Patient is hemodynamically unstable. In the setting of instability (hypotension with systolic BP <90 mmHg, altered mental status, ischemic chest pain, acute heart failure, pulmonary edema, or cardiogenic shock), immediately proceed to synchronized DC cardioversion regardless of the rhythm mechanism. Do NOT delay treatment to apply diagnostic algorithms.

STATISTICAL REALITY: 80% of all wide-complex tachycardias are VT. In patients over 50 years of age or with known structural heart disease (prior MI, cardiomyopathy, heart failure), that figure exceeds 95%. CLINICAL IMPLICATION: When in doubt about the Brugada algorithm results, ALWAYS default to treating the rhythm as VT. Misdiagnosing VT as SVT can lead to administration of AV nodal blocking agents (adenosine, verapamil, diltiazem, beta-blockers) which are contraindicated in VT (may cause hemodynamic collapse, degeneration to VF, or death). The safer diagnostic error is to treat SVT as VT (with synchronized cardioversion or procainamide) rather than VT as SVT.