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Exercise Intolerance and Syncope

Key Points

• Syncope is an uncommon occurrence in cats.
• When it occurs, it most commonly is the result of an arrhythmia—typically a pathologic bradycardia—in a cat with underlying
structural heart disease, but systemic illness and tachycardias can cause syncope in cats.
• Detailed diagnostic evaluation is essential in order to confirm syncope and rule out neurologic or other phenomena.

INTRODUCTION seizures or other disorders (Figure 2.1). The profound
hypotension that accompanies syncope (mean arterial
Syncope is a “sudden and brief loss of consciousness pressure typically is <25 mm Hg) (Kittleson 1998), if it
associated with a loss of postural tone, from which persists sufficiently long as to cause >30 seconds of
recovery is spontaneous” (Kapoor 2000). To the layper- unconsciousness, is likely to be fatal. When the mecha-
son, syncope is “fainting” or “passing out.” A synonym nism causing syncope (e.g., arrhythmia) terminates, a
for syncope caused by a cardiac arrhythmia is a “Stokes spontaneous resumption of adequate cerebral circula-
Adams attack” or “Stokes Adams syndrome” (Harbison tion is responsible for the return of consciousness. Brief
et al. 2002). reactive cerebral hyperemia can occur initially, but com-
plete recovery likely takes longer than clinical signs
ETIOLOGY AND PATHOPHYSIOLOGY
suggest. For example, a persistently subnormal cerebral
Syncope is caused by a temporary, marked decrease or blood flow has been noted for 3 hours after a 1-minute
cessation of cerebral blood flow. It manifests as sudden- burst of ventricular tachycardia at 300 beats/minute in
onset ataxia and disorientation, immediately followed cats (Kobari et al. 1992). Nevertheless, the most dramatic
by loss of all skeletal muscle tone and consciousness. overtly visible aspect of termination of syncope is the
This collapse and unconsciousness may occur quietly or speed and completeness of clinical recovery. In contrast
may be preceded by profound disorientation, vocalizing, to patients with seizures or other forms of episodic dis-
and signs of extreme distress. In either scenario, clients turbances, syncopal patients generally recover a normal
witnessing syncope often describe initially believing that or near-normal mentation, posture, gait, and general
the cat has died. Indeed, syncope may be terminal in demeanor within 1 minute of regaining consciousness.
cases where the incriminating mechanism—e.g., The mechanism of recovery separates survivors of
arrhythmia—does not resolve quickly. Therefore one of syncope from those patients in which syncope becomes
the characteristics of syncope is that it rarely lasts more sudden cardiac death (Figure 2.2). Recovery is likely due
than a few seconds and virtually never more than 30 to multiple factors that make up the response to acute
seconds; longer-lasting episodes are more likely to be cerebral hypoperfusion, including reduced baroreceptor

Feline Cardiology, First Edition. Etienne Côté, Kristin A. MacDonald, Kathryn M. Meurs, Meg M. Sleeper.
© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

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