LOW VOLTAGE OF THE P WAVE ON 12-LEAD ELECTROCARDIOGRAM IN PATIENTS WITH SEVERE CARDIOPATHIES AND ELECTRICAL VENTRICULAR ABNORMALITIES:  THE PARADOXAL P WAVE. 
A PRELIMINARY REPORT

Paulo Ginefra, Eduardo C. Barbosa, Flávia G. Brasil,
Alfredo S. Bomfim, Sílvia H. Boghossian, Paulo R. B. Barbosa,
Francisco M Albanesi Fº
Rio de Janeiro State University School of Medicine, Rio de Janeiro, Brazil.

Abstract: The low voltage (LV) and aparent normal duration of the P wave on ECG in severe cardiopathies with electrical ventricular abnormalities (EVA), is a paradoxal event and frequently neglected.  Thirty-one consecutive patients (pts) have been studied with ECG and vectocardiogram (VCG).  Eight pts underwent Signal-Averaged ECG (SAECG) of the P wave on time and frequence domains.  Results are summarized on table 1.  We concluded the low voltage of P wave, with normal or high voltage of QRS complexes associated to EVA may be considered a new aspect of intra-atrial conduction disturbance.

INTRODUCTION

There are several known factors wich atenuate the ECG voltage during the spread of electrical current from the epicardium to the body surface:  pulmonar emphysema, lung congestion, pleural and pericardial effusions, anasarca, diffuse myocardial fibrosis, hypothyroidism, obesity, etc.  It is a paradox that, in severe cardiopathies the P wave has a very LV in contrast with the normal or increased voltage of the QRS complexes.  The aim of this study is to evaluate the LV of the P wave with 12-lead ECG, VCG and SAECG.

METHODS

Thirty-one pts. (18 male, ages ranging from 23 to 78 y.o. mean = 50 ± 18.2 VAR 332.80) have been studied:  11 Hypertrophic, 9 Dilated Cardiomyopathies, 5 Hypertensive Heart Disease, 4 Myocardial Infarction and 2 Valvular Heart Disease.  EVA was complete left and right BBB, left ventricular hypertrophy, electrical inactive areas, 1^st and 2^nd degree AV block, ventricular extrasistoles, all these events were isolated or associated.  Five patients had recurrent   atrial fibrillation.  The  analysis  of  P wave  was  performed      with ECG and Frank-System Vectorcardiogram (VCG).  Echocardiogram (ECHO) was used for measuring the dimension of the left atrium (LA) and ejection-fraction (EF) of the left ventricle.  On ECG the voltage (V) and duration (D) of the P wave were studied; the VCG was performed with interruption of the electron-beam at intervals of 0.0025s (each instantaneous vector = 0.0025s) for recording the total duration of the P loop (LOD) and duration of localized delay (DD) in the loop.  Eight pts. underwent time domain and frequence domains Signal-Averaged-ECG (SAECG) of P wave.

TABLE I

V = Voltage; D = Duration; LOD = Loop Duration; DD = Delay Duration; LA = Left Atrium; EF = Ejection-Fraction.

RESULTS

Are summarized on Table 1.  Despite the normal P duration on ECG, the total P loop duration on VCG was increased, with delays and many instantaneous vectors cancelling each-others, mainly in the terminal portion of the loop.  From 8 pts., 5 (62.5%) had P duration increased on SAEG time domain (³ 155ms).  All variables of frequence domain were normal.

DISCUSSION

The spread of the electrical current from the epicardium to the body surface depends on several factors.  The LV of the P wave in presence of normal or increased voltage of the abnormal QRS complexes in severe cardiopathies is still unknown.  In this study the mean value of P voltage was less than 1mv and its duration was less than 0.10s on ECG, wich characterizes the normality of P wave.  Despite this configuration on ECG, on VCG the P loop had a irregular shape with mean duration of 136ms, specially on left transverse plane.  We also observed in the P loop many instantaneous vectors cancelling each-others and also dellays on the preterminal and terminal portion of the loop with mean DD of 44.3ms.  It is possible that the cancellation of some vectors may explain the attenuation of P wave voltage on body surface by loosing its pollarity.  Those facts suggest disturbance of electrical atrial conduction by changes on myocardial structure of fibrous tissues, without fragmented potentials, since the SAECG did not record electrical turbulence on frequence domain, which was normal in all pts.  SAECG also demonstrated usefullness in detecting the increasing duration of the P wave (more than 155ms). We conclude that LV of P wave with EVA may be considered a paradox and the events observed in this study suggest a new aspect of intra-atrial electrical conduction disturbance.

REFERENCES

1 - Madias JE, Bazaz R, Agarwal H, et al..  Anasarca-mediated attenuation of the amplitude of eletrocardiogram complexes:  A description of a heretofore unreconized phenomenon, JACC, vol. 38(3), pp. 756-64, 2001.

2 - Cooksey   JD,  Dunn  M,  Massie  E.  Clinical Vectocardiography and Electrocardiography.  Chicago:  Year Book Med Publ Inc, 2^nd Ed., 1977, pp. 128-130.

3  - Kelen GJ, Henkin R, Starr AM et al..  Spectral turbulence analysis of the signal-averaged electrocardiogram and its predictive accuracy for inducible sustained monomorphic ventricular tachycardia, Am J Cardiol, vol. 67, pp. 965-75, 1991.

4  -  Barbosa EC, Barbosa PRB, Ginefra P et al..  The frequency analysis of the Signal-Averaged ECG of the P wave is a good predictor of the efficacy of class III antiarrhythmic drugs to mantain the sinus rhythm in patients with recurrent atrial fibrillation.  Ann Noninvasive Electrocardiol, vol. 6(1), pp. 43-49, 2001.