thus, exercise added to dipyridamole infusion compared to dipyridamole infusion alone results in fewer noncardiac side effects, the same prevalence of angina pectoris, and a higher incidence of ST segment changes.

Reversibility by dipyridamole of thallium-201 myocardial scan defects in patients with sarcoidosis

In order to clarify the significance of anginal pain and myocardial thallium-201 scan defects in cardiac sarcoidosis, the pharmacologic effect of dipyridamole on myocardial perfusion was assessed by planar thallium-201 myocardial scintigraphy in patients with sarcoidosis. Thallium-201 myocardial scintigraphy was performed at rest and after 0.56 mg/kg intravenous dipyridamole during four minutes in 16 patients with sarcoidosis. The myocardial scan (45-degree and 70-degree left anterior oblique, and anterior views) was divided into 15 segments. Results were evaluated by the number of segmental defects and with a global perfusion score (from 0 to 60) by a semi-quantitative index depending on the size and severity of myocardial thallium-201 defects. Thirteen of the 16 patients showed partial or total reversion of their thallium-201 defects on redistribution scanning either at rest or after dipyridamole. The mean (+/- SD) number of myocardial perfusion defects that were present in all the patients decreased from 5.31 +/- 1.78 at rest to 3.25 +/- 2.52 after redistribution (p less than 0.001) and to 2.19 +/- 2.10 after dipyridamole (p less than 0.001). The mean global perfusion score increased from 53.2 +/- 3.0 at rest to 56.2 +/- 2.9 after redistribution (p less than 0.001) and to 57.2 +/- 2.7 after dipyridamole (p less than 0.001). A significant correlation (r = 0.82, p less than 0.001) was found between the increase of global perfusion score on redistribution and after dipyridamole. The reversibility of myocardial scan defects is a common finding in sarcoidosis. It makes unlikely the role of scar fibrosis or extensive confluent granulomas as a mechanism for such defects. The effect of dipyridamole suggests the presence of reversible disorders lying at the coronary microvascular level.

Alterations in myocardial thallium-201 distribution in patients with chronic systemic hypertension undergoing single-photon emission computed tomography

To characterize thallium-201 distribution in singlephoton emission computed tomography (SPECT) cardiac images and polar bullseye maps, 100 patients with chronic systemic hypertension due to end-stage renal disease were studied and the results compared with those in 35 normotensive control subjects. Thallium-201 SPECT was performed after exercise in all control subjects and 70 hypertensive patients, and after intravenous dipyridamole in 30 patients. A frequent finding in hypertensive patients was a fixed decrease in the normal lateral-to-septal count density ratio in immediate thallium-201 SPECT images (1.02 ± 0.10 vs 1.17 ± 0.08 in control subjects, p < 0.00001) and in 3-hour delayed images (1.02 ± 0.11 vs 1.11 ± 0.08 in control subjects, p < 0.00001). No significant difference in count density ratio was present in patients undergoing treadmill versus diypridamole intervention. In 35 patients the count density ratio was >2.0 standard deviations below the normal mean, creating the false impression of a fixed lateral defect (i.e., myocardial infarction).In 12 patients, myocardial wall thickness was measured at end-diastole by 2-dimensional echocardiography. Wall thickness was increased (>11 mm) in all patients. The mean lateral-to-septal wall thickness ratio was 1.08 ± 1.11; in no patient was the ratio < 0.76 to indicate selective septal hypertrophy. The lateral-to-septal wall thickness and lateral-to-septal thallium-201 count density ratios correlated poorly (r = 0.43).It is concluded that in hypertensive patients with diffuse myocardial hypertrophy there is a decrease in thallium-201 count density ratio in SPECT images, frequently creating apparent lateral wall fixed defects and mimicking myocardial infarction.

Aspirin and Dipyridamole in the Prevention of Re-Stenosis after Percutaneous Transluminal Coronary Angioplasty

To examine the role of antiplatelet therapy in the prevention of arterial restenosis after percutaneous transluminal coronary angioplasty (PTCA), we conducted a randomized, double-blind, placebo-controlled study in 376 patients. The active treatment consisted of an oral aspirin-dipyridamole combination (330 mg-75 mg) given three times daily, beginning 24 hours before PTCA. Eight hours before PTCA, the oral dipyridamole was replaced with intravenous dipyridamole at a dosage of 10 mg per hour for 24 hours, and oral aspirin was continued. Sixteen hours after PTCA, the initial combination was reinstituted. Treatment was continued in patients with a successfully dilated vessel until follow-up angiography four to seven months after PTCA--or earlier, if symptoms dictated. Of 249 patients who underwent follow-up angiography, 37.7 percent of patients receiving the active drug had restenosis in at least one segment, as compared with 38.6 percent of patients taking placebo (P not significant). The number of stenotic segments was virtually the same in the two groups. Among the 376 randomized patients, there were 16 periprocedural Q-wave myocardial infarctions--13 in the placebo group and 3 in the active-drug group (6.9 percent vs. 1.6 percent, P = 0.0113). Although the use of this antiplatelet regimen before and after PTCA did not reduce the six-month rate of restenosis after successful coronary angioplasty, it markedly reduced the incidence of transmural myocardial infarction during or soon after PTCA. Thus, the short-term use of antiplatelet agents in relation to PTCA can be recommended.

Effect of maintenance oral theophylline on dipyridamole-thallium-201 myocardial imaging using SPECT and dipyridamole-induced hemodynamic changes

To evaluate the effect of maintenance oral theophylline therapy on the diagnostic efficacy of dipyridamole-thallium-201 single photon emission computed tomography (SPECT) imaging for coronary artery disease, dipyridamole-thallium-201 SPECT imaging was performed in eight men with documented coronary artery disease before intiation of theophylline treatment and repeated while these patients were receiving therapeutic doses of oral theophylline. Before theophylline treatment, intravenous dipyridamole caused a significant increase in heart rate, decrease in blood pressure, angina in seven of eight patients, and ST segment depression in four of eight patients. While they were being treated with theophylline, none of the patients had angina or ST segment depression, and there were no hemodynamic changes with intravenous dipyridamole. Before theophylline treatment, dipyridamole-thallium-201 SPECT imaging showed reversible perfusion defects in myocardial segments supplied by stenotic coronary arteries. With theophylline treatment, dipyridamole-thallium-201 SPECT showed total absence of reversible perfusion defects. Treatment with theophylline markedly reduced the diagnostic accuracy of dipyridamole-thallium-201 imaging for coronary artery disease.

Dynamic cerebral and systemic circulatory effects of adenosine, theophylline and dipyridamole

The effects of intravenous adenosine, dipyridamole and theophylline on local cerebral blood flow were studied in conscious rabbits. Long-term quantitative blood flow measurements were performed in 5 cerebral structures together with tissue pO 2 and pCO 2 measurements by a mass spectrometry technique. In an additional study, the time course of the cerebrovascular changes was determined by thermal clearance. It was found that: firstly, adenosine failed to modify local blood flow except in the caudate nucleus; secondly, dipyridamole increased cerebral blood flow in all 5 structures under study; and lastly, theophylline decreased cerebral blood flow in the same 5 structures. The increase in caudate blood flow induced by adenosine was instantaneous and lasted only for the duration of the infusion, whereas the cerebrovascular changes induced by dipyridamole and theophylline were gradual and persisted after their administration. Theophylline blocked the systemic and cerebrovascular changes caused by adenosine alone and by dipyridamole alone. In anesthetized rabbits, the intracarotid infusion of adenosine showed that the caudate reaction only occurred in the ipsilateral hemisphere. Taken together, our findings suggest that the transport system for adenosine in cerebral vessels is not only species-dependent but also structure-dependent. Furthermore, perivascular adenosine helps to maintain resting cerebrovascular tone and finally, cerebral adenosine may be involved in the control of cerebral blood flow via specific adenosine receptors.

Coronary Blood Flow Velocities in Humans Evaluated During Cardiac Surgery Using a 20 MHz 80+1 Channel Ultrasound Pulsed Doppler Velocimeter

We have developed an 80 + 1 channel high resolution pulsed Doppler velocimeter for measuring in detail the blood flow velocities in relatively small human vessels (1-5 mm in diameter). Real time velocity measurements were performed at 80 sample points using a multigated zero-cross method. The Doppler signal in the desired channel was subjected to real time Fourier analysis. This facilitated analyzing in detail the blood flow velocity profile across vessel, as well as the velocity distribution in a sample volume. The sampling volume was pi X 0.5(2) X 0.2 mm3 and the maximum depth was 1.5 cm. When the incidence angle was selected as 60 degrees, the velocity resolution and maximum velocity were 1.5 and 1.9 m/sec, respectively. Blood flow velocities were measured in the coronary artery and in the aorto-coronary bypass graft in patients during cardiac surgery. The blood flow velocities in the normal coronary artery had a predominantly diastolic pattern which is characteristic of coronary artery flow. Comparing with the systolic forward velocities in the left coronary artery, those of the right coronary artery were more prominent. The velocity wave forms in the graft and in the coronary artery distal to the insertion of the graft had a predominantly diastolic pattern when there was sufficient coronary blood flow through the graft. In contrast, during the occlusion of the graft, the blood velocity wave form in the distal coronary artery became predominantly systolic, indicating insufficient myocardial inflow before the bypass graft. Intravenous dipyridamole administration increased the bypass flow by 50% in a patient who had 100% occlusion before the bypass operation. This indicates that the coronary reserve can still be preserved in some cases of total coronary occlusion. With an intra-aortic balloon pumping (IABP) assist (2:1), the velocity wave form in the graft had predominantly diastolic in both IABP-on and -off beats. However, diastolic augmentation and systolic reduction of the velocity wave form were clearly observed in beats with IABP-on. The velocity wave forms in the anterior descending coronary artery in a patient with aortic regurgitation showed a predominantly systolic pattern with a broad velocity spectrum. After aortic valve replacement, the blood velocity pattern became predominantly diastolic, indicating improvement of the coronary perfusion into the myocardium. In conclusion, our velocimeter proved effective for evaluating coronary blood flow velocities in patients during cardiac surgery.

Monoclonal antibody against the platelet glycoprotein (GP) IIb/IIIa receptor prevents coronary artery reocclusion after reperfusion with recombinant tissue-type plasminogen activator in dogs.

Localized thrombosis was produced in the left anterior descending (LAD) coronary artery of open chest dogs by constricting a segment so as to produce greater than 90% stenosis (reducing blood flow to 40 +/- 10% of baseline), and placing a thrombus in the segment immediately proximal to the stenosis by inducing endothelial cell injury and instilling a mixture of blood and thrombin. Intravenous infusion of recombinant tissue-type plasminogen activator (rt-PA) at a rate of 15-30 micrograms/kg per min for 30 or 60 min in eight dogs induced coronary artery reperfusion within 23 +/- 7 min (mean +/- SD), but reocclusion occurred despite heparin anticoagulation in all but one of these dogs within 7 +/- 5 min. Intravenous injection of 0.8 mg/kg of the F(ab')2 fragment of a monoclonal antibody (7E3) directed against the platelet GPIIb/IIIa receptor, prevented reocclusion in 10/10 dogs during an observation period of 2 h (P less than 0.001 vs. rt-PA alone). The antibody abolished ADP-induced platelet aggregation and markedly prolonged the bleeding time. Intravenous aspirin or dipyridamole prevented reocclusion for 1 h or more in only 2/7 and 1/6 dogs, respectively. We conclude that the monoclonal antibody is very effective in preventing reocclusion after successful thrombolysis of occluded coronary arteries with rt-PA.

Coronary flow and resistance reserve in patients with chronic aortic regurgitation, angina pectoris and normal coronary arteries

Left ventricular hypertrophy has been found to be associated with a reduction of coronary vascular reserve, which could be responsible for episodes of myocardial ischemia. To evaluate coronary flow and resistance reserve in patients with chronic aortic regurgitation, coronary sinus blood flow and coronary resistance were measured before and after an intravenous dipyridamole infusion (0.14 mg/kg per min × 4 min) in eight control subjects and eight patients with aortic regurgitation, exertional angina pectoris and normal coronary arteriograms.Coronary flow reserve, evaluated by the dipyridamole/ basal coronary sinus blood flow ratio, and coronary resistance reserve, evaluated by the basal/dipyridamole coronary resistance ratio, were both significantly reduced in patients with aortic regurgitation (1.67 ± 0.40 versus 4.03 ± 0.52 in control subjects, p < 0.001 and 1.71 ± 0.50 versus 4.38 ± 0.88 in control subjects, p < 0.001, respectively). In patients with aortic regurgitation, basal coronary sinus blood flow was higher than in control subjects (276 ± 81 versus 105 ± 24 ml/min, respectively, p < 0.001) and basui coronary resistance was lower (0.31 ± 0.13 versus 0.95 ± 0.17 mm Hg/ml per min, respectively, p < 0.001), but coronary blood flow and resistance after dipyridamole were not significantly different in the two groups (461 ± 159 versus 418 ± 98 ml/min in control subjects, 0.19 ± 0.11 versus 0.22 ± 0.04 mm Hg/ml per min in control subjects, respectively).These data demonstrate that coronary reserve is severely reduced in patients with chronic aortic regurgitation and exertional angina. This reduction of coronary reserve might contribute to the pathogenesis of stress-induced episodes of myocardial ischemia and may participate in the progressive deterioration of left ventricular function in patients with chronic aortic regurgitation.

Augmentation of coronary bypass graft flow induced by dipyridamole and its relation to bypass graft patency.

To evaluate the effect of dipyridamole on coronary bypass graft flow, 10 mg of dipyridamole was injected intravenously, during the measurement of graft flow, at the time of surgery. Its concentration in serum was measured and compared with that after oral administration. In 50 individual vein grafts performed on 35 patients, graft flow increased from 65 +/- 37 to 96 +/- 55 ml/min (p less than 0.001) after the dipyridamole injection and the arterial pressure decreased slightly. In 40 grafts whose graft flow was increased by more than 10 ml/min by dipyridamole, the patency rate (at 5 weeks) was 98 per cent, whereas that of the 10 other grafts, which responded poorly, was only 50 per cent (p less than 0.01). The serum concentration of dipyridamole, 3 minutes after intravenous injection, was 1.46 +/- 0.68 micrograms/ml, while the level of orally administered dipyridamole, in 3 groups of patients who were given 50 mg, 75 mg and 100 mg, three times a day, respectively, was steady, being 0.68 +/- 0.20 micrograms/ml, 1.43 +/- 0.41 micrograms/ml and 1.73 +/- 0.50 micrograms/ml, 2 hours following ingestion. We concluded that intravenous dipyridamole increases the graft flow and that a better patency is obtained in those grafts in which the graft flow is increased by more than 10 ml/min. It is also expected that routine doses of oral dipyridamole possibly increase the graft flow after coronary bypass surgery.

Safety and diagnostic accuracy of dipyridamole-thallium imaging in the elderly

The noninvasive diagnosis of coronary artery disease in the elderly can occasionally be difficult. Intravenous dipyridamole-thallium imaging is a potentially useful diagnostic test to determine presence and severity of coronary disease; however, the safety of the procedure has not been determined in an older population. The side effect profile and frequency of severe ischemic responses after 0.56 mg/kg of intravenous dipyridamole were compared in 101 patients ≥70 years old and 236 patients <70 years old. There were no side effects in 64% and 62% of patients ≥70 and <70 years old, respectively (p = NS). Among the 337 patients tested, there were no complications of myocardial infarction or death. The most common cardiac side effect was chest pain, which occurred in 21 (21%) of the 101 patients aged ≥70 years and in 64 (27%) of the 236 patients <70 years (p = NS). Aminophylline was required to reverse cardiac or noncardiac side effects in 15 (15%) and 36 (15%) of the patients ≥ 70 and <70 years old, respectively (p = NS). A severe ischemic response occurred in 2% and 2.5% of patients ≥70 and <70 years old, respectively (p = NS).The sensitivity of intravenous dipyridamole-thallium imaging for obstructive coronary artery disease was 86% (25 of 29) and 83% (68 of 82) in older and younger patients, respectively (p = NS): the specificity was 75% (6 of 8) and 70% (16 of 23). respectively (p = NS). Thus, intravenous dipyridamole-thallium imaging is a safe noninvasive method for assessment of older patients with obstructive coronary disease; its side effect profile and diagnostic accuracy are similar to those seen in younger patients. The technique is associated with severe ischemic responses in only a small minority of patients.

Dipyridamole cardiac imaging

Dipyridamole cardiac imaging is a useful alternative technique to exercise stress testing in the evaluation of patients with ischemic heart disease. Intravenous dipyridamole is still in the investigational phase, while oral dipyridamole is widely available. The hemodynamic effects of dipyridamole include an increase in coronary blood flow (due to coronary vasodilation) which is in excess of the increase in myocardial oxygen consumption and cardiac output. The disparity in the increase in coronary blood flow relative to the cardiac output results in an increase in myocardial thallium activity and an increase in the myocardial/background activity ratio. The quality of the thallium images is better or similar to that of exercise thallium images. The opiimal dose of intravenous dipyridamole is 0.56 mg/kg, and of the oral dose it is 300 to 400 mg, although higher doses may be necessary in some patients. Analysis of the thallium images has been to a large extent based on visual inspection of the planar images. Delayed images are helpful to establish the nature of the perfusion abnormalities (transient or fixed). The process of redistribution is based on disparate rates of washout from the normal and abnormal zones. The sensitivity and specificity of dipyridamole thallium imaging, whether intravenous or oral, have been shown in a number of studies to be quite adequate and comparable to that achieved during exercise thallium imaging. Dipyridamole two-dimensional echocardiography has also been used in the detection of coronary artery disease; transient (new or worsening of preexisting) wall motion abnormalities have been found to be a specific marker of coronary artery disease. Transmural as well as regional coronary steal phenomena have been postulated as the mechanism for dipyridamole-induced regional wall motion abnormalities. Compared to exercise two-dimensional echocardiography, dipyridamole echocardiography provides high-quality studies and in higher proportions of patients. The results of dipyridamole thallium imaging have also been extremely important in identifying high-risk patients after acute myocardial infarction or patients with peripheral vascular disease undergoing elective vascular surgery; the presence of a dipyridamole-induced perfusion abnormality identifies patients at high risk for future cardiac events. Thus, dipyridamole cardiac imaging is helpful in the diagnosis of coronary artery disease and in risk stratification.

Diagnostic value for coronary artery disease of chest pain during dipyridamole-thallium stress testing

Intravenous dipyridamole with thallium imaging permits stress testing for coronary artery disease (CAD) without exercise. Chest pain may occur with dipyridamole-thallium testing, but its diagnostic significance is uncertain. Forty-five patients who had coronary angiography, no revascularization and chest pain during dipyridamole-thallium testing were identified. These patients were matched blindly by sex and age to 45 patients who had coronary angiography, no revascularization and no chest pain reported during the dipyridamole-thallium test. In the groups with versus without chest pain, 9 versus 24% had no CAD, 16 versus 16% had 1-vessel disease, 38 versus 29% had 2-vessel CAD and 38 versus 29% had 3-vessel CAD. These differences did not achieve statistical significance. Also, there were no evident differences in the severity of angiographie CAD by vessel or by percent of stenosis (p > 0.50). There was only a moderate association with ischemic ST changes (40 versus 16%, p < 0.02). Chest pain with concurrent ischemic ST changes also failed to predict any difference in distribution or severity of angiographic stenoses. We conclude that chest pain during dipyridamole-thallium testing is not closely related to the severity of CAD and has little diagnostic value.