Effect of intravenous dipyridamole on regional coronary blood flow with 1-vessel coronary artery disease: evidence against coronary steal

Ejection fraction change and coronary artery disease severity: a vasodilator contrast stress-echocardiography study

BACKGROUND

An important goal of noninvasive stress testing is the identification of patients with left main coronary artery or three-vessel disease, because coronary artery disease extension and severity are major prognostic factors in ischemic heart disease. Wall motion abnormalities during vasodilator stress echocardiography become apparent in more than one coronary territory only in a small number of patients with multivessel disease. The aim of this study was to assess the value of change in left ventricular ejection fraction change (ΔLVEF) to identify patients with multivessel obstructive coronary artery disease during dipyridamole stress echocardiography.

METHODS

All dipyridamole stress echocardiographic studies performed at the authors' institution from October 2007 through March 2010 were retrospectively reviewed, and 150 patients who underwent coronary angiography within the next 60 days were selected. Left ventricular end-diastolic volume and end-systolic volume were measured at baseline and at the end of high-dose dipyridamole; ΔLVEF was calculated as stress ejection fraction minus rest ejection fraction. Patients were divided into four groups (controls and patients with single-vessel, two-vessel, and three-vessel disease) on the basis of coronary angiographic results.

RESULTS

The mean LVEF increased significantly from rest to peak stress in all groups except the three-vessel disease group. Mean ΔLVEF was negative in patients with three-vessel or left main coronary artery disease (-2.8 ± 5.1%) and significantly lower compared with all other angiographic groups (10.2 ± 5.1% and 6.2 ± 4.1%, respectively, for single-vessel and two-vessel disease). The negative value of ΔLVEF for three-vessel disease was due mainly to increased end-systolic volume at peak stress. Receiver operating characteristic curves demonstrated excellent accuracy of ΔLVEF compared with change in wall motion score index in identifying patients with multivessel disease, with areas under the curves of 0.96 and 0.62, respectively.

CONCLUSIONS

ΔLVEF is significantly lower in patients with severe coronary artery disease compared with those with single-vessel or two-vessel disease; reduced ΔLVEF identifies high-risk patients, who are likely to benefit from a more aggressive therapeutic strategy.

Enzymatic oxidation of dipyridamole in homogeneous and micellar solutions in the horseradish peroxidase–hydrogen peroxide system

Enzymatic oxidation of dipyridamole (DIP) by horseradish peroxidase-hydrogen peroxide system (HRP-H2O2) in aqueous and micellar solutions was carried out. The reaction was monitored by optical absorption and fluorescence techniques. In aqueous solution at pH 7.0 and pH 9.0, the disappearance of the characteristic bands of DIP centered at 400 nm and 280 nm was observed. A new strong band at 260 nm is observed for the oxidation product(s) with shoulders at 322 nm and 390 nm. A non-fluorescent product is formed upon oxidation. In cationic cethyl trimethyl-1-ammonium chloride (CTAC) and zwitterionic 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS) micellar solutions the same results are observed: three, well-defined, isosbestic points in the optical spectra suggest the transformation between two species. In anionic micellar sodium dodecylsulfate solution (SDS), the appearance of a new band centered around 506 nm was observed, associated to a solution color change from the usual yellow to deep blue/violet, characteristic of a radical species associated to the one-electron oxidation of DIP to its cation radical (DIP*+), observed previously in electrochemical oxidation. Experiments of radical decay kinetics monitoring the absorbance change at 506 nm were performed and analyzed in the frame of a kinetic model taking into account the species both in homogeneous and micellar media. The reaction medium is composed of bulk solution, SDS micelle/solution interface and enzyme catalytic site(s). The variation of DIP*+ concentration was analyzed assuming: (1) synthesis of DIP*+ by HRP through one-electron oxidation; (2) decomposition of DIP*+ by further one-electron oxidation; (3) direct two-electron oxidation of DIP by HRP; (4) bimolecular DIP*+ disproportionation. The main results of the analysis are as follows: (1) kinetic data can be divided in two phases, an HRP active phase and another phase which proceeds in the absence of enzyme activity due to consumption of all H2O2; (2) the reactions of DIP*+ formation, DIP*+ decomposition and DIP two-electron oxidation are HRP concentration dependent; (3) since DIP*+ formation constant seems to be overestimated, it is proposed that two-electron oxidation is another source of DIP*+, through the comproportionation reaction. Evidences for this reaction were also observed previously in electrochemical experiments; and (4) the kinetic analysis provides evidences that the bimolecular reaction of DIP*+ takes place mainly in the absence of active HRP and in this phase the combination of, at least, two second-order kinetic processes is needed to model the experimental data. Our data suggest that HRP oxidizes DIP in general by a two-electron process or that the cation radical is very unstable so that the one-electron process is only detected in the presence of anionic surfactant, which stabilizes significantly the DIP*+ intermediate.

Solubilization and controlled release of a hydrophobic drug using novel micelle-forming ABC triblock copolymers

Amphiphilic ABC triblock copolymers composed of monomethoxy-capped poly(ethylene glycol) (MPEG), poly(2-(dimethylamino)ethyl methacrylate) (DMA), and poly(2-(diethylamino)ethyl methacrylate) (DEA) have been synthesized by atom transfer radical polymerization (ATRP). These copolymers dissolve molecularly in acidic aqueous media at room temperature due to protonation of the tertiary amine groups on the DMA and DEA residues. On adjusting the pH with base, micellization occurred at pH 8, with the water-insoluble, deprotonated DEA block forming the hydrophobic cores and the MPEG and DMA blocks forming the hydrophilic micellar coronas and inner shells, respectively. This pH-induced micellization has been exploited to develop a solvent-free protocol for drug loading. A model hydrophobic drug, dipyridamole (DIP), which dissolves in acid but is insoluble above pH 5.8, was incorporated into the micelles by increasing the pH of an aqueous drug/copolymer mixture to 9. Both the empty and the drug-loaded micelles were characterized by dynamic light scattering and fluorescence studies. The interaction of both pyrene and DIP with the MPEG-DMA-DEA micelles was studied by fluorescence; both compounds had relatively high partition coefficients into the micelles, 4.5 x 10(5) and 1.5 x 10(4), respectively. Intensity-average micelle diameters ranged from 20 to 90 nm, depending on the polymer composition and concentration. Shorter MPEG blocks (Mn = 2000) produced larger micelles than longer MPEG blocks (Mn = 5000) due to the shift in the hydrophilic-hydrophobic balance of the copolymer. Transmission electron microscopy studies of the drug-loaded micelles indicated spherical morphologies and reasonably uniform particle size distributions, which is in marked contrast to the needlelike morphology observed for pure DIP in the absence of the copolymer. Experiments on controlled release demonstrated that DIP-loaded MPEG-DMA-DEA micelles act as a drug carrier, giving slow release to the surrounding solution over a period of days. Rapid release can be triggered by reducing the pH to reverse the micellization.

Mechanism of inducible regional dysfunction during dipyridamole stress

BACKGROUND

We hypothesized that increased myocardial oxygen demand resulting from hypotension and reflex tachycardia unmasking a reduced endocardial myocardial blood flow (MBF) reserve is the mechanism of dipyridamole-induced regional dysfunction in chronic coronary artery disease.

METHODS AND RESULTS

Ameroid constrictors were placed around the proximal coronary arteries and their major branches in 15 dogs to create chronic coronary stenosis. Seven days later, radiolabeled microsphere-derived MBF and 2-dimensional echocardiography-derived percent wall thickening (%WT) were measured at rest and after 0.56 mg/kg dipyridamole. Dipyridamole caused an increase (mean, 21%) in the rate-pressure product secondary to reflex tachycardia resulting from mild systemic hypotension. %WT in myocardial segments with an endocardial MBF reserve (dipyridamole/resting MBF) of 1.5 to 2.5 (n=35) did not change after dipyridamole, whereas it decreased in segments with an endocardial MBF reserve of <1.5 (n=30) and increased in those with an endocardial MBF reserve of > or =2.5 (n=45) (P<0.05). Most (80%) segments with endocardial MBF reserve of <1.5 and 14% with an endocardial MBF reserve of 1.5 to 2.5 showed inducible dysfunction after dipyridamole, whereas none of the segments with an endocardial MBF reserve of > or =2.5 showed this finding. A sigmoid relation (y=-6.74/[1+exp (19.9. [x-1.84])]+1.35. x, r=0.93, P<0.0001) was noted between endocardial MBF reserve and Delta%WT. In contrast, neither the epicardial MBF reserve nor the endocardial/epicardial MBF ratio during hyperemia was associated with inducible regional dysfunction.

CONCLUSIONS

Increased myocardial oxygen demand resulting from hypotension and reflex tachycardia unmasking a reduced endocardial MBF reserve is the primary mechanism of dipyridamole-induced regional dysfunction in chronic coronary artery disease.

Pharmacological stress testing

Pharmacological stress in conjunction with radionuclide myocardial perfusion imaging has become a widely used noninvasive method of assessing patients with known or suspected coronary artery disease. In the United States, over one third of perfusion imaging studies are performed with pharmacological stress. Pharmacological stress agents fall into two categories: coronary vasodilating agents such as dipyridamole and adenosine, and cardiac positive inotropic agents such as dobutamine and arbutamine. For both, in the presence of coronary artery disease (CAD), perfusion image abnormalities result from heterogeneity of coronary blood flow reserve. Vasodilating agents work directly on the coronary vessels to increase blood flow, whereas inotropic agents work indirectly by increasing myocardial work load, which then leads to an increase in coronary blood flow. Both classes of agents have high accuracies for diagnosing coronary artery disease, and they have excellent safety records with acceptably low occurrences of side effects. For dipyridamole planar thallium imaging, pooled analysis yields a sensitivity of 85% and a specificity of 87% for diagnosis of coronary disease, but there is a large variation in reported values depending on various factors, such as the extent of postcatheterization referral bias, the type of imaging (planar versus single photon emission computed tomography [SPECT]), the types of patients being studied (single versus multivessel disease, men versus women), and the imaging agent used (thallium versus one of the technetium-based agents). Diagnostic accuracies for adenosine are similar to those of dipyridamole, with reported overall sensitivities ranging from 83% to 97%, and specificities ranging from 38% to 94%. For dobutamine, pooled analyses yield a sensitivity of 82% and a specificity of 75%. There is some concern that dobutamine may interfere with uptake of technetium-99m sestamibi, lowering the sensitivity for detection of disease, and thus the vasdodilating agents are generally preferred. Pharmacological stress testing has high clinical use for risk stratifying patients with known or suspected CAD, in patients after myocardial infarction, and in patients needing noncardiac surgery. Vasodilating agents are particularly advantageous in assessing post-myocardial infarction patients, allowing testing as soon as 2 days after the event. Like patients undergoing exercise stress testing, patients with normal perfusion images by pharmacological stress have a <1% annual incidence of cardiac events. The likelihood of an event increases with the extent and severity of perfusion abnormalities. However, it is important to consider clinical variables when using perfusion imaging for risk stratification, particularly in the presurgery patients. As with exercise testing, adjunct markers such as ST segment depression during testing, lung uptake of radiotracer (if thallium is used), and ventricular cavity dilatation add additional prognostic information to that available from the perfusion images alone. The aim of current research is to find better agents that are easier to use and that have fewer side effects. MRE-0470 is an experimental vasodilating agent that is more receptor selective than adenosine and promises a lower incidence of hypotension. Arbutamine more closely simulates exercise than dobutamine, and it can be administered by a closed-loop computerized delivery device. Work is also underway to look at novel uses of pharmacological stress agents, such as acquiring gated SPECT images during dobutamine infusion to enhance detection of myocardial viability. With increasing use of noninvasive testing in elderly patients and in patients with comorbidities that preclude adequate exercise, pharmacological stress testing has become an indispensable tool for radionuclide myocardial perfusion imaging studies. A good understanding of pharmacological stress testing is essential for performing high-quality nuclear cardiology

Flow profiles in the left anterior descending and the right coronary artery assessed by MR velocity quantification: effects of through-plane and in-plane motion of the heart

PURPOSE

The purpose of this work was to compare the temporal profiles of volume flow in the left anterior descending artery (LAD) and the right coronary artery (RCA) and to assess the effect of through-plane and in-plane myocardial motion.

METHOD

In eight healthy volunteers, MR phase-difference velocity quantification was applied with prospective ECG triggering, pixel size of 1.16 x 0.98 mm2 (LAD) or 1.25 x 0.98 mm2 (RCA), velocity sensitivity of 40 cm/s, and data acquisition time window of 64 ms for LAD (3 ky lines per heartbeat) and 24 ms for RCA. In-plane motion was measured from the magnitude images.

RESULTS

In the LAD, systolic peak and mean flow values were 0.94+/-0.28 and 0.30 +/-0.22 ml/s, respectively. Diastolic peak and mean flows were 2.42+/-0.56 and 1.38+/-0.43 ml/s. The systolic to diastolic ratio was 0.37+/-0.12 for peak flow and 0.22+/-0.15 for mean flow. Mean flow through the cardiac cycle was 59.1+/-15.0 ml/min. In the RCA, systolic peak and mean flow values were 1.96+/-0.69 and 0.74+/-0.31 ml/s, respectively. Diastolic peak and mean flows were 1.80+/-0.53 and 0.83+/-0.20 ml/s. The systolic to diastolic ratio was 0.97+/-0.58 for peak flow and 0.85+/-0.39 for mean flow. Mean flow through the cardiac cycle was 38.4+/-10.8 ml/min. The in-plane velocity of the coronary artery cross-section was 6.4+/-1.8 cm/s for the LAD and 14.9 +/-4.0 cm/s for the RCA (given by peak values in diastole).

CONCLUSION

It is confirmed noninvasively with MR that the LAD shows a predominantly diastolic flow, whereas the RCA shows about equal flow values in systole and diastole. Through-plane motion correction is required for assessing the true flow patterns. The in-plane velocities of the coronary artery cross-sections imply a maximum data acquisition time window, estimated at 58 ms for the LAD and at 23 ms for the RCA.

Severe transmural myocardial ischemia after dipyridamole administration implicating coronary steal

Myocardial perfusion imaging with coronary vasodilators is routinely used for patients with suspected coronary disease who are unable to exercise. Since these agents work by increasing blood flow without significantly changing myocardial oxygen demand, they generally do not produce ischemia. A minority of patients show evidence of ischemia which some investigators suggest is due to a coronary steal phenomenon, but this has been challenged by several investigators. We present the case of a patient who developed severe transmural myocardial ischemia manifested by ST-segment elevation and severe perfusion defects which occurred after dipyridamole administration and which were reversed with aminophylline and nitroglycerin. This case supports the notion that coronary vasodilation with dipyridamole can induce a coronary steal.

Coronary flow and coronary flow reserve measurements in humans with breath-held magnetic resonance phase contrast velocity mapping

Objective evidence for coronary lesion significance can be obtained with ischemic stress testing. Since flow-limiting stenoses have already undergone compensatory vasodilatation to maintain flow, the response to vasoactive stimulation is dampened. The degree of response limitation is reflected by the coronary flow reserve (CFR). Absolute volume flow rates can be accurately and noninvasively measured with MRI techniques. The purpose was to assess the ability to measure coronary volume flow rate noninvasively, and characterize the effect of pharmacologic stress on coronary flow quantitatively by using ultrafast, breath-held segmented k-space phase-contrast-MR imaging (PC-MRI). Ten healthy volunteers were examined by using ultrafast breath-held PC-MRI. Coronary volume flow rates were measured in the anterior descending coronary artery (LAD) at rest and following intravenous administration of dipyridamole. CFR was determined based on these data. Mean LAD volume flow rates increased from 38 +/- 11 ml/min before application of dipyridamole to 169 +/- 42 ml/min. The mean CFR amounted to 5.0 +/- 2.6 (median = 4.15). This study demonstrates the feasibility of breath-held PC-MRI to noninvasively quantify coronary volume flow rates over the cardiac cycle. Pharmacologically induced changes in volume flow rate and thus CFR can be quantitated.

Localization of dipyridamole molecules in ionic micelles: effect of micelle and drug charges

The localization of the coronary vasodilator dipyridamole (DIP) in cationic cetyltrimethylammonium chloride (CTAC), anionic sodium dodecylsulfate (SDS) and zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate and lysophosphatidylcholine (HPS and LPC) micelles was investigated using fluorescence quenching by quenchers with known localization in the micelle (TEMPO and 5-doxyl and 12-doxyl stearic acids). The use of fluorescence quenching jointly with fluorescence and 1H-NMR spectral measurements shows that DIP molecules in both protonated and nonprotonated forms are localized in micelles near the region which separates their polar and nonpolar parts, the polarizable heteroaromatic cycle of DIP being close to the polar part and the nonpolar substituents penetrating the hydrophobic interior of the micelle. The electrostatic interaction between the protonated DIP molecules and micelle charges either moves DIP into the micelle interior (for cationic and zwitterionic micelles) or draws it closer to the micelle surface (for anionic ones). Our results could be relevant to the mechanism of DIP action since many data indicate the interaction of the drug with cell membranes. The ability of DIP to localize near the membrane surface with the substituents immersed into a hydrophobic moiety could be essential for the drug interaction with P-glycoprotein, which is responsible for mediation of the effects of several antitumour drugs.

Quantitative demonstration of dipyridamole-induced coronary steal and alteration by angioplasty in man: analysis by simultaneous, continuous dual Doppler spectral flow velocity

In the course of studying the effects of coronary angioplasty on branch vessel flow using two Doppler flow velocity guidewires, we quantitated simultaneous blood flow responses proximal and distal to a stenosis. The alterations of flow documented a horizontal epicardial steal induced during dipyridamole hyperemia, hyperemic flow reversal by intravenous aminophylline, and subsequent normalization of distal hyperemia after endoluminal enlargement by successful angioplasty. The quantitative physiology of the patient described here confirms one postulated mechanism of abnormal myocardial perfusion stress scintigraphy. Continuous dual flowire spectral coronary flow determinations appear to be a valuable method in verifying postulated mechanisms of various pharmacologic and mechanical stimuli influencing coronary blood flow in patients with atherosclerotic coronary artery disease.

Usefulness of myocardial contrast echocardiography in detecting the immediate changes in anterograde blood flow reserve after coronary angioplasty

Myocardial contrast echocardiography has revealed that successful coronary angioplasty results in an immediate decrease in the amount of collateral blood flow to the perfusion bed supplied by the dilated vessel. This information could potentially be used with pharmacologic stress in the catheterization laboratory to also assess the improvement in coronary flow reserve after angioplasty. The immediate changes in area under the time intensity curve produced by a 1 ml slow injection of sonicated albumin immediately proximal to a stenosis before and after 14 angiographically successful angioplasties was studied in 12 patients. Area under the curve was assessed before and after an 8 mg selective injection of papaverine. The changes in area under the curve were correlated with percent improvement in epicardial area stenosis. Visually successful angioplasty resulted in > 30% improvement in area under the curve after papaverine in 9 of 14 studies. There was a significant correlation between improvement in area under the curve after papaverine and percent improvement in epicardial area stenosis (r = 0.75; p < 0.01). No patient had left ventricular wall motion abnormalities after papaverine before or after angioplasty. These changes suggest that quantitatively successful angioplasty results in decreased collateral blood flow to the involved myocardium during pharmacologic stress. These improvements in coronary flow reserve cannot be predicted by visual analysis of angioplasty results.

Interaction of dipyridamole with micelles of lysophosphatidylcholine and with bovine serum albumin: fluorescence studies

The interaction of the coronary vasodilator dipyridamole with biological systems, protein and membranes has been studied through optical absorption and fluorescence spectroscopies. Using the analysis of the spectra and fluorescence intensity of dipyridamole (DIP) in solution, the interaction of this compound with the transport protein albumin (BSA) and with a model of cell membranes, namely micelles of lysophosphatidylcholine (L-PC), was investigated. Measurements were performed at pH 5.0 and pH 7.0 where the molecule of DIP is fully protonated and partially protonated, respectively. The quenching of fluorescence with nitroxide-stable radicals 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) as well as with acrylamide and iodide allowed the localization of the drug in the polar interface of micelles. Quenching by acrylamide and iodide in L-PC micelles demonstrated the effect of micelle protonation which increased the accessibility of iodide to the chromophore. An effective association constant was obtained both at pH 7.0 (7.5 x 10(3) M-1) and pH 5.0 (2.5 x 10(3) M-1) and a very good agreement with the proposed binding model was observed. The quantum yields of fluorescence data agree very well with the fluorescence lifetimes. The measurement of lifetimes was important to understand the kinetic data obtained from Stern-Volmer plots both of radical, acrylamide and iodide quenching of fluorescence. It was observed that, in the presence of micelles, the kq value increased for TEMPO while decreased for TEMPOL. This result, together with the vanishing solubility of DIP in saturated hydrocarbons and the preferential partition of TEMPO in micelles, suggested the localization of DIP in the polar micellar interface. This is also supported by the enhanced iodide quenching at pH 5.0, constancy of acrylamide quenching in the range of pH 7.0-5.0 and the partition of TEMPO and TEMPOL in SDS micelles. The association constant of DIP to BSA was also estimated both at pH 7.0 (2 x 10(4) M-1) and pH 5.0 (4 x 10(3) M-1). Quenching studies with nitroxide radicals, acrylamide and iodide also suggested the binding of the drug to a hydrophobic region of the protein. At pH 5.0, the protein undergo a conformational change which leads to a loosening of the overall structure so that the accessibility of the nitroxide radicals for DIP is increased at this pH. The differences in kq values at pH 7.0 and pH 5.0 suggested that at pH 7.0 the chromophore is protected in the protein site.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of the findings on preoperative dipyridamole perfusion scintigraphy and intraoperative transesophageal echocardiography: implications regarding the identification of myocardium at ischemic risk

The evidence of myocardium at potential ischemic risk on preoperative dipyridamole perfusion scintigraphy was compared with that of manifest ischemia on intraoperative transesophageal echocardiography in 26 patients at high risk of a coronary event undergoing noncardiac surgery. The clinical outcome was also assessed. Induced intraoperative wall motion abnormalities were more common in patients and myocardial segments with, than in those without, a preoperative reversible perfusion defect (both p less than 0.05). Conversely, a preoperative reversible perfusion defect was more common in patients and segments with, than in those without, a new intraoperative wall motion abnormality (both p less than 0.05). Six patients, five with a reversible scintigraphic defect but only three with a new wall motion abnormality, had a hard perioperative ischemic event. Events occurred more often among patients with, than in those without, a reversible perioperative scintigraphic defect (5 [33%] of 15 vs. 1 [9%] of 11) but this difference did not reach significance (p = 0.14), probably owing to the sample size. Intraoperative wall motion abnormalities were all reversible and did not differentiate between risk groups; these findings were possibly influenced by treatment. These preliminary data support the known relation between reversible scintigraphic defects and perioperative events and identify another manifestation of ischemic risk in the relation between reversible scintigraphic defects and induced intraoperative wall motion abnormalities. The value of intraoperative echocardiography in identifying ischemia and guiding therapy in patients with a reversible scintigraphic abnormality should be further assessed.

Dipyridamole perfusion scintigraphy

Dipyridamole is one of several agents that may be infused intravenously to nonivasively evaluate coronary perfusion without dynamic exercise. Among such agents it is the most investigated, and it is associated with the greatest clinical experience. Its mechanism of action utilizes intrinsic adenosine and does not require the induction of ischemia. Rather, the method tests the coronary flow reserve by dilating the precapillary and arteriolar capillary beds. Vessels with a limited coronary flow reserve demonstrate reduced responsiveness with relative flow reduction and a resultant defect on perfusion scintigraphy. Side effects are common and generally benign, but deaths have been reported and they generally relate to severe hypotension, prolonged dense ischemia and resultant infarction, or bronchospasm. Severe complications are rare and can be avoided by the prompt administration of aminophylline, the dipyridample antedote. Diagnostic accuracy for the identification of coronary disease appears similar to that for exercise perfusion scintigraphy. It should be applied to patients with known or suspected coronary disease who require coronary evaluation, but who cannot exercise adequately for diagnostic or prognostic purposes. In such patients, the method is useful for the preoperative assessment of risk at peripheral vascular and other major noncardiac surgery. It may be of value as well in the assessment of the otherwise uncomplicated patient postinfarction. Not yet established is its application to the patient with unstable angina or in the acute setting, after coronary reperfusion. Similarly, its comparison with direct adenosine infusion or with pharmacological agents whose mechanism rests entirely on ischemia induction, as does dobutamine, has until now been limited. Unlike its use with perfusion scintigraphy, the application of dipyridamole with echocardiography and other functional ischemic indicators is totally dependent on the induction of ischemia. This is likely less frequent than the induction of nonischemic perfusion heterogeneity. The agent is now commonly available and will make a significant beneficial impact on patient evaluation and management.

Two-dimensional Doppler echocardiographic correlation of dipyridamole-thallium stress testing with isometric handgrip

To determine how frequently new wall-motion abnormalities that are indicative of ischemia accompany thallium redistribution, 47 consecutive patients underwent two-dimensional echocardiography during routine dipyridamole-thallium stress testing. A secondary aim of the study was to determine whether the addition of isometric handgrip exercises to the standard dipyridamole imaging protocol increased the frequency of wall-motion abnormalities or thallium redistribution. Echocardiograms and thallium scans were independently interpreted, and wall-motion abnormalities that appeared with dipyridamole, handgrip exercise, or both were compared with results of thallium imaging. Five of 24 patients with thallium redistribution had new wall-motion abnormalities, and the extent (number of segments) of thallium redistribution in these five patients was significantly greater than in those who did not have well-motion abnormalities (p less than 0.03). The addition of isometric handgrip exercises to the imaging protocol did not distinguish between patients with and without new wall-motion abnormalities or thallium redistribution. Thus new wall-motion abnormalities infrequently accompany thallium redistribution in routine dipyridamole stress testing in spite of the addition of handgrip exercises, but when new wall-motion abnormalities are present, they are associated with a greater area of thallium redistribution.

Pharmacological and other nonexercise alternatives to exercise testing to evaluate myocardial perfusion and left ventricular function with radionuclides

Pharmacological vasodilatation with either dipyridamole or adenosine is a safe and accurate alternative to exercise testing to diagnose coronary artery disease with thallium 201 myocardial perfusion imaging. The technique also provides important prognostic information with regard to future cardiac events in patients undergoing diagnostic testing, in those evaluated preoperatively, and in those with recent myocardial infarctions. Multigated equilibrium and first-pass radionuclide ventriculography also are well suited to evaluate the effects of interventional procedures. Success has been achieved using this methodology in a variety of interventions including conventional exercise testing, pharmacological stress testing, atrial pacing, assessment of myocardial viability with nitroglycerin, mental stress testing, and ambulatory monitoring of left ventricular ejection fraction.

Effects of atrial pacing and dipyridamole administration on coronary hemodynamics of collateralized myocardial regions in stable angina pectoris

Great cardiac vein blood flow by thermodilution and great cardiac vein oxygen saturation were measured in 14 patients with stable exertional angina and an angiographic pattern of complete occlusion of the proximal left anterior descending artery retrogradely filled by collateral vessels supplying still viable myocardium. Measurements were obtained under control conditions, at peak atrial pacing and after dipyridamole administration (0.56 mg/kg intravenously over 4 minutes). Both stress tests induced ischemic electrocardiographic changes in all patients, but dipyridamole administration resulted in greater ST-segment depression in 11 patients (1.6 +/- 0.5 vs 2.4 +/- 1.6 mm, p less than 0.05) and transient ST-segment elevation in 3 patients. Dipyridamole provoked ischemia at a lower value of rate-pressure product (145.3 +/- 30.6 vs 202.9 +/- 36.6 beats/min . mm Hg . 10(-2), p less than 0.0005) and anterior region myocardial oxygen consumption (9.32 +/- 4.76 vs 11.39 +/- 3.91 ml/min, p less than 0.05), despite a greater increase in great cardiac vein flow (139.4 +/- 45 vs 93 +/- 27.4 ml/min, p less than 0.0025) and a greater decrease in the calculated index of anterior region coronary resistance (0.87 +/- 0.27 vs 1.46 +/- 0.43 mm Hg/ml/min, p less than 0.0005). Moreover, great cardiac vein oxygen saturation increased more significantly during dipyridamole-induced ischemia than at peak pacing (63 +/- 12 vs 35 +/- 8%, p less than 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of regional myocardial perfusion by contrast echocardiography. II. Detection of changes in transmural and subendocardial perfusion during dipyridamole-induced hyperemia in a model of critical coronary stenosis

Measurements of myocardial contrast (sonicated meglumine diatrizoate) intensity were compared with myocardial flow by radioactive microspheres before and after administration of dipyridamole (0.5 mg/kg body weight intravenously) in 10 open chest dogs with a critical stenosis in the left circumflex coronary artery. Computer measurements of contrast time-intensity curves corrected for background myocardial intensity were made along 12 transmural segments of the left ventricle at mid-papillary level and for the subendocardial and subepicardial half of each segment. After administration of dipyridamole, transmural flow in the control region increased significantly (p less than 0.001), resulting in a dipyridamole/baseline flow ratio (i.e., coronary reserve ratio) of 2.54 +/- 0.95. Similar changes (p less than 0.001) were seen by contrast echocardiography; the coronary reserve ratio was 2.10 +/- 0.60 with use of peak intensity and 3.48 +/- 1.58 with use of area under the time-intensity curve. In contrast, no significant changes were observed in myocardial flow, peak contrast intensity or area under the curve in the ischemic region after dipyridamole. In the control region the ratio of subendocardial to subepicardial flow was similar at baseline and after dipyridamole administration as assessed by microspheres (1.08 +/- 0.24 versus 1.17 +/- 0.25) or by area under the time-intensity curve (1.11 +/- 0.45 versus 1.11 +/- 0.56). In the ischemic region, the subendocardial/subepicardial flow ratio decreased significantly after dipyridamole administration as measured by microspheres (1.15 +/- 0.19 to 0.82 +/- 0.25; p less than 0.001) or by area under the curve (1.10 +/- 0.28 to 0.70 +/- 0.47; p less than 0.01). Thus, myocardial contrast echocardiography appears to be a sensitive technique with which to detect changes in myocardial flow induced by dipyridamole in the various myocardial layers of normal segments as well as of segments supplied by a critically stenotic coronary artery.

The effect of dipyridamole on transmural blood flow gradients

The effect of dipyridamole (DP) on subendocardial (ENDO) and subepicardial (EPI) blood flow in stenosed and normal regions was determined with radioactive microspheres before and after intravenous infusion of 0.08 mg/kg.min-1 of DP in two groups of dog hearts in situ. Group 1 (n = 6) had coronary stenoses that did not reduce distal perfusion at rest, but did attenuate hyperemic response, and group 2 (n = 6) had stenoses which reduced resting blood flow. In nonstenosed zones, a doubling in perfusion during DP infusion induced proportionate changes in ENDO and EPI flows (unchanged ENDO/EPI ratio) in group 1 hearts, but increased EPI more than ENDO flows in group 2 hearts (decreased ENDO/EPI ratio). In mildly stenosed regions, a 47 percent increase in perfusion during DP was associated with an increase in only EPI flow, which thereby reduced the ENDO/EPI ratio. In severely stenosed zones, the ENDO/EPI ratio was already significantly reduced at rest and a further reduction in ENDO flow during DP caused a significant decline in the ENDO/EPI ratio. Therefore, during pharmacologic vasodilation, a redistribution of coronary transmural flow occurs (relative ENDO to EPI steal) in non- and mildly stenosed regions while an absolute decrease or steal in ENDO flow was noted only in regions distal to more severe stenoses. These studies suggest that an interaction between the stenosis severity and vasodilation is a determining factor in ENDO/EPI ratios with dipyridamole.

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 less than 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 less than 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.

Comparative electrocardiographic and myocardial blood flow effects of rapid atrial pacing and dipyridamole infusion in dogs with chronic coronary artery occlusion

Altering regional myocardial flow by the use of potent vasodilators as well as increasing oxygen demand by exercise have been employed as diagnostic methods for detecting coronary arterial obstruction. We sought to define the relative capabilities of these two methods to produce abnormal ECG patterns and to alter myocardial blood flow after Ameroid constriction of the left circumflex coronary artery. Atrial pacing to rates of 210 beats/min was performed, followed by intravenous administration of 0.25 and 0.50 mg/kg of dipyridamole. ECGs were recorded to construct body surface isopotential distributions. Flow was measured by serial injections of radiolabelled microspheres. In 15 animals studied after 3 to 5 weeks of Ameroid constriction, pacing increased epicardial flow by 19.14 +/- 7.11% but reduced endocardial flow by 35.69 +/- 12.32%, with a significant reduction (to less than 0.67) in the endocardial/epicardial flow ratio in 12 (80%) dogs; both endocardial and epicardial flows were significantly lower in the ischemic than in the nonischemic bed. Ten dogs developed abnormal ST segment responses of subendocardial ischemia. In contrast, dipyridamole produced a dose-dependent rise in both endocardial (25.33 +/- 8.54% and 55.80 +/- 9.22% after 0.25 and 0.5 mg/kg, respectively) and epicardial (29.13 +/- 7.49% and 66.33 +/- 7.64% after 0.25 and 0.5 mg/kg, respectively) flows without a significant fall in the transmural ratio. These increases were, however, significantly less than those observed in nonischemic bed flow, resulting in a transventricular gradient of blood flow. No dog developed abnormal ECG patterns after dipyridamole infusion. Thus pacing produces both a transmural and a transventricular gradient in blood flow, whereas vasodilation causes only a transventricular flow abnormality.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-invasive detection of coronary artery disease by body surface electrocardiographic mapping after dipyridamole infusion

Electrocardiographic changes after dipyridamole infusion (0.568 mg/kg/4 min) were studied in 41 patients with coronary artery disease and compared with those after submaximal treadmill exercise by use of the body surface mapping technique. Patients were divided into three groups; 19 patients without myocardial infarction (non-MI group), 14 with anterior infarction (ANT-MI) and eight with inferior infarction (INF-MI). Eighty-seven unipolar electrocardiograms (ECGs) distributed over the entire thoracic surface were simultaneously recorded. After dipyridamole, ischemic ST-segment depression (0.05 mV or more) was observed in 84% of the non-MI group, 29% of the ANT-MI group, 63% of the INF-MI group and 61% of the total population. Exercise-induced ST depression was observed in 84% of the non-MI group, 43% of the ANT-MI group, 38% of the INF-MI group and 61% of the total. For individual patients, there were no obvious differences between the body surface distribution of ST depression in both tests. The increase in pressure rate product after dipyridamole was significantly less than that during the treadmill exercise. The data suggest that the dipyridamole-induced myocardial ischemia is caused by the inhomogenous distribution of myocardial blood flow. We conclude that the dipyridamole ECG test is as useful as the exercise ECG test for the assessment of coronary artery disease.

Acute effect of systemic versus intracoronary dipyridamole on coronary circulation

Dipyridamole has been proposed as an ideal agent to evaluate coronary vascular reserve because it produces selective coronary vasodilation without systemic hemodynamic effect. The actions of intracoronary (IC) and intravenous (IV) dipyridamole on coronary blood flow and systemic hemodynamics were compared in 15 patients with chest pain syndrome and normal coronary arteries. They received IC dipyridamole, followed 10 minutes later by 0.5 mg/kg of IV dipyridamole. IC dipyridamole produced a 73% increase in coronary sinus flow without hemodynamic changes, except for a slight increase in pulmonary systolic and diastolic pressures. IV dipyridamole administration produced an additional 88% increase in coronary sinus flow, reaching 172% over baseline; it was also associated with a significant (p less than 0.01) increase in heart rate (78 +/- 14 vs 102 +/- 19 beats/min), cardiac index (4 +/- 0.7 vs 6.3 +/- 1.7 liters/min/m2), and pulmonary artery systolic (27 +/- 5 vs 34 +/- 7 mm Hg) and diastolic pressures (12 +/- 4 vs 19 +/- 7 mm Hg). These data suggest that the coronary vasodilatory effect seen after IV dipyridamole administration is related to mechanisms other than direct coronary vasodilation.

Dipyridamole versus intracoronary injection of contrast medium for the evaluation of coronary reserve in man: a comparative study

Coronary reserve can be assessed by the ratio of coronary blood flow after "maximum" vasodilation to control flow. The intravenous infusion of dipyridamole (0.56 mg X kg-1) is considered to elicit maximum coronary vasodilation. The present study was designed to compare coronary flow and resistance responses to intravenous dipyridamole and intracoronary injection of contrast medium (ioxaglate), this latter technique being frequently used in digital radiology to stimulate hyperemia. The comparison was performed in seven normal patients, nine patients with coronary artery disease, and 16 patients with dilated cardiomyopathy. Coronary flow reserve was calculated as the ratio of peak flow after dipyridamole or contrast medium to control flow, and coronary resistance reserve was calculated as the ratio of minimal to control coronary resistance after each stimulus. Although flow reserve after dipyridamole was approximately twice that obtained after contrast medium in the normal group (4.01 +/- 0.56 vs 2.02 +/- 0.24) there was a close and linear relationship between coronary flow and resistance reserve estimated by both techniques (r = 0.846, p less than 0.001 for flow reserve ratios, and r = 0.844 p less than 0.001 for resistance reserve ratios). However, contrast-induced hyperemia identified 13/25 (52%) of patients with coronary artery disease or dilated cardiomyopathy as having a reduced flow reserve, while dipyridamole revealed a restrained coronary flow reserve in 20/25 (80%) of these patients. Similar proportions were obtained when using coronary resistance reserve (56% for contrast vs 80% for dipyridamole). (ABSTRACT TRUNCATED AT 250 WORDS)