1-2-3-LQTS Risk Calculator – Long QT Syndrome 5-Year Arrhythmic Risk

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5-Year Arrhythmic Risk Assessment

Enter the corrected QT interval and the patient's LQTS genotype to estimate baseline 5-year risk.

—5-year risk

Estimated absolute risk of a life-threatening arrhythmic event

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Calculation details

This is a prognostic estimate, not a diagnosis or an automatic indication for ICD implantation. Interpret the result with the patient's clinical history, treatment status, ECG phenotype, and specialist assessment.

About the 1-2-3-LQTS Risk Model

The 1-2-3-LQTS-Risk model estimates the 5-year absolute risk of a life-threatening arrhythmic event in patients with long QT syndrome using QTc duration and genotype (LQT1, LQT2, or LQT3). The model was developed from a longitudinal cohort and subsequently evaluated in an independent cohort from the International LQTS Registry.

Model equation

Prognostic Index (PI)	0.01365 × (QTc − 469.9075194) + 0.83454 × LQT2 + 0.94523 × LQT3
5-year risk (%)	100 × [1 − (0.9849143482)^exp(PI)]
Genotype indicators	LQT2 = 1 for LQT2, otherwise 0; LQT3 = 1 for LQT3, otherwise 0. LQT1 is the reference.

Outcome definition

The composite life-threatening arrhythmic endpoint includes sudden cardiac death, aborted cardiac arrest, and hemodynamically non-tolerated polymorphic ventricular tachycardia.

Important model considerations

The equation does not incorporate sex, age, syncope, prior cardiac arrest, specific variant location, or beta-blocker treatment.
The derivation publication described QTc values of 460 ms or less as a group with a relatively benign outcome for which further risk stratification by QTc and genotype was not indicated. Interpret estimates in this range cautiously.
The 5% threshold was explored in the external validation study as a balanced ROC-derived threshold in relation to ICD consideration; it is not a universal treatment threshold or an automatic ICD indication.

References

Mazzanti A, Maragna R, Vacanti G, et al.Interplay Between Genetic Substrate, QTc Duration, and Arrhythmia Risk in Patients With Long QT Syndrome. Journal of the American College of Cardiology. 2018;71(15):1663–1671.
doi:10.1016/j.jacc.2018.01.078

Mazzanti A, Trancuccio A, Kukavica D, et al.Independent validation and clinical implications of the risk prediction model for long QT syndrome (1-2-3-LQTS-Risk). Europace. 2022;24(4):614–619.
doi:10.1093/europace/euab238

Zeppenfeld K, Tfelt-Hansen J, de Riva M, et al.2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. European Heart Journal. 2022;43(40):3997–4126.
doi:10.1093/eurheartj/ehac262

Clinical disclaimer: This calculator is intended for healthcare professionals as an adjunct to clinical assessment. The estimated risk is derived from a published population model and may not fully represent an individual patient's risk. It must not be used as the sole basis for treatment decisions, beta-blocker selection, or ICD implantation. Patients with prior cardiac arrest or other high-risk clinical features require individualized specialist assessment.