Page 992 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Cardiovascular system 967

VetBooks.ir Table 8.3 Murmur types and causes

POINT OF
PHASE OF INTENSITY MAXIMAL
CYCLE TIMING CHARACTER (GRADE) INTENSITY RADIATION LESION
Systolic Early to Crescendo– 1–3 Heart base No Functional
mid-systolic decrescendo or
band/plateau
Holo-pansystolic Band/plateau; 2–6 LAVV Yes; dorsal to LAVVR
complex if valve valve, variable
prolapse extent
Holosystolic Band/plateau; 2–6 RAVV Yes; dorsal to RAVVR
complex if valve valve, variable
prolapse extent
Pansystolic Band/plateau; may 3–6 Variable; right Yes; often widely VSD
be coarse sternal border; left and may radiate
sternal border; to the left
less common
Diastolic Early to Whoop or 1–3 Heart base No Functional
mid-systolic decrescendo
Holodiastolic Decrescendo or 1–6 Left heart base Yes AR
musical
Holodiastolic Variable 1–4 Right heart base Variable Aortic root rupture
Continuous Throughout; Variable 1–4 Left heart base Variable PDA
diastolic quieter
Throughout Variable, 1–4 Heart base; often Variable Aortic root rupture
often complex on right
Throughout Variable 1–6 Right heart base Variable Arteriovenous fistula
LAVV = left atrioventricular valve; RAVV = right atrioventricular valve; LAVVR = left atrioventricular valve regurgitation; RAVVR = right atrioven-
tricular valve regurgitation; VSD = ventricular septal defect; AR = aortic regurgitation; PDA = patent ductus arteriosus.

lead can therefore be used in the horse. The electro- Electrocardiography should be performed in
cardiogram (ECG) is used to assess cardiac rate and the resting animal to demonstrate resting rhythm.
rhythm and to evaluate the generated complexes. Electrocardiography is indicated in any animal
A standardised system should be used for elec- in which an arrhythmia is detected during physi-
trocardiography in order to allow comparison. cal examination. In the horse the ECG should be
In general, a base–apex ECG is used, with some recorded at 25 mm/s and at a sensitivity of 1 mV/cm
variation in the exact electrode positioning. Large for several minutes to allow for evaluation of baseline
complexes are usually generated and are therefore cardiac rhythm. The short duration of ECG record-
easily evaluated. With the Y-lead (base–apex) lead ing means that only those arrhythmias that are pres-
system the negative electrode (right arm) is placed ent either continuously or at the time the recording
at the manubrium and the positive electrode (left is generated can be evaluated. If cardiac arrhythmia
arm) is placed at the xyphoid. The ground electrode or sporadic abnormal complexes are considered as
(right limb) is placed on either side at the shoulder potential causes of poor performance, weakness
(Fig. 8.3). Alternatively, the positive electrode can or collapse, either 24-hour ambulatory recording
be positioned at the right side of the withers and the (Holter monitor) or exercise electrocardiography
negative electrode at the ventral midline. (telemetry) may be indicated. This is of particular