[Late potentials and mitral valve prolapse].

Signal averaged electrocardiogrammes were recorded in 100 consecutive patients with echocardiographic mitral valve prolapse (MVP) and compared with 50 normal control subjects. Criteria of normality were defined in the reference population: QRS duration after averaging < 113 ms, Simson's vector of the last 40 ms (RMS40) > or = 17 microV, and duration of the terminal potential within the 40 microV range < 38 ms, using a high-pass bidirectional 40 Hz filter. Of the 100 patients with MVP, late ventricular potentials (LP) were recorded in 38 cases with at least 2 criteria of positivity, compared to only 3 out of 50 (6%) in the control group (p < 0.01). The prevalence of LP was very dependent on the appearances of the valve; when the valve was of normal thickness and only showed slight systolic bulging there were only 5/46 cases of LP (10.9%) which did not differ significantly from the control group. On the other hand, when the valve showed myxoid changes, the prevalence of LP was very high: 33/54 = 61% (p < 0.001 versus controls). Six patients had severe ventricular arrhythmias (sustained ventricular tachycardia or ventricular fibrillation): all had LP. In cases of MVP with frequent ventricular extrasystoles (VEs) the prevalence of LP was the same with normal valves (2/23 = 9% and 2/22 = 9%, NS) whereas LPs were more common in cases of VEs with myxoid valve (23/33 = 70% versus 5/16 = 31%; p = 0.01). The high prevalence of LP in MVP with myxoid valves is a convincing argument in favour of myocardial abnormality in this disease.(ABSTRACT TRUNCATED AT 250 WORDS)