By Michael Crawford, MD, Editor
SOURCES: Gaibazzi N, et al. Prognostic value of echocardiographic calcium score in patients with a clinical indication for stress echocardiography. JACC Cardiovasc Imaging 2015;8:389-396.
Gardin JM. Can calcium supplementation improve stress echocardiography? JACC Cardiovasc Imaging 2015;8:397-939.
Aortic valve sclerosis and mitral annular calcification detected by echocardiography are known to be associated with atherosclerosis and are predictive of cardiovascular (CV) morbidity and mortality. These investigators from Italy hypothesized that an echo calcium score (eCS) could predict CV events in subjects without known coronary artery disease (CAD). They retrospectively selected 1303 subjects from five European and one U.S. institution without known CAD, significant valvular disease, or chronic kidney disease, who had stress echoes done by either pharmacologic stress (60%) or exercise stress for clinical reasons (40%). Transthoracic echoes were evaluated for evidence of calcium in the aortic valve, mitral annulus, ascending aorta, and papillary muscles, which was scored as a range from 0 to 8. Outcomes were determined by chart review or patient or primary physician phone calls. Mean subject age was 63 years, and 57% were men. Scores of 0 were present in 58%, and 98% of the subjects had scores between 0 and 4. Positive stress tests were found in 12%, and they were more likely to have an eCS > 0 (P < 0.001). During the median follow-up of 27 months, 58 patients experienced the primary endpoint of death (n = 37) or myocardial infarction (n = 21). In addition to age and diabetes, eCS and a positive stress echo were multivariate predictors of the combined endpoint, but only stress echo demonstrated incremental discrimination over clinical variables. Subjects with eCS > 0 and a positive stress echo had the worst prognosis with a 3-year event rate of 24% vs 2% in those with no calcium and a negative stress test (P < 0.001). The authors concluded that eCS has significant independent prognostic value for predicting CV events.
The detection of coronary artery calcium by CT scan has been known to have considerable predictive and prognostic value for CAD. The detection of cardiac and vascular calcification by echocardiography has also been shown to be associated with atherosclerosis. So the concept that cardiac and proximal aortic calcium detected on echo may be of value in the evaluation of patients suspected of having CAD is an interesting idea that was tested in this study. Unlike CT scans, echo does not expose the patient to radiation and costs much less. Also, if a stress echo has been deemed clinically indicated, one can more or less evaluate calcium in the heart and aorta for little or no incremental cost. This study demonstrated that eCS does have independent predictive value for death and myocardial infarction at any level of calcium detected. The sensitivity and specificity of eCS for these hard events was 74% and 60%, respectively. However, as the authors stated, eCS “failed to demonstrate incremental value on top of clinical and stress wall motion data.” Consequently, it is difficult to know how to use this information clinically from this study.
The strengths of this study are that the reproducibility of the eCS was good (correlation coefficient 0.80) and any calcium detected was equally good, a predictor compared to no calcium, so there is no need to calculate a score. Unfortunately, there are important weaknesses in this study. The study population is biased toward subjects with suspected CAD undergoing clinically indicated stress testing. However, few had a positive stress test (12%), and few had eCS scores > 3 out of 8, so many were lower risk. Also, it is not clear if the patients at each of the six centers were similar, especially since many centers used pharmacologic stress echo, which is rarely used in the United States. In addition, the distinction between calcium and fibrosis on echo is not always accurate. Finally, in this retrospective study, the blinding of the stress results from the eCS value would be difficult to do.
Despite these caveats and limitations, I believe this study demonstrates that there is some value to making a note of what appears to be calcium on an echocardiogram, as it is probably evidence of an atherosclerotic process. The echo images in this paper are shown side by side with CT images, and there is remarkable similarity. Of course, these are undoubtedly the best images they have. Nevertheless, although not a game changer, calcium in the heart and aorta on echo is worth adding to the evidence for vascular disease in a patient.