Evaluation of the extent and timing of the coronary hyperemic response to dipyridamole: a study with transesophageal echocardiography and positron emission tomography with oxygen 15 water

Echocardiographic assessment of coronary microvascular dysfunction: Basic concepts, technical aspects, and clinical settings

Coronary flow reserve is the capacity of the coronary circulation to augment the blood flow in response an increase in myocardial metabolic demands and has a powerful prognostic significance in different clinical situations. It might assess with invasive and noninvasive technique. Transthoracic echocardiography Doppler is an emerging diagnostic technique, noninvasive, highly feasible, safe for patient and physician, without radiation, and able to detect macrovascular and microvascular anomalies in the coronary circulation. This review aims to describe the benefit and limits of echocardiographic assessment of coronary flow reserve.

Single-scan rest∕stress imaging (18)F-labeled flow tracers

PURPOSE

The authors report a novel measurement strategy to obtain both rest and stress blood flow during a single, relatively short, scan session.

METHODS

Measurement of rest-stress myocardial blood flow with long-lived tracers usually requires separate scan sessions to remove the confounding effects of residual radioactivity concentration in the blood and tissue. The innovation of this method is to treat the rest-stress scan as a single entity in which the flow parameters change due to pharmacological challenge. With this approach the fate of a tracer molecule is naturally accounted for, no matter if it was introduced during the rest or stress phase of the study. Two new dual-injection kinetic models are considered that represent the response to pharmacological stress as a transitional or transient increase of myocardial blood flow. The authors present the theory of the method followed by the specific application of the theory to (18)F-Flurpiridaz, a new myocardial flow-imaging agent.

RESULTS

Myocardial blood flow was accurately and precisely estimated from a single-scan rest∕stress study for the long half-lived tracer (18)F-Flurpiridaz. By accounting for the time-dependence of the kinetic parameters, the proposed models achieved good accuracy and precision (5%) under different vasodilators and different ischemic states.

CONCLUSIONS

Detailed simulations predict that accurate and precise rest-stress blood flow measurements can be obtained in 20-30 min.

Quantitative cardiac positron emission tomography: the time is coming!

In the last 20 years, the use of positron emission tomography (PET) has grown dramatically because of its oncological applications, and PET facilities are now easily accessible. At the same time, various groups have explored the specific advantages of PET in heart disease and demonstrated the major diagnostic and prognostic role of quantitation in cardiac PET. Nowadays, different approaches for the measurement of myocardial blood flow (MBF) have been developed and implemented in user-friendly programs. There is large evidence that MBF at rest and under stress together with the calculation of coronary flow reserve are able to improve the detection and prognostication of coronary artery disease. Moreover, quantitative PET makes possible to assess the presence of microvascular dysfunction, which is involved in various cardiac diseases, including the early stages of coronary atherosclerosis, hypertrophic and dilated cardiomyopathy, and hypertensive heart disease. Therefore, it is probably time to consider the routine use of quantitative cardiac PET and to work for defining its place in the clinical scenario of modern cardiology.

Detection of impaired coronary flow reserve in coronary artery disease using transthoracic echocardiographic assessment of coronary sinus blood flow

In order to establish whether coronary flow reserve (CFR) can be measured by transthoracic echocardiography (TTE) with pulse wave Doppler echocardiography, 14 patients with coronary artery disease (CAD) and 12 normal subjects were studied. Coronary sinus blood flow was measured at rest and 2 minutes after intravenous injection of 0.56 mg/kg dipyridamole (DP). CFR was calculated as the DP to rest flow ratio. Patients with CAD were found to have significantly decreased CFR when compared to normal subjects. These findings suggest that TTE may be useful in diagnosing CAD.

Clinical and functional determinants of coronary flow reserve in non-ischemic dilated cardiomyopathy

Coronary flow reserve (CFR) is impaired in non-ischemic dilated cardiomyopathy (DCM). Mechanisms by which such impairment occurs are still unknown, but cofactors such as diastolic compressive force, left ventricular hypertrophy, and microvascular disease have been implied. In order to characterize the determinants of CFR in non-ischemic DCM, we evaluated 110 non-ischemic DCM patients (58 men; age=61+/-12 years) and 21 age- and gender-matched control patients (14 men; age=59+/-13 years) by transthoracic (n=88) or transesophageal (n=22) dipyridamole (0.84 mg/ kg in 10') stress echocardiography. All patients showed angiographically normal coronary arteries. Non-ischemic DCM patients had an ejection fraction <45% while control patients had normal left ventricular systolic function. CFR was assessed on LAD by pulsed Doppler as the ratio of maximal vasodilation (dipyridamole) to rest peak diastolic coronary flow velocity. Mean CFR value was 2.0+/-0.6 for DCM patients and 3.2+/-0.5 for controls (p<0.01). At individual non-ischemic DCM patient analysis, 46 patients had normal CFR> or =2 (Group 1) and 64 patients had abnormal CFR<2 (Group 2). On univariate analysis, CFR reduction correlated with NYHA functional class (r=-0.33, p=0.001), left ventricular ejection fraction ( r=0.23, p=0.02), end-systolic volume (r=-0.23, p=0.02), systolic pulmonary artery pressure (r=-0.42, p=0.0001), deceleration time (r=0.24, p=0.02). Logistic multiregression analysis showed that only NYHA functional class significantly and negatively correlated with CFR (odds ratio=0.9; 95% confidence intervals: 0.03-.35, p=0.0001). In patients with non-ischemic DCM, CFR is reduced but with substantial individual variability, only partially accounted for by level of systolic and diastolic dysfunction. The clinical functional class is the strongest predictor of CFR reduction in these patients, with lowest flow reserve found in more advanced NYHA class.

Incremental Benefit of Myocardial Contrast to Combined Dipyridamole-Exercise Stress Echocardiography for the Assessment of Coronary Artery Disease

Background— Although assessment of myocardial perfusion by myocardial contrast echocardiography (MCE) is feasible, its incremental benefit to stress echocardiography is not well defined. We examined whether the addition of MCE to combined dipyridamole-exercise echocardiography (DExE) provides incremental benefit for evaluation of coronary artery disease (CAD).

Methods and Results— MCE was combined with DExE in 85 patients, 70 of whom were undergoing quantitative coronary angiography and 15 patients with a low probability of CAD. MCE was acquired by low-mechanical-index imaging in 3 apical views after acquisition of standard resting and poststress images. Wall motion, left ventricular opacification, and MCE components of the study were interpreted sequentially, blinded to other data. Significant (>50%) stenoses were present in 43 patients and involved 69 coronary territories. The addition of qualitative MCE improved sensitivity for the detection of CAD (91% versus 74%, P =0.02) and accurate recognition of disease extent (87% versus 65% of territories, P =0.003), with a nonsignificant reduction in specificity.

Conclusions— The addition of low-mechanical-index MCE to standard imaging during DExE improves detection of CAD and enables a more accurate determination of disease extent.

Myocardial perfusion during long-term angiotensin-converting enzyme inhibition or beta-blockade in patients with essential hypertension

Hypertension is associated with reduced coronary vasodilatory capacity, possibly caused by structural changes in the coronary resistance vessels. Because vasodilatory treatment may correct abnormal structure better than nonvasodilating treatment, we compared whether long-term angiotensin-converting enzyme (ACE) inhibition has a greater effect on coronary reserve and cardiovascular structure than beta-blockade in patients with essential hypertension. Thirty previously untreated hypertensive patients were randomized in a double-blind design to treatment for 1 year with either perindopril (4 to 8 mg per day, n=15) or atenolol (50 to 100 mg per day, n=15) and furthermore compared with normotensive controls. Cardiac output and left ventricular mass were measured with echocardiography and resistance artery structure was determined in vitro. Using positron emission tomography, myocardial perfusion (MP) was determined at rest and during dipyridamole-induced hyperemia while still on medication. Perindopril reduced left ventricular mass by 14+/-4% (P<0.01), peripheral vascular resistance by 12+/-6% (P<0.01), and media thickness-to-lumen diameter ratio of resistance arteries by 16+/-4% (P<0.05), whereas atenolol had no effect. Resting MP was decreased both by perindopril (-11+/-4%, P<0.01) and by atenolol (-25+/-4%, P<0.01) in parallel to the reduction in rate pressure product. Hyperemic MP was unaltered by perindopril (+2+/-6%, P=NS), but reduced by atenolol (-32+/-5%, P<0.01). Compared with atenolol, perindopril treatment resulted in higher coronary reserve (P<0.05). We conclude that compared with beta-blockade, ACE inhibition increases coronary reserve and results in regression of hypertensive resistance artery structure and left ventricular hypertrophy. Vasodilating may thus be superior to nonvasodilating treatment in repairing the hypertensive myocardial microcirculation.

Simultaneous analysis of wall motion and coronary flow reserve of the left anterior descending coronary artery by transthoracic doppler echocardiography during dipyridamole stress echocardiography

BACKGROUND

Coronary flow reserve (CFR) can be measured in the left anterior descending artery (LAD) by dipyridamole transthoracic Doppler echocardiography (DTTDE). This information may critically improve the diagnostic accuracy of dipyridamole stress echocardiography, which is limited by moderate sensitivity.

OBJECTIVE

We sought to assess the feasibility and accuracy of value of DTTDE.

METHODS

We evaluated 752 consecutive patients (478 men; mean age, 64.7 years) referred for dipyridamole stress echocardiography. The diastolic velocity in the LAD was continuously monitored with pulsed Doppler at baseline and during hyperemia induced by the infusion of 0.84 mg/kg of dipyridamole. CFR was calculated as the ratio of maximal and basal diastolic velocity; a value < 2 was considered to indicate decreased CFR. Wall motion was assessed semiquantitatively. Coronary angiography was performed in 132 patients the week after DTTDE.

RESULTS

Adequate tracings were obtained in 95% of patients studied (715 of 752). In the subset of 132 patients undergoing coronary angiography, 71 patients (group A) showed a nonsignificant (<70%) and 61 patients (group B) a significant stenosis of the LAD. In group A, 65 had a normal wall-motion response (91.5% specificity) and 19 patients showed a decreased CFR (73.2% specificity; P =.1). In group B, new wall-motion abnormalities were seen in 42 patients (68.8% sensitivity), whereas CFR was decreased in 52 patients (86.8% sensitivity; P <.02).

CONCLUSION

Simultaneous assessment of wall motion and CFR of the LAD with DTTDE was highly feasible and safe. The information about CFR had a significantly higher sensitivity than the analysis of wall motion during dipyridamole stress echocardiography.

Transthoracic Doppler echocardiography - noninvasive diagnostic window for coronary flow reserve assessment

This review focuses on transthoracic Doppler echocardiography as noninvasive method used to assess coronary flow reserve (CFR) in a wide spectrum of clinical settings. Transthoracic Doppler echocardiography is rapidly gaining appreciation as popular tool to measure CFR both in stenosed and normal epicardial coronary arteries (predominantly in left anterior descending coronary artery). Post-stenotic CFR measurement is helpful in: functional assessment of moderate stenosis, detection of significant or critical stenosis, monitoring of restenosis after revascularization. In the absence of stenosis in the epicardial coronary artery, decreased CFR enable to detect impaired microvascular vasodilatation in: reperfused myocardial infarct, arterial hypertension with or without left ventricular hypertrophy, diabetes mellitus, hypercholesterolemia, syndrome X, hypertrophic cardiomyopathy. In these diseases, noninvasive transthoracic Doppler echocardiography allows for serial CFR evaluations to explore the effect of various pharmacological therapies.

Verapamil improves the pacing-induced vasodilatation in symptomatic patients with hypertrophic cardiomyopathy

The purpose of the study was to assess the effect of verapamil on the response of diastolic coronary flow velocity and coronary vascular resistance to pacing in symptomatic patients with hypertrophic cardiomyopathy. In 14 patients with hypertrophic cardiomyopathy, the coronary flow velocity was detected in the left anterior descending coronary artery using transthoracic Doppler echocardiography. The peak diastolic coronary flow velocity and coronary vascular resistance was measured at baseline and during pacing. Changes of these parameters induced by the pacing (expressed as the percentage of baseline values) were compared on verapamil treatment and after verapamil withdrawal. The same measurements were obtained in ten control subjects. The results show that, in hypertrophic cardiomyopathy patients, increase in coronary flow velocity during pacing was significantly higher on than off verapamil therapy (64.8+/-32.5 vs. 41.1+/-21.3%, P<0.05). In control subjects, pacing-induced increase in coronary flow velocity was comparable to changes in coronary flow velocity in hypertrophic cardiomyopathy patients receiving verapamil (80.2+/-18.4 vs. 64.8+/-32.5%, P>0.05). After verapamil withdrawal in hypertrophic cardiomyopathy patients, coronary flow velocity increase during pacing was significantly lower than in control subjects (41.1+/-21.3 vs. 80.2+/-18.4%, P<0.05). During pacing the coronary vascular resistance decreased more on verapamil than after drug withdrawal (-34.7+/-11.7 vs. -24.6+/-12.9%, P<0.05). In control subjects the coronary vascular resistance decreased during pacing -38.6+/-6.3% to similar extent as in hypertrophic cardiomyopathy patients on verapamil. We can conclude that endothelium-dependent vasodilatation during pacing was impaired in symptomatic patients with hypertrophic cardiomyopathy. Verapamil treatment was able to restore adequate vasodilator response to pacing stress.

Overview of stress echocardiography: uses, advantages, and limitations

Responses of the heart to changes in our environment are probably even more important than how the heart functions at rest. Accordingly, stress testing with noninvasive imaging has become important for diagnosis, prognosis, and monitoring the effects of therapy. Echocardiography at rest and with stress permits characterization of global and segmental left ventricular function as well as valvular structure and function. Moreover, echocardiography can be performed during or after a number of different physical or even mental stressors. Advantages of stress echocardiography include its ready availability, relatively low capital cost, and incremental value in that it allows characterization of cardiac anatomy as well as the myocardial response to a potentially ischemic stimulus. Moreover, echocardiography has the potential to image myocardial perfusion along with wall motion and wall thickening. Substantial literature has now been accumulated on the value of stress echocardiography for the diagnosis of ischemic disease, preoperative risk assessment, and assessment of myocardial viability. Echocardiography has compared generally well with nuclear imaging techniques for the detection of angiographic coronary artery disease. Overall sensitivity, however, has been slightly less, particularly for the detection of single-vessel coronary disease, although specificity has been on average somewhat higher than nuclear cardiology techniques. Because of the potential for variability in study acquisition as well as interpretation, careful safeguards need to be employed. Specifically, meticulous technique needs to be applied to obtain high-quality images and to assure that those images are obtained promptly after treadmill exercise stress. Only readers with specific interest and expertise should interpret stress echocardiography studies. Continuing efforts need to be made to assess and minimize variability and to assure continuing quality improvement. Advances in instrumentation, including evolving technology for real-time 3-dimensional imaging, and echocardiography contrast assessment of myocardial perfusion will likely improve the sensitivity of echocardiography and further extend its usefulness.

Assessment of coronary flow reserve with transthoracic Doppler echocardiography: comparison among adenosine, standard-dose dipyridamole, and high-dose dipyridamole

Coronary flow reserve (CFR), defined as a ratio of hyperemic-to-basal coronary flow velocity, provides important information about the functional aspect of coronary circulation. However, it usually is determined by invasive methods during catheterization. Recent studies have shown that transthoracic Doppler echocardiography (TTDE) may be useful in the measurement of coronary flow velocity in the distal portion of the left anterior descending coronary artery (LAD). The vasodilators used for hyperemia are adenosine and dipyridamole. However, the coronary vasodilative response and systemic hemodynamic effects of the two agents have not been directly compared with TTDE. We assessed blood flow velocity and vascular resistance in the distal LAD by TTDE during an intravenous 2-minute adenosine infusion (140 microg/kg/min) and low- (0.56 mg/kg) and high-dose dipyridamole (0. 84 mg/kg) infusion in 25 patients with patent LAD. Coronary flow velocity was successfully recorded in 20 patients (80%) during baseline and the consecutive vasodilator-infusion period. Compared with low-dose dipyridamole, adenosine infusion induced a higher CFR (3.7 +/- 0.87 vs 2.73 +/- 0.65; P <.05) and a lower coronary resistance index (0.31 +/- 0.04 vs 0.35 +/- 0.08; P <.05). But by increasing the dipyridamole dose to 0.84 mg/kg, the values of the CFR and coronary resistance index became comparable to those of adenosine infusion (2.85 +/- 0.78 vs 3.03 +/- 0.7, P = not significant [NS]; 0.33 +/- 0.04 vs 0.32 +/- 0.09, P = NS; respectively). We conclude that adenosine seems to be a favorable vasodilator for the measurement of CFR with TTDE.

The flow-function relationship in patients with chronic coronary artery disease and reduced regional function: a Doppler transesophageal and bidimensional transthoracic echocardiography study

BACKGROUND

Infra-low dose dipyridamole allows one to selectively explore myocardial viability. Transesophageal echocardiography Doppler measurement of left anterior descending coronary artery flow at baseline and following dipyridamole is an efficient tool to assess coronary flow response. Aim of this study was to determine the flow-function relationship during coronary vasodilatory stress in patients with coronary artery disease and baseline dysfunction.

METHODS AND RESULTS

Twelve patients with resting dyssynergies and 6 controls underwent assessment of regional function and of left anterior descending blood flow velocity. Flow and function were evaluated at rest and following infra-low dose dipyridamole (0.28 mg/Kg over 4 min). Controls showed a normal function at rest and after dipyridamole. Six patients ('Responders') with resting dyssynergies showed an improvement in segments of left anterior descending artery territory, whereas the other six ones ('Non-responders') showed no functional change. Controls and 'Responders' had similar values of resting peak diastolic left anterior descending artery flow velocity both at rest and after dipyridamole, whereas 'Non-responders' showed a blunted flow response to dipyridamole.

CONCLUSION

Myocardial segments with a resting dysfunction and a contractile reserve more often exhibit a residual flow response, whereas segments with fixed pattern show a flat flow response during coronary vasodilator stress.

Assessment of coronary flow reserve by transesophageal echocardiography in cardiac transplant recipients

This study investigated the feasibility of dipyridamole Doppler transesophageal echocardiography to assess coronary flow reserve in 26 patients with orthotopic heart transplantation and compared it with positron emission tomography. We found an 85% success rate in obtaining Doppler flow signals in the proximal left anterior descending coronary artery. Our data also showed that the correlation between transesophageal echocardiography and dipyridamole N-13 ammonia positron emission tomography increases when respective resting rate-pressure products are taken into account. However, comparison between the two methods should be made with caution because coronary flow reserve derived from transesophageal echocardiography tends to be higher than that obtained with positron emission tomography.

Mechanisms of coronary flow reserve impairment in human hypertension. An integrated approach by transthoracic and transesophageal echocardiography

The purpose of this study was to investigate the different mechanisms responsible for an impairment of coronary vasodilator capacity in hypertensive subjects by an integrated echocardiographic approach, including transesophageal Doppler echocardiography, which allows noninvasive monitoring of coronary flow velocity in the left anterior descending artery during pharmacological vasodilation. The study population consisted of 17 healthy control subjects and 33 hypertensive subjects: 10 without hypertrophy, 16 with mild to moderate hypertrophy, and 7 with severe left ventricular hypertrophy. Mean systolic and diastolic flow velocities were monitored basally (together with indexes of myocardial oxygen demand, such as heart rate, myocardial inotropism, and left ventricular wall stress) and during infusion of low-dose (0.56 mg/kg per 4 minutes) and high-dose (0.84 mg/kg per 9 minutes) dipyridamole. Coronary reserve was assessed as the ratio of mean diastolic velocity after high-dose dipyridamole and basal diastolic velocity, and minimum coronary resistance as the ratio of diastolic blood pressure and diastolic velocity after high-dose dipyridamole. Compared with the control group, in all hypertensive groups, coronary reserve was similarly decreased (3.54 +/- 0.84 versus 2.59 +/- 0.42, 2.29 +/- 0.46, and 2.43 +/- 0.71; P < .01) and minimum resistance increased (0.56 +/- 0.15 versus 0.75 +/- 0.31, 0.75 +/- 0.19, and 0.78 +/- 0.21 mm Hg.s-1.cm-1; P = NS). These results confirm that coronary reserve in hypertensive individuals is reduced even before the occurrence of left ventricular hypertrophy. The reduction in coronary reserve depends on both an increase in resting coronary flow and an impairment in maximal vasodilator capacity. An increase in resting flow is dependent on higher heart rate and wall stress in hypertensive subjects without ventricular hypertrophy and on increased myocardial mass in hypertensive subjects with hypertrophy. Hypertensive subjects with ventricular hypertrophy also demonstrated a significantly blunted response to low-dose dipyridamole.