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01-01-1970, 07:00 AM

BMJ 1999;319:1092 ( 23 October )

News
MRI found suitable for detecting coronary heart disease Deborah Josefson , San Francisco

Traditional electrocardiographic exercise stress tests for heart disease may soon be supplanted by cardiac magnetic resonance imaging (MRI).

Researchers from Wake Forest University School of Medicine in Winston Salem, North Carolina, investigated the technique of fast cinematic, cardiac magnetic resonance imaging to detect ischaemic heart disease in patients unsuitable for the usual stress echocardiography (Circulation 1999;100:1676-9, 1697-702).

Classically, patients with suspected coronary artery disease are referred for exercise stress testing and are hooked up to electrocardiographic and blood pressure monitors while doing progressively more intensive exercise on a treadmill.

Treadmill based stress tests are not suitable for many people, such as some postoperative patients, frail elderly people, amputees, and many patients who are obese or have chronic lung diseases that limit their exercise capacity.

To accommodate this problem, pharmacological stress tests were introduced to mimic the effect of exercise on the heart. Stress tests using the drugsdobutamine, dipyridamole, or adenosinecoupled with either echocardiographic or radionuclide based imaging of the heart are usually performed.

The drugs are used to induce vasodilation and tachycardia, simulating exercise. Echocardiography is then done to assess the effect of these vasodilatory drugs on left ventricular contractility. Wall motion abnormalities induced by these drugs may signify underlying coronary artery disease.

Alternatively, radionuclide perfusion scans which measure the uptake of various radioactive substances by the heart are also performed in this population.

Unfortunately, both tests have serious limitations, which may make them unsuitable for the very population for which they were intended. Because echocardiography relies on transmission of sound waves and their reflection back to produce an image, patients who are obese, have chronic lung conditions (such as emphysema), or have had cardiothoracic surgery will have suboptimal stress echo results with poor image quality.

To circumvent these problems, Dr Gregory Hundley and colleagues from Wake Forest University investigated fast cinematic cardiac magnetic resonance imaging as a technique for dobutamine based stress tests. A total of 163 patients ranging in age from 30 to 88 years were selected for the tests. Ten patients were removed from the study, six because they could not fit into the machine and four because of anxiety.

Of the remaining 153 patients, 139 underwent the full testing. The test lasted an average of 144 minutes, including preparation and recovery time; time in the scanner itself averaged 53 minutes.

All patients had previously undergone traditional dobutamine stress echocardiography, but had suboptimal images, despite the use of an advanced techniquesecond harmonic imagingto improve resolution.

Most of the patients tested were obese, with 41%of patients above 150%of their ideal body weight and 80%above 120%of ideal weight. Thirty two per cent of the patients had had a coronary artery bypass graft, and 21%had chronic obstructive lung disease.

Thirty six of the 139 patients had evidence of ischaemia induced by dobutamine; 103 lacked it. Forty one of the study subjects underwent coronary angiography within five weeks of the imaging stress test.

As measured against this gold standard, fast cinematic magnetic resonance imaging was 82%sensitive in detecting 70%or greater stenosis in a single coronary artery and 88%sensitive in detecting that degree of stenosis in two vessels. It was 100%accurate in diagnosing left main coronary artery disease as well as occlusion in three vessels.

The authors concluded that "MRI can be used to assess contractility continuously during a stress test and to detect inducible ischemia in patients poorly suited for stress echocardiograms."

01-01-1970, 07:00 AM	#3
Hồ sơ MRI Số bài viết: n/a Tiền:	BMJ 1999;319:1092 ( 23 October ) News MRI found suitable for detecting coronary heart disease Deborah Josefson , San Francisco Traditional electrocardiographic exercise stress tests for heart disease may soon be supplanted by cardiac magnetic resonance imaging (MRI). Researchers from Wake Forest University School of Medicine in Winston Salem, North Carolina, investigated the technique of fast cinematic, cardiac magnetic resonance imaging to detect ischaemic heart disease in patients unsuitable for the usual stress echocardiography (Circulation 1999;100:1676-9, 1697-702). Classically, patients with suspected coronary artery disease are referred for exercise stress testing and are hooked up to electrocardiographic and blood pressure monitors while doing progressively more intensive exercise on a treadmill. Treadmill based stress tests are not suitable for many people, such as some postoperative patients, frail elderly people, amputees, and many patients who are obese or have chronic lung diseases that limit their exercise capacity. To accommodate this problem, pharmacological stress tests were introduced to mimic the effect of exercise on the heart. Stress tests using the drugsdobutamine, dipyridamole, or adenosinecoupled with either echocardiographic or radionuclide based imaging of the heart are usually performed. The drugs are used to induce vasodilation and tachycardia, simulating exercise. Echocardiography is then done to assess the effect of these vasodilatory drugs on left ventricular contractility. Wall motion abnormalities induced by these drugs may signify underlying coronary artery disease. Alternatively, radionuclide perfusion scans which measure the uptake of various radioactive substances by the heart are also performed in this population. Unfortunately, both tests have serious limitations, which may make them unsuitable for the very population for which they were intended. Because echocardiography relies on transmission of sound waves and their reflection back to produce an image, patients who are obese, have chronic lung conditions (such as emphysema), or have had cardiothoracic surgery will have suboptimal stress echo results with poor image quality. To circumvent these problems, Dr Gregory Hundley and colleagues from Wake Forest University investigated fast cinematic cardiac magnetic resonance imaging as a technique for dobutamine based stress tests. A total of 163 patients ranging in age from 30 to 88 years were selected for the tests. Ten patients were removed from the study, six because they could not fit into the machine and four because of anxiety. Of the remaining 153 patients, 139 underwent the full testing. The test lasted an average of 144 minutes, including preparation and recovery time; time in the scanner itself averaged 53 minutes. All patients had previously undergone traditional dobutamine stress echocardiography, but had suboptimal images, despite the use of an advanced techniquesecond harmonic imagingto improve resolution. Most of the patients tested were obese, with 41%of patients above 150%of their ideal body weight and 80%above 120%of ideal weight. Thirty two per cent of the patients had had a coronary artery bypass graft, and 21%had chronic obstructive lung disease. Thirty six of the 139 patients had evidence of ischaemia induced by dobutamine; 103 lacked it. Forty one of the study subjects underwent coronary angiography within five weeks of the imaging stress test. As measured against this gold standard, fast cinematic magnetic resonance imaging was 82%sensitive in detecting 70%or greater stenosis in a single coronary artery and 88%sensitive in detecting that degree of stenosis in two vessels. It was 100%accurate in diagnosing left main coronary artery disease as well as occlusion in three vessels. The authors concluded that "MRI can be used to assess contractility continuously during a stress test and to detect inducible ischemia in patients poorly suited for stress echocardiograms."