Inferior ST-Elevation Myocardial Infarction Presenting When Urgent Primary Percutaneous Coronary Intervention Is Unavailable: Should We Adhere to Current Guidelines?

Why do we keep missing left circumflex artery myocardial infarctions?

BACKGROUND

Diagnosis of left circumflex artery (LCx) myocardial infarctions via 12‑lead electrocardiogram (ECG) has posed a challenge to healthcare professionals for many years.

METHODS AND RESULTS

A retrospective observational study was performed to analyze patients admitted with myocardial infarction. The study used electronic medical records and specific ICD-10 codes to identify eligible patients, resulting in 2032 encounters. After independent adjudication of cardiac biomarkers, coronary angiography, and electrocardiographic changes, a final patient population of 58 encounters with acute occlusion myocardial infarction (OMI) with a culprit LCx lesion was established. OMI was defined as a lesion with either thrombolysis in myocardial infarction flow (TIMI) 0-2 or TIMI 3 with Troponin I > 1 ng/mL (Reference range 0.00-0.03 ng/mL). ECGs of these patients were then independently evaluated and grouped into 8 different classifications based on the presence or absence of ST elevation and/or depression in corresponding leads. ECG patterns and anatomical characteristics (proximal or distal to the first obtuse marginal artery) of the LCx lesions were then correlated. The appropriateness of triage and delay in reperfusion therapy were also assessed. Those with a left dominant or codominant circulation, and with LCx lesions proximal to the first obtuse marginal artery, were more likely to present with no or subtle ST-segment changes that led to delays in reperfusion therapy.

CONCLUSIONS

Patients with left or codominant coronary artery circulation, with OMI proximal to the first obtuse marginal artery, may be less likely to have "classic" findings of ST-segment elevation on ECG due to cancellation forces in the limb leads.

The Role of ECG in the Diagnosis and Risk Stratification of Acute Coronary Syndromes: an Old but Indispensable Tool

PURPOSE OF REVIEW

Since its inception in 1902 by Willem Einthoven, the electrocardiogram (ECG) has fundamentally undergone minimal technological advances. Nevertheless, its clinical utility is critical, and it remains an essential tool to diagnose, risk stratify, and guide reperfusion and invasive strategies in patients with suspected acute coronary syndromes. ECG reading can be demanding, with many healthcare professionals lacking the necessary expertise to accurately interpret them. This is exacerbated by the need to constantly revisit old dogmas pertinent to the interpretation of ECGs.

RECENT FINDINGS

Notably, ECG leads record the global electrical activity of the heart toward and away from each electrode rather than local events. The long-held central paradigm that the various ECG leads record local events underneath specific electrodes should therefore be reassessed. For example, ST segment elevation in leads V1 and V2 usually denote antero-apical rather than septal infarction, often a misnomer utilized by the majority of clinicians. The ECG diagnosis of ST-elevation myocardial infarction (STEMI) is sometimes challenging and discerning it from non-ST-elevation myocardial infarction (NSTEMI) is of paramount importance to implement timely acute reperfusion therapy. In fact, when qualifications for emergency reperfusion therapy are based on STEMI ECG criteria, nearly one-third of cases with acute coronary occlusion are missed. Diagnostic ST elevation in the absence of left ventricular (LV) hypertrophy or left bundle-branch block (LBBB) is defined by a specific set of sex-specific criteria for new ST elevation at the J point in contiguous precordial or limb leads. However, other ECG criteria need to be kept in mind. These include, but are not limited to, new or presumably new left bundle branch block (LBBB), which is often considered as an STEMI-equivalent; ST depression in two or more precordial leads (V1-V4), denoting a true inferolateral transmural myocardial infarction; and the infrequent presentation with hyperacute T-wave changes. As our understanding of the pathology of ischemic reperfusion injury has evolved and following the introduction of new imaging modalities such as cardiac magnetic resonance imaging, we need to re-assess the old dogmas pertinent to the interpretation of ECGs and update the terms and classifications.

The Efficacy of Thrombolytic Therapy in Inferior Myocardial Infarction with Damage to the Right Ventricular

Aim. To study the results of thrombolytic therapy and accuracy of electrocardiographic assessment of thrombolysis efficiency in inferior myocardial infarction with and without right ventricular lesion.

Material and methods. The118 patients with inferior myocardial infarction were included in this study. They received TLT in the first 12 hours of the disease. The dynamics of ST-segment in 90 minutes from the TLT start and coronary angiography data were analyzed.

Results. Right ventricular myocardial infarction (RVMI) was diagnosed in 49 (41.5%) of 118 patients by echocardiography. Patients with and without RVMI did not differ in age, gender and comorbidities, but patients with RVMI were more likely to have arterial hypotension, atrioventricular block, and atrial fibrillation. All patients with RVMI had occlusion of the right coronary artery (RCA) in the proximal (34.7%) or medial segment (65.3%). Occlusion of the circumflex coronary artery was found in 20 (29.0%) patients without RVMI, and RCA occlusion - in other patients. The infarction-associated artery blood flow equal TIMI 2-3 was found in 17 (34.7%) patients with RVMI and in 46 (66.7%) patients without RVMI (p<0.005). ST-segment decrease by 50% or more in 90 minutes from the TLT was found in 35 (71.4%) patients with RVMI and in 49 (71.0%) patients without RVMI (p>0.05). The false-positive assessment of thrombolysis efficiency was noted in patients with and without RVMI in 21 (42.9%) and 11 (15.9%) cases (p <0.005), respectively. There were no false-positive assessments in patients with RVMI when using ST-segment decrease to the isoline.

Conclusion. TLT should be considered effective in patients with inferior myocardial infarction with the right ventricle lesion, if ST-segment decreases to isoline in 90 minutes from the TLT start.

STEMI: A transitional fossil in MI classification?

An important task in emergency cardiology is distinguishing patients with acute coronary occlusion (ACO), who will benefit from emergent reperfusion therapy, from those without ongoing myocyte loss who can be managed with medical therapy and for whom potentially harmful invasive interventions can be deferred. The electrocardiogram is critical in this process. Although the ST-segment elevation myocardial infarction (STEMI)/non-STEMI paradigm is well-established, with "STEMI" representing ACO, its evidence base is poor, and this can have dire consequences. The universally recommended STEMI criteria do not accurately diagnose ACO; in fact, they miss more than one-fourth of the patients with ACO, and also result in a substantial burden of unnecessary catheterization laboratory activations. We here discuss why we believe it is time to change the current STEMI/non-STEMI paradigm.