resuscitation in small animals - Maravet

4. PATHOPHYSIOLOGY OF
CONGESTIVE HEART FAILURE
Wayne E. Wingfield, D.V.M., M.S.
1. What is heart failure?
Heart failure in the small animal results from the combined effects of chronic cardiac insufficiency
and attempts by the neurohumeral system to compensate. Peripheral venous congestion
(i.e., pulmonary edema) results when the left ventricle begins to fail, systemic venous
congestion (i.e., ascites, hepatic congestion, and rarely, peripheral edema) occurs when the
right ventricle begins to fail, and generalized heart failure results when both right and left
ventricles fail.
2. What are the four common mechanisms accounting for heart failure in small animals?
List common causes for each.
l. Pressure or volume overload (mitral valvular insufficiency, systemic hypertension)
2. Myocardial failure (dilated cardiomyopathy)
3. Diastolic failure (hypertrophic cardiomyopathy)
4. Cardiac dysrhythmias (atrial fibrillation, ventricular fibrillation)
3. Describe the predominant underlying cause of heart failure for the various cardiac diseases
ofsmall animals.
SYSTOLIC
HEART FAILURE
Dilated cardiomyopathy
DIASTOLIC
HEART FAILURE
Pericardia! effusion
Hypertrophic cardiomyopathy
Restrictive cardiomyopathy
Hyperthyroidism
VALVULAR
DISEASES
Endocardiosis
Endocarditis
Valvular dysplasia
Valvular stenosis
RHYTHM
DISTURBANCES
Bradyarrhythmias
Tachyarrhythmias
CARDIOVASCULAR
SHUNTS
Patent ductus
arteriosus
Ventricular septal
defect
Atrial septal defect
4. Define the relationship between pressure and flow as they relate to vascular resistance.
The heart generates pressure and flow. Both must be maintained within certain limits to produce
viable organ function. Thus the relationship between pressure and flow is defined by vascular
resistance.
. Pressure
Vascular resistance = Flow
5. How can I use the relationship between vascular resistance, pressure, and flow in the
clinical use of cardiac drugs?
Arterial vasoconstriction improves blood pressure, but it also decreases blood flow and possibly
tissue perfusion. Arterial vasodilation decreases blood pressure but improves blood flow
and tissue perfusion.
6. What is cardiac output? What are its determinants?
Cardiac output is the total forward blood flow coming from the heart and is the product of
stroke volume and heart rate. The three determinants of stroke volume are (I) preload. (2) afterload,
and (3) contractility.
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