What the Modified Sgarbossa Criteria Calculator does
This calculator applies the Smith-modified Sgarbossa criteria to help identify acute myocardial infarction (STEMI, now often described as acute coronary occlusion) in patients whose ECG shows a left bundle branch block (LBBB) or a ventricular paced rhythm. In these rhythms the QRS complex and ST segments are already abnormal, so the usual ST-elevation thresholds do not apply and a true infarction can be easily missed. The modified criteria give a structured, evidence-based way to flag an ECG as concerning.
The tool checks three independent criteria and reports the result as Positive or Negative. The rule is positive if any single criterion is met.
How to use it
Answer the three criteria for the ECG in front of you:
- Criterion 1 – Concordant ST elevation: choose Yes if any lead with a predominantly positive (upright) QRS shows ST elevation of at least 1 mm.
- Criterion 2 – Concordant ST depression: choose Yes if lead V1, V2, or V3 shows ST depression of at least 1 mm.
- Criterion 3 – Excessively discordant ST elevation: for a lead with a predominantly negative QRS, enter the amount of ST elevation in millimetres and the depth of the S wave that precedes it. The calculator works out the ST/S ratio for you.
The result updates to show which criteria are met and the overall interpretation.
The formula explained
The first two criteria are simple yes/no checks. The third criterion — the key change introduced by Smith and colleagues in 2012 — replaces the original absolute "≥ 5 mm" rule with a proportion. It compares the discordant ST elevation with the depth of the S wave in the same lead:
$$ R = \frac{a}{b} $$
where a is the discordant ST elevation (in mm) and b is the depth of the preceding S wave (in mm). Criterion 3 is met when the ST segment is elevated by at least 1 mm and the ratio R is at least 0.25 — that is, when the discordant ST elevation reaches 25% or more of the S-wave depth. In the original sign convention this is written as an ST/S ratio of −0.25 or more negative, because the discordant elevation sits opposite the deep S wave. The modified rule is positive whenever criterion 1, criterion 2, or criterion 3 is satisfied.
Worked example
Suppose an ECG in LBBB shows no concordant ST elevation and no concordant ST depression in V1–V3, but lead V2 (with a deep, negative QRS) has 3 mm of ST elevation on top of an S wave that is 10 mm deep. The ratio is:
$$ R = \frac{3}{10} = 0.30 $$
Because the ST elevation is at least 1 mm and the ratio 0.30 is greater than 0.25, criterion 3 is met. With one criterion satisfied, the Modified Sgarbossa result is Positive, which should prompt urgent evaluation for acute coronary occlusion.
Frequently asked questions
How is the modified rule different from the original Sgarbossa score? The original 1996 criteria used a weighted point system — 5 points for concordant ST elevation, 3 for concordant ST depression, and 2 for at least 5 mm of discordant elevation — and called a total of 3 or more positive. The modified rule keeps the first two criteria, replaces the absolute 5 mm cut-off with the ST/S ratio of 0.25, and is positive if any one criterion is met, which improves sensitivity for occlusion MI.
Does a negative result rule out a heart attack? No. A negative result lowers suspicion but does not exclude acute coronary occlusion. Serial ECGs, clinical context, and troponin testing remain essential, and a patient with ongoing ischaemic symptoms should be managed accordingly.
Can I use this with a ventricular paced rhythm? Yes. The modified Sgarbossa criteria have been validated for both left bundle branch block and ventricular paced rhythms, in which the QRS is similarly wide and discordant.
