Abstract 15703: Hypertrophic Cardiomyopathy with Normal ECG: Clinical Meaning and Prognostic Implications

Objectives: The present study was designed to assess proportion of patients with hypertrophic cardiomyopathy (HCM) showing no electrocardiographic (ECG) changes or isolated increase of QRS voltage, which overlap with either a normal ECG or an athlete's heart ECG. The aim was to assess the risk to miss a diagnosis of HCM due to false negative ECG.

Methods: Using accepted criteria, we examined the ECG tracings of 245 (172, 70% males, mean age 44±7 years) patients with clinical and echocardiographic diagnosis of HCM and correlated ECG findings with echocardiographic features of left ventricular hypertrophy (LVH).

Results: An abnormal ECG was found in 234 of 245 (95%) HCM patients and showed one or more of the following changes: ST/T abnormalities in 199 (81%), pathologic Q waves (Q waves ≥0.04 s in duration or ≥25% of the height of the ensuing R wave) in 89 (36%); left atrial enlargement in 91 (37%), intraventricular conduction abnormalities (QRS duration ≥90 ms) in 30 (12%) and left axis deviation in 26 (11%). ECG was completely normal in 11 patients (4%) and showed an isolated increase of QRS voltages (Sokolow-Lyon criteria, i.e. SV1+RV5 or RV6 >35 mm) in 6 (2%). Compared with the remaining HCM patients, those who had either a normal ECG or pure QRS voltage criteria for LVH showed a significantly less severe LVH (maximal LV wall thickness =17±2mm vs 21±5; p=0.001), which was limited to ≤2 segments, most often anterior basal septum (53% vs 6, p<0.0001). There were no statistically significant differences with regard to age (38±14 yrs vs 44±17;p=0.16), LV cavity dimension (LV end diastolic diameter=47±3 mm vs 45±6; p=0.1), and LV systolic function (shortening fraction=43±10% vs 43±9; p=1.0). During a follow-up of 8±6 years no patients with a normal ECG or an isolated increase of QRS voltage experienced arrhythmic events, such as ventricular tachycardia/fibrillation and sudden death, compared with 8% of other HCM patients.

Conclusions: The estimated risk to miss a diagnosis of HCM due to false negative ECG was about 7%. However, HCM patients with normal ECG or isolated increase of QRS voltages had a less severe and segmental LVH, associated with a low arrhythmic risk. These results may have significant implications for ECG screening of competitive athletes for HCM.