SEOUL, KOREA — A new study finds widely varying periprocedural MI rates after CABG surgery or PCI, depending on which contemporary definition of MI is used, reigniting calls for a universal MI definition.[1]
Among 7697 consecutive patients with multivessel coronary artery disease, MI rates after PCI were 18.7%, 3.2%, and 5.5% with the second universal definition of MI (UDMI), third UDMI, and the Society for Cardiac Angiography and Interventions (SCAI) definition, respectively.
Post-CABG MI rates were even more lopsided, at 2.9% and 1.9% with the second and more stringent third UDMI, but 18.3% with the biomarker-driven SCAI definition.
In addition, only the SCAI definition significantly predicted the 5-year risk of all-cause mortality after CABG, the investigators reported August 14, 2017 in JACC: Cardiovascular Interventions.
Commenting for theheart.org | Medscape Cardiology, Dr Issam D Moussa (Rutgers Robert Wood Johnson School of Medicine, New Brunswick, NJ) said the findings have implications for clinical practice and quality assurance because both coronary bypass and PCI are used to treat the same disease.
“It’s really time for us to deal with these two procedures similarly in terms of how we define this complication,” he said. “Death is clearly death, with stroke it’s clear it’s stroke, but for MI we’re not really clear what MI is. We define it differently.”
Moussa, who coauthored an accompanying editorial[2] that calls for adoption of the SCAI definition, said the results also have clear implications for the design and interpretation of clinical trials comparing PCI and CABG, including the previously reported SYNTAX, EXCEL, and NOBLE trials.
“If these findings are reproducible in another study or randomized trial and the difference in bypass MI incidence is about 12%, then there is no doubt that the primary end point of all of these trials would have changed more, favoring PCI,” he said.
ASAN-Registry
The study, led Dr Min Soo Cho (University of Ulsan College of Medicine, Seoul, Korea), analyzed data from 4514 patients who underwent PCI and 3183 who underwent CABG and were enrolled between January 2003 and December 2016 in the prospective ASAN Medical Center Multivessel Revascularization registry. All had serial measurement of creatine kinase-MB (CK-MB).
CK-MB is the preferred biomarker for the SCAI definition, with an increase of CK-MB >10 times the upper reference limit regarded as a clinically relevant MI after PCI and CABG or to >5 times the upper limit for patients with new pathologic Q waves.
Cardiac troponin (cTn), however, is the preferred biomarker in the UDMI. Between the second and third universal definition, cTn thresholds were increased from >3 times to >5 times the 99th percentile of the upper reference limit for PCI-related MI and from >5 times to >10 times the 99th percentile of the upper reference limit for CABG-related MI, with an added requirement of clinical, ECG, or imaging documentation of myocardial injury.
“In the real world, the peri-CABG enzyme elevation more than 10 times is often without any ischemic symptoms or signs. Therefore, such mandatory requirement of ECG, angiographic, or imaging evidence in the UDMI makes a big discrepancy between the UDMI and SCAI definitions,” senior author Dr Seung-Jung Park (University of Ulsan College of Medicine) told theheart.org | Medscape Cardiology in an email.
Moussa said the marked differences observed in postbypass MI incidence are a novel finding and noted that ECG changes are often nonspecific after bypass and that few patients go the catheterization lab after bypass unless they’re hemodynamically unstable.
“I think this particular finding is very telling about why it’s really important to have a dramatic [enzyme] elevation but not require these clinical, ECG, and angiographic findings, because you could miss a lot of large MI,” he said.
During a median of 4.7 years follow-up, 998 patients died (779 from cardiovascular causes) and 150 had an MI.
Risk-adjusted 5-year rates of future major CV events (CV death or spontaneous MI) after a periprocedural MI were similar after PCI and CABG with the second and third UDMI, but significantly higher after PCI than CABG using the SCAI definition (24.3% vs 20.4%; hazard ratio 1.61, 95% CI 1.07–2.41).
Adjusted 5-year Event Rates*
| Outcome | PCI (%) | CABG (%) | HR (95% CI) | P |
|---|---|---|---|---|
| Second definition of MI | ||||
| Major cardiovascular events | 16.7 | 20.9 | 0.79 (0.43–1.44) | 0.44 |
| Death | 11.5 | 14.3 | 0.61 (0.29–1.26) | 0.18 |
| Third definition of MI | ||||
| Major cardiovascular events | 17.3 | 20.9 | 0.58 (0.22–1.58) | 0.29 |
| Death | 14.8 | 17.6 | 0.51 (0.15–1.75) | 0.29 |
| SCAI definition of MI | ||||
| Major cardiovascular events | 24.3 | 20.4 | 1.61 (1.07–2.41) | 0.02 |
| DeathHR (95% CI) | 14.4 | 20.2 | 0.70 (0.44–1.12) | 0.13 |
*Hazard ratios are for patients with periprocedural MI after PCI compared with those with periprocedural MI after CABG
Both the investigators and editorialists acknowledge that a major limitation of the study is that cTn levels were not collected.
“However, given the greater sensitivity of cTn compared with CK-MB, it is highly likely that using cTn with the same thresholds would have substantially increased the overall incidence of periprocedural MI after PCI and CABG,” Moussa and fellow editorialist Dr Gregg W Stone (Columbia University Medical Center, NY) write.
“In addition, because cTn-based MIs indicate substantially less myonecrosis compared with CK-MB–based MIs for the same threshold multiple, including smaller infarctions with cTn-based MIs would have decreased the overall prognostic significance of periprocedural MI events.”
The exact reasons or mechanisms for the significant association observed only between SCAI-defined postbypass MI and all-cause mortality are still unclear, and future studies are needed to adequately address this issue, Park said.
The editorial, however, highlights supportive evidence including a 2016 analysis from the FREEDOM trial, in which CK-MB elevations of at least 7 to 10 times the upper reference limit significantly predicted subsequent mortality at a median 3.6 years after CABG in patients with multivessel disease and diabetes.[3]
Moussa and Stone agree further study with cardiac MRI is needed to determine whether the extent of myonecrosis after PCI and CABG is similar for any given postprocedure biomarker but say that absent such data the roughly comparable adjusted hazard for 5-year mortality after MI for both procedures using the SCAI definition supports it use.
“The time has come to adopt a unifying common definition for PCI-related and CABG-related MI (for both clinical trial use and clinical practice). In this regard, the SCAI definition is simple to implement, uses the same criteria for PCI and CABG, avoids ascertainment bias, and has been associated with subsequent mortality for both PCI and CABG,” they write.
The study was partially supported by the Cardiovascular Research Foundation, Seoul, Korea. The authors and editorialists report no relevant financial relationships.
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