Right ventricular outflow obstruction secondary to nonpenetrating blunt trauma to the canine myocardium.

The purpose of this study was to investigate the development of a right ventricular (RV) outflow tract obstruction of sufficient severity to produce a systolic murmur following blunt cardiac trauma. A nonpenetrating impact directly on the anterior surface of the heart was produced in 34 open chest anesthetized dogs. Impact velocity was 12 m/sec in 15 dogs and 18 m/sec in 19 dogs. Seventeen dogs died immediately following impact. Pressures in the pulmonary artery and RV were measured during the control period in all dogs, and intermittently for 90 minutes following impact in ten of the 17 surviving dogs. At 90 minutes following impact a systolic pressure gradient of 9 +/- 2 mm Hg (range, 3 to 22 mm Hg) developed across the RV outflow tract and was associated with a prominent ejection murmur. At autopsy, RV wall thickness measured at the midventricular level was 13.5 +/- 1 mm (mean +/- SEM) which was thicker than in dogs that died immediately following impact, 6 +/- 1 mm (p less than 0.001). Microscopy of the RV myocardium of dogs that survived impact showed interstitial bleeding with prominent accumulations of blood between muscle bundles, whereas dogs that died immediately after impact showed no interstitial bleeding. The obstruction seems to have resulted from the increased RV wall thickness due to interstitial bleeding. In the absence, therefore, of other evidence to explain a new systolic murmur in patients following nonpenetrating cardiac trauma, the possibility of RV outflow obstruction might be considered.