Cardiac surgery is an excellent tool for treating a wide range of heart diseases, whether congenital or acquired. Due to this diversity of pathologies, the available surgical techniques are also varied. Over the evolution of the specialty, these techniques have been refined, making them today procedures with low rates of serious complications. However, inevitably, all cardiac surgeries result in secondary myocardial injury.
This postoperative myocardial injury generally arises from various insults to the heart during surgery: direct manipulation, including cannulation and access; ablation and defibrillation techniques; inflammation; cardioplegic arrest, leading to hypoxia-reperfusion injury; metabolic damage, etc. The most common form of PMI occurs in the perioperative period of coronary bypass surgery, often related to graft occlusion, accounting for approximately two-thirds of PMIs. Other frequent causes include the appearance of new coronary lesions in native beds due to coronary damage during surgery or distortion of existing plaques/stents, as well as coronary spasm.
One of the immediate, and likely most utilized, methods for diagnosing PMI is determining biochemical markers of myocardial injury (troponinemia or serum creatine kinase levels) in the initial hours or days post-surgery. These parameters are highly sensitive but not very specific, as they may be markedly elevated in any cardiac insult, not solely ischemic in nature. Until now, no consensus has existed regarding the cut-off point for these biomarkers to be considered diagnostic of PMI. Consequently, significant disparities arise in results and their interpretation across different workgroups evaluating PMI. In this review, the authors explore the current evidence, comparing PMI definitions and prognoses across patient groups based on the definition used.
The task force included experts in the field (cardiac surgeons, clinical and interventional cardiologists, anesthesiologists, epidemiologists, and biostatisticians), all free from conflicts of interest. A systematic literature review was conducted, focusing on recent and highly impactful studies (mainly randomized or prospective studies). Only English-language publications were included. Data from each study were compiled in detailed tables, summarizing the study year, sample size, PMI definition criteria, and outcomes, among other factors.
Typically, the threshold for troponinemia used in PMI diagnosis ranges between 10 and 35 times the upper limit of normal (ULN). Complementary tests support myocardial ischemia detection, such as new electrocardiogram alterations, new segmental ventricular dysfunction in echocardiography, and/or pathological findings in coronary angiography. However, a large proportion of patients with biomarker elevations above these cut-offs show no signs of hypoperfusion or necrosis on magnetic resonance imaging, nor increased mortality compared to control patients. Therefore, this review proposes a higher biomarker threshold for PMI diagnosis.
The consensus concludes that biomarker elevation only has prognostic impact for PMI diagnosis when associated with additional ischemia signs or when the elevation is pronounced, regardless of accompanying findings. Thus, a user-friendly algorithm was developed, based on postoperative biomarker determinations at immediate postoperative and 24-hour intervals. PMI is defined only when troponin values exceed 35 times the ULN with additional ischemia signs or in cases where troponinemia exceeds 500 times the ULN without additional tests. The remaining scenarios (troponinemia <35xULN and troponinemia 35-500xULN, without other ischemia signs) are defined as perioperative biomarker elevation and perioperative myocardial damage, respectively. This algorithm also applies to serum creatine kinase levels, with cut-offs at 10xULN and 20xULN.
COMMENTARY:
Accurately defining perioperative myocardial infarction is complex, and establishing firm diagnostic criteria even more so. The fourth and latest international definition of myocardial infarction defined cardiac surgery-related myocardial infarction (type 5) as having troponinemia >10xULN persisting 48 hours post-surgery, accompanied by electrocardiographic or echocardiographic changes or angiographic evidence of flow-limiting lesions. This study revisits the concept, introducing two new terms for perioperative biomarker elevation and myocardial injury, previously undefined.
In cardiac surgery’s inherently injurious context, a “normal” degree of myocardial injury is expected. Besides direct damage mechanisms, various confounding factors (brady- or tachyarrhythmias, anemia, respiratory failure, hemodynamic instability) may contribute to myocardial oxygen supply-demand imbalance, causing type 2 infarctions. Additionally, renal clearance should be considered when assessing troponinemia levels.
Given the above, it is logical that the biomarker elevation threshold for diagnosing infarction in post-cardiac surgery patients should be higher than in non-surgical patients. Until now, no standard threshold existed, with arbitrary levels set at x10 or x35 ULN based on consulted documents. Reviewing available evidence shows that this threshold is highly sensitive but not specific for PMI diagnosis and lacks clear prognostic relevance.
Thus, this consensus document seeks to standardize PMI definitions by establishing significantly higher biomarker cut-offs and distinguishing myocardial infarction from perioperative injury. This aims to reclassify truly at-risk patients who may benefit from additional medical or surgical intervention.
The document’s main strength lies in its exhaustive review of numerous high-sample studies, enabling robust result extraction and comparison. These findings have guided the establishment of prognostic cut-offs for PMI, relying on biomarker plasma levels and additional findings.
As a primary limitation, this document presents an algorithm applicable to all cardiac surgery patients. However, biomarker elevation and PMI risk vary significantly by surgical technique, urgency, clinical status, and patient comorbidities. Therefore, a single algorithm may struggle to adequately differentiate PMI across scenarios. Ideally, patient- and technique-specific algorithms would be developed, though impractical in clinical settings.
The document also addresses the controversy over whether PMI should be included among adverse events in revascularization study outcomes. Logically, it should be included, as it is an inherent procedural complication with prognostic implications for surgical patients. Excluding it risks overestimating procedural benefits, particularly in studies comparing cardiac surgery with less invasive methods. The lack of evidence and a robust PMI definition has led to wide variability in reported PMI incidence across studies, resulting in weak conclusions about its actual risk. Hence, this study’s most critical conclusion is the universal validation of a single PMI definition and the prognostic impact of new intermediate biomarker elevation categories and perioperative myocardial injury.
REFERENCE:
Gaudino M, Flather M, Capodanno D, Milojevic M, Bhatt DL, Biondi Zoccai G, et al. European Association of Cardio-Thoracic Surgery (EACTS) expert consensus statement on perioperative myocardial infarction after cardiac surgery. Eur J Cardiothorac Surg. 2024 Feb 1;65(2):ezad415. doi: 10.1093/ejcts/ezad415. PMID: 38420786.
