Heart murmurs in apparently healthy cats caused by iatrogenic dynamic right ventricular outflow tract obstruction

Background Heart murmurs are detected commonly in apparently healthy cats during routine physical examination, and Doppler echocardiography ultimately is required to identify the source of flow turbulence causing the murmur. However, in some cases, the origin of the murmur cannot be identified on echocardiographic examination, even by experienced clinicians. The application of gentle pressure with the ultrasound transducer against the chest wall of a cat can induce temporary narrowing of the mid-right ventricular (RV) lumen, causing blood flow turbulence even in the absence of cardiac abnormalities. Objectives/Hypotheses To evaluate the effect of pressure of the ultrasound transducer against the chest wall of cats during echocardiography (provocative testing) on RV blood flow. The main hypothesis is that provocative testing can increase RV outflow velocity and cause flow turbulence. The second hypothesis is that the effect of this maneuver is independent of changes in heart rate during testing. Animals Sixty-one client-owned, apparently healthy cats with heart murmurs on physical examination. Methods Retrospective review of echocardiographic examinations of 723 cats presented for investigation of a heart murmur. Results Outflow systolic velocity increased from 1.05 +/- 0.26 to 1.94 +/- 0.51 m/s during provocative testing (P < .0001); no correlation was found between RV outflow peak velocity and heart rate during provocative testing (P = .34; r = 0.1237). Conclusions and Clinical Relevance Right ventricular outflow tract obstruction and associated heart murmur can be iatrogenically induced in apparently healthy cats by increasing pressure on the right chest wall with an ultrasound probe.