AIM: Noninvasive CV imaging doesn't help with primary prevention
Noninvasive cardiovascular (CV) imaging showed no benefit of improving primary prevention measures for patients; however, the authors wrote that future studies will be necessary to provide hard evidence on how these imaging tests impact prevention efforts, according to a meta-analysis published June 13 in the Archives of Internal Medicine.

“The past 30 years have seen substantial improvements in the treatment of most major forms of cardiovascular disease. Despite this, significant gaps in the application of proven treatments remain; these include deficiencies in the use of evidence-based therapies and failure to provide and follow up on recommendations relating to diet, physical activity, and smoking cessation,” wrote Daniel G. Hackman, MD, PhD, of the University of Western Ontario in London, Ontario, and colleagues.

Noninvasive cardiovascular imaging may help improve primary prevention measures by improving lifestyle modification and use of evidence-based therapies. To study the influence noninvasive CV imaging has on practice, Hackman et al conducted a meta-analysis of seven randomized trials that compared imaging with standard care and reported the following outcomes: medication prescribing, lifestyle modification (diet, exercise or smoking cessation), angiography or revascularization.

The seven trials screened patients for inducible myocardial ischemia (two trials), coronary calcifications (three trials), carotid atherosclerosis (one trial) or left ventricular hypertrophy (one trial).

Trials enrolled an average of 153 patients, had a median follow-up of 12 months and the median age was 55 years. Common imaging modalities used within the trial were CT, echocardiography and myocardial perfusion imaging.

Of the four trials reporting medication use, the researchers found no effect of imaging on prescribing overall or within most of the drug classes, except insulin prescribing. The researcher also reported no effect of imaging on smoking cessation during the meta-analysis or association between imaging and angiography or revascularization.

“We found limited evidence supporting a major influence of noninvasive cardiovascular imaging on markers of care in primary prevention settings,” Hackman et al wrote.

The authors noted that a potential limitation of the study could be the trials’ small sample sizes, which could have been limiting in the detection of clinically important effects on care markers.

“There may be additional and appropriate reasons why clinicians select screening tests that provide enhancements in care beyond those detectable in this review,” the authors wrote. They noted that while routine testing in asymptomatic populations may be too low to justify broad screening, individually selecting patients for screening could provide “reassurance to anxious patients, risk stratification for provision of cardioprotective therapies (in particular in intermediate-risk patients) or assist in “fine tuning” the management of a specific clinical problem (i.e., echocardiographic screening for target organ damage in sustained hypertension).”

Hackman and colleagues concluded that imaging trials powered for CV events will need to include large study populations or induce greater “shifts in the intensity and prevalence of evidence-based medical therapies (a phenomenon not [in] evidence from the trials conducted to date).”

In an accompanying AIM editorial, Patrick G. O’Malley, MD, MPH, of the Walter Reed Army Medical Center in Washington, D.C., said that evidence that shows that testing improves outcomes is lacking. “The modest evidence that does exist is clearly not powered sufficiently to draw any conclusive inferences about the impact of testing on important patient-centered outcomes. Why is this?” he asked.

O’Malley offered that the FDA’s approval of these imaging technologies is not what it should be and he said that proof of safety and construct validity are the tools necessary for approval. Additionally, he said that the evidence threshold for payors is too low and he said that payors may be persuaded by professional societies who drive the culture of care practice. “Culture trumps evidence, unless the evidence is overwhelming. As such, there is little incentive to perform such studies, especially given the enormous cost of providing benefit in primary prevention settings.”

O’Malley said that the benefit will be low because of the limited efficacy of prevention treatments in populations who are not at high risk.

He also offered that there are two main reasons why clinicians pursue diagnostic testing for subclinical atherosclerosis in asymptomatic patients without known coronary artery disease. These reasons are to refine risk to find better treatment options and motivate patients at risk to optimize health behaviors.

“The way forward for this field seems clear,” O’Malley noted. First, he said that there is opportunity to prevent harm (unnecessary waste, follow-up testing and radiation risk) by limiting atherolsclerosis testing in asymptomatic patients to research studies to gain a better understanding of its role. He said that policy makers should also “rethink the thresholds of evidence, financing and oversight of the use of expensive diagnostic technologies and their relative value in patient-centered terms.”

O’Malley said that more high-quality evidence is required, especially for the intermediate risk patient population. This could be done, he said, with randomized controlled trials that are powered to assess the impact on hard outcomes. “Only then will we know whether the benefits outweigh the risks of this all too common a practice,” he concluded.