CARDIOLOGY
Cardiac Murmurs
in Dogs and Cats
Causes, Diagnosis and Significance
Dr Russell Leadsom
BVSc Certificate Vet.Cardiology
Tel: 083 218 6562 (Alphen Vets 021 794 1522) E-mail: [email protected]
A murmur is an audible sound produced by vibrations of cardiovascular structures as a
result of disturbed or turbulent blood flow replacing normal laminar flow.
loudest; intensity on a 1/6 to 6/6 scale; radiation over
the thorax and neck; timing within the cardiac cycle
- systolic, diastolic or continuous; and quality such as
“soft”, “musical” or “harsh”.
Further descriptive terms include the timing within the
systole or diastole e.g. early or late systole. The fast
heart rates of dogs and cats usually make this difficult
without phonocardiography.
Fig 1. Laminar and turbulent blood flow
There is a critical velocity at which laminar flow becomes turbulent, it is expressed by Reynold`s number
and is dependent on the velocity of the blood, viscocity and the vessel diameter (fig. 1).
Fig 2. Left side PMI's. (P = pulmonic valve, A = aortic valve,
M = mitral valve, PDA = patent ductus arteriosus).
Diagnosis needs good auscultatory skills that require
patience, time and practice. A quality stethoscope
and a quiet environment are vital.
Murmurs may be masked by obesity, pleural and pericardial effusions, and respiratory sounds. Tachypnoea
breathing, panting may be mistaken for murmurs.
Murmurs are described by their point of maximum
intensity (PMI) (figures 2 & 3) noting the location, intercostal space, and valve over which the murmur is
Fig 3. Right side PMI's. Right side (T = tricuspid valve, A =aortic
valve, VSD = ventricular septal defect)
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