Imaging

SAN FRANCISCO — Echocardiography provides a great deal of information to help determine a patient's risk following a myocardial infarction, Dr. Thomas Ryan said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

“There are a lot of ways we can [risk stratify patients], but I think our goals should be to do it in the most efficient, the most effective, and the most cost-responsible fashion possible,” said Dr. Ryan of Duke University, Durham, N.C

Echocardiography provides a variety of perspectives on left ventricular function. It allows for a calculation of ejection fraction. Doppler plus the principle of continuity of flow allows for the measurement of stroke volume across both valves, which in turn allows for the calculation of cardiac output. The contour of the mitral regurgitation depth can be used to measure the rate of change in left ventricular pressure (dP/dt). And finally, one can generate a wall-motion score.

Together, the degree of left ventricular dysfunction and the presence and severity of mitral regurgitation are the most powerful predictors of early risk after acute MI. The results of a study of more than 3,000 patients in the Duke database show that an echo score derived from these two factors neatly stratifies patients into three categories.

Patients get no points for a good ejection fraction or good mitral regurgitation. They get 2 points each for poor ejection fraction and poor mitral regurgitation, and they get 1 point each for intermediate values. The echo score is the sum of the ejection fraction and mitral regurgitation scores.

Patients with an echo score of 0 have better than 90% 2-year survival. Those with an echo score of 3 or 4 have about a 50% 2-year survival, and those with a score of 1 or 2 have about a 75% 2-year survival.

Diastolic function has prognostic implications as well. If the deceleration time of the mitral P wave is 115 milliseconds or more, then the 30-month survival is 100%. Those with mitral deceleration times of less than 115 milliseconds have a 30-month survival rate of about 40%.

The combination of these measures means that the physician will get a great deal of information even before resorting to stress echocardiography.

SAN FRANCISCO — Echocardiography provides a great deal of information to help determine a patient's risk following a myocardial infarction, Dr. Thomas Ryan said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

“There are a lot of ways we can [risk stratify patients], but I think our goals should be to do it in the most efficient, the most effective, and the most cost-responsible fashion possible,” said Dr. Ryan of Duke University, Durham, N.C

Echocardiography provides a variety of perspectives on left ventricular function. It allows for a calculation of ejection fraction. Doppler plus the principle of continuity of flow allows for the measurement of stroke volume across both valves, which in turn allows for the calculation of cardiac output. The contour of the mitral regurgitation depth can be used to measure the rate of change in left ventricular pressure (dP/dt). And finally, one can generate a wall-motion score.

Together, the degree of left ventricular dysfunction and the presence and severity of mitral regurgitation are the most powerful predictors of early risk after acute MI. The results of a study of more than 3,000 patients in the Duke database show that an echo score derived from these two factors neatly stratifies patients into three categories.

Patients get no points for a good ejection fraction or good mitral regurgitation. They get 2 points each for poor ejection fraction and poor mitral regurgitation, and they get 1 point each for intermediate values. The echo score is the sum of the ejection fraction and mitral regurgitation scores.

Patients with an echo score of 0 have better than 90% 2-year survival. Those with an echo score of 3 or 4 have about a 50% 2-year survival, and those with a score of 1 or 2 have about a 75% 2-year survival.

Diastolic function has prognostic implications as well. If the deceleration time of the mitral P wave is 115 milliseconds or more, then the 30-month survival is 100%. Those with mitral deceleration times of less than 115 milliseconds have a 30-month survival rate of about 40%.

The combination of these measures means that the physician will get a great deal of information even before resorting to stress echocardiography.

SAN FRANCISCO — Echocardiography provides a great deal of information to help determine a patient's risk following a myocardial infarction, Dr. Thomas Ryan said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

“There are a lot of ways we can [risk stratify patients], but I think our goals should be to do it in the most efficient, the most effective, and the most cost-responsible fashion possible,” said Dr. Ryan of Duke University, Durham, N.C

Echocardiography provides a variety of perspectives on left ventricular function. It allows for a calculation of ejection fraction. Doppler plus the principle of continuity of flow allows for the measurement of stroke volume across both valves, which in turn allows for the calculation of cardiac output. The contour of the mitral regurgitation depth can be used to measure the rate of change in left ventricular pressure (dP/dt). And finally, one can generate a wall-motion score.

Together, the degree of left ventricular dysfunction and the presence and severity of mitral regurgitation are the most powerful predictors of early risk after acute MI. The results of a study of more than 3,000 patients in the Duke database show that an echo score derived from these two factors neatly stratifies patients into three categories.

Patients get no points for a good ejection fraction or good mitral regurgitation. They get 2 points each for poor ejection fraction and poor mitral regurgitation, and they get 1 point each for intermediate values. The echo score is the sum of the ejection fraction and mitral regurgitation scores.

Patients with an echo score of 0 have better than 90% 2-year survival. Those with an echo score of 3 or 4 have about a 50% 2-year survival, and those with a score of 1 or 2 have about a 75% 2-year survival.

Diastolic function has prognostic implications as well. If the deceleration time of the mitral P wave is 115 milliseconds or more, then the 30-month survival is 100%. Those with mitral deceleration times of less than 115 milliseconds have a 30-month survival rate of about 40%.

The combination of these measures means that the physician will get a great deal of information even before resorting to stress echocardiography.

SAN FRANCISCO — Cardiac MRI with late gadolinium enhancement is the imaging technique of choice when the goal is tissue characterization and infarct detection in heart failure, Dr. Christopher M. Kramer said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

Cardiac magnetic resonance (CMR) provides outstanding image quality, excellent quantification, and tissue characterization, said Dr. Kramer of the University of Virginia, in Charlottesville. In addition, Gadolinium contrast is easy to use and safe with CMR and also offers the ability to assess intramural function.

However, CMR devices are not portable, are quite expensive, and are not readily available. Physicians need to have extensive training in the use of CMR and the technique is not suitable for patients with implanted metallic devices such as pacemakers and implantable cardioverter defibrillators. Furthermore, assessment of diastolic function is not routine with CMR.

Echocardiography also has a number of advantages. The devices are portable and relatively inexpensive, and they are readily available. Generations of cardiologists have established its validity and all cardiologists become proficient in the use of echo during their training. Contrast can be added to echocardiography, and the assessment of diastolic function has become routine.

But the technique is subject to variable image quality and poor windows. The results tend to be qualitative, and quantitation can be difficult. Newer 3-D echocardiographic techniques address some of these issues, but such devices are not widely available.

Gadolinium-enhanced CMR is useful in determining if cardiomyopathy is ischemic or nonischemic. Studies have also shown the value of enhanced CMR as a marker in late-stage myocarditis, hypertrophic cardiomyopathy, amyloidosis, sarcoidosis, and Chagas disease.

Dr. Kramer noted that echocardiography is useful in several circumstances, especially for diastolic function and when “quick and easy” is adequate, but CMR is best for regional systolic function, for differential diagnosis and tissue characterization, and when quantitation is needed and 3-D echo is unavailable.

SAN FRANCISCO — Cardiac MRI with late gadolinium enhancement is the imaging technique of choice when the goal is tissue characterization and infarct detection in heart failure, Dr. Christopher M. Kramer said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

Cardiac magnetic resonance (CMR) provides outstanding image quality, excellent quantification, and tissue characterization, said Dr. Kramer of the University of Virginia, in Charlottesville. In addition, Gadolinium contrast is easy to use and safe with CMR and also offers the ability to assess intramural function.

However, CMR devices are not portable, are quite expensive, and are not readily available. Physicians need to have extensive training in the use of CMR and the technique is not suitable for patients with implanted metallic devices such as pacemakers and implantable cardioverter defibrillators. Furthermore, assessment of diastolic function is not routine with CMR.

Echocardiography also has a number of advantages. The devices are portable and relatively inexpensive, and they are readily available. Generations of cardiologists have established its validity and all cardiologists become proficient in the use of echo during their training. Contrast can be added to echocardiography, and the assessment of diastolic function has become routine.

But the technique is subject to variable image quality and poor windows. The results tend to be qualitative, and quantitation can be difficult. Newer 3-D echocardiographic techniques address some of these issues, but such devices are not widely available.

Gadolinium-enhanced CMR is useful in determining if cardiomyopathy is ischemic or nonischemic. Studies have also shown the value of enhanced CMR as a marker in late-stage myocarditis, hypertrophic cardiomyopathy, amyloidosis, sarcoidosis, and Chagas disease.

Dr. Kramer noted that echocardiography is useful in several circumstances, especially for diastolic function and when “quick and easy” is adequate, but CMR is best for regional systolic function, for differential diagnosis and tissue characterization, and when quantitation is needed and 3-D echo is unavailable.

SAN FRANCISCO — Cardiac MRI with late gadolinium enhancement is the imaging technique of choice when the goal is tissue characterization and infarct detection in heart failure, Dr. Christopher M. Kramer said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

Cardiac magnetic resonance (CMR) provides outstanding image quality, excellent quantification, and tissue characterization, said Dr. Kramer of the University of Virginia, in Charlottesville. In addition, Gadolinium contrast is easy to use and safe with CMR and also offers the ability to assess intramural function.

However, CMR devices are not portable, are quite expensive, and are not readily available. Physicians need to have extensive training in the use of CMR and the technique is not suitable for patients with implanted metallic devices such as pacemakers and implantable cardioverter defibrillators. Furthermore, assessment of diastolic function is not routine with CMR.

Echocardiography also has a number of advantages. The devices are portable and relatively inexpensive, and they are readily available. Generations of cardiologists have established its validity and all cardiologists become proficient in the use of echo during their training. Contrast can be added to echocardiography, and the assessment of diastolic function has become routine.

But the technique is subject to variable image quality and poor windows. The results tend to be qualitative, and quantitation can be difficult. Newer 3-D echocardiographic techniques address some of these issues, but such devices are not widely available.

Gadolinium-enhanced CMR is useful in determining if cardiomyopathy is ischemic or nonischemic. Studies have also shown the value of enhanced CMR as a marker in late-stage myocarditis, hypertrophic cardiomyopathy, amyloidosis, sarcoidosis, and Chagas disease.

Dr. Kramer noted that echocardiography is useful in several circumstances, especially for diastolic function and when “quick and easy” is adequate, but CMR is best for regional systolic function, for differential diagnosis and tissue characterization, and when quantitation is needed and 3-D echo is unavailable.

SAN FRANCISCO — Chest pain represents one of the most common presenting symptoms in emergency departments, and it also represents a diagnostic challenge: Is it a pulmonary embolism? Is it an aortic dissection? Is it coronary artery disease? Or is it nothing?

Now, new CT technology promises to revolutionize this diagnosis, giving the ability to rule out all three conditions with a single 15-second scan.

In theory, this scan can replace stress testing for coronary artery disease, echocardiography or CT for aortic dissection, and CT pulmonary angiography or a ventilation-perfusion scan for pulmonary embolism, Matthew J. Budoff, M.D., said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

Although no diagnostic or prognostic studies on the triple rule out have yet been published, there's some indication that the single scan will have 90% accuracy or better for each of the three conditions, said Dr. Budoff of Harbor-UCLA Medical Center in Torrance, Calif.

The technology involves a 64-slice CT scan from the apex to the base of the lungs. Patients will have to hold their breath for 20–30 seconds as contrast is injected and the images are acquired. Acquisition of the slices will be gated to the heart's rhythm, allowing for stable, high-resolution images of the heart and lungs. The slice thickness will be 0.625 mm.

Software and a sophisticated workstation will allow the clinician to construct three-dimensional images of the heart, lungs, or aorta, and to manipulate three-dimensional and two-dimensional images in a variety of ways.

In addition to aortic dissection, pulmonary embolism, and coronary artery disease, the technique will allow clear views of the pericardium, permitting the diagnosis of calcified or thickened pericardium and sometimes pericarditis.

In addition, “you might pick up pneumonia, and you might pick up pulmonary adhesions or even pericardial adhesions,” Dr. Budoff said. “There are a lot of things you could possibly see. And it could be done during the chest pain episode, which is a great advantage over some of the other modalities where you'd want to wait until their chest pain is quiescent.”

Dr. Budoff described the case of an elderly woman who complained of chest pain and shortness of breath. Because of her age, he was reluctant to order a stress test. The CT angiography showed that her coronary arteries were normal and that her ejection fraction was acceptably high. When he examined the lung images closely, however, he discovered several pulmonary emboli.

“We admitted her to the hospital, put her on heparin, and it all cleared up,” he said.

Despite its promise, the triple rule out does have some limitations. For one thing, it subjects patients to a relatively high dose of radiation—in the neighborhood of 24–30 millisieverts, equivalent to 240–300 chest x-rays.

Because it's a gated study, more contrast must be used and the injection time is longer than for a standard CT. Some patients may have trouble holding their breath for 20–30 seconds.

Then there's the issue of who is going to read these images when a patient presents at 3 a.m. The radiologist staffing the emergency department may not be facile with cardiac CT angiography. Although the images could be transferred over data lines, the cardiologist is not likely to have a workstation with the proper software at home. In all likelihood, someone will have to come to the hospital to read the study.

Still, Dr. Budoff expects the triple rule out to become a routine test in the emergency department, a prospect he greets with mixed emotions.

“We really need to see how this is going to pan out, and work out the reading issues before we start applying this to everybody who comes in with a twinge in their chest or shortness of breath,” he said. “I'm a little leery … to say just because we can do it we should.”

Views of aortic dissection: Left, it is shown as a long, thin dissection flap in the descending aorta; right, the true lumen (larger area) and false lumen are shown endoscopically. Photos courtesy Dr. Matthew J. Budoff

SAN FRANCISCO — Chest pain represents one of the most common presenting symptoms in emergency departments, and it also represents a diagnostic challenge: Is it a pulmonary embolism? Is it an aortic dissection? Is it coronary artery disease? Or is it nothing?

Now, new CT technology promises to revolutionize this diagnosis, giving the ability to rule out all three conditions with a single 15-second scan.

In theory, this scan can replace stress testing for coronary artery disease, echocardiography or CT for aortic dissection, and CT pulmonary angiography or a ventilation-perfusion scan for pulmonary embolism, Matthew J. Budoff, M.D., said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

Although no diagnostic or prognostic studies on the triple rule out have yet been published, there's some indication that the single scan will have 90% accuracy or better for each of the three conditions, said Dr. Budoff of Harbor-UCLA Medical Center in Torrance, Calif.

The technology involves a 64-slice CT scan from the apex to the base of the lungs. Patients will have to hold their breath for 20–30 seconds as contrast is injected and the images are acquired. Acquisition of the slices will be gated to the heart's rhythm, allowing for stable, high-resolution images of the heart and lungs. The slice thickness will be 0.625 mm.

Software and a sophisticated workstation will allow the clinician to construct three-dimensional images of the heart, lungs, or aorta, and to manipulate three-dimensional and two-dimensional images in a variety of ways.

In addition to aortic dissection, pulmonary embolism, and coronary artery disease, the technique will allow clear views of the pericardium, permitting the diagnosis of calcified or thickened pericardium and sometimes pericarditis.

In addition, “you might pick up pneumonia, and you might pick up pulmonary adhesions or even pericardial adhesions,” Dr. Budoff said. “There are a lot of things you could possibly see. And it could be done during the chest pain episode, which is a great advantage over some of the other modalities where you'd want to wait until their chest pain is quiescent.”

Dr. Budoff described the case of an elderly woman who complained of chest pain and shortness of breath. Because of her age, he was reluctant to order a stress test. The CT angiography showed that her coronary arteries were normal and that her ejection fraction was acceptably high. When he examined the lung images closely, however, he discovered several pulmonary emboli.

“We admitted her to the hospital, put her on heparin, and it all cleared up,” he said.

Despite its promise, the triple rule out does have some limitations. For one thing, it subjects patients to a relatively high dose of radiation—in the neighborhood of 24–30 millisieverts, equivalent to 240–300 chest x-rays.

Because it's a gated study, more contrast must be used and the injection time is longer than for a standard CT. Some patients may have trouble holding their breath for 20–30 seconds.

Then there's the issue of who is going to read these images when a patient presents at 3 a.m. The radiologist staffing the emergency department may not be facile with cardiac CT angiography. Although the images could be transferred over data lines, the cardiologist is not likely to have a workstation with the proper software at home. In all likelihood, someone will have to come to the hospital to read the study.

Still, Dr. Budoff expects the triple rule out to become a routine test in the emergency department, a prospect he greets with mixed emotions.

“We really need to see how this is going to pan out, and work out the reading issues before we start applying this to everybody who comes in with a twinge in their chest or shortness of breath,” he said. “I'm a little leery … to say just because we can do it we should.”

Views of aortic dissection: Left, it is shown as a long, thin dissection flap in the descending aorta; right, the true lumen (larger area) and false lumen are shown endoscopically. Photos courtesy Dr. Matthew J. Budoff

SAN FRANCISCO — Chest pain represents one of the most common presenting symptoms in emergency departments, and it also represents a diagnostic challenge: Is it a pulmonary embolism? Is it an aortic dissection? Is it coronary artery disease? Or is it nothing?

Now, new CT technology promises to revolutionize this diagnosis, giving the ability to rule out all three conditions with a single 15-second scan.

In theory, this scan can replace stress testing for coronary artery disease, echocardiography or CT for aortic dissection, and CT pulmonary angiography or a ventilation-perfusion scan for pulmonary embolism, Matthew J. Budoff, M.D., said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

Although no diagnostic or prognostic studies on the triple rule out have yet been published, there's some indication that the single scan will have 90% accuracy or better for each of the three conditions, said Dr. Budoff of Harbor-UCLA Medical Center in Torrance, Calif.

The technology involves a 64-slice CT scan from the apex to the base of the lungs. Patients will have to hold their breath for 20–30 seconds as contrast is injected and the images are acquired. Acquisition of the slices will be gated to the heart's rhythm, allowing for stable, high-resolution images of the heart and lungs. The slice thickness will be 0.625 mm.

Software and a sophisticated workstation will allow the clinician to construct three-dimensional images of the heart, lungs, or aorta, and to manipulate three-dimensional and two-dimensional images in a variety of ways.

In addition to aortic dissection, pulmonary embolism, and coronary artery disease, the technique will allow clear views of the pericardium, permitting the diagnosis of calcified or thickened pericardium and sometimes pericarditis.

In addition, “you might pick up pneumonia, and you might pick up pulmonary adhesions or even pericardial adhesions,” Dr. Budoff said. “There are a lot of things you could possibly see. And it could be done during the chest pain episode, which is a great advantage over some of the other modalities where you'd want to wait until their chest pain is quiescent.”

Dr. Budoff described the case of an elderly woman who complained of chest pain and shortness of breath. Because of her age, he was reluctant to order a stress test. The CT angiography showed that her coronary arteries were normal and that her ejection fraction was acceptably high. When he examined the lung images closely, however, he discovered several pulmonary emboli.

“We admitted her to the hospital, put her on heparin, and it all cleared up,” he said.

Despite its promise, the triple rule out does have some limitations. For one thing, it subjects patients to a relatively high dose of radiation—in the neighborhood of 24–30 millisieverts, equivalent to 240–300 chest x-rays.

Because it's a gated study, more contrast must be used and the injection time is longer than for a standard CT. Some patients may have trouble holding their breath for 20–30 seconds.

Then there's the issue of who is going to read these images when a patient presents at 3 a.m. The radiologist staffing the emergency department may not be facile with cardiac CT angiography. Although the images could be transferred over data lines, the cardiologist is not likely to have a workstation with the proper software at home. In all likelihood, someone will have to come to the hospital to read the study.

Still, Dr. Budoff expects the triple rule out to become a routine test in the emergency department, a prospect he greets with mixed emotions.

“We really need to see how this is going to pan out, and work out the reading issues before we start applying this to everybody who comes in with a twinge in their chest or shortness of breath,” he said. “I'm a little leery … to say just because we can do it we should.”

Views of aortic dissection: Left, it is shown as a long, thin dissection flap in the descending aorta; right, the true lumen (larger area) and false lumen are shown endoscopically. Photos courtesy Dr. Matthew J. Budoff

SAN FRANCISCO — Quantitative nuclear cardiology allows for highly sensitive, specific, and reproducible estimates of a patient's risk and assists in the decision of who should be sent for revascularization, Daniel S. Berman, M.D., said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

When quantitative techniques are used with single proton emission computed tomography (SPECT), the results are operator independent, said Dr. Berman of Cedars-Sinai Medical Center, Los Angeles. A quantitative SPECT assessment of myocardial perfusion and function reduces the reliance on expert observers, standardizes results from center to center, facilitates serial assessments, and ultimately improves patient outcomes.

The technology produces reliable assessments of a number of important parameters of cardiac function. (See box.) And numerous studies have shown how these parameters relate to cardiac risk.

For example, pooled data from more than 17,000 patients show that those with a normal stress myocardial perfusion SPECT had only a 0.6% chance of suffering cardiac death or a nonfatal MI over a mean follow-up of 27 months. This low rate of cardiac events is especially impressive because these were patients with known or suspected coronary artery disease.

This study included patients who were under either exercise or pharmacologic stress. According to another study, a normal stress myocardial perfusion SPECT has less prognostic value if the patient fails to reach at least 70% of the predicted maximal heart rate (PMHR) during exercise. Among more than 5,000 patients, the cardiac event rate for patients who failed to reach 70% PMHR was more than three times that of those who reached 70%–100% PMHR.

Patients who are unable to reach 70% PMHR during exercise need to undergo myocardial perfusion SPECT with pharmacologic stress, Dr. Berman said.

The presence of diabetes is another factor that modifies a patient's risk after myocardial perfusion SPECT. For any given summed stress score (SSS)—an estimate of the overall size and severity of a perfusion defect during stress—nondiabetics have the lowest level of risk, insulin-dependent diabetics have the highest level of risk, and non-insulin-dependent diabetics have an intermediate risk.

SSS alone isn't enough, however. The summed difference score, which subtracts the summed rest score from the SSS, is a more reliable measure.

Better still is to normalize these scores based on the maximum possible score. This yields measures of percent myocardium perfused that are independent of the specific SPECT system employed. When applied to the summed difference score, the percent myocardium perfused is a measure of ischemia.

This measure of ischemia is important in deciding whether to refer patients to revascularization or to treat them with medical therapy. On the one hand, studies have shown that patients with extensive ischemia have a much lower risk of cardiac death with revascularization than with medical therapy. On the other hand, patients with less than about 10% ischemia have a lower risk of cardiac death with medical therapy.

Despite its value, cardiac perfusion SPECT does have a number of limitations, Dr. Berman said. Because the test detects only hydrodynamically significant lesions, it won't pick up early atherosclerosis. It also won't pick up some of the patients at the very highest risk, those with a balanced reduction in perfusion. And it may underestimate the extent of ischemia and cardiovascular disease as well as the amount of viable myocardium.

Measurements Possible With Quantitative Cardiac Perfusion SPECT

Percent hypoperfusion

Percent reversibility

Lung-to-heart ratio

Transient ischemic dilatation

Left ventricular mass

Left ventricular ejection fraction

End diastolic volume

End systolic volume

Wall motion

Wall thickening

Peak filling rate

Source: Dr. Berman

SAN FRANCISCO — Quantitative nuclear cardiology allows for highly sensitive, specific, and reproducible estimates of a patient's risk and assists in the decision of who should be sent for revascularization, Daniel S. Berman, M.D., said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

When quantitative techniques are used with single proton emission computed tomography (SPECT), the results are operator independent, said Dr. Berman of Cedars-Sinai Medical Center, Los Angeles. A quantitative SPECT assessment of myocardial perfusion and function reduces the reliance on expert observers, standardizes results from center to center, facilitates serial assessments, and ultimately improves patient outcomes.

The technology produces reliable assessments of a number of important parameters of cardiac function. (See box.) And numerous studies have shown how these parameters relate to cardiac risk.

For example, pooled data from more than 17,000 patients show that those with a normal stress myocardial perfusion SPECT had only a 0.6% chance of suffering cardiac death or a nonfatal MI over a mean follow-up of 27 months. This low rate of cardiac events is especially impressive because these were patients with known or suspected coronary artery disease.

This study included patients who were under either exercise or pharmacologic stress. According to another study, a normal stress myocardial perfusion SPECT has less prognostic value if the patient fails to reach at least 70% of the predicted maximal heart rate (PMHR) during exercise. Among more than 5,000 patients, the cardiac event rate for patients who failed to reach 70% PMHR was more than three times that of those who reached 70%–100% PMHR.

Patients who are unable to reach 70% PMHR during exercise need to undergo myocardial perfusion SPECT with pharmacologic stress, Dr. Berman said.

The presence of diabetes is another factor that modifies a patient's risk after myocardial perfusion SPECT. For any given summed stress score (SSS)—an estimate of the overall size and severity of a perfusion defect during stress—nondiabetics have the lowest level of risk, insulin-dependent diabetics have the highest level of risk, and non-insulin-dependent diabetics have an intermediate risk.

SSS alone isn't enough, however. The summed difference score, which subtracts the summed rest score from the SSS, is a more reliable measure.

Better still is to normalize these scores based on the maximum possible score. This yields measures of percent myocardium perfused that are independent of the specific SPECT system employed. When applied to the summed difference score, the percent myocardium perfused is a measure of ischemia.

This measure of ischemia is important in deciding whether to refer patients to revascularization or to treat them with medical therapy. On the one hand, studies have shown that patients with extensive ischemia have a much lower risk of cardiac death with revascularization than with medical therapy. On the other hand, patients with less than about 10% ischemia have a lower risk of cardiac death with medical therapy.

Despite its value, cardiac perfusion SPECT does have a number of limitations, Dr. Berman said. Because the test detects only hydrodynamically significant lesions, it won't pick up early atherosclerosis. It also won't pick up some of the patients at the very highest risk, those with a balanced reduction in perfusion. And it may underestimate the extent of ischemia and cardiovascular disease as well as the amount of viable myocardium.

Measurements Possible With Quantitative Cardiac Perfusion SPECT

Percent hypoperfusion

Percent reversibility

Lung-to-heart ratio

Transient ischemic dilatation

Left ventricular mass

Left ventricular ejection fraction

End diastolic volume

End systolic volume

Wall motion

Wall thickening

Peak filling rate

Source: Dr. Berman

SAN FRANCISCO — Quantitative nuclear cardiology allows for highly sensitive, specific, and reproducible estimates of a patient's risk and assists in the decision of who should be sent for revascularization, Daniel S. Berman, M.D., said at a cardiovascular imaging conference sponsored by the American College of Cardiology.

When quantitative techniques are used with single proton emission computed tomography (SPECT), the results are operator independent, said Dr. Berman of Cedars-Sinai Medical Center, Los Angeles. A quantitative SPECT assessment of myocardial perfusion and function reduces the reliance on expert observers, standardizes results from center to center, facilitates serial assessments, and ultimately improves patient outcomes.

The technology produces reliable assessments of a number of important parameters of cardiac function. (See box.) And numerous studies have shown how these parameters relate to cardiac risk.

For example, pooled data from more than 17,000 patients show that those with a normal stress myocardial perfusion SPECT had only a 0.6% chance of suffering cardiac death or a nonfatal MI over a mean follow-up of 27 months. This low rate of cardiac events is especially impressive because these were patients with known or suspected coronary artery disease.

This study included patients who were under either exercise or pharmacologic stress. According to another study, a normal stress myocardial perfusion SPECT has less prognostic value if the patient fails to reach at least 70% of the predicted maximal heart rate (PMHR) during exercise. Among more than 5,000 patients, the cardiac event rate for patients who failed to reach 70% PMHR was more than three times that of those who reached 70%–100% PMHR.

Patients who are unable to reach 70% PMHR during exercise need to undergo myocardial perfusion SPECT with pharmacologic stress, Dr. Berman said.

The presence of diabetes is another factor that modifies a patient's risk after myocardial perfusion SPECT. For any given summed stress score (SSS)—an estimate of the overall size and severity of a perfusion defect during stress—nondiabetics have the lowest level of risk, insulin-dependent diabetics have the highest level of risk, and non-insulin-dependent diabetics have an intermediate risk.

SSS alone isn't enough, however. The summed difference score, which subtracts the summed rest score from the SSS, is a more reliable measure.

Better still is to normalize these scores based on the maximum possible score. This yields measures of percent myocardium perfused that are independent of the specific SPECT system employed. When applied to the summed difference score, the percent myocardium perfused is a measure of ischemia.

This measure of ischemia is important in deciding whether to refer patients to revascularization or to treat them with medical therapy. On the one hand, studies have shown that patients with extensive ischemia have a much lower risk of cardiac death with revascularization than with medical therapy. On the other hand, patients with less than about 10% ischemia have a lower risk of cardiac death with medical therapy.

Despite its value, cardiac perfusion SPECT does have a number of limitations, Dr. Berman said. Because the test detects only hydrodynamically significant lesions, it won't pick up early atherosclerosis. It also won't pick up some of the patients at the very highest risk, those with a balanced reduction in perfusion. And it may underestimate the extent of ischemia and cardiovascular disease as well as the amount of viable myocardium.

Measurements Possible With Quantitative Cardiac Perfusion SPECT

Percent hypoperfusion

Percent reversibility

Lung-to-heart ratio

Transient ischemic dilatation

Left ventricular mass

Left ventricular ejection fraction

End diastolic volume

End systolic volume

Wall motion

Wall thickening

Peak filling rate

Source: Dr. Berman

KEVIN FOLEY, RESEARCH

KEVIN FOLEY, RESEARCH

KEVIN FOLEY, RESEARCH