Dobutamine MRI: A serious contender in pharmacological stress imaging?

Pharmacological stress cardiovascular magnetic resonance

Over the past decade, cardiovascular magnetic resonance (CMR) has evolved into a cardiac stress testing modality that can be used to diagnose myocardial ischemia using intravenous dobutamine or vasodilator perfusion agents such as adenosine or dipyridamole. Because CMR produces high-resolution tomographic images of the human heart in multiple imaging planes, it has become a highly attractive noninvasive testing modality for those suspected of having myocardial ischemia. The purpose of this article is to review the clinical, diagnostic, and prognostic utility of stress CMR testing for patients with (or suspected of having) coronary artery disease.

Assessment of ventricular function with cardiovascular magnetic resonance

The high spatial and temporal resolution of cardiovascular magnetic resonance (CMR) images makes it well-suited for use in the assessment of right ventricular and left ventricular function in patients who have cardiovascular disorders. This article reviews CMR methods used to assess regional and global ventricular function.

Dobutamine cardiovascular magnetic resonance: A review

Dobutamine cardiovascular magnetic resonance (DCMR) is useful for identifying myocardial ischemia and viability in patients with known or suspected coronary artery disease (CAD). This article reviews the performance and utility of DCMR, its association with dobutamine stress echocardiography (DSE), and areas of active investigative research.

Clinical Applications of ECG-gated Myocardial Perfusion SPECT

Erectrocardiogram (ECG)-gated myocardial perfusion single photon emission computed tomography (SPECT) can be used to assess myocardial perfusion and left ventricular function simultaneously. Various clinical applications of gated SPECT and their usefulness have been reported. The functional variables that can be determined with gated SPECT have been limited to systolic indices. Therefore, we evaluated left ventricular diastolic function with gated SPECT using data obtained from various frames per cardiac cycle and found that date generated from 32-frames are suitable for clinical use. Serial assessment of left ventricular function was also performed during bicycle exercise and dobutamine stress by means of gated SPECT using short-time data collection. These techniques, therefore, have the potential to provide useful information for evaluating myocardial conditions, such as hibernation and residual ischemia in infarct areas. Recently, we have developed a new technique for three-dimensional registration of CT coronary angiography (CTCA) and ECG-gated myocardial perfusion SPECT. This technique of registration may assist the integration of information from gated SPECT and CTCA and may have clinical application for the diagnosis of ischemic heart disease. These various applications would contribute to the development of nuclear cardiology.

Cardiovascular magnetic resonance imaging: current and emerging applications

Magnetic resonance (MR) imaging is gaining importance in cardiology as the newest, most complex, and rapidly emerging noninvasive test of choice for patients with a multitude of cardiovascular problems. It has long been recognized to provide an accurate and reliable means of assessing the function and anatomy of the heart and great vessels, but its emerging role as one of the dominant imaging modalities in other aspects of cardiology such as perfusion imaging, atherosclerosis imaging, and coronary artery imaging cannot be understated. As MR technology evolves, newer therapeutic applications are also being developed, including specific MR-compatible catheters for electrophysiology studies/ablation as well as interventional cardiology related procedures, which may alter the way we practice cardiology in the future. Also, MR is entering an important phase in its evolution, with an anticipated exponential growth in its current applications and through the development of newer molecular imaging applications. It is anticipated that such developments will be coupled to the utilization of molecular markers to index biologic processes to allow for their in vivo visualization. This combination of biochemical markers and imaging methodology will also usher in an era of molecular imaging during which much progress in the diagnosis and treatment of cardiovascular disease is anticipated.

High-Dose Dobutamine-Atropine Stress Cardiovascular MR Imaging after Coronary Revascularization in Patients with Wall Motion Abnormalities at Rest

PURPOSE

To determine the value of high-dose dobutamine-atropine stress cardiovascular magnetic resonance (MR) imaging for diagnosis of ischemia in patients with coronary artery disease (CAD) who had undergone revascularization and have wall motion abnormalities at rest, with quantitative invasive coronary angiography serving as reference standard.

MATERIALS AND METHODS

One hundred sixty consecutive patients (mean age, 59 years +/- 8 [standard deviation]) who had undergone revascularization for CAD and have wall motion abnormalities at rest underwent stress cardiovascular MR imaging prior to clinically indicated invasive coronary angiography. Turbo gradient-echo MR images were acquired at rest and during a standardized high-dose dobutamine-atropine protocol with three short-axis and two long-axis views. Regional wall motion was assessed by a blinded observer by using a 16-segment model and a four-point scoring system. New or worsening wall motion abnormality in at least one segment was considered positive for myocardial ischemia.

RESULTS

Significant CAD (stenoses of at least 50% diameter at angiography) was found in 119 patients (74%). Target heart rate was not reached in nine patients (6%). Overall sensitivity and specificity for detection of significant CAD were 89% and 84%, respectively. Diagnostic accuracy was 88%, and positive and negative predictive values were 94% and 73%, respectively. Overall sensitivity for detection of significant CAD in patients with single-, double-, and triple-vessel disease was 87%, 88%, and 100%, respectively.

CONCLUSION

High-dose stress cardiovascular MR imaging can be used for follow-up of patients after coronary revascularization procedures. Diagnostic accuracy is similar to stress cardiovascular MR imaging data for patients suspected of having CAD and compares favorably with that of other established noninvasive techniques.

Dobutamine stress MRI. Part I. Safety and feasibility of dobutamine cardiovascular magnetic resonance in patients suspected of myocardial ischemia

The aim of the study was to evaluate safety and feasibility of dobutamine cardiovascular magnetic resonance (CMR) in patients with proven or suspected coronary artery disease. Dobutamine CMR was evaluated retrospectively in 400 consecutive patients with suspicion of myocardial ischemia. Dobutamine was infused using an incremental protocol up to 40 microg/kg body weight per minute. All anti-anginal medication was stopped 4 days before the CMR study and infusion time of dobutamine was 6 min per stage. Hemodynamic data, CMR findings and side effects were reported. Patients with contraindications to CMR (metallic implants and claustrophobia) were excluded from analysis. Dobutamine CMR was successfully performed in 355 (89%) patients. Forty-five (11%) patients could not be investigated adequately because of non-cardiac side effects in 29 (7%) and cardiac side effects in 16 (4%) patients. Hypotension (1.5%) and arrhythmias (1%) were the most frequent cardiac side effects. One patient developed a severe complication (ventricular fibrillation) at the end of the study. There were no myocardial infarctions or fatal complications of the stress test. The most frequent non-cardiac side effects were nausea, vomiting and claustrophobia. Age >70 years, prior myocardial infarction and rest wall motion abnormalities showed no significant differences with side effects (P>0.05). Dobutamine CMR is safe and feasible in patients with suspicion of myocardial ischemia.

Real-time MR image acquisition during high-dose dobutamine hydrochloride stress for detecting left ventricular wall-motion abnormalities in patients with coronary arterial disease

PURPOSE

To compare the accuracy of real-time magnetic resonance (MR) imaging with that of standard echo-planar MR imaging for detecting myocardial wall-motion abnormalities at rest and during dobutamine hydrochloride-induced stress in patients with coronary arterial disease.

MATERIALS AND METHODS

In 22 patients with coronary arterial disease, left ventricular wall motion was examined at rest and during dobutamine hydrochloride stress, by using echo-planar MR imaging and a new technique with real-time segmented k-space turbo gradient-echo echo-planar MR imaging (repetition time, 16.5 msec; echo time, 6.8 msec). Wall-motion abnormalities were determined visually for each perfusion territory, and Cohen kappa coefficients were calculated for real-time imaging in comparison with echo-planar imaging. Coronary angiography was performed in all patients. Sensitivity and specificity for real-time and echo-planar imaging were calculated for detecting significant coronary arterial stenosis.

RESULTS

kappa values for detecting wall-motion abnormalities at real-time imaging, in comparison with echo-planar MR imaging, were 0.97 at rest and 0.94 at maximum dobutamine hydrochloride stress. At comparison with those of angiography, the sensitivity and specificity for detecting significant coronary arterial stenosis were 88% (14 of 16 patients) and 83% (five of six patients), respectively, for echo-planar imaging and 81% (13 of 16 patients) and 83% (five of six patients), respectively, for real-time imaging.

CONCLUSION

Real-time MR imaging is possible under stress conditions and allows accurate detection of wall-motion abnormalities.

Magnetic resonance tagging and echocardiographic response to dobutamine and functional improvement after reperfused myocardial infarction

OBJECTIVE

Our objective was to compare the qualitative response to low-dose dobutamine by echocardiography (DSE) with the quantitative response of magnetic resonance myocardial tagging (DMRT) in the prediction and evaluation of functional improvement after reperfused myocardial infarction (MI).

METHODS

Twenty-two patients with a reperfused first MI (aged 51 +/- 2 years, 20 male, 13 anterior MI) were studied. On day 3 +/- 1 after MI, patients underwent both DSE and DMRT at baseline and during infusion of 5 microg/kg/min and 10 microg/kg/min of dobutamine. The patients returned at week 8 +/- 1 for follow-up echocardiogram and MRT at rest. Two experienced observers interpreted the DSE for the presence of contractile reserve and functional improvement in dysfunctional segments. By DMRT, a 5% increase in percent intramyocardial circumferential shortening at peak response to dobutamine was defined as evidence of contractile reserve. Functional improvement by echocardiography was defined as the gold standard.

RESULTS

Ejection fraction improved from 46% +/- 10% at week 1 to 51% +/- 12% at week 8 (P <.001) in the patients. Sixty-seven transmural segments with baseline dysfunction matched between imaging modalities by location were studied. For 51 (76%) of the segments, echocardiography and MR tagging were concordant in the assessment of functional improvement (kappa value 0.52). Twenty-nine segments (43%) demonstrated improvement by echocardiography, whereas 33 segments (49%) improved by MR tagging. With improvement of function by echocardiography as gold standard, the sensitivity and specificity of DMRT for prediction of functional improvement was 86% and 69%, respectively, with an overall accuracy of 76%. The sensitivity, specificity, and accuracy of DSE was 86%, 87%, and 85%, respectively. Overall accuracy was similar between techniques.

CONCLUSIONS

Both DSMRT and DSE are sensitive and accurate techniques for predicting functional improvement after reperfused MI.

Pharmacological stress agents for evaluation of ischemic heart disease

Ischemic heart disease is the leading cause of death in the developed countries for those older than 65 years of age. In patients suspected to have coronary artery disease a stress test should be performed to identify the vulnerability of the myocardium to ischemia. As a rule of thumb, the evaluation of coronary artery disease is best done by exercise stress test. In patients who are not able to exercise adequately, pharmacological stress agents are used. The commonly used agents are the coronary vasodilators, adenosine and dipyridamole and the catecholamines, dobutamine and arbutamine. These agents are combined with imaging techniques to increase the sensitivity and specificity of the test. These agents have been widely used and have an excellent safety profile. Another advantage in using pharmacological stress agents is that they do not affect the image quality, especially with echocardiography and magnetic resonance imaging. Ongoing developments hold promise for safer and more reliable pharmacological stress agents in the future.

Comparison of low-dose dobutamine ventriculography with low-dose dobutamine echocardiography for predicting regional improvement in left ventricular function after coronary artery bypass grafting

The demonstration of a contractile reserve during low-dose dobutamine echocardiography (LDDE) identifies viable myocardium and predicts recovery of left ventricular (LV) function after myocardial revascularization in patients with chronic coronary artery disease. However, a technically difficult transthoracic visualization may limit the use of LDDE, thus requiring an alternative diagnostic procedure. The present study compares LDDE with low-dose dobutamine ventriculography (LDDV) in predicting an improvement in regional LV function after surgical revascularization. We studied 18 patients with coronary artery disease and LV dysfunction who were to undergo coronary artery bypass grafting. Preoperatively, all patients were evaluated for the presence of viable myocardium using LDDE and LDDV. Follow-up echocardiography at rest and left ventriculography were performed 4 months after successful revascularization to assess recovery of LV function. The sensitivity and specificity of LDDE to identify dysfunctional segments capable of recovering function were 63% and 71%, respectively, with a diagnostic accuracy of 68%. The sensitivity, specificity, and diagnostic accuracy of LDDE improved to 81%, 72%, and 76% when patients with optimal transthoracic evaluation were selected, whereas they were 30%, 77%, and 57%, respectively, in those who underwent suboptimal evaluation. The sensitivity, specificity, and diagnostic accuracy of LDDV were 66%, 75%, and 71%, respectively, with no difference in subgroups of patients. This study demonstrates that LDDV can be considered a useful technique for identifying the presence of myocardial viability and may provide an advantage over LDDE in patients with suboptimal echocardiographic visualization.

Functional MRI in ischemic heart disease based on detection of contraction abnormalities

Even though several non-invasive techniques are available for the assessment of coronary artery disease and the detection of myocardial ischemia, many coronary angiograms yield negative results, thus, warranting higher accuracy for non-invasive tests. The detection of obstructive coronary artery disease is only possible during physical or pharmacological stress. Currently, the assessment of wall motion abnormalities by echocardiography is clinically the most widely used method. However, a significant number of patients yield suboptimal or non-diagnostic images despite improvements with harmonic imaging. Cardiovascular magnetic resonance (CMR) imaging allows a non-invasive visualization of the heart with high spatial and temporal resolution. Gradient echo CMR images permit an exact and reproducible determination of global and regional left ventricular function, wall thickness and wall thickening and identical pharmacological stress protocols, as currently used for dobutamine stress echocardiography, can be implemented for CMR imaging. A review of the literature on dobutamine stress CMR for the detection of stress induced wall motion abnormalities is presented and the safety of CMR stress examinations is discussed. The results show, that especially in those patients with suboptimal echocardiographic image quality dobutamine stress CMR is superior in comparison with dobutamine stress echocardiography and may replace echocardiography in these patients. Further possibilities by the use of myocardial tagging or intravascular contrast agents are outlined.

Assessment of myocardial viability by MRI

Assessment of myocardial viability has become an important issue in patients presenting with either acute myocardial infarction or presenting with chronic ischemic left ventricular dysfunction. In patients with viable myocardium recovery of left ventricular function can be anticipatedm, spontaneously in patients with acute myocardial infarction or following revascularization in patients with ischemic cardiomyopathy. In contrast, patients without viable tissue are not likely to improve in left ventricular function. Currently, nuclear imaging techniques and dobutamine stress echocardiography are used for assessment of viability; recent studies with magnetic resonance imaging (MRI) have however demonstrated the potential usefulness of this technique for the assessment of viability. Various parameters, derived from resting MRI, can be used as markers of myocardial viability, including the end-diastolic wall thickness, systolic wall thickening and signal intensity without contrast-enhancement. Other studies have combined the information from resting MRI with the assessment of contractile reserve during dobutamine stimulation. Finally, recent studies have evaluated the use of contrast-enhanced MRI to detect viable myocardium. All of these parameters are potentially useful and MRI provide an alternative approach for the assessment of viable myocardium.