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Clinical approach to cardiac murmurs

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Abstract

The practice of cardiac auscultation remains one of the most widely used diagnostic techniques in veterinary medicine. Technical considerations of cardiac auscultation and interpretation of heart sounds and murmurs are therefore of wide interest to the veterinary practitioner. Although it may not be possible to establish the diagnosis of a specific heart disease with the sole use of a stethoscope, or in combination with a phonocardiogram (PCG), optimal use can narrow down the list of differential diagnoses substantially. A gentle approach and quiet environment are essential for the animal to relax and for the auscultator to be undisturbed. It is also essential to auscultate all cardiac areas to detect local murmurs and, in the case of a heart murmur, the point of maximum intensity (PMI). The chapter covers Stethoscopes; Origin of murmurs; Auscultation and the point of maximum intensity; and the Differential diagnoses for different cardiac murmurs.

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Figures

Image of 4.1
4.1 ECG lead II and PCG from a healthy large dog, recorded at the mitral area. The PCG was recorded with the dog standing on the examination table. Notice the timing between the ECG and the PCG. Artefacts (noise) will also be recorded on the PCG, but appear differently timed to S1, S2 and the ECG (artefacts are marked A). Undulations of the baseline can be caused by noise from the surroundings, muscle tension and respiration. If respiratory sounds cause PCG deflections, limit interpretation to expiratory phases only, or occlude the mouth and nostrils of the patient while recording the PCG.
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4.2 Points of maximum intensity. Left side of the thorax. 1 = Mitral area; 2 = Aortic area; 3 = Pulmonic area. Right side of the thorax. 4 = Tricuspid area. IV = 4th intercostal space. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission
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4.3 Common differential diagnoses for cardiac murmurs. The blue circle shows the point of maximum intensity. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission IV = 4th intercostal space.
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4.4 Physiological flow murmurs are caused by turbulent flow in the aorta or pulmonary artery during early systole with a duration of less than half of systole. The PCG recorded in a puppy showed that murmur intensity was low/moderate at the aortic/pulmonic area. The murmur had disappeared when the dog was re-examined as a 1-year-old. (Left image © C. Kvart.)
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4.5 Hypertrophy of the upper portion of the interventricular septum may cause obstruction and turbulent blood flow. (© C. Kvart.)
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4.6 PDA is characterized by turbulent flow from the aorta to the pulmonary artery both during systole and greater flow at the end of systole and beginning of diastole. diastole, with greater flow at the end of systole and beginning of diastole. (© C. Kvart.)
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4.7 Incompetence of the mitral valve causes mitral regurgitation with turbulent blood flow, usually throughout systole. This causes a holosystolic murmur. (© C. Kvart.)
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4.8 A moderate-intensity systolic murmur from a dog with moderate MMVD. This patient was still asymptomatic and not in need of therapy. Note that the second heart sound is of decreased intensity but still visible. A low-intensity (often inaudible) third heart sound (S3) is sometimes present, as in this case.
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4.9 Turbulent blood flow is caused by shunting of blood from the LV to the RV throughout systole. This is due to a significant difference in blood pressure during systole, a difference that disappears during diastole. (© C. Kvart.)
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4.10 Incompetence of the tricuspid valve causes tricuspid regurgitation with turbulent blood flow, usually throughout systole, causing a holosystolic murmur. (© C. Kvart.)

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