Transient prolongation of the QTc interval after balloon valvuloplasty and angioplasty in children.

QTc-interval changes were evaluated in 39 children who had undergone balloon dilation procedures. In 30 children who had undergone balloon pulmonary valvuloplasty (BPV), QTc intervals were measured on standard electrocardiograms recorded before and 16 to 24 hours after the procedure and at follow-up during the next 1 to 15 months (mean 7). The QTc interval increased from 0.380 +/- 0.027 second before BPV to 0.429 +/- 0.027 second after BPV (p less than 0.002) and returned to 0.377 +/- 0.026 second at follow-up. To determine when during the catheterization-dilation procedure the QTc interval increased, QTc intervals were measured on monitor electrocardiograms recorded during cardiac catheterization. The baseline QTc was 0.382 +/- 0.041 second, was unchanged after angiography and increased to 0.427 +/- 0.043 second after BPV (p less than 0.002). A similar prolongation occurred in 3 of 4 children who had undergone balloon aortic valvuloplasty and in 4 of 5 who had undergone coarctation angioplasty. In control children, who had undergone catheterization without dilation, QTc was unchanged. Thus, transient increases in QTc interval occur after semilunar valvuloplasty and coarctation angioplasty. These dilation procedures are a cause of QTc prolongation; however, the mechanism is unknown. It is possible that the sudden unilateral increase in afterload affects the myocardium or myocardial sympathetic receptors. Because QTc prolongation may predispose children to the R-on-T phenomenon, postprocedure monitoring appears to be warranted.