The future of nuclear cardiac imaging: Reflection and a vision

My editor’s page will be excerpts from my plenary lecture given at the International Conference on Nuclear Cardiology and Cardiac CT, Vienna, Austria, on May 7, 2017.

It was indeed a pleasure and an honor to address the audience of this meeting, which has a track record of > 20 years bringing people from around the world to learn and share knowledge.

The predictions are that in the United States by 2035, > 123 million will have hypertension; > 24 million will have coronary artery disease (CAD); > 11 million will have had a stroke; > 9 million will have heart failure; and > 7 million will have atrial fibrillation. That adds to a projected increase in heart disease costs are to double from $555 billion in 2016 to $1.1 trillion in 2035! One would predict similar increases in both developed and developing countries although Sweden recently reported considerable declines in death from any cause, death from cardiovascular disease, death from coronary heart disease, and hospitalization for cardiovascular disease between 1998 and 2014 in both general population and in those with diabetes mellitus.1 This change and other changes (Table 1) imply that imaging in general, and nuclear imaging especially will continue to be a popular imaging modality for sometimes to come.

Table 1 Nuclear imaging in the future

It is very likely that positron emission tomography (PET) use and measurement of myocardial blood flow (MBF) will increase. A recent study may shed some light, women though having less severe CAD by coronary angiography than men, had worse outcome especially those with reduced coronary flow reserve ratio (ratio of hyperemic to rest MBF) measured by PET.2 Historically, the prominent physician from University of Paris wrote in 1902 “Another point to remember is that angina pectoris is, like gout, a disease of men, and not women. When it does manifest itself in females, as is occasionally the case, it is often so confused with the common and frequent pains in the left side, due to flatulence or other causes, to which that sex is especially prone, that its recognition may be a matter of some difficulty.” His views were probably shared until very recently by many physicians!

Though MBF use will increase (Figure 1), it does not mean that all problems have been solved such variability in measurements. Kitkungvan et al reported test-retest methodological precision of global PET myocardial perfusion by serial rest performed within minutes apart is ± 10% while the day-to-different-day biological plus methodological variability was ± 21%. Further, the global myocardial perfusion at 8 minutes after 4 minutes dipyridamole infusion was 10% higher than at standard 4 minutes after dipyridamole.3 The editorial by Beanlands concluded “… ultimately the value of flow quantification must be shown in multicenter clinical trials.”4 Dilsizian et al concluded “…trust the quantitative analysis but verify it by visual analysis.”5 Clearly more studies are needed to address the variability and impact of using different hardware, software, stress agent, and protocol.

Figure 1

The common PET tracers for clinical applications

In additions to the tracers in Figure 1 and other tracers to study cardiac metabolism and innervation, there are a host of newer tracers; a partial list is provided in Table 2 and many of these are presented in this meeting. What is encouraging in the new list is that these tracers will expand the use of nuclear imaging in other cardiac conditions such as acute coronary syndromes, myocarditis, chemotherapy-related cardiotoxicity, and valvular heart diseases.

Table 2 Partial list of new tracers and applications

As we move forwards, it is equally important to remain grounded and acknowledge the achievements and shortcoming of past performances. Table 3 provides a partial list of Noble laureates (courtesy of H William Strauss, MD) and their contributions. On the downside, Table 4 provides a partial list of products we studied but faded away!

Table 3 A partial list of Nobel Laureates in physics and chemistry who contributed to nuclear medicine (courtesy of H William Strauss, MD). The number between parenthesis is the year the Award was received

Table 4 A partial list of products that were tested but were not long-lasting

It is likely that future research will be more complex and demanding as it will require comparative cost-effectiveness and hence involvement of broader presentation of share-holders. Boden and Meadows concluded “The need for updated models of risk in this era of low event rates; a broader understanding of CAD beyond the prevailing paradigm of obstructive epicardial CAD; inclusion of novel, patient-centered and efficiency outcomes; and the need for evidence of optimal post-test treatment. Given the inherent variability in patient phenotypes and clinical presentations, there is a compelling need to translate group data derived from randomized clinical trials to individual patient management, such as distinguishing between modifiable and non-modifiable risk factors, accounting for competing comorbidities, and better defining patient-centered measures.”7

The ACC/AHA and ESC guidelines and appropriateness use criteria deserve are slowly but surely changing to reflect recent evidence-based findings.8,9,10,11,12,13 Stirrup et al summarized the similarities and differences between the 2 with regard to the utilization of imaging.14 There were two editorials in response to this report.15 ^, 16 Excerpts from the report by Christian are shown in Table 5.

Table 5 ACC/AHA and ESC guidelines for myocardial revascularization in stable patients

Finally, my reflections and conclusions as to the future are summarized in Table 6.

Table 6 Reflections and conclusions

In summary, the anticipated increase in number of patients with ischemic heart disease in the future, the expanded role of nuclear imaging in non-ischemic heart diseases, the use of PET imaging and MBF, and the availability of newer tracers, hardware and software are only few of the reasons to be optimistic about the future of nuclear cardiac imaging. Lessons learned from the past experiences and newer guidelines and position papers and statements are important. It is likely that future studies are going to be more complex and demanding and require broad participation of broader spectrum of shareholders as well as across Atlantic co-operation.

Ami E. Iskandrian, MD, MASNC

Editor-in-Chief