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Published on: May 13, 2019
Heart murmurs in apparently healthy cats caused by iatrogenic dynamic right ventricular outflow tract obstruction
Luca Ferasin1, Heidi Ferasin1, Eoin Kilkenny2
1Specialist Veterinary Cardiology Consultancy, Alton, Hampshire, United Kingdom.
Insights
Applying pressure during echocardiography can create artificial heart murmurs in cats. This provocative testing increases right ventricular outflow velocity, mimicking abnormalities even in healthy animals.
Area of Science:
- Veterinary Cardiology
- Diagnostic Imaging
- Feline Medicine
Background:
- Heart murmurs are common in cats, often requiring Doppler echocardiography for diagnosis.
- Unexplained murmurs can occur even with expert echocardiographic evaluation.
- Applying transducer pressure can narrow the right ventricular lumen, inducing flow turbulence.
Purpose of the Study:
- To assess the impact of ultrasound transducer pressure (provocative testing) on feline right ventricular (RV) blood flow.
- To test if provocative testing increases RV outflow velocity and causes turbulence.
- To determine if this effect is independent of heart rate changes.
Main Methods:
- Retrospective review of echocardiographic exams from 723 cats with murmurs.
- Analysis focused on 61 apparently healthy cats with murmurs.
- Echocardiographic data before and during transducer pressure application was compared.
Main Results:
- Systolic outflow velocity significantly increased from 1.05 ± 0.26 to 1.94 ± 0.51 m/s with provocative testing (P < .0001).
- No correlation was found between RV outflow peak velocity and heart rate during testing (P = .34).
- This suggests the velocity increase is not heart rate dependent.
Conclusions:
- Iatrogenic right ventricular outflow tract obstruction and murmurs can be induced in cats by applying ultrasound probe pressure.
- This finding is crucial for interpreting echocardiograms in cats with murmurs.
- Distinguishing true cardiac abnormalities from artifact is essential for accurate diagnosis.
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.
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