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Chapter 27: Anesthesia in the Patient with Cardiac Disease 413

• Eccentric hypertrophy of the ventricle (e.g., ventricu- volume expansion if hypovolemia is present; and if
lar septal defect) hypotension persists, administration of a vasoconstric-
• Ventricular underload/decreased preload (e.g., dehy- tor such as phenylephrine, titrated to achieve acceptable
dration, hypovolemia of any cause) (Kittleson and arterial blood pressure (see “Treatment of Hypotension”
Kienle 1998a). below).
With eccentric hypertrophy (e.g., ventricular septal
A fifth category could be considered with signs of defect), circulating volume optimization, a normal heart
cardiac abnormalities but a structurally normal heart in rate, and normal to low systemic vascular resistance are
a stable, euvolemic patient (e.g., physiologic murmur). beneficial. This means that volume underload (e.g.,
Such murmurs are common in cats (Paige et al. 2009), dehydration) warrants treatment with intravenous
and an echocardiogram definitively establishes the diag- fluids, for example, whereas intravascular volume excess
nosis by exclusion of structural heart disease. Each of (e.g., congestive heart failure) requires fluid removal,
the different types of cardiac disorders listed above such as with diuretics and/or centesis.
requires specific, individual adjustments in anesthetic Cats with decreased preload/volume underload
management. (e.g., dehydration, hypovolemia) benefit from intravas-
Systolic myocardial failure (e.g., dilated cardiomyopa- cular volume optimization. Therefore, it is of critical
thy) is characterized by a decrease in myocardial con- importance to administer a fluid volume (IV crystalloid
tractility. Anesthestic management relies on the use of fluids, blood transfusion, or other, as dictated by
positive inotropes if needed and avoidance of negative clinical need) sufficient to restore normovolemia
inotropes such as beta blockers unless required for the prior to anesthetic induction. Ideally, these measures
treatment of severe supraventricular tachycardia. should be performed prior to echocardiography,
Specifically, hypotensive crises in patients with systolic because chamber dimensions and wall thicknesses
myocardial failure may benefit from intravenous infu- are altered by fluid balance (Campbell and Kittleson
sion of dopamine or dobutamine, titrated to achieve 2007).
acceptable arterial blood pressure. Cats with systolic The choice of drugs (Table 27.2) and support during
myocardial failure who are already receiving beta block- anesthesia will be directed at achieving the goals men-
ers such as atenolol orally prior to anesthesia should tioned above. Arrhythmias may be associated with other
continue to receive them pre- and postoperatively, cardiac diseases, or they may be the primary disorder.
barring bradycardia and/or active congestive heart Their short-term treatment during general anesthesia is
failure discussed here (see Chapter 18 for in-depth discussion
Diastolic dysfunction (e.g., RCM, UCM, or concen- of arrhythmia management). An atropine challenge test
tric hypertrophy/ventricular thickening such as seen (0.04 mg/kg SC or IV) should be done in all cats with
with HCM) is characterized by decreased ventricular sinus bradycardia, second-degree AV block, or third-
relaxation and compliance, and possibly dynamic left degree AV block. Cats with high-grade second-degree
ventricular outflow tract obstruction (e.g., systolic ante- atrioventricular block or third-degree atrioventricular
rior motion of the mitral valve) in cases of HCM. block probably will not have any improvement in ven-
Patients with diastolic dysfunction usually benefit from tricular rate following atropine challenge, because anti-
a slow normal heart rate (to decrease myocardial oxygen muscarinic drugs (e.g., atropine, glycopyrrolate) are
consumption and maximize preload), avoidance of unlikely to increase the heart rate of these patients; these
positive inotropes such as dopamine or dobutamine cats have a high anesthetic risk without a temporary
(which increase myocardial oxygen consumption and pacemaker. Referral is therefore indicated for temporary Anesthesia
may increase outflow obstruction), and increased cardiac pacing in such cases. Serum potassium levels
systemic vascular resistance (which increases coronary should be measured in cats with significant bradycardia
perfusion pressure and may decrease outflow obstruc- to evaluate for life-threatening hyperkalemia (see
tion). In practical terms, this translates to not skipping Chapter 18).
the dose of beta blocker or calcium-channel blocker
on the morning of the anesthesia for cats receiving PREANESTHETIC PREPARATION
these medications, avoiding dopamine and dobutamine,
and avoiding drugs that cause vasodilation (e.g., Prior to sedating and/or anesthetizing a cat with
acepromazine) or stimulate the sympathetic nervous known or suspected cardiac disease, a current assess-
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system (e.g., ketamine, Telazol ). Hypotension in cats ment of the severity of the disease should be obtained.
with left ventricular thickening is addressed by decreas- Complete blood count and serum biochemical evalua-
ing inhalant anesthetic concentration if possible; careful tion, thoracic radiographs, an electrocardiogram, and