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Chapter 19: Congestive Heart Failure 259

Congestive Heart Failure: Functional Classes and Etiologies

Functional Categories

Diastolic Heart Failure Primary Myocardial Failure Ventricular Volume Overload Pressure Overload

Pathophysiology:
Predominant abnormality
• ↑ Ventricular stiffness • Systolic myocardial failure • Eccentric ventricular • ↑ Ventricular afterload
hypertrophy
• Abnormal ventricular early (↓ Contractility) • Concentric ventricular
diastolic relaxation • ↑ Ventricular preload hypertrophy
• ↑ Ventricular stiffness

Etiology

Hypertrophic Cardiomyopathy Atrioventricular valve insufficiency Aortic stenosis Congestive Heart Failure
Dilated Cardiomyopathy
Restrictive Cardiomyopathy Acquired Pulmonic stenosis
Taurine Deficiency
Unclassified Cardiomyopathy Degenerative; infective (Typically cause diastolic heart
Tachycardiomyopathy
Pericardial Disease Congenital failure)
Cardiac Tamponade MVD, TVD Systemic hypertension
Constrictive Pericarditis Left to right shunting cardiac (Not an independent cause of
defects heart failure)
VSD, PDA, ASD
MVD, mitral valve dysplasia; TVD, tricuspid valve dysplasia; VSD, ventricular septal defect; PDA, patent ductus arteriosus; ASD, atrial septal defect
Figure 19.2. Algorithm of Functional Categories and Etiologies of Congestive Heart Failure in Cats.

ary to HCM have identifiable precipitating events, heart failure (Pion et al. 1992). Over half (55%) of cats
including fluid administration, anesthesia and surgery, diagnosed with RCM present with clinical signs of CHF,
or recent corticosteroid administration (Depo-medrol characterized mostly by pleural effusion (55%), fol-
or long-acting triamcinolone) 1–2 weeks prior to heart lowed by pulmonary edema (41%) and ascites (23%).
failure development (Rush et al. 2002). Pulmonary Similarly, a majority (64%) of cats diagnosed with
edema is more common than pleural effusion in cats unclassified cardiomyopathy present with clinical signs
with CHF due to HCM, and is seen in 32–66% of cats of CHF, including pleural effusion (50%) and pulmo-
diagnosed with HCM, although longitudinal studies of nary edema (9%)l (Ferasin et al. 2003). The prototypical
the incidence of CHF in cats with HCM over time have disease of right heart failure is ARVC. A majority of cats
not been conducted (Rush et al. 2002; Atkins et al. 1992). with ARVC present with clinical evidence of right-sided
Dyspnea is attributed to pulmonary edema in 80% of heart failure (67%), including pleural effusion (67%)
cats with CHF due to HCM, compared to only 14% of and ascites (33%) and dilated caudal vena cava (17%).
cats that are dyspneic from pleural effusion (Rush et al. It is interesting to note that pleural effusion was much
2002). All cats (11/11) diagnosed with idiopathic DCM more common than ascites in cats with right heart
present with clinical signs of CHF, which consist of failure secondary to ARVC. It is possible that there is a
pleural effusion (91%), ascites (55%), and pulmonary contribution of left-sided heart failure, because cats
edema (36%) (Ferasin et al. 2003). Similarly, 84% often have concurrent left atrial dilation in this disease
(31/37) of cats diagnosed with taurine deficiency (5/8 cats with mild left atrial dilation, 3/8 cats with
induced myocardial failure have clinical evidence of severe left atrial dilation) (Fox et al. 2000).