Page 25 - Feline Cardiology

16 Section A: Clinical Entities

a cat’s episode of syncope describe such signs as “appear- by owner or clinician. Increasingly severe manifestations
ing dazed,” “seeming glassy-eyed,” “stumbling,” vocaliz- are found across the spectrum, and at the most extreme
ing, ptyalism, and/or appearing disoriented before point of severity lies sudden cardiac death. Often, a
Clinical Entities warning. The prelude is variable, and cats may have between collapse and syncope (Fox et al. 1991; Penning
collapsing, or the cat may simply collapse without fore-
patient’s episodes may blur the line of demarcation
syncopal episodes while physically active, while at rest,
et al. 2009), and owners, or even attentive clinicians, may
be uncertain as to whether consciousness was preserved
or between the two extremes. For example, in the midst
of physical exertion, a cat will typically dramatically slow
down, such as suddenly slowing mid-run, lie in sternal during a brief, subtle, and/or poorly witnessed episode.
Therefore, cats that manifest any clinical signs on this
recumbency, and then roll into lateral recumbency, spectrum are candidates for evaluation as described in
unconscious. Although the duration of unconsciousness Figure 2.1.
in syncope is very brief (<30 seconds), an owner may Seizures are easily distinguished from syncope based
not recall time accurately due to his or her own emotional on well-recognized characteristics (see Figure 2.1).
distress. Individual cats may have specific inciting factors However, in certain individuals with syncope, seizures
(e.g., type of intense physical activity or arousal, such as can occur during the syncopal event. It is theorized that
being startled or stimulated to play) that owners recog- cerebral hypoxia is responsible for the crossing of the
nize as often leading to syncope. The main value of seizure threshold. In such cases, features of both syncope
recognizing such triggers is to recommend their reduc- at first, and then seizures, are seen, with the features of
tion so as to avoid more episodes. seizures often predominating in an owner’s or clinician’s
There may or may not be prodromal signs, physical memory. Any cat thought to have seizures but that also
manifestations suggesting that syncope is about to occur has manifestations of heart disease (e.g., heart murmur
as described above. Historically, prodromal signs were or arrhythmia on physical exam; abnormalities on the
felt to indicate seizures rather than syncope, but evi- electrocardiogram (ECG), thoracic radiographs, or
dently the onset of syncope may be preceded by several echocardiogram) should be investigated thoroughly as
seconds’ duration of such signs while consciousness is indicated in Figure 2.1. Testing is particularly important
maintained. These signs may sometimes terminate if the neurologic signs are about to be pursued with
before collapse/syncope occurs, a situation referred to as cerebrospinal fluid sampling or imaging, which gener-
near-syncope, presyncope, or aborted syncope. ally require general anesthesia and therefore could pose
a substantial risk to an uncontrolled arrhythmia patient.
PHYSICAL EXAMINATION Instances of cats being induced under general anesthesia
for magnetic resonance imaging of the brain (to inves-
Physical findings likewise reflect the inciting cause. A tigate seizures) and developing intractable, fatal 3rd-
heart murmur, gallop sound, arrhythmia (particularly degree AV block (because the seizures were cardiogenic
bradycardia), or combination of these signs is a common and a subtle clue such as a relative bradycardia or soft
finding. Many cats with syncope, however, present only heart murmur had not been detected) have been
mild if any abnormal physical findings, or physical reported anecdotally. Vigilance and complete diagnostic
abnormalities that are sufficiently mild (e.g., soft evaluation of the cardiovascular system is warranted in
murmur in an otherwise bright, alert, responsive cat; these cases: in a landmark study, 31/74 (41%) of human
echocardiogram is within normal limits) as to make the epilepsy patients were found to be misdiagnosed and to
clinician question whether they are related to the more in fact have a cardiovascular cause for their clinical dis-
dramatic clinical signs of syncope.
order (Zaidi et al. 2000).
DIFFERENTIAL DIAGNOSIS
DIAGNOSTIC TESTING
Differentiation between syncope and other phenomena
is described in Figure 2.1. The distinction between col- In all cats with suspected or confirmed syncope, a com-
lapse and syncope should be clear, because collapse indi- plete medical and cardiovascular evaluation is warranted
cates a loss of muscle tone, whereas syncope specifically (see Figure 2.1). Specific parameters for investigating
identifies collapse with concurrent loss of consciousness. cardiac arrhythmias are described further in Chapter 18.
In practice, however, collapse and syncope can represent In most cases, a bradyarrhythmia is the underlying
discrete points on a spectrum of clinical signs (see Figure arrhythmia. Two cases of syncope in cats with HCM—
2.2). The mildest point on this spectrum likely consists one with supraventricular tachycardia (Harpster 1977)
of subtle weakness or sluggishness, or even milder true and one with ventricular tachycardia (Bright and Call
symptoms that only the cat feels but that are not noted 2000)—are important exceptions.