Echocardiography

The management of patients with severe mitral regurgitation due to myxomatous degeneration of the valve, particularly if asymptomatic, remains vexing. Naji and colleagues¹ reported on exercise echocardiographic and clinical data in almost 900 patients with myxomatous mitral regurgitation, the majority of whom were asymptomatic. Patients were followed for a composite outcome for an average of over 6 years. Significant predictors of adverse outcomes included percent of age-/sex-predicted metabolic equivalents, heart rate recovery, resting right ventricular systolic pressure, atrial fibrillation, and LV ejection fraction. The importance of this paper lies not only in the large population with long-term follow-up, but also with the incorporation of exercise parameters into the usual clinical data, which had not been done before in such a large population. In the absence of randomized trials addressing timing of mitral valve surgery for asymptomatic severe mitral regurgitation, which are unlikely to be performed, this type of observational data set will inform guidelines and practice patterns.

Nuclear Cardiology

Almost 10 years ago, the American College of Cardiology published the first of a series of papers on the appropriate use of medical testing, originally called “Appropriateness Criteria,” now referred to as “Appropriate Use Criteria” (AUC). The goal of these recommendations is to optimize the efficiency and value of cardiac testing, based as much as possible on the published literature but also incorporating critical expert opinion. Recommendations are grouped by common clinical indications, and are categorized as “appropriate,” “may be appropriate” (formerly “uncertain”), or “rarely appropriate” (formerly “inappropriate”). Studies categorized as rarely appropriate are generally thought to be low-yield, in low-risk populations as an example. While AUC documents have been published for all common cardiac imaging tests and also for disease states such as stable ischemic heart disease or heart failure, there exists almost no literature validating the AUC categories in a prospective way against clinical outcomes. In this important paper, Doukky and colleagues² report on over 1500 outpatients who were clinically referred for SPECT myocardial perfusion imaging. The studies were classified based on the 2009 AUC for SPECT myocardial perfusion imaging into two categories as appropriate/uncertain or as inappropriate. Patients were followed for an average of over 2 years for adverse events. Among the studies categorized as being of appropriate/uncertain indication, the SPECT results showed the usual prognostic value, in that an abnormal study was associated with a higher risk for adverse events compared with a normal study. However, among the SPECT studies characterized as inappropriate, there was not demonstrable prognostic association. To some degree, this was a result of the very low event rate among those with inappropriate studies, in turn related to the very low prevalence of abnormal studies. Nonetheless, these data are the first to examine the AUC recommendations in terms of association with outcomes, and validate the recommendations of the AUC documents. The importance of this paper lies in the fact that, within the next few years, payors including CMS will be mandating incorporation of AUC into the stream of test-ordering behavior. Having well-validated criteria is a critical element in the widespread acceptance of this approach.

Cardiac MR Imaging

Several relatively small studies have suggested that the presence and/or extent of late gadolinium hyperenhancement (LGE) on CMR imaging in patients with hypertrophic cardiomyopathy is associated with the risk for adverse events or with markers of adverse events. In this largest study to date,³ the authors assembled almost 1300 patients with hypertrophic cardiomyopathy from several centers around the world who had CMR imaging and were followed for a median of over 3 years. There was a significant association between the extent of LGE and risk for sudden death events. Among patients without established risk factors for sudden death, the extent of LGE was associated with sudden death risk, and, among those without LGE, risk was very low. The importance of this data set is that it more clearly establishes the role of CMR imaging in the prediction of sudden death risk in patients with hypertrophic cardiomyopathy. For those in whom the ICD decision may be uncertain on the basis of the usual clinical risk factors, the presence or absence of a certain mass of LGE on CMR imaging can tip the scales one way or the other on that critical decision point. For patients without any of the established risk factors, the presence and extent of LGE may drive consideration for an ICD that might not otherwise have been entertained. This study population is much larger with longer follow-up than all previous studies, allowing much more statistical power in analysis.

Cardiac CT Imaging

The technology of cardiac CT angiography has evolved substantially over the last decade, and, while the focus of much of the literature has been to recapitulate and expand the application of this modality in the same way as invasive angiography has been done, more recently, increasing attention has been on the evaluation of “non-obstructive” coronary artery disease (CAD). This can be imaged more routinely with contemporary CT techniques. In this paper, Bittencourt and colleagues⁴ report on over 3000 patients who had CT angiography whose scans were evaluated for the presence and extent of obstructive as well as non-obstructive CAD, and who were followed for a median of over 3 years for the occurrence of cardiovascular death or nonfatal myocardial infarction. The expected relation of obstructive CAD to events was seen, but, of great interest, those patients with extensive non-obstructive CAD had a risk for events that was similar to that in patents with less extensive obstructive CAD. Non-obstructive plaque extent added incremental information to risk stratification. These data are important for advancing the possibility of incorporating information on extent of imaged plaque into risk assessments, which may, in the future, help guide treatment decisions, or decisions regarding intensity of risk-factor management.

Conclusions

While the mature imaging modalities of echocardiography and nuclear cardiology have long had published data sets involving thousands of patients with sophisticated statistical analyses, the studies cited above suggest that the more recently evolved modalities of cardiac MR and cardiac CT have also reached a similar point regarding the rigor of prognostic data sets and publications. As always, finer gradations of risk assessment and stratification do not necessarily translate into enhanced management for patients, and must be tested separately and not simply be assumed.