Sgarbossa criteria is a scoring system developed to improve the diagnosis of acute myocardial infarction (MI) in patients with pre-existing or new left bundle branch block (LBBB) 1,3. LBBB can distort the ST-segment changes typically seen in ST-elevation myocardial infarction (STEMI), making diagnosis challenging. The algorithm assigns points based on specific ST-segment and T-wave abnormalities on the ECG, aiming to identify patients who likely have an acute MI despite the LBBB pattern 1,3. A higher score increases the likelihood of MI, guiding clinical decision-making regarding urgent management, such as reperfusion therapy 1,3,5.
Epidemiology
The prevalence of LBBB in the general population increases with age and is associated with underlying cardiovascular disease. The Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO-1) trial, which provided the data for the original Sgarbossa criteria, included patients with LBBB presenting with suspected MI 1. The exact incidence of MI in patients with LBBB is not specified in the provided sources, but LBBB is known to be present in approximately 10-20% of patients presenting with acute MI 1,5.
Aetiology
secondary associations / risk factors: LBBB is associated with various cardiac conditions, including hypertension, coronary artery disease, cardiomyopathy, and valvular heart disease. These underlying conditions are risk factors for both LBBB and MI 1.
primary causes / triggers: The Sgarbossa criteria themselves are diagnostic criteria, not a disease with primary causes. They are applied to patients who present with symptoms suggestive of MI and have LBBB on ECG. The underlying cause of the MI (e.g., coronary artery thrombosis) is the primary trigger, while LBBB is often a pre-existing condition or develops acutely during the MI event 1.
Pathophysiology
The pathophysiology involves the ECG changes associated with acute MI (ST-segment elevation or depression, T-wave inversion) occurring in the context of LBBB. LBBB causes a characteristic wide QRS complex morphology. The Sgarbossa criteria attempt to differentiate true MI-related ST changes from the ST abnormalities inherent to LBBB itself. The criteria focus on ST deviation (elevation or depression) at the J-point, considering its direction relative to the QRS complex (concordant or discordant) 1. The underlying mechanism of MI (e.g., coronary occlusion leading to myocardial ischaemia and injury) remains the same, but its ECG manifestation is altered by the LBBB.
Clinical presentation
physical examination signs: Physical examination findings may be non-specific or consistent with acute MI, such as signs of heart failure (e.g., pulmonary oedema), hypotension, or arrhythmias. The presence of LBBB itself does not have specific physical signs beyond those related to the underlying cardiac condition 1.
presenting symptoms: Patients typically present with symptoms suggestive of acute MI, such as chest pain, shortness of breath, nausea, vomiting, or diaphoresis. The presence of LBBB on ECG may complicate the interpretation of these symptoms in the context of ECG changes 1,5.
Investigations
Bedside & Laboratory
laboratory / bedside studies: The primary investigation is the 12-lead ECG. Cardiac biomarkers (e.g., troponin) are crucial for confirming myocardial injury, although they may be elevated in LBBB even without acute MI. Serial ECGs and cardiac biomarker measurements are typically performed 1,5.
Imaging & Special Investigations
imaging / specialist studies: Echocardiography may be used to assess left ventricular function and identify regional wall motion abnormalities consistent with MI. Coronary angiography is the definitive investigation to identify coronary artery occlusion 1,5.
Management
definitive / long-term management: Definitive management involves addressing the underlying coronary artery disease, typically via coronary angiography and revascularization (PCI or coronary artery bypass grafting). Long-term management includes secondary prevention strategies (e.g., antiplatelet therapy, statins, ACE inhibitors/ARBs, beta-blockers) and management of any underlying cardiac conditions 1,5.
acute / first-line management: Management depends on the Sgarbossa score, clinical presentation, and cardiac biomarker results. A high Sgarbossa score (≥3) increases the suspicion for MI and prompts urgent management, potentially including reperfusion therapy (e.g., primary percutaneous coronary intervention [PCI] or thrombolysis) if STEMI is suspected 1,3,5. Initial management includes oxygen, aspirin, nitrates (if appropriate), and pain relief. Serial ECGs and troponin measurements are essential 1,5.
Differential diagnosis
Left Bundle Branch Block (chronic): Chronic LBBB itself can cause ST-segment and T-wave changes that mimic MI. The Sgarbossa criteria help differentiate acute MI superimposed on LBBB from chronic LBBB changes.
Ventricular Paced Rhythm: ECG changes in ventricular pacing can resemble LBBB. The Sgarbossa criteria have also been investigated for use in patients with ventricular pacing 4, although their primary validation is for LBBB.
Acute Myocardial Infarction without LBBB: Distinguishing features are the absence of LBBB on ECG and the presence of typical ST-segment elevation or depression patterns in STEMI or NSTEMI, respectively. Sgarbossa criteria are specifically for use *in the presence* of LBBB.
Prognosis & complications
MI in the setting of LBBB, especially if diagnosed late due to ECG interpretation challenges, can be associated with higher morbidity and mortality compared to MI without LBBB 1,5. Complications include heart failure, arrhythmias, cardiogenic shock, and death. Prompt diagnosis using tools like the Sgarbossa criteria aims to improve outcomes by facilitating timely intervention.
