Low noise level unmasks late potentials on signal-averaged electrocardiography.

INTRODUCTION: Identification of late potentials requires the reduction of random noise by signal averaging. The importance of using a very low noise level (NL) as the end point of the averaging process in patients with ventricular tachycardia, the variation of results when a lower than standard NL was used and the modification of the sensitivity of the test when a very low NL was reached were evaluated. METHODS AND RESULTS: Signal-averaged electrocardiograms were recorded in 36 patients with ischemic heart disease and spontaneous or induced sustained or nonsustained ventricular tachycardia. Thirteen patients showed negative or indeterminate results on recordings with an NL of 0.3 µV. Eight patients (group 1) underwent a second recording with an NL of 0.1 µV. Eight normal volunteers constituted the control group (group 2). The total duration of the filtered QRS vector magnitude (QRSd), the root mean square voltage of the terminal 40 ms of the vector magnitude (RMS(40)) and the low amplitude signal duration under 40 µV in the terminal portion of the vector magnitude (LAS) modifications were evaluated. A significant difference (P<0.01) in these parameters was observed in group 1 (15.88%, 48.25% and 68.5%, respectively) when both recordings were compared. Tests were positive in all patients (100%) with NL reduction. In group 2, tests were negative in all patients (100%) at both NLs (0.3 µV and 0.1 µV). QRSd was 1.18% longer, RMS(40) was 1.38% lower and LAS was 3.55% longer with NL reduction. CONCLUSION: Late potentials in patients with ischemic heart disease, ventricular tachycardia, and a negative or indeterminate signal-averaged electrocardiogram may be detected if the NL is reduced to 0.1 µV. Reduction of the NL increased the sensitivity of the test without modifying its specificity.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy. A review and update.

The arrhythmogenic right ventricular dysplasia/cardiomyopathy is an important cause of sudden arrhythmic death, often exertional, in young individuals and athletes. Although the aetiology remains partially unknown, genetic abnormalities have been demonstrated. Reported prevalence is 1 in 5000 individuals but it is considered there are many non-diagnosed cases. The characteristic pathologic finding is the progressive fibro-fatty replacement of the right ventricular myocardium. The clinical manifestations vary from asymptomatic patients with an episode of sudden cardiac death as first symptom to chronically symptomatic patients with recurrent palpitations and/or right or biventricular failure. Approximately a third of the patients show the characteristic Epsilon wave in the 12-lead ECG which is a useful screening test. Signal-averaged ECG frequently demonstrates late potentials. The two-dimensional echocardiography, magnetic resonance imaging, computerized tomography and right ventricular cineangiography show morphologic abnormalities in the right ventricle. Therapy is directed to prevent and/or treat malignant ventricular tachyarrhythmias with medications, implantable cardioverter defibrillator and radiofrequency ablation in selected cases.

Aquagenic urticaria: report of a case.

Aquagenic urticaria is a very rare form of physical urticaria induced by contact with water. In this case report, we describe a child with a typical form of the disease in whom other types of physical urticaria were ruled out. Clinical manifestations, investigational methodology, and available treatments were reviewed. Treatment with hydroxyzine, 25 mg daily, was successful after a month follow-up in preventing wheals and erythema. However, mild pruritus is still present after contact with water.