there is head or chewing motions.
Pulse strengthThe normal pulse pressure is usually moderate in the healthy horse at rest; however, a very mild pulse may be present, especially in the distal limbs, when the horse is at rest.Decreased pulse strength may occur with peripheral vasoconstriction due to inactivity or cool ambient temperatures. May also be due to disease processes resulting in decreased perfusion or decreased cardiac output (e.g. hypovolemia, cardiac disease).Increased pulse strength occurs with increased peripheral vascular demand such as excitement, exercise or transportation. Examples of disease‐associated increases in pulse pressure include laminitis (may have increased pulse pressure in the distal limbs) and aortic valve regurgitation (common in older horses).
Pulse profileThe normal pulse profile consists of an initial rapid increase in the pulse pressure during systole, followed by a decreased pressure in very early diastole, then another increase in pressure due to the elastic‐recoil properties of the aorta and a subsequent decrease in pressure to baseline. The transition from the initial decrease to the second increase is termed the dicrotic notch. This second increase is typically palpable in the normal horse. An increase in pulse pressure above normal and a loss of the dicrotic notch occurs in horses with aortic valve regurgitation (see below).
E Peripheral veins
The jugular veins are the main veins assessed in the horse; however, all regions of the body should be observed and potentially palpated for vascular abnormalities.
The following are recommendations for jugular vein assessment:Examine the jugular veins for signs of inflammation (heat, pain, swelling) and obstruction (thrombosis/thrombophlebitis).Cranial neck and head swelling may occur, especially with acute venous obstruction.Note: IV injections of various drugs and compounds are commonly given to performance horses of most all disciplines, so careful evaluation of the jugular veins is important as partial to complete obstructions are commonplace.
Jugular vein waveforms
It is common to see fluid waves in the distal jugular vein (at the thoracic inlet) in the normal horse.
These waveforms are due to the presence of blood within the distal jugular vein, as the vein serves as a reservoir when the heart chambers are full and during systole.
The waveforms are generated in the blood column by the continuous flow of blood from the periphery to the jugular veins, carotid artery pulsation, and atrial & ventricular contractions.
These typically extend one‐third of the way up the neck when the horse is at rest and has its head and neck elevated.
The waveforms may extend one‐half of the way up the neck if the head and neck are held in a lower position or may go the length of the entire jugular vein if the head and neck are lowered such as when eating off the ground.
Occluding the jugular vein
Occlude each jugular vein in turn just caudal to the angle of the jaw (cranial jugular furrow) and milk the luminal blood distally toward the thoracic inlet; the vein should empty readily. Examine the vein for any spontaneous filling from the heart while the vein is still occluded (see jugular waveforms, above). Retrograde filling (jugular pulse) occurs with marked right AV valve regurgitation. A “true” jugular pulse is rare in the horse.
Next occlude the jugular vein distally at the thoracic inlet and observe the time for the vein to refill. The jugular vein will normally fill with blood over several seconds in the normal resting horse. Then release the vein and watch for rapid emptying.
F Heart
Cardiac silhouette
Refers to the region of the chest where the heart can be auscultated or palpated. An increased area of auscultation occurs due to cardiac enlargement or (caudal) displacement, thoracic masses or pulmonary/pleural disease.
Heart rate
The normal HR in the resting adult horse is 24–50 beats/min.
Some older, unfit horses may have a slightly higher resting HR.
The neonatal foal will have a resting HR of 80–100 beats/min and this rate will decrease as the animal ages.
The horse is very reactive to autonomic input to the heart, and some normal horses will have resting HRs less than 24 beats per/min due in part to parasympathetic nerve input (vagal stimulation).
Heart rhythm
The heart rhythm is typically regular with even timing between beats. Slight irregularity may normally occur spontaneously or in response to the respiratory cycle.
Auscultation
Heart sounds are generated by the turbulence in blood flow resulting from closure of the heart valves. The valves do not have sufficient mass to generate sounds.
Auscultation on the left side is performed between the third and fifth intercostal spaces (ICS) on the lower third of the chest. Sounds associated with the aortic, pulmonic, and mitral valve closure are heard at the base of the heart, the mitral sound is located in a more caudal position.
Auscultation on the right side is performed between the fourth and fifth ICS on the lower third of the chest. Sound associated with closure of the tricuspid valve is heard at the base of the heart.
Left side heart sounds:
Mitral valve at fifth ICS, caudal to the elbow.
Aortic valve at fourth ICS, just dorsal to the elbow.
Pulmonic valve at third ICS, under the triceps muscle, just below the level of the elbow.
Right side heart sounds:
Tricuspid valve at fourth ICS, just under the triceps muscle.
Normal heart sounds (see Figure 3.1)
Two to four heart sounds may be heard in the horse.
S1 and S2 are usually louder than S3 and S4.
S1 may be “split” (two sounds) due to slight variation in contraction in the right and left sides of the heart (uncommon).S1 is associated with closure of the left and right AV valves.S2 is associated with closure of the aortic and pulmonic valves.S3 is associated with rapid ventricular filling.S4 is associated with atrial contraction.
ECG
