LATE VENTRICULAR POTENTIALS AND MITRAL-VALVE PROLAPSE

Signal averaged electrocardiogrammes were recorded in 100 consecutive patients with echocardiographic mitral valve prolapse (MVP) and compar ed with 50 normal control subjects. Criteria of normality were defined in the reference population: QRS duration after averaging < 113 ms, S imson's vector of the last 40 ms (RMS40) greater-than-or-equal-to 17 m uV, and duration of the terminal potential within the 40 muV range < 3 8 ms, using a high-pass bidirectional 40 Hz filter. Of the 100 patient s 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 d ependent on the appearences of the valve; when the valve was of normal thickness and only showed slight systolic bulging there were only 5/4 6 cases of LP (10.9 %) which did not differ significantly from the con trol group. On the other hand, when the valve showed myxoid changes, t he prevalence of LP was very high: 33/54 = 61 % (p < 0.001 versus cont rols). Six patients had severe ventricular arrhythmias (sustained vent ricular tachycardia or ventricular fibrillation): all had LP. In cases of MVP with frequent ventricular extrasystoles (VEs) the prevalence o f LP was the same with normal valves (2/23 = 9 % and 2/22 = 9 %, NS) w hereas LPs were more common in cases of VEs with myxoid valve (23/33 = 70 % versus 5/16 = 31 %; p = 0.01). The high prevalences of LP in MVP with myxoid valves is a convincing argument in favour of myocardial a bnormality in this disease. Conversely, the low prevalence of LP in pa tients with mild systolic bulging of a valve of normal thickness confi rms that these subjects should not be considered as having a severe co ndition : this population is comparable to that of subjects with idiop athic ventricular arrhythmias. The search for prognostic criteria in t his series of patients with MVP showed that if a QRS greater-than-or-e qual-to 116 ms, a duration LP greater-than-or-equal-to 43 ms and a RMS 40 less-than-or-equal-to 11 muV are present, 4 out of 6 patients with spontaneous VT/VF are correctly identified with only 8 false positives in the subgroup of patients with myxoid valves and frequent VES. Thes e criteria, therefore, provide a good assessment of the risk of severe arrhythmias in MVP with a sensitivity of 67 %, a specificity of 91.5 % and a relative risk of 21. These results deduced from a retrospectiv e analysis should, however, be confirmed by a prospective study.