Differential Diagnosis Between Catecholaminergic Polymorphic Ventricular Tachycardia and Long QT Syndrome Type 1　― Modified Schwartz Score ―

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia (CPVT) has been often misdiagnosed as long QT syndrome (LQTS) type 1 (LQT1), which phenotypically mimics CPVT but has a relatively better prognosis. METHODS AND RESULTS: The derivation and validation cohorts consisted of 146 and 21 patients, respectively, all of whom had exercise- or emotional stress-induced cardiac events. In the derivation cohort, 42 and 104 patients were first clinically diagnosed with CPVT and LQTS, respectively. Nine of 104 patient who had initial diagnosis of LQTS were found to carry RYR2 mutations. They were misdiagnosed due to 4 different reasons: (1) transient QT prolongation after cardiopulmonary arrest; (2) QT prolongation after epinephrine test; (3) absence of ventricular arrhythmia after the exercise stress test (EST); and (4) assumption of LQTS without evidence. Based on genetic results, we constructed a composite scoring system by modifying the Schwartz score: replacing the corrected QT interval (QTc) at 4 min recovery time after EST >480 ms with that at 2 min, or with ∆QTc (QTc at 2 min of recovery-QTc before exercise) >40 ms and assigning a score of -1 for ∆QTc <10 ms or documented polymorphic ventricular arrhythmias. This composite scoring yielded 100% sensitivity and specificity for the clinical differential diagnosis between LQT1 and CPVT when applied to the validation cohort. CONCLUSIONS: The modified Schwartz score facilitated the differential diagnosis between LQT1 and CPVT.