BACKGROUND: The appearance of a discrete upward deflection of the ST segment 
termed "the ST hump sign" (STHS) during exercise testing has been associated 
with resting hypertension and exaggerated blood pressure response to exercise.
OBJECTIVE: We investigated the prevalence and clinical significance of this sign 
in a population of patients with hypertrophic cardiomyopathy.
METHODS: Eighty-one patients with hypertrophic cardiomyopathy (HCM) who 
underwent cardiopulmonary exercise testing were followed in a retrospective 
cohort study for a mean period of 5.3 years.
RESULTS: The appearance of the STHS at the peak of exercise testing was observed 
in 42 patients (52%), particularly in the inferior and the lateral leads. 
Patients with the STHS had higher fractional shortening and maximum left 
ventricular wall thickness and exhibited more frequently outflow tract gradient 
>30 mmHg at rest. Furthermore, the presence of STHS was a strong independent 
predictor of the risk of sudden cardiac death (SCD), as the latter occurred in 
eight of the patients with this sign (8/42, 19%) and in none of the patients 
without it (0/39, 0%) (P < 0.001).
CONCLUSION: The appearance of a "hump" at the ST segment during exercise testing 
appears to be a risk factor for SCD in patients with HCM. However, further 
studies are necessary to validate this finding in larger populations and to 
elucidate the mechanism of the appearance of the "hump."