Page 991 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

966 CHAPTER 8

VetBooks.ir Heart murmurs equine thorax is typically limited to referral centres.
Secondly, only lateral radiography is possible in adult
Heart murmurs are generated when flow distur-
bances in the heart or major blood vessels cause
diseases are not radiographically apparent. There is
vibrations in surrounding tissues. Once detected, a animals. Thirdly, many performance-limiting cardiac
murmur should be characterised in terms of timing limited data providing normal ranges for cardiac size
within the cardiac cycle, intensity (grade), character on equine thoracic radiographs. Usually, only the cau-
and point of maximal intensity (PMI). Terms used dal border of the heart is readily visible. Radiography
to describe heart murmurs are outlined in Table 8.2. may be of benefit in evaluating pulmonary or pleural
Common murmurs and their characteristics are out- abnormalities that may accompany, confound or be
lined in Table 8.3. differential diagnoses for cardiac disease.

DIAGNOSTIC TOOLS Electrocardiography
Multiple-lead systems have been developed for use
Once the physical examination and specific cardiac in human and small-animal electrocardiography.
examination are complete, ancillary diagnostic tools This allows the evaluation of cardiac rhythm, car-
may be required to further characterise and evaluate diac dimensions and the cardiac conduction system.
the significance of findings. In hoofed animals, the elaborate branching of the
Purkinje system allows the ventricles to depolarise
Radiography almost instantaneously. Such anatomy precludes the
Thoracic radiography is of limited value for cardiac use of electrocardiography in the horse as a measure
evaluation in the adult horse. Firstly, the equipment of diagnosing cardiac enlargement or conduction
necessary to generate sufficient-quality images of an abnormalities, such as bundle branch block. A single

Table 8.2 Murmur characterisation

TERM DEFINITION DESCRIPTIONS
Timing When it occurs in the • Systolic: between S1 and S2
cardiac cycle • Holosystolic: throughout systole, S1 and S2 audible
• Pansystolic: throughout systole, S1 and S2 obscured
• Early systolic
• Mid-systolic
• Diastolic: occurs after S2
• Holodiastolic
• Early diastolic
• Continuous: present throughout all phases
Intensity Ease of detection; graded • Grade 1: not easily detected
from 1 to 6 • Grade 2: soft, but easily detected
• Grade 3: easily detected
• Grade 4: intense sound, louder than transients
• Grade 5: loud murmur with palpable thrill
• Grade 6: palpable thrill, murmur heard when stethoscope held away from body wall
Character Shape of sound • Crescendo–decrescendo: sound appears to intensify and then decrease in intensity
• Band/plateau: smooth/uniform intensity
• Decrescendo: sound appears to decrease in intensity
• Musical: variable high-pitch components
• Coarse: not smooth sounding, but intensity stable
• Complex: sounds vary or multiple sounds present