How Applicable is ISCHEMIA Trial to US Clinical Practice?

November 03, 2021

The applicability of the results of the ISCHEMIA trial to real-world clinical practice in the United States has been called into question by a new study showing that less than a third of US patients with stable ischemic heart disease (IHD) who currently undergo intervention would meet the trial's inclusion criteria.

The ISCHEMIA trial, first reported in 2019, showed that, for stable patients with moderate-to-severe ischemia, an invasive approach using percutaneous coronary intervention (PCI) did not significantly reduce major cardiovascular events after a median 3.2 years of follow-up, compared with a conservative medical strategy.

For the current study, a group of interventionalists analyzed contemporary US data on patients undergoing PCI and found that a large proportion of patients receiving PCI for stable ischemic heart disease in the United States would not have met criteria of the ISCHEMIA trial population.

The study was published online November 1 in JACC: Cardiovascular Interventions.  

"While ISCHEMIA was a very well conducted trial, our results show that it only applies to about one third of stable IHD patients undergoing intervention in US clinical practice in the real world. In this group, while ISCHEMIA did not show a reduction in event rate in the intervention group, there was a reduction in symptoms," lead author Saurav Chatterjee, MD, Long Island Jewish Medical Center, New York, told | Medscape Cardiology.

"But ISCHEMIA did not really answer the question for 67% of stable IHD in current US practice. We may be abIe to defer PCI in these patients, but we don't know that from the ISCHEMIA trial, as these patients were not included in the trial," Chatterjee said.  

"There is some concern that people will accept the ISCHEMIA results as being universal, but we cannot apply these results to all stable IHD patients who currently undergo intervention," he added. "We believe that patients who do not fall into the ISCHEMIA population need a nuanced individual approach, taking into account symptom burden and patient preferences."

In the new report, Chatterjee et al note that the applicability of the ISCHEMIA findings to contemporary practice has been questioned by some, because of the exclusion of a significant proportion of patients that are routinely considered for revascularization, both within and outside of the United States.

They point out that the ISCHEMIA trial recruited 16.5% of its participants from the United States, and the proportion of patients in contemporary US practice that would have qualified for the trial is not clear.

They therefore examined the proportion of stable IHD patients meeting inclusion criteria for the ISCHEMIA trial in a US nationwide PCI registry.

The researchers used data from the National Cardiovascular Data Registry (NCDR) CathPCI Registry, which includes patients undergoing PCI at 1662 institutions and accounts for more than 90% of PCI-capable hospitals in the United States.

All PCI procedures performed at institutions participating in the NCDR CathPCI Registry from October 2017 to June 2019 were identified. Patients presenting with acute coronary syndrome (ACS), cardiogenic shock, or cardiac arrest were excluded, as there is significant evidence in favor of revascularization in these groups and they were not included in the ISCHEMIA trial.

Subsequently, all remaining stable IHD patients were classified into 1 of 4 groups.

  1. ISCHEMIA-like: these patients had intermediate- or high-risk findings on a stress test but no high-risk features that would have excluded enrolment into the ISCHEMIA trial

  2. High risk: this group comprised patients with stable IHD and left ventricular ejection fraction less than 35%, significant unprotected left main stenosis (> 50%), preexisting dialysis, recent heart-failure exacerbation, or heart transplant. These patients would have met exclusion criteria for the ISCHEMIA trial

  3. Low risk: this group included patients with stable and negative or low-risk findings on stress test and would have met exclusion criteria for the ISCHEMIA trial

  4. Not classifiable: this group comprised patients with stable IHD not fitting any of the other cohorts, including no stress test or extent of ischemia not reported on stress testing. These patients would have not had enough information to clearly meet inclusion or exclusion criteria for the ISCHEMIA trial

Results showed that during the study period 927,011 patients underwent PCI as recorded in the NCDR CathPCI Registry. Of these, 58% had ACS, cardiogenic shock, or cardiac arrest and were excluded; the remaining 388,212 patients who underwent PCI for stable IHD comprised the study population.

Of these, 125,302 (32.28%) had a moderate- or high-risk stress test without high-risk anatomic or clinical features and met ISCHEMIA trial inclusion criteria.

Among stable IHD patients not meeting ISCHEMIA trial inclusion criteria, 71,852 (18.51%) had high-risk criteria that would have excluded them from the ISCHEMIA trial, a total of 67,159 (17.29%) patients had low-risk criteria that would have excluded them from the ISCHEMIA trial, and 123,899 (31.92%) were unclassifiable, either owing to lack of stress testing or the extent of ischemia not being reported on stress testing.

The authors suggest that the unclassifiable patients appear to represent a "higher-risk" population than those closely resembling the ISCHEMIA trial population, with more prior myocardial infarction and heart failure.

ISCHEMIA Investigators Respond

In an accompanying editorial, ISCHEMIA investigators David J. Maron, MD, Stanford University School of Medicine, California, and Sripal Bangalore, MD, and Judith S. Hochman, MD, New York University Grossman School of Medicine, New York City, argue that many of the patients highlighted by Chatterjee et al were excluded from the ISCHEMIA trial for good reason.

They explain that ISCHEMIA was designed under the premise that prior stable IHD strategy trials such as COURAGE and BARI 2D included lower risk patients, and the remaining gap was to evaluate the utility of invasive management in those at higher risk with moderate or severe stress-induced ischemia.

They point out that, among the NCDR patients with stable IHD in the current study by Chatterjee et al who did not meet ISCHEMIA entry criteria, 18.5% had high-risk features, including 35.2% with left main coronary artery disease, 43.7% with left ventricular systolic dysfunction, and 16.8% with end-stage renal disease.

Although ISCHEMIA results do not apply to patients who were excluded from the trial, there is little controversy regarding the benefit of revascularization in patients with stable IHD with left main coronary artery disease or left ventricular ejection fraction < 35%, which is why they were excluded from ISCHEMIA, the editorialists note.  

They also report that patients with end-stage renal disease, who were also designated as not meeting ISCHEMIA inclusion criteria, were included in the companion ISCHEMIA CKD trial.

They further point out that, at the other end of the risk spectrum, 17.3% of stable IHD patients in the current analysis had negative or low-risk functional testing, and these patients were excluded from ISCHEMIA because they were shown in COURAGE and BARI 2D to not benefit from revascularization, and they do not meet guideline recommendations for elective PCI in the absence of symptoms.

On the 31.9% of stable IHD patients who had missing data on ischemic burden, the ISCHEMIA investigators say that some of these would have qualified for the trial, although it is not possible to say how many. They suggest a conservative estimate of 50%.

Taking these arguments into account, the editorialists recalculated the proportion of NCDR PCI patients with stable IHD who would have been included in ISCHEMIA as between 62.1% and 68.6% of patients.

They say the current NCDR analysis by Chatterjee et al should be interpreted at worst that the ISCHEMIA trial results apply to only 32% of patients undergoing elective PCI in the United States, and at best "that the results apply to a far higher proportion, excluding only those at high risk (18.5%) or with unacceptable symptoms despite maximal medical therapy (percentage unknown), for whom PCI is clearly indicated."

The editorialists conclude: "The purpose of the analysis by Chatterjee et al is to inform the cardiovascular community of the proportion of patients with stable IHD in clinical practice who would have been excluded from ISCHEMIA without regard for the logic of each exclusion criterion. The purpose of this editorial is to provide context for the analysis, admittedly from the perspective of ISCHEMIA investigators, with the hope that this helps readers clearly see the relevance of the trial to patients under their care."

They add: "For practical and ethical reasons, ISCHEMIA excluded stable patients with high-risk features, angina inadequately controlled by medication, and low-risk features who do not meet evidence-based guidelines for revascularization. That leaves a large percentage of patients for whom the ISCHEMIA trial is highly relevant; exactly what percentage on the basis of NCDR data is hard to say."

The ISCHEMIA trial was supported by the National Heart, Lung, and Blood Institute.

JACC: CV Interventions. Published online November 1, 2021. Abstract, Editorial.

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