Formula, criteria and sources
HCM Risk-SCD
P(SCD at 5 y) = 1 − 0.998 ^ exp(PI)
PI = 0.15939858 × MWT − 0.00294271 × MWT² + 0.0259082 × LA + 0.00446131 × LVOT gradient + 0.4583082 × FHSCD + 0.82639195 × NSVT + 0.71650361 × syncope − 0.01799934 × age
MWT is the greatest wall thickness on 2D echo (anterior and posterior septum, lateral and posterior wall, at the mitral, papillary-muscle and apical levels); LA diameter by M-mode or 2D echo in the parasternal long axis; the LVOT gradient is the maximal instantaneous gradient at rest or with Valsalva by continuous-wave Doppler. Binary variables are 1 when present: family history is SCD in a first-degree relative under 40, or in a first-degree relative with HCM at any age; NSVT is ≥ 3 consecutive ventricular beats at ≥ 120 bpm lasting < 30 s on ≥ 24 h of Holter monitoring; syncope is unexplained syncope at or before the evaluation. Age in years. Derived in 3,675 consecutive patients from six European centres, with sudden cardiac death or an equivalent event (resuscitated cardiac arrest or an appropriate ICD shock) within 5 years as the endpoint.
Inputs are held to the development cohort: age 16–80, MWT 10–35 mm, LA 28–67 mm and a gradient up to 154 mmHg (a gradient under 2 mmHg is used as entered, with a note). The model isn’t for patients under 16, competitive athletes, metabolic or syndromic phenocopies such as Fabry disease or Noonan syndrome, or anyone who has survived cardiac arrest or sustained VT, and should be used with caution after myectomy or alcohol septal ablation. Data beyond 35 mm are sparse: only 47 patients in the same cohort had walls of 35 mm or more, with one sudden death over a median 9.5 years, so the model isn’t extrapolated beyond 35 mm.
O’Mahony C, Jichi F, Pavlou M, et al. A novel clinical risk prediction model for sudden cardiac death in hypertrophic cardiomyopathy (HCM Risk-SCD). Eur Heart J 2014;35:2010–2020. DOI
O’Mahony C, Jichi F, Monserrat L, et al. Inverted U-shaped relation between the risk of sudden cardiac death and maximal left ventricular wall thickness in hypertrophic cardiomyopathy. Circ Arrhythm Electrophysiol 2016;9:e003818. DOI
ESC 2023 ICD recommendations
Cardiac arrest due to VT or VF, or sustained VT with haemodynamic compromise: ICD recommended (I) · haemodynamically tolerated sustained VT: ICD should be considered (IIa) · 5-year risk ≥ 6 %: ICD should be considered (IIa) · 4 to < 6 %: ICD may be considered (IIb) · < 4 %: ICD generally not indicated, but LGE ≥ 15 % or LVEF < 50 % may be weighed in a shared decision (IIb)
HCM Risk-SCD is the recommended way to estimate the 5-year risk from age 16, and a validated paediatric model such as HCM Risk-Kids under 16 (both Class I); the risk is reassessed every 1–2 years or when the clinical picture changes (Class I). A primary-prevention ICD follows a detailed clinical assessment that weighs lifelong complications and the impact on lifestyle, socioeconomic status and psychological health. With an LV apical aneurysm, the ICD decision should rest on the overall risk assessment (IIa).
The 2023 guideline keeps two risk modifiers for low- and intermediate-risk patients: LGE ≥ 15 % of LV mass and LVEF < 50 %. The 2022 ESC ventricular arrhythmia guideline also listed an apical aneurysm, an abnormal blood-pressure response to exercise and a pathogenic sarcomeric variant, and made an ICD IIa at intermediate risk with any of them; the 2023 guideline doesn’t use those three and doesn’t regard an apical aneurysm as an independent risk factor. The 2022 guideline is the source used here for tolerated sustained VT (IIa) and for children with an HCM Risk-Kids estimate ≥ 6 % (ICD should be considered, IIa). The 4 % and 6 % thresholds date from the 2014 HCM guideline.
Arbelo E, Protonotarios A, Gimeno JR, et al. 2023 ESC Guidelines for the management of cardiomyopathies. Eur Heart J 2023;44:3503–3626. DOI
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. Eur Heart J 2022;43:3997–4126. DOI
Elliott PM, Anastasakis A, Borger MA, et al. 2014 ESC Guidelines on diagnosis and management of hypertrophic cardiomyopathy. Eur Heart J 2014;35:2733–2779. DOI
Norrish G, Ding T, Field E, et al. Development of a novel risk prediction model for sudden cardiac death in childhood hypertrophic cardiomyopathy (HCM Risk-Kids). JAMA Cardiol 2019;4:918–927. DOI
AHA/ACC 2024 ICD recommendations
Cardiac arrest or sustained VT: ICD recommended (1) · ≥ 1 major risk factor: ICD reasonable (2a) · no major risk factor, but extensive LGE or NSVT: ICD may be considered (2b) · no risk factors: ICD should not be placed (3: Harm)
Major risk factors in adults: sudden death judged definitively or likely due to HCM in a first-degree or close relative aged ≤ 50 (close relatives are generally second-degree; multiple sudden deaths among tertiary relatives are also relevant); massive LVH ≥ 30 mm in any segment, with borderline values ≥ 28 mm counted at the treating cardiologist’s discretion; ≥ 1 recent syncope judged arrhythmic rather than vasovagal or due to LVOT obstruction, especially within 6 months (events more than 5 years earlier don’t appear relevant); an LV apical aneurysm with transmural scar or LGE, of any size; and LVEF < 50 % by echo or CMR. Extensive LGE is ≥ 15 % of LV mass, quantified or estimated visually. NSVT has generally meant ≥ 3 beats at ≥ 120 bpm, with more weight on frequent (≥ 3), longer (≥ 10 beats) or faster (≥ 200 bpm) runs over 24–48 h of monitoring.
Calculating the 5-year risk from age 16 is reasonable (2a), and with ≥ 1 major risk factor, discussing it and mortality rates is useful in shared decision-making (2a). CMR is recommended when a patient isn’t otherwise high risk or the decision is uncertain (1). In children, ≥ 1 conventional risk factor (unexplained syncope; massive LVH, where no threshold is established but a z-score ≥ 20, or > 10 alongside other risk factors, appears reasonable; NSVT faster than the baseline sinus rate by more than 20 %; family history of early HCM-related sudden death) makes an ICD reasonable (2a) after weighing the high rate of long-term complications, and extensive LGE and systolic dysfunction can also be weighed (2b). An ICD placed solely to allow competitive athletics is also 3: Harm.
Ommen SR, Ho CY, Asif IM, et al. 2024 AHA/ACC/AMSSM/HRS/PACES/SCMR guideline for the management of hypertrophic cardiomyopathy. Circulation 2024;149:e1239–e1311. DOI
LGE extent
Extensive LGE: ≥ 15 % of LV mass
In the study behind the threshold, LGE ≥ 15 % of LV mass was associated with about a two-fold higher risk of sudden death in patients otherwise considered at lower risk. Both guidelines use 15 %.
Chan RH, Maron BJ, Olivotto I, et al. Prognostic value of quantitative contrast-enhanced cardiovascular magnetic resonance for the evaluation of sudden death risk in patients with hypertrophic cardiomyopathy. Circulation 2014;130:484–495. DOI
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