While the clinical classification scheme groups pulmonary hypertension patients into classes based on the underlying cause
of pulmonary hypertension, the functional classification scheme groups these patients into classes based on the severity of
pulmonary hypertension-induced clinical signs (Table 2). This schematic was also developed at the 1998 WHO Evian meeting and is used in human medicine to help determine when to
institute therapy, to decide which treatments may be most beneficial, and to provide an objective treatment goal.25 Although not explicitly evaluated in dogs, the information can be easily extrapolated from people to dogs.
Table 2: WHO Functional Classification Scheme of Pulmonary Hypertension
Functional class I
This class includes patients with pulmonary hypertension that do not suffer any decrease in physical activity and can exercise
without signs of dyspnea, fatigue, chest pain, or syncope.
Functional class II
Class II patients are comfortable at rest but suffer a mild decrease in activity associated with dyspnea, fatigue, chest pain,
Functional class III
These patients have pulmonary hypertension that results in marked limitations in physical activity and have severe dyspnea,
fatigue, chest pain, or syncope even with minimal activity. These patients are comfortable at rest.
Functional class IV
The final class includes patients with pulmonary hypertension that are unable to participate in physical activity, and any
activity leads to severe signs. These patients are symptomatic at rest and have right-sided heart failure secondary to pulmonary
Canine pulmonary hypertension is a complex condition caused by an imbalance in pulmonary arterial vasoconstriction and vasodilation
and is associated with enhanced platelet actions and vascular remodeling. Patients with pulmonary hypertension may be classified
into clinical groups based on the underlying cause of disease and into functional groups based on the severity of signs. Ultimately,
the classification schemes should help practitioners diagnose pulmonary hypertension, formulate an effective treatment plan,
and evaluate a patient's prognosis.
Rebecca L. Quinn, DVM, DACVIM (internal medicine)
Department of Cardiology
Angell Animal Medical Center
350 S. Huntington Ave.,
Boston, MA 02130
Justin G. Williams, DVM, DACVIM (cardiology)
VCA Animal Care Center of Sonoma County
6470 Redwood Drive
Rohnert Park, CA 94928