Conduction system injury after aortic valve dilation in the dog single- versus double-balloon catheters.

The range of morbidity induced by valvuloplasty is not fully known, but transient conduction disturbances are common. The authors performed aortic valve balloon dilatation on 10 closed-chest dogs with normal aortic valves, using a femoral cutdown approach and fluoroscopic guidance. Four were done with a single 15 mm balloon catheter, and in the other 6 two 12 mm balloon catheters were used. Balloons were inflated to 5 to 12 atms pressure with contrast solution. After several inflations the dogs were sacrificed, the hearts removed and examined. Gross examinations revealed subendocardial hemorrhage in the outflow tract in 5 of the 6 in which double balloons had been used. Microscopically, all aortic valve areas showed hemorrhage, mostly in loose connective tissues of the valve leaflets. The severity of injury appeared greater when two balloons had been used. Histologic examination showed definite injury to the myocytes of the left bundle branch in all 6 of the double-ballooned dogs, but in none of those subjected to the single-balloon procedure. During aortic valve dilation the only manifestation of conduction system injury was prolongation of the QRS complex in 3 of the 6 dogs in which a double-balloon catheter had been used. The results suggest that electrocardiographic conduction disturbances observed in patients undergoing aortic valvuloplasty may be the result of direct injury of conduction tissue and may be more likely to occur when larger balloons are used.

Complete heart block developing during aortic valvuloplasty.

We report the occurrence of CHB consequent to ABV in an 80-year-old white woman with calcific aortic stenosis. The patient underwent ABV with a balloon 20 mm in diameter, resulting in only a modest increase in aortic valve area and a decrease in aortic valve gradient. The procedure was complicated by transient intermittent CHB which required temporary transvenous pacemaking and resolved within 72 hours. A second ABV was performed four weeks later with a balloon 23 mm in diameter. This was complicated by persistent CHB which required placement of a dual-chamber pacemaker.

Cation/proton antiport systems in Escherichia coli. Absence of potassium/proton antiporter activity in a pH-sensitive mutant.

Alkaline-sensitive strains of Escherichia coli were selected by mutagenesis followed by penicillin killing in medium at pH 8.3. One such strain was found to lack K+/H+ exchange. At neutral pH, the doubling time of the mutant was not significantly different from that of the parent, but at pH 8.3 the doubling time of the mutant increased over 5-fold. No energy-dependent uptake of 204Tl+ was observed in the mutant, but addition of the K+/H+ exchanger Nigericin resulted in identical 204Tl+ uptake in the mutant and parent. These results are consistent with the hypothesis that the K+/H+ antiporter is responsible for regulation of cytosolic pH in E. coli. In the absence of antiporter, the organism would be unable to grow at alkaline pH due to alkalinization of the cytosol.