Vectorcardiographic QRS loop in spontaneous pneumothorax

Vectorcardiographic QRS loops were recorded in twenty-nine patients with primary spontaneous pneumothorax (SP), comprised of eighteen of left SP and eleven of right SP. The configurations of QRS loops in acute to recovery phases were compared. The patients were classified into three groups according to the degree of collapse of the lung (Group A: 25% or less, Group B: 25% to 50%, Group C: 50% or more). The major features of the QRS loop in SP were as follows: Left SP--Leftward QRS force was markedly reduced and the mean QRS axis showed a shift to the inferior and posterior. The greatest changes in the QRS loop appeared in group B. Right SP--The mean QRS axis tended to shift to the posterior and to the right. For clarifying the cause of the changes in the QRS loop, a simulation study was performed with a two-dimensional electrical field model. The results of the simulation study strongly suggested that the alterations of the QRS loop in spontaneous pneumothorax were mainly due to extracardiac reasons.