Page 447 - Clinical Small Animal Internal Medicine

42 Cardiogenic Shock 415

ectopic thyroid carcinoma, hemangiosarcoma, and oste- development of atrial fibrillation. Cats are rarely able to
VetBooks.ir osarcoma, among others. propagate atrial fibrillation due to their relatively small
atrial mass but cats with severe atrial enlargement due
Cardiogenic shock in cats occurs infrequently. When it
does occur, it is usually due to cardiomyopathy (dilated
be considered to be at risk.
[DCM], restrictive [RCM) or hypertrophic [HCM] with to cardiomyopathy (Maine Coon, Himalayans) should
or without left ventricular outflow tract obstruction
[LVOT]). The clinical importance of LVOT obstruction
in cats with HCM is not fully understood but in cats with History and Clinical Signs
severe LVOT secondary to HCM, the dynamic obstruc-
tion of the left ventricular outflow tract can result in sig- A common historical complaint for animals presenting
nificant decreases in cardiac output. A more common with cardiogenic shock is collapse or syncope. Owners
cause of cardiogenic shock in cats is a form of “low‐out- commonly describe “seizures” rather than syncope so a
put” heart failure, usually characterized by hypothermia, careful history must be taken to determine if intracranial
bradycardia, and severe hypotension. This form of heart disease or seizures are in fact a contributing factor. A
failure appears to be more common in cats with RCM thorough history includes the patient’s activity and
and may be the result of ischemic heart injury. behavior immediately preceding and following the event,
state of consciousness during the event, and frequency of
events. Syncope can result from many different cardiac
Signalment conditions but brady‐ or tachyarrhythmias and pulmo-
nary hypertension are the most common. Often syncope
Cardiogenic shock can occur in a patient of any age or in these animals is exercise induced and the occurrence
breed, making it difficult to describe a typical signal- of syncope at rest should be considered evidence of
ment, but because myocardial failure or neoplasia is advanced disease. If a patient presenting in shock has a
often the inciting cause of cardiac dysfunction, these history of syncope or collapse or if the owner describes
patients tend to be older middle‐aged to geriatric ani- exercise‐induced “seizures,” the clinician should be alert
mals. Pericardial effusion occurs most commonly in to the potential for a cardiogenic cause of shock. Most, if
large‐ and giant‐breed dogs, although endocardial rup- not all, patients in cardiogenic shock will present with
tures resulting in acute pericardial effusion appear to be acute exercise intolerance or weakness.
more common in older male small‐breed dogs, with Regardless of the underlying cause of cardiogenic
dachshunds and cocker spaniels being overrepresented. shock, all of these patients will present with perceptible
Young dogs and cats with congenital cardiac abnor- derangements in perfusion parameters. The mucous
malities can develop cardiogenic shock. These patients membranes may be pale (evidence of poor perfusion) or
are often identified as having a cardiac abnormality dur- cyanotic (evidence of hypoxemia). Delayed capillary
ing an early veterinary visit and have frequently exhausted refill time is an indicator of poor peripheral perfusion. In
most if not all management options by the time cardio- cases of severe shock, the mucous membranes may fail to
genic shock develops. Therefore, when it occurs in these blanch altogether. Often, the distal extremities will be
patients, it is usually a terminal, irreversible event. cooler to the touch than the trunk. As shock progresses
Canine heartworm disease occurs in middle‐aged dogs from compensated to the early, then late decompensa-
of both sexes. Smaller dogs appear to be at greater risk of tory stages, the mental status will change and the patient
developing caval syndrome and subsequently would be will become obtunded. Patients presenting obtunded to
at greater risk for development of cardiogenic shock, stuporous are in the late stages of shock and without
likely due to the smaller worm burdens required to cause timely intervention are likely to die.
significant clinical disease in these smaller patients. As a general rule, patients in cardiogenic shock will
Certain breed predispositions for cardiac disease exist have one or more abnormal findings during cardiac aus-
and by extension, these breeds may be at increased cultation. Animals with pericardial disease will often
risk for development of cardiogenic shock. Boxer dogs have decreased heart sounds. Auscultation of animals
are much more likely than other breeds to develop with myocardial dysfunction may reveal either brady‐ or
arrythmogenic right ventricular cardiomyopathy while tachyarrhythmias. When present, arrhythmias can either
Doberman Pinschers are considered most at risk for be regular (e.g., sustained ventricular tachycardia) or
development of dilated cardiomyopathy. Both of these irregular (e.g., atrial fibrillation). Cats often have gallop
conditions can lead to ventricular tachycardia with rhythms although extra heart sounds can be present in
cardiogenic shock. Besides the potential for tachyar- the dog also and usually indicate structural cardiac dis-
rhythmias, dogs with DCM are at risk for systolic fail- ease. Increases in adventitial lung sounds (crackles) may
ure. Large‐ to giant‐breed dogs are at increased risk for be present in cases with forward failure that results in the