Higher Baseline Troponin I Linked to Vulnerable Plaque in Elective PCI Patients
Approximately 1 in 5 patients with stable angina undergoing elective PCI have subclinical increases in cardiac troponin I at hospital admission, according to a single-center study published online in the April 2015 issue of Circulation: Cardiovascular Interventions. Elevated troponin was independently associated with signs of unstable plaque on OCT imaging and increased odds of periprocedural myocardial injury.
Tsunekazu Kakuta, MD, of Tsuchiura Kyodo General Hospital (Tsuchiura, Japan), and colleagues assessed 206 patients (n = 206 lesions) with stable angina who underwent OCT before elective PCI at their center between 2010 and 2012.
Troponin I was measured using the Architect i2000SR system (Abbott Diagnostics) at admission, within 1 hour after PCI, at 6 and 20 hours after PCI, and thereafter in cases of increasing levels.
Sign of Susceptibility to Myocardial Injury
At baseline, subclinical troponin I elevation (≥ 0.03 ng/mL) was seen in 47 patients (22.8%). Patients in this group were more likely to have serum C-reactive protein (CRP) values greater than 0.05 mg/dL (80.9% vs 47.8%; P < .001) and multivessel disease (55.3% vs 34.0%; P = .008) compared with those with normal troponin levels.
On preprocedural OCT, patients with elevated troponin had higher prevalence of thin-cap fibroatheroma (TCFA), greater median lipid arc, and longer lipid length (table 1).
On multivariable logistic regression analysis, factors independently associated with subclinical troponin I elevation were:
- CRP level > 0.05 mg/dL: OR 4.38 (95% CI 1.90-10.08)
- TCFA on OCT: OR 2.89 (95% CI 1.22-6.86)
In all, 46 patients (23.2%) had evidence of periprocedural myocardial injury (defined as post-PCI peak troponin I level > 1.0 ng/mL [5x the upper reference limit]). Such patients had longer lesion and stented lengths compared with those without injury. They also were more likely to have had subclinical troponin I elevation at admission (41.3% vs 17.8%; P = .001).
On multivariable analysis, independent predictors of myocardial injury were:
- TCFA on OCT: OR 5.63 (95% CI 2.29-13.82)
- Elevated troponin I at baseline: OR 2.43 (95% CI 1.08-5.50)
- Longer stented length, mm: OR 1.05 (95% CI 1.01-1.08)
Clinical Significance Unclear
“Our present findings implicate chronic, clinically silent coronary microembolization associated with OCT-derived, unstable culprit-lesion characteristics as a potential pathophysiological source of minor [cardiac troponin I] leakage in patients with stable coronary artery disease scheduled for elective PCI,” the researchers say.
“Such microembolization may occur in the absence of flow-limiting stenosis,” they add. “Thus, the dissociation between troponin leakage and lumen narrowing or symptom severity as observed in our study is not surprising.”
One question, Dr. Kakuta and colleagues acknowledge, is whether “smaller enzymatic myocardial injury in patients with otherwise successful PCI,” as seen in the current report, is clinically important.
While earlier studies have linked high postprocedural levels of troponin T and creatine kinase–myocardial band (CK-MB) to adverse events, they caution that “[b]iomarker elevation, particularly a small or mild increase after PCI, may also be a risk marker for disease burden or lesion complexity and not a causal mediator of late cardiac events.”
Even with these caveats, however, “assessment of low-level, chronic myocardial necrosis represented by a subclinical elevation in troponin may represent a new means by which clinicians can stratify risk among patients for stable coronary artery disease scheduled for elective PCI,” the researchers conclude. “Furthermore, preventing troponin release or a therapeutic strategy to reduce chronic subclinical troponin elevation may become an additional, new target for the treatment of patients with [stable angina] undergoing elective stenting.”
Lee T, Murai T, Yonetsu T, et al. Relationship between subclinical cardiac troponin I elevation and culprit lesion characteristics assessed by optical coherence tomography in patients undergoing elective percutaneous coronary intervention. Circ Cardiovasc Interv. 2015;8:e001727.
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- Dr. Kakuta reports no relevant conflicts of interest.