Anasarca-mediated attenuation of the amplitude of electrocardiogram complexes: a description of a heretofore unrecognized phenomenon.

OBJECTIVES: The relationship between the changes of weight (WT) and electrocardiogram (ECG) QRS amplitude in patients with anasarca (AN) was evaluated.
BACKGROUND: Attenuation of the ECG voltage occurs as the electrical current spreads from the epicardium to the body surface. The voltage registered is a function of the cardiac potentials, the electrical resistivities of the intervening tissues and the orientation of the ECG leads with respect to the direction of propagation of excitation. Lung congestion and pericardial and pleural effusions can cause attenuation in the ECG potentials; additionally, a similar change was recently observed in patients with AN.
METHODS: A prospective study of this phenomenon in 28 patients with a critical illness was carried out. Electrocardiograms and patients' WTs were recorded daily. Pericardial effusions were excluded by serial echocardiograms. The sums of the amplitude of QRS complexes from the 12 ECG leads (Sigma QRS) were correlated with the corresponding WTs. Intracardiac ECGs, done in three patients, were correlated with surface ECGs.
RESULTS: Admission WT was 148.9 +/- 37.8 lbs, and it peaked to 197.8 +/- 52.3 lbs (p = 0.0005). Admission Sigma QRS was 120.2 +/- 41.6 mm and dropped to 54.8 +/- 26.9 mm at time of peak WT (p = 0.0005). Regression of Sigma QRS on WT revealed an r = 0.61 and a p = 0.0005. Subsequent WT loss in 13 patients (from 219.0 +/- 40.7 lbs to 179.5 +/- 41.7 lbs, p = 0.001) led to an increase of Sigma QRS from 53.5 +/- 24.5 mm to 86.8 +/- 38.2 mm (p = 0.001). Intracardiac ECGs remained stable, while surface ECGs changed with perturbations of WT.
CONCLUSIONS: Attenuation of ECG voltage in patients with AN correlates with WT gain, and it can be attributed to a shunting of the cardiac potentials due to the low resistance of the AN fluid.