Background: Mavacamten has revolutionised the treatment of hypertrophic obstructive cardiomyopathy (HOCM) but requires frequent follow-up. Routine ECG may offer an accessible tool to indicate response to therapy. This study evaluates ECG-based indices of left ventricular hypertrophy (LVH) in patients with HOCM receiving mavacamten therapy.

Methods: In this retrospective study, after screening of 62 consecutive patients with HOCM treated at a German tertiary referral centre from August 2023 to February 2025, 31 patients (42% female, mean age 61±12 years) were included. During the first 12 weeks of myosin inhibitor treatment, echocardiographic parameters, laboratory values, symptoms and ECG LVH indices were assessed.

Results: Mavacamten reduced the mean left ventricular outflow tract obstruction (LVOTO) during Valsalva from 103 mm Hg (73-145) to 32 mm Hg (19-60), (p<0.001). All ECG LVH indices significantly decreased with treatment (Sokolow-Lyon Index: 2.56±0.97 mm vs 2.04±0.75 mm, p<0.001; Cornell criteria: 1.23 mm (0.92-2.21) vs 0.92 mm (0.75-1.75), p=0.001; Peguero-Lo Presti criteria: 2.39 mm (1.62-3.22) vs 1.61 mm (1.12-2.01), p<0.001; all pre vs post mavacamten). Notably, an increase in the Sokolow-Lyon Index and Peguero-Lo Presti criteria correlated with worsening LVOTO (area under the curve 0.72 and 0.88, respectively). Sensitivity and specificity of ECG LVH indices for detecting LVOTO progression during therapy were 100% and 88.6%, respectively.

Conclusion: A combinatory ECG-based approach using the Sokolow-Lyon Index and Peguero-Lo Presti criteria may serve as an accessible tool for monitoring LVOTO progression in patients with HOCM on mavacamten. Prospective validation is warranted.