of the Cardiovascular System
Daniel G. Kenney
Evaluation of the horse should include detailed evaluation of the medical and performance history. Of particular note for the cardiovascular system is whether there is an unexplained decrease in body condition, the presence of respiratory abnormalities, edema formation, and decreased exercise tolerance.
A thorough physical examination should be performed in a systematic fashion, including detailed assessment of the cardiovascular system.
I Cardiovascular evaluation
A Body condition
Poor body condition and decreased exercise tolerance may indicate cardiovascular disease.
B Edema
Presence of edema in ventral areas (abdomen, thorax, prepuce, udder, limbs) may be indicative of cardiovascular disease.
C Mucous membranes
Assess for hydration, color, and capillary refill time.
The oral mucous membranes are readily assessed in most horses.
Vulva membranes and sclera (observation only) may also be assessed.
Color:
The mucous membranes are visually assessed; normal membranes are pink.
Pale membranes (pale pink to whitish) may be due to poor cardiac output/poor perfusion and/or anemia.
Dark membranes (deep pink, red, brown, purple) may be due to poor perfusion, vascular congestion, septicemia, and/or toxemia.
Bluish membranes may indicate poor perfusion.
Yellow membranes occur with elevated bilirubin concentrations (icterus/jaundice). Horses with reduced feed intake often have a mild yellow component to the membrane color. Icterus also occurs to a more severe extent with hemolysis (intravascular or extravascular) or with liver disease.
Hemorrhagic membranes may present as “pinpoint” to “expansive” lesions (petechiae to ecchymosis). These may occur with thrombocytopenia, coagulopathies or microangiopathies.
Moistness:
Hydration is assessed by:Observation and by touching the membranes.Normal membranes are moist.Tacky to dry membranes can occur due to dehydration resulting from many disease processes. The effects of dehydration can be categorized into three groups:
Mild dehydration (~5% of body weight) – slight tacky membranes. Skin turgor is normal and eyes are not sunken.
Moderate dehydration (6–8% of body weight) – moderately tacky membranes and increased duration of skin tenting (decreased turgor). Eyes are not sunken.
Severe dehydration (10–12% of body weight) – markedly tacky membranes, decreased skin turgor (prolonged tenting), eyes are sunken.
Note: Caution should be used when assessing sunken eyes as this may also occur with a decrease in the retrobulbar fat pad due to weight loss. The sunken appearance may also occur with ocular disease. Decreases in skin turgor may occur in the neonate, the very old horse, and animals with marked weight loss.
Exposure:
Mucous membranes may be tacky to dry with exposure secondary to swelling, trauma, neurologic dysfunction or other cause.
Capillary refill time (CRT):
Is assessed by rapid light touch of the observer's finger or thumb to the membranes resulting in blanching of the tissue, and the time to reestablish color is noted (see Figure 3.2).
Normal CRT is <2 seconds. A prolonged CRT may occur due to dehydration, toxemia/septicemia and/or decreased cardiac output. Prolongation usually reflects systemic problems but may also occur due to local disease processes.
D Peripheral arteries (pulses)
Peripheral pulses can be assessed at the head or on the limbs of a horse.
Caution must be used when palpating the hind limb arteries to avoid injury to the examiner. Figure 3.2 Normal mucous membrane color, blanching of mucous membranes with pressure for assessment of capillary refill time.
Sites for palpation:
Transverse facial arteryRuns horizontally on the lateral aspect of the head, behind the zygomatic arch, cranioventral to the ear.
Facial (submandibular artery)Can be palpated at the ventral aspect of the mandible, just cranial to the ramus, easy to palpate by “trapping” the somewhat movable artery between the skin and medial aspect of the mandible.
Maxillary arteryRostral to the infraorbital canal.This is a useful site in foals to palpate the pulse.
Posterior digital and abaxial sesamoid arteriesLocated at the caudolateral and caudomedial aspects of the pastern and fetlock, respectively.Palpable in all limbs.
Radial arteryLocated at the medial aspect of the carpus.
Median arteryLocated at the medial aspect of the forearm.
Great metatarsal arteryCaudolateral aspect of the hind limbs, runs vertically in the groove formed by the apposition of the canon and lateral splint (MT 3 and 4) bones.
Femoral arteryDeep palpation at the medial aspect of the thigh. Not a practical site for palpation in the adult horse.
Coccygeal arteryMore readily palpable in foals than adult horses.
Assessment of the pulse:
Pulse rateNormal rate is similar to the HR (24–50 pulses per minute).Assess the pulse while auscultating the heart to determine whether there are any heart beats without pulse generation (“dropped beats” or “pulse deficit”).
Pulse rhythmThe normal rhythm is regular. Slight irregularities may occur in the normal horse due to irregularities in the sinus firing (inherent or respiration associated).Rhythm assessment can be
