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ACC 2005 ANNUAL SESSION HIGHLIGHT

Noninvasive Imaging

Mayo Clinic College of Medicine, Cardiovascular Disease and Internal Medicine, Mayo Clinic, Rochester, Minnesota

^_* Reprint requests and correspondence: Dr. Bijoy K. Khandheria, Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905. (Email: Khandheria{at}mayo.edu).

	Cardiac magnetic resonance imaging (MRI)

Top Cardiac magnetic resonance... Computed tomography (CT) Positron emission tomography... Radionuclide perfusion imaging Echocardiography References

 
Ischemic heart disease.   Gadoversetamide-enhanced MRI is highly effective in the diagnosis and assessment of myocardial infarction (MI) independent of infarct age. This was the conclusion based on a study of 514 patients in 22 centers spread across the globe (1).

In a study of 100 patients with prior MI, extent of the infarct as determined by cardiac magnetic resonance (CMR) was found to be an independent predictor of death (2).

Right ventricular (RV) involvement in acute inferior wall MI is difficult to diagnose with conventional techniques. However, clinically detected right ventricular infarction has been shown to be associated with worse prognosis. In a study of 45 consecutive patients with first time MI, CMR detected this condition five times more often than was clinically suspected (3).

Left ventricular (LV) dysfunction.   The role of CMR in predicting functional recovery of nonischemic LV systolic dysfunction was studied in 37 patients with nonischemic LV dysfunction. Delayed hyperenhancement, assessed by CMR, is associated with functional recovery in nonischemic LV systolic dysfunction (4).

	Computed tomography (CT)

Top Cardiac magnetic resonance... Computed tomography (CT) Positron emission tomography... Radionuclide perfusion imaging Echocardiography References

 
The theme for this modality was that "multislice" CT is gaining ground. In a study of 30 patients with stable angina pectoris or acute coronary syndrome, 64-slice multi-detector computed tomography (MDCT) reliably detected significant coronary stenoses (sensitivity 96%, specificity 89%) (5). A limitation of MDCT includes extent of calcification; this was demonstrated in a study of 53 patients wherein the specificity of detecting lesions in severely calcified segments was only 30% (6).

The results of a meta-analysis from a total of 50 studies indicate that MDCT currently has a substantial advantage over MRI. Thus, MDCT may be considered the technique of choice to evaluate coronary artery anatomy noninvasively (7).

In a general, unselected population in Europe, coronary artery calcium (CAC) scores were lower than in most previous reports, which included volunteers and subjects referred by their physicians. Classification of the CAC score with reference to the previous referral cohorts would underestimate true risk when compared with our data in a truly unselected population with no history of coronary artery disease (CAD). This was the conclusion from the Heinz Nixdorf Recall Cohort wherein 4,472 subjects with no history of CAD were studied (8).

The distribution of CAC scores in the unselected general population is not well defined, and the influence of cardiovascular medication use has never been reported. The Heinz Nixdorf Recall study is a population-based study that recruited a total of 4,814 unselected participants age 45 to 74 years in the German Ruhr area. Medication use was meticulously recorded, allowing delineating CAC scores in subjects with no cardiovascular medication. In subjects with no cardiovascular medication, there appeared to be a time-lag of up to five years before the same levels of CAC developed, as in the entire group. These lower values may be used as a reference for "truly healthy" individuals (9).

Is it safe to conduct MDCT coronary angiograms? How much radiation exposure exists with this technique compared to conventional angiography? This was answered in a study of 94 patients undergoing both 16-slice MDCT and conventional coronary angiography.

The mean effective dose for MDCT coronary angiography was significantly higher than that for conventional angiography. Calcium scoring alone is a relatively low-dose technique, particularly if electrocardiographic-controlled tube current modulation is used (10).

Abdominal aortic plaque by MRI and CAC are two methods for detection of atherosclerosis. The abdominal aortic plaque was compared to CAC in 2,514 Dallas Heart Study participants. In this study cohort, abdominal aortic plaque is present in younger women and may be a better detector of atherosclerosis than CAC in this population. A fatal blow to coronary calcium? No, but something to ponder as future atherosclerosis detection techniques are being contemplated (11).

	Positron emission tomography (PET)

Top Cardiac magnetic resonance... Computed tomography (CT) Positron emission tomography... Radionuclide perfusion imaging Echocardiography References

 
Results from 246 consecutive patients with ischemic LV dysfunction who underwent a PET study demonstrated a strong association between myocardial viability on PET testing and improved survival after revascularization in patients. Viable tissue seems to represent a risk factor, as lack of revascularization is associated with increased mortality. Absence of viability is associated with no significant difference in outcomes, irrespective of treatment strategy (12).

Patients with systolic heart failure pose a unique clinical challenge when it comes to strategies involving revascularization. Early intervention was associated with improved survival independent of the degree of viability based on a study of 765 patients with an ejection fraction (EF) 35% or less (13).

It is recognized that, not only do cardiologists need to be using cutting-edge diagnostic techniques to help improve outcomes of their patients, but also be prudent to the cost of the procedure and use procedures that have a proven cost-benefit ratio. The PET scan is an expensive technique, and the impact of this technique on downstream utilization of angiograms and coronary revascularization procedures was studied in 2,159 patients. Coronary artery disease management with PET results in over 50% reduction in angiograms and coronary artery bypass grafting, over 25% reduction in cost, and excellent one-year outcomes (14).

	Radionuclide perfusion imaging

Top Cardiac magnetic resonance... Computed tomography (CT) Positron emission tomography... Radionuclide perfusion imaging Echocardiography References

 
The ACC/American Heart Association (AHA) guidelines recommend the exercise tolerance test in women with intermediate or high pretest probability for CAD. In a study of 1,020 women with intermediate or high pretest likelihood of coronary artery disease followed for 2.38 ± 1.49 years, single-photon emission computed tomography (SPECT) myocardial perfusion imaging reclassified women with a moderate or high Duke Treadmill Score and more accurately identified those at risk for adverse events (15). Similar conclusions were derived when studying women of Asian origin (16).

The information and knowledge we have gained from these studies lead to a call for using SPECT myocardial perfusion studies as the test for women regardless of the ethnic origin.

Metabolic syndrome represents a constellation of risk factors resulting from insulin resistance, dyslipidemia, hypertension, and obesity. Individuals who are affected are at high risk for adverse events from CAD. Using a multicenter prospective registry of 7,849 patients, a relationship was shown between the metabolic syndrome and risk stratification with stress Tc-99m tetrofosmin SPECT. Patients with all five risk factors for the metabolic syndrome were at highest risk, with relative risk ratios from 7.8- to 14.1-fold for a mild to severely abnormal SPECT. For patients with the metabolic syndrome, the presence of stress perfusion abnormalities is a harbinger for near-term major cardiovascular events (17).

The most appropriate test to detect silent myocardial ischemia in diabetic patients unable to perform an exercise test is unknown, as is the long-term outcome after therapy of ischemia. In a study comparing SPECT to dobutamine echocardiography in 100 patients, ischemia was detected with higher frequency by SPECT, leading to the conclusion that SPECT imaging may be better suited for detection of silent ischemia in patients with diabetes mellitus (18). More studies need to be performed to validate this finding.

	Echocardiography

Top Cardiac magnetic resonance... Computed tomography (CT) Positron emission tomography... Radionuclide perfusion imaging Echocardiography References

 
Highlights from numerous presentations on the use of echocardiography lead one to conclude that this technique is becoming a commodity. Ubiquitous use is clearly the direction that was evident from the large number of presentations not only in the noninvasive imaging section but throughout the program—be it in novel percutaneous procedures such as valve implantation or in established procedures such as cardiac resynchronization therapy (CRT). However, this is far from the reality given the plethora of new and exciting advances being made in the field of echocardiography.

Doppler myocardial imaging (DMI).   Assessment of LV dyssynchrony to predict response to CRT is complex and time-consuming. However it has been shown that dyssynchrony is better detected by DMI. In an effort to simplify this technique, a new dyssynchrony index was defined as the time difference from earliest to latest peak strain, and was compared to the six-site standard deviation (Yu Index) previously shown to predict response to CRT in humans. This study was conducted in 10 open-chest dogs, and the new index was found to correlate strongly with the multisite index (19). However, this index remains to be tested in human beings.

Doppler myocardial imaging can be used to predict hemodynamic improvement early after CRT; this was the conclusion based on a study of 100 consecutive patients (20). However, not all questions regarding DMI and dyssynchrony have been clarified.

Although various dyssynchrony parameters derived by DMI are proposed in patients with left bundle branch block (LBBB) and impaired EF, those in normal EF subjects have not been clarified. In a prospective study of 33 patients (14 with normal EF and QRS duration, 10 with normal EF and LBBB, 9 with depressed EF and LBBB), multiple measures of dyssynchrony by DMI were studied. The investigators conclude that even in populations with normal EF without conduction delay, there is considerable variability in the time-to-peak systolic velocity. The message from this study is that further clinical investigations are necessary to identify the most optimal dyssynchrony parameter (21). The final chapter on which parameters to use in the echocardiographic evaluation of dyssynchrony has not yet been written.

Three-dimensional (3D) echocardiography.   Evolution of this exciting new modality was evident in the large number of presentations dealing with real-time 3D echocardiography.

The value of 3D echocardiography for evaluating left atrial size and function was demonstrated in 46 normal subjects undergoing both this procedure and CMR (22). Normal values for end-systolic and diastolic volumes were established, and they compared favorably with CMR (23).

The value of being able to predict reverse LV remodeling is important in patients undergoing CRT. Real-time 3D echocardiography was found to be a useful tool in predicting this. Reverse remodeling was defined as a reduction in LV end-diastolic volume of 20% or more compared to baseline (24). The utility of 3D echocardiography in elucidating the mitral annulus—both in normal individuals and in those with functional mitral regurgitation—was demonstrated. The corrected mitral valve tenting area appears to be the strongest geometric measure determining the severity of mitral regurgitation (25,26).

Finally, the presence of noninvasive imaging at the ACC 2005 Scientific Sessions was very obvious regardless of the track one attended. Noninvasive imaging has become the mainstay of the diagnostic techniques used in the practice of cardiology.

	References

Top Cardiac magnetic resonance... Computed tomography (CT) Positron emission tomography... Radionuclide perfusion imaging Echocardiography References

 

1. Kim RJ, Albert TSE, Wible Jr. JH, et al. Efficacy of gadoversetamide-enhanced MRI for the diagnosis and assessment of myocardial infarctionan international, multicenter, double-masked, randomized, phase 2 trial. (abstr) J Am Coll Cardiol 2005;45(Suppl A):287A-288A.
2. Bello D, Kaushal R, Fieno D, et al. Cardiac MRIinfarct size is an independent predictor of mortality in patients with coronary artery disease. (abstr) J Am Coll Cardiol 2005;45(Suppl A):288A.
3. Paterson DI, Natanzon A, Pessahna B, Arai AE. Detection of right ventricular infarction by cardiac magnetic resonance imaging(abstr) J Am Coll Cardiol 2005;45(Suppl A):288A.
4. Park S, Rim S-J, Cho BW, et al. Delayed hyperenhancement magnetic resonance imaging is useful in predicting functional recovery of nonischemic LV systolic dysfunction(abstr) J Am Coll Cardiol 2005;45(Suppl A):275A.
5. Mollet NR, Cademartiri F, van Mieghem C, et al. Non-invasive 64-slice multi-detector CT coronary angiography of the entire coronary tree in patients with stable angina pectoris or an acute coronary syndrome(abstr) J Am Coll Cardiol 2005;45(Suppl A):267A.
6. Ishiki R, Iwase M, Kurebayashi N, et al. The extent of calcification may lead to overdiagnosis of coronary artery stenoses in multidetector spiral computed tomography(abstr) J Am Coll Cardiol 2005;45(Suppl A):266A.
7. Schuijf JD, Bax JJ, Shaw LJ, et al. Meta-analysis of comparative diagnostic performance of magnetic resonance imaging and multi-slice computed tomography for non-invasive coronary angiography(abstr) J Am Coll Cardiol 2005;45(Suppl A):9A.[CrossRef]
8. Schmermund A, Mohlenkamp S, Berenbein S, et al. Heinz Nixdorf Recall Study Investigative Group Underestimation of coronary risk by measuring subclinical coronary atherosclerosis in referral cohortsevidence from the large unselected Heinz Nixdorf Recall Cohort. (abstr) J Am Coll Cardiol 2005;45(Suppl A):311A.
9. Schmermund A, Mohlenkamp S, Berenbein S, et al. Heinz Nixdorf Recall Study Investigative Group Corrected "normal values" for subclinical coronary atherosclerosis in truly healthy subjects with no use of cardiovascular medication in a large population-based surveyHeinz Nixdorf Recall Study. (abstr) J Am Coll Cardiol 2005;45(Suppl A):258A.
10. Coles DR, Smail M, Negus I, et al. Effective dose from multislice CT calcium scoring and coronary angiography compared with conventional diagnostic coronary angiography(abstr) J Am Coll Cardiol 2005;45(Suppl A):267A.
11. Lo HS, McColl R, Stanek G, et al. Abdominal aortic plaque by magnetic resonance imaging is seen more frequently than coronary artery calcium in young women in the Dallas Heart Study(abstr) J Am Coll Cardiol 2005;45(Suppl A):287A.
12. Pollack C, Hellermann JP, Namdar M, et al. Impact of myocardial viability testing with pet and revascularization on long-term prognosis in patients with ischemic left ventricular dysfunction(abstr) J Am Coll Cardiol 2005;45(Suppl A):162A-163A.
13. Tarakji K, Brunken R, McCarthy P, et al. Prognostic value of myocardial viability and the impact of early surgical or percutaneous intervention in patients with severe left ventricular systolic dysfunction(abstr) J Am Coll Cardiol 2005;45(Suppl A):163A.
14. Merhige M, Oliverio J, Shelton V, et al. Impact of pharmacologic stress/rest myocardial perfusion imaging with positron emission tomography and rubidium-82 on invasive procedure utilization, cost, and outcomes in coronary disease management(abstr) J Am Coll Cardiol 2005;45(Suppl A):310A.
15. Lundbye JB, Kazi FA, Werden S, et al. Myocardial perfusion imaging risk stratifies women with intermediate or high Duke treadmill score(abstr) J Am Coll Cardiol 2005;45(Suppl A):278A.
16. Wong RC, Ho KT. Normal Tc-tetrofosmin myocardial perfusion SPECT studies in Asian women predict good cardiac outcome(abstr) J Am Coll Cardiol 2005;45(Suppl A):278A.
17. Shaw LJ, Hendel R, Alazraki N, et al. The prognostic value of stress SPECT Tc 99m tetrofosmin imaging in patients with the metabolic syndromeresults from the Multicenter Myoview Registry. (abstr) J Am Coll Cardiol 2005;45(Suppl A):14A-15A.
18. Le Feuvre C, Barthelemy O, Dubois D, et al. Stress myocardial scintigraphy and dobutamine echocardiography in the detection of coronary disease in asymptomatic patients with type 2 diabetes(abstr) J Am Coll Cardiol 2005;45(Suppl A):212A.
19. Dohi K, Pinsky MR, Suffoletto MS, Severyn DA, Gorcsan III J. A new rapid and simple index of mechanical dyssynchrony by color-coded strain dyssynchrony imaging(abstr) J Am Coll Cardiol 2005;45(Suppl A):289A.
20. Taub CC, Fan D, Singh J, Mela T, Picard MH. Acute synchrony changes during cardiac resynchronization therapy predicts acute hemodynamic response(abstr) J Am Coll Cardiol 2005;45(Suppl A):287A.
21. Miyazaki C, Miller FA, Karon BL, et al. Measurement of intraventricular mechanical dyssynchrony by tissue Doppler imagingis time to peak velocity the best parameter for dyssynchrony?. (abstr) J Am Coll Cardiol 2005;45(Suppl A):1A-2A.[Medline]
22. Mathew ST, Gopal AS, Toole RS, Schapiro W, Reichek N. Real-time three-dimensional echocardiographya new method for assessing left atrial size and function. (abstr) J Am Coll Cardiol 2005;45(Suppl A):282A.
23. Mathew ST, Gopal AS, Krishnaswamy RR, Toole RS, Schapiro W, Reichek N. Partition values for normal left and right ventricular volumes by three-dimensional echocardiography(abstr) J Am Coll Cardiol 2005;45(Suppl A):307A-308A.
24. Kapetanakis S, Kearney M, Gall N, Murgatroyd F, Monaghan MJ. Can quantification of left ventricular mechanical dyssynchrony by real-time 3D echo predict reverse left ventricular remodeling following cardiac resynchronization therapy?(abstr) J Am Coll Cardiol 2005;45(Suppl A):308A.
25. Park SM, Chai J, Jeon MJ, et al. 3D geometry of mitral annulus in mitral valve prolapse in comparison with normalreal-time 3D echocardiography study. (abstr) J Am Coll Cardiol 2005;45(Suppl A):281A.
26. Kwan J, Park SM, Jeon MJ, et al. Geometry of mitral apparatus in functional mitral regurgitationreal-time 3D echocardiography study. (abstr) J Am Coll Cardiol 2005;45(Suppl A):281A.

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