3.6 The practice of auscultation
It is important that auscultation is performed in a methodical manner and that sufficient time is allowed for rhythm and rate to be assessed, and for the heart sounds to be heard over the entire cardiac silhouette, on both sides of the chest, at a true resting heart rate.
The stethoscope should first be placed over the apex beat. The beginning of systole can be recognised by movement of the stethoscope by the apical impulse. In the apex beat area, S1 will be clearly heard. S3 is best heard just ventral to this area. It may be helpful to establish the rhythm and rate of the heart initially, and then identify the beginning of systole and diastole. Then it is helpful to inch the stethoscope cranially and dorsally until it is over the cardiac base, where S2 will be heard best. As the stethoscope is moved, it may help first to concentrate on the heart sounds, then on systolic murmurs and then on diastolic murmurs. It is sometimes useful to 'listen-in' to different frequencies so that one can conon low-pitched sounds and then on high-pitched sounds. The bell of the stethoscope transmits low-pitched sounds best and should be used in addition to the diaphragm. Once the cardiac area has been completely covered on the left side of the chest, the same process can be completed on the right. It is common for inexperienced clinicians to fail to advance the stethoscope far enough into the axilla and consequently they may miss important sounds. It may be helpful to make the horse stand with the leg advanced on the side of auscultation, if it is well tolerated.
After careful auscultation, it is helpful to make a note of the findings in the form of diagrams, as shown for the different murmur classifications, annotated onto an anatomical drawing of the cardiac area (Figure 3.12). This can be combined with case details and history into a clinical record sheet (Figure 3.13).