The Sgarbossa Criteria are diagnostic tools used in electrocardiography (ECG) to identify heart attacks in individuals with complex ECG patterns like Left Bundle Branch Block (LBBB) or ventricular paced rhythms. They improve the accuracy of diagnosing ST-elevation myocardial infarction (STEMI) when standard ECG interpretation is difficult.
Why Sgarbossa Criteria Were Needed
While ECGs often diagnose heart attacks easily, Left Bundle Branch Block (LBBB) or paced rhythms pose significant challenges. They alter the heart’s normal electrical activity, affecting the ST segment and T wave on an ECG. These alterations can mimic ST-elevation myocardial infarction (STEMI), causing false positives, or mask it, leading to missed or delayed diagnoses. This dilemma required a specialized approach to accurately identify heart attacks in these patients, preventing misdiagnosis or delayed treatment.
The Original Criteria
Dr. Elena Sgarbossa developed the original criteria to address the diagnostic difficulties posed by LBBB. These criteria established a scoring system based on specific ECG findings.
The first criterion is a concordant ST elevation of at least 1 millimeter in leads where the QRS complex is predominantly positive, indicating electrical activity moving in the same direction, and this finding contributes 5 points to the score. The second criterion involves a concordant ST depression of at least 1 millimeter in leads V1, V2, or V3, which adds 3 points. The third criterion is an excessively discordant ST elevation of at least 5 millimeters in leads where the QRS complex is predominantly negative, meaning the electrical activity is moving in the opposite direction, and this earns 2 points.
A total score of 3 points or more using these criteria suggested a likely myocardial infarction. While these original criteria demonstrated high specificity (90-98%), their sensitivity was low (20-36%), meaning many true heart attacks could still be missed.
The Modified Criteria
The limitations of the original Sgarbossa criteria, particularly their low sensitivity, prompted the need for refinement. The third original criterion, which relied on an absolute 5 millimeter threshold, was problematic because normal electrical variations in patients with LBBB could also cause such large deviations, leading to missed diagnoses or false positives. To improve diagnostic accuracy, Smith’s modified Sgarbossa criteria were introduced.
This modification refines the third criterion by replacing the absolute 5 millimeter threshold with a proportional rule. It defines excessively discordant ST elevation as ST elevation of at least 1 millimeter that is also at least 25% of the depth of the preceding S-wave in leads with a negative QRS complex. This proportional approach (ST/S ratio ≤ -0.25) accounts for the natural electrical variations seen in LBBB. Unlike the original scoring system, the modified criteria consider a diagnosis positive if any one of the three refined criteria is met. This change significantly improved sensitivity (80-91%) while largely preserving high specificity (90-99%).
Using the Criteria in Practice
Healthcare professionals apply the Sgarbossa Criteria, particularly the modified version, as a structured approach within a broader clinical assessment. When a patient presents with symptoms suggesting a heart attack and their ECG shows Left Bundle Branch Block or a paced rhythm, these criteria help determine if an underlying heart attack is present. ECG interpretation is not done in isolation; it is combined with a thorough evaluation of the patient’s symptoms (e.g., chest pain or shortness of breath), medical history, and other diagnostic tests like cardiac enzyme levels.
A positive finding based on the Sgarbossa Criteria indicates a high likelihood of an acute heart attack, guiding immediate clinical decision-making. This often involves activating specialized teams, such as the cardiac catheterization laboratory, to quickly restore blood flow to the heart. The criteria facilitate rapid and appropriate medical intervention, important for improving patient outcomes in these challenging diagnostic scenarios.
Key Considerations and Importance
While valuable, the Sgarbossa Criteria have limitations. Even in modified form, they are not perfect and can result in false positive or false negative findings. ECG interpretation can also vary between healthcare professionals, influencing consistent application.
Despite these considerations, the Sgarbossa Criteria remain an important aid for timely diagnosis and treatment of heart attacks in patients with Left Bundle Branch Block or paced rhythms. They provide a structured framework for assessing complex ECGs that would otherwise be difficult to interpret. When used with a complete clinical picture, including patient symptoms and other diagnostic information, these criteria contribute to more accurate and prompt identification of heart attacks, supporting better patient care and outcomes.