Page 26 - Feline Cardiology

Chapter 2: Exercise Intolerance and Syncope 17

TREATMENT causes here is useful because owners can be instructed
to reduce the intensity and duration of these activities
Ideally, the underlying cause is addressed. Doing so to a level that is well below the level of intolerance. Cats
is often difficult, both because many lesions are subject to exercise intolerance appear to be most com-
irreversible (e.g., fibrosis of the conduction system in monly affected with hypertrophic cardiomyopathy that
HCM [Kaneshige et al. 2006]) and because often the is characterized by moderate to marked ventricular Clinical Entities
cause of syncope is not recognized (e.g., structurally thickening, left ventricular outflow tract obstruction,
normal heart and no identifiable systemic extracardiac and/or congestive heart failure. A subset of cats with
disorder). compensated hypertrophic cardiomyopathy that are
When a cardiac arrhythmia is conclusively identified treated with beta-blockade (e.g., atenolol at a standard
at the time of a syncopal event, antiarrhythmic treat- dosage) have improved in their exercise capacity, indicat-
ment may be initiated. Broadly, such treatment generally ing an unnoticed intolerance to exercise previously, likely
consists of medications for pathologic tachycardias and due to left ventricular outflow tract obstruction or
cardiac pacemaker implantation for pathologic brady- angina pectoris. Because exercise intolerance and
cardias (see Chapter 18 for detailed recommendations syncope share a mechanism of reduced oxygen delivery
based on the specific arrhythmia identified). to tissues, it is expected that the two clinical syndromes
may overlap in a given patient (see Figure 2.2).
OUTCOME AND PROGNOSIS
Ten cats with HCM and syncope lived 28–1505 REFERENCES
(median = 654) days after initial diagnosis, which was
longer than the median survival times of cats with HCM Boldface font indicates key references.
and congestive heart failure (563 days) or those with Atkins CE, de Francesco TC, Coats JR, Sidley JA, Keene BW.
Heartworm infection in cats: 50 cases (1985–1997). J Am Vet Med
HCM and aortic thromboembolism (184 days), but Assoc 2000;217:355–358.
shorter than the median survival time of cats with HCM Bright JM, Cali JV. Clinical usefulness of cardiac event recording in
and no overt clinical signs (1129 days) (Rush et al. 2002). dogs and cats examined because of syncope, episodic collapse, or
The influence of long-term treatment such as pacemaker episodic weakness: 60 cases (1997–1999). J Am Vet Med Assoc
implantation is not described in this case series, and thus 2000;216:1110–1114.
it is unknown whether these survival times were natu- Chetboul V, Charles V, Nicolle A, Carlos Sampedrano C, Gouni V,
Pouchelon J-L, Tissier R. Retrospective study of 156 atrial septal
rally occurring, treated, or some of each. defects in dogs and cats (2001–2005). J Vet Med A 2006;53:
179–184.
EXERCISE INTOLERANCE Côté E, Charuvastra E, Richter K. Event-based cardiac monitoring in
small animal practice. Comp Cont Ed Pract Vet 1999;21:
Exercise intolerance occurs as a result of poor oxygen 1025–1033.
delivery to skeletal muscle, to the brain, or both. It is a Darke PGG, McAreavey D, Been M. Transvenous pacing in 19 dogs
and one cat. J Small An Pract 1989;30:491–9.
rare chief complaint in cats. In a nocturnal species such Ferasin L, van de Stadt M, Rudorf H, Langford K, Hotston Moore A.
as the cat, whose members are estimated to spend 85% Syncope associated with paroxysmal atrioventricular block and
of a given day sleeping, it is understandable that exercise ventricular standstill in a cat. J Small Anim Pract 2002;43:
intolerance is rarely noted, and the subject should be 124–128.
brought up by the clinician with this acknowledgment Forterre S, Nürnberg J-H, Forterre F, Skrodzki M, Lange PE.
immediately, to reassure the cat’s owner that the clini- Transvenous demand pacemaker treatment for intermittent com-
plete heart block in a cat. J Vet Cardiol 2001;3:21–26.
cian has a good understanding of feline behavior in Fox PR, Liu S-K, Maron BJ. Echocardiographic assessment of spon-
general. taneously occurring feline hypertrophic cardiomyopathy. An
When exercise intolerance occurs in the cat, owners animal model of human disease. Circulation. 1995;92:
typically note that a cat fails to continue an activity that 2645–2651.
was previously accomplished without difficulty. Such Fox PR, Maron BJ, Basso C, Liu S-K, Thiene G. Spontaneously occur-
ring arrhythmogenic right ventricular cardiomyopathy in the
activities are often initiated by the owner and include domestic cat: A new animal model similar to the human disease.
chasing a toy such as a feather on the end of a metal Circulation 2000;102:1863–1870.
wire, running after the dot from a laser pointer, or Fox PR, Moïse NS, Woodfield JA, Darke PGG. Techniques and com-
playing fetch. An exercise-intolerant cat may stop during plications of pacemaker implantation in four cats. J Am Vet Med
Assoc 1991;199:1742–1753.
exertion, with or without signs of dyspnea such as open- Guyton AC, Hall JE. Textbook of Medical Physiology, 11th ed.
mouth breathing/panting and exaggerated abdominal Philadelphia, Elsevier Saunders, 2006, 204–215.
respiratory movements (exertional dyspnea), or in severe Harbison J, Newton JL, Seifer C, Kenny RA. Stokes Adams attacks and
cases, pallor and/or cyanosis. Identifying the inciting cardiovascular syncope. Lancet 2002;359:158–160.