Page 392 - Feline Cardiology

412 Section O: Anesthesia in the Patient with Cardiac Disease

INTRODUCTION Cats with severe atrial dilation may be more likely to
be on the brink of developing congestive heart failure
Risk associated with sedation or general anesthesia of and/or thromboembolic disease, and may pose a higher
cats with naturally occurring heart disease is understood risk than the cat with mild heart disease and minimal
via clinical reports and objective experience, but not atrial dilation. This does not indicate that cats with
blinded prospective studies. In general, studies of small severe atrial dilation cannot be anesthetized, but it
animal morbidity and mortality show good correlation reflects that their heart disease is usually more severe.
with the American Society of Anesthesiologists (ASA) The clinician must weigh the importance of the proce-
physical status classification (Table 27.1) (Broadbelt et dure with the risk of the anesthesia and recovery. For
al. 2007, 2008; Dyson et al. 1998; Gaynor et al. 1999). As example, dental prophylaxis may carry an increased risk
expected, this correlation suggests that increased sever- of anesthetic complications in a cat with cardiomyopa-
ity of the disease increases anesthetic risk. Therefore, a thy and atrial enlargement, but if the periodontal disease
cat with cardiac disease that is currently life-threatening is severe, and both the dental disorder and the cardio-
(ASA class 4 or 5) is at higher risk of anesthetic compli- myopathy are expected to worsen over time, general
cations than a cat with stable, yet even severe, cardiac anesthesia and dental work may be optimal at that time.
disease (ASA class 3), and all efforts should be made to Cats with cardiac disease have a higher risk for malig-
convert decompensated/symptomatic patients to stable/ nant arrhythmias than normal cats. Anesthetic agents
asymptomatic patients prior to anesthesia. In particular, largely impact cardiovascular function in normal cats,
nonurgent procedures on cats with congestive heart and the effects are even more pronounced in cats with
failure should be postponed until medical management cardiac disease. Selection of the correct agents, support,
is started and signs of heart failure have resolved or and monitoring are all critical to a positive outcome. In
improved. Similarly, if medical management of cardiac particular, cats with active congestive heart failure, or a
disease without heart failure is indicated (e.g., beta history of heart failure, require extremely careful man-
blocker administration in an asymptomatic cat with agement and intensive monitoring; anesthesia of these
hypertrophic cardiomyopathy), elective procedures patients is best conducted by a specialist.
should be postponed until the patient has been medi- Cardiac disorders can be functionally classified into
cated for at least a few days, and reevaluated. Feline the following categories:
cardiovascular patients with the highest anesthetic risk
are those with
• Systolic myocardial failure (e.g., dilated cardiomyopa-
thy)
• Active congestive heart failure • Diastolic dysfunction (increased ventricular wall stiff-
• Clinically significant bradyarrhythmias such as third- ness secondary to restrictive cardiomyopathy (RCM),
degree atrioventricular block or high-grade second- unclassified cardiomyopathy (UCM), concentric
degree atrioventricular block hypertrophy; ventricular thickening due to pressure
• Clinically significant tachycardias such as rapid (>280 overload, such as with systemic hypertension, or
beats/minute) ventricular tachycardia hypertrophic cardiomyopathy [HCM]); or pericardial
• Intracardiac thrombi disease)

Anesthesia Table 27.1. American Society of Anesthesiologists classification system

ASA Class Definition Example

I A normal healthy patient Young healthy cat undergoing a spay
II A patient with mild systemic disease Cat with mild mitral regurgitation without left
atrial enlargement
III A patient with severe systemic disease Cat in congestive heart failure, stable with medical
management
IV A patient with severe systemic disease that is a Cat with ventricular tachycardia
constant threat to life
V A moribund patient that is not expected to survive Cat with major abdominal hemorrhage, in
without the operation hypovolemic shock