Optimizing the acute PMI management: The AHA clinical guidance

31 Jul 2023

Acute postoperative myocardial ischemia (PMI) is an uncommon yet life-threatening complication after cardiac surgery.1 Due to the complex nature of acute PMI after cardiac surgery, a multitude of factors, such as the patient’s baseline characteristics, the cause of acute PMI, the severity of the complication and logistical limitations, must be considered before making any therapeutic decisions.1 As such, the American Heart Association (AHA) has formed a multidisciplinary group to summarize the existing evidence, providing clinical guidelines on diagnosing and treating acute PMI.1

The clinical diagnosis of acute PMI in patients undergoing cardiac surgery was the first issue tackled in the guidelines.1 However, universally accepted criteria for diagnosis of acute PMI after cardiac surgery was not established in the past due to the asymptomatic nature of the complication.1 This is because patients are often sedated, making it hard for them to report any potential ischemic symptoms, which can be camouflaged under other early postoperative complications.1

Additionally, acute PMI after cardiac surgery can be attributed to multiple factors of both coronary and non-coronary surgeries, which include graft-related factors ranging from acute graft failure to graft spasms, as well as non-graft-related factors including incomplete revascularization and new native coronary artery lesions.1 Hence, identifying the symptoms and underlying causes of acute PMI in patients undergoing cardiac surgery could be a complicated task.1

The guidelines recommend a criterion for multiple aspects of acute PMI diagnosis.1 For patients with extubation failure from cardiopulmonary bypass (CPB), any sudden need for increased vasoactive support or mechanical circulatory support (MCS), signs of postcardiotomy cardiogenic shock (PCS), symptoms of low cardiac output syndrome (LCOS), or chest pain disproportionate to usual post-surgical pain are recommended to be investigated for the possibility of acute PMI.1 Serial electrocardiograms (ECGs) are vital in accurately diagnosing acute PMI, particularly in cases where there is an appearance of new pathological Q waves, dynamic S-segment and T-wave changes, arrhythmias, or a left bundle branch block (LBBB) appearing in patients without baseline left ventricular hypertrophy (LVH) or LBBB that is correlated to an individual's clinical presentation.1

Moreover, the 4th Universal Definition of Myocardial Infarction states that coronary artery bypass graft (CABG)-related (type 5) myocardial infarction (MI) is diagnosed within 48 hours after surgery if the cardiac troponin (cTn) levels increase to >10 times the 99th percentile of the upper reference limit (URL) in patients with normal baseline cTn, or by >20% in those whose cTn levels are already elevated but stable, in addition to new evidence of MI through ECG, angiography, or imaging or new loss of viable myocardium.1 The Academic Research Consortium (ARC)-2 expert consensus document further states that MI is diagnosed based on high sensitivity cTn increases of >35 times the URL in the presence of new evidence of ischemia or >70 times the URL as a standalone criterion.1

Echocardiography is a valuable tool used to assess ischemia as it is able to detect new regional wall motion abnormalities (RWMA), characteristic cTn changes, and other nonischemic causes of chest pain, aortic dissection (AoD), and mechanical complications of MI immediately after the onset of symptoms.1 The extent of late gadolinium enhancement (LGE) is strongly associated with the severity of cTn elevation, the presence of non-viable myocardium, and the likelihood of major adverse cardiovascular events (MACEs), such as non-fatal MI, hospitalization for unstable angina (UA) or heart failure (HF), ventricular arrhythmias, and mortality.1 Therefore, cardiac magnetic resonance (CMR) provides valuable prognostic information, although it cannot be performed in the critical postoperative period.1

The guidelines also propose an algorithm for the treatment of acute PMI after cardiac surgery,  recommending that MCS should be applied as a first-line treatment to stabilize patient conditions and treat the underlying ischemic mechanism.1 The selection of MCS type should be based on patient characteristics, their underlying conditions and center experience.1 Once patient conditions are stabilized, coronary angiography should be performed to determine the underlying cause of acute PMI, after which intervention approaches, such as percutaneous coronary intervention (PCI) or CABG, can be performed or redone if the conditions are appropriate for these solutions.1 If intervention is not needed, conservative options should be considered instead.1

To conclude, the guidelines expound on a series of suggested diagnosis criteria and treatment options for medical practitioners to diagnose and treat acute PMI after cardiac surgery.1 Nevertheless, additional, higher and more rigorous clinical evidence is required to refine a more optimal diagnostic criteria and treatment algorithm.1 Additionally, the guidelines also emphasize the significance of retaining high suspicion for acute PMI in all postoperative cardiac surgery patients so as to ensure a timely diagnosis and treatment.1

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