1. Fact Sheet Sponsored by:
Cardiology: The Equine Heart
Cardiac disease is thought to be the third-most-common cause of “poor performance” in athletic horses
Overview EquinE HEarT
coronary
The equine heart is a hollow organ com- aorta aortic valve
groove pulmonary aorta pulmonary
prised of two chambers—one with two atria brachiocephalic veins veins
cranial vena
and the other with two ventricles—that trunk cava
function in concert to receive deoxygenated
blood from veins into the right side and sub-
sequently propel oxygenated blood through
the body via arteries from the left side. left atrium pectinate
Cardiac disease is considered the third- pulmonary muscle left atrium
trunk
most-common cause of “poor performance”
cranial vena
in athletic horses (after musculoskeletal
cava
disease and respiratory disorders); how-
dr. roBIn PeTerSon IlluSTraTIonS
ever, cardiac abnormalities are rare. Horses
with cardiac dysfunction typically present
with a history of poor performance/exercise right
intolerance, distended veins, swelling of the ventricle coronary
limbs, weakness, or collapse. left ventricle vessels
right atrium
Structure and Function right atrium
The equine heart is located in the ante- interventricular
groove right ventricle chordaetendineae
rior region, largely covered (externally) by left ventricle
the forelimbs. The exact anatomic loca- complex network of arteries, arterioles,
interventricular septum
tion within the chest cavity and the overall and capillaries to deliver the oxygenated
size of the heart is breed-dependent. The blood to the organs and tissues. H e a r t m u r m u r s a n d va l v u l a r h e a r t
equine heart is a four-chambered, hollow, In horses, 100% of the blood volume disease The heart valves play an impor-
muscular organ divided into right and left passes through the heart each minute. tant role in ensuring unidirectional (mov-
sides by a septum (wall). Each side has an Thus, coordinated contraction of the heart ing one direction) flow blood through
atrium (a receiving chamber) and a ven- chambers and proper functioning of the the heart. Leaky valves, often referred to
tricle (an ejecting chamber). valves located between the atria, ventri- as insufficient valves, are those that per-
Blood is dumped into the right ventricle cles, and their associated blood vessels is mit blood to flow back across the valve
from the venous circulation via the infe- essential. The sinoatrial node, located in either through the atria or the ventricles.
rior and superior vena cava. This oxygen- the right atria, is the heart’s pacemaker. This backflow, depending on the severity
poor blood then flows through the right It is responsible for controlling the rate and the exact valve that is affected, is of-
atrioventricular valve (also known as the of atrial and ventricular contractions. It ten associated with a heart murmur. The
tricuspid valve) to the right ventricle. The achieves this by initiating an electrical sig- murmur itself simply indicates that the
right ventricle contracts to pump the blood nal that travels through the heart between blood flow in a specific region of the heart
through the pulmonic valve and pulmo- the right and left atria to the atrioventricu- is turbulent, not that the horse has heart
nary arteries to the lungs, where oxygen lar node and via “Purkinje fibers” located disease.
is loaded onto the hemoglobin within the throughout the ventricles. Cardiac arrhythmias An arrhythmia re-
red blood cells. Oxygenated blood returns fers to any irregular heartbeat. In some
to the heart by way of pulmonary veins to When Things Go Wrong horses, particularly fit ones, the most com-
the left atrium and ventricle, which are While horses are technically at-risk of mon arrhythmia is second degree atrio-
separated by the left atrioventricular (mi- suffering from either congenital (present ventricular heart block. It is characterized
tral) valve. Finally, the oxygenated blood in at birth) or acquired cardiac conditions, by a “missed” heart beat. This arrhythmia
the muscular left ventricle is pumped out heart disease is rare in horses. Some of the is regular in its irregularity and usually
of the heart through the aortic valve and more common conditions include cardiac resolves with an increased heart rate.
into the aorta. The aorta branches into a arrhythmias and valvular insufficiencies. Atrial fibrillation is the most common
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2. Fact Sheet
Fast FaCts
arrhythmia associated with poor perfor- ECG (electrocardiogram) Used to assess ■ The equine heart is a hollow organ com-
mance. It’s caused by malfunctioning of the the electrical activity of the heart and pro- prised of two atria and two ventricles
sinoatrial node. Instead of a single signal vide a visual representation of the electrical that function in concert to receive blood
stimulating contraction of the ventricles, signals generated in the heart. ECGs can be from veins and subsequently propel blood
several signals are generated in the atria, performed for a short period of time while through the body via arteries.
resulting in an irregular heart rate and de- the horse is at rest or can be done continu- ■ Cardiac disease is thought to be the third-
creased cardiac function during exercise. ously in ECG recordings that collect 24 most-common cause of “poor performance”
Treatment and prognosis for the various hours worth of data (or more). This latter in athletic horses after musculoskeletal dis-
cardiac abnormalities that can occur in technique is a useful adjunct for the diag- ease and respiratory tract disorders; however,
horses is dependent on the use of the horse, nosis of infrequent arrhythmias, for assess- cardiac abnormalities in horses are rare.
the underlying cause, and the exact nature ing the severity of an arrhythmia, and for ■ The most common and relevant cardiac ab-
of the disease process. monitoring response to therapy (e.g., hors- normalities diagnosed in horses are valvular
es with atrial fibrillation that are treated insufficiencies and atrial fibrillation.
Diagnosis with quinidine sulfate). In addition, some ■ Diagnosing a cardiac abnormality that
Since many horses have murmurs or ar- ECGs are fitted with a radiotelemetry unit negatively impacts performance can be
rhythmias that are not clinically relevant for use while the horse is on a high-speed challenging. Typical tests include ausculta-
(i.e., do not impact health or performance) treadmill or under saddle. This allows vet- tion, an electrocardiogram, and cardiac
or occur only intermittently, obtaining a di- erinarians to evaluate cardiac function dur- ultrasound.
agnosis and interpreting test results can be ing and immediately after exercise. ECGs
challenging. Key diagnostic tests include: can also be sent electronically to specialists
Cardiac auscultation A stethoscope is for additional diagnoses. allows veterinarians to evaluate the speed
used to note heart rate and rhythm, detect X-rays Used infrequently to assess the and pattern of blood flow within the heart
the presence of a murmur, and assess the size and shape of heart, although they do and great vessels at rest or immediately
status of the valves. The location and spe- not provide enough specific information. after exercise. The use of telemedicine
cific characteristics of the murmur (e.g., Cardiac ultrasound (echocardiography) allows field veterinarians to perform an
duration and intensity of the murmur) Used to assess the valve’s function and ultrasound and ECGs examinations and
provide some information regarding the the size, shape, and structure of the heart send the data to a cardiac specialist for
significance and cause of the murmur. in motion. Color-flow Doppler imaging his/her expert opinion. h
IDEXX Telemedicine
CARDIOLOGY • RADIOLOGY • INTERNAL MEDICINE Performance can
change in a heartbeat
Make sure your diagnostics keep pace
When equine performance is in question,
nothing is more reliable than the
electrocardiogram (ECG) at documenting
cardiac rhythms. Consider running an ECG
when:
• Evaluating for poor performance
• Investigating clinical findings such as
murmur or arrhythmia
• Performing a prepurchase examination
IDEXX Telemedicine gives you
a clear picture of equine
heart health.
Call 1-800-726-1212 or go to
www.idexx.com/equinetelemedicine
© 2009 IDEXX Laboratories, Inc. All rights reserved. • 7075-00
to learn more.
All ®/TM marks are owned by IDEXX Laboratories, Inc. or its affiliates in the United States
and/or other countries.
7075-00 HorseAd_FactSht.indd 1 5/21/09 2:29:47 PM