Page 30 - Small Animal Internal Medicine, 6th Edition

2 PART I Cardiovascular System Disorders

BOX 1.1 BOX 1.2
VetBooks.ir Clinical Signs of Heart Failure Causes of Syncope or Intermittent Weakness

Cardiovascular Causes
Congestive Signs—Left (↑ Left Heart Filling Pressure)
Pulmonary venous congestion Bradyarrhythmias (second- or third-degree AV block,
Pulmonary edema (causes tachypnea, ↑ respiratory effort, sinus arrest, sick sinus syndrome, atrial standstill)
cough, orthopnea, pulmonary crackles, tiring, Tachyarrhythmias (paroxysmal atrial or ventricular
cyanosis, hemoptysis) tachycardia, reentrant supraventricular tachycardia,
Postcapillary pulmonary hypertension atrial fibrillation)
Secondary right-sided heart failure Congenital ventricular outflow obstruction (pulmonic
Cardiac arrhythmias stenosis, subaortic stenosis)
Acquired ventricular outflow obstruction (heartworm
Congestive Signs—Right (↑ Right Heart Filling Pressure) disease and other causes of pulmonary hypertension,
Systemic venous congestion (causes ↑ central venous hypertrophic obstructive cardiomyopathy, intracardiac
pressure, jugular vein distention) tumor, thrombus)
Hepatic ± splenic congestion Cyanotic heart disease (tetralogy of Fallot, pulmonary
Pleural effusion (causes ↑ respiratory effort, orthopnea, hypertension, and “reversed” shunt)
cyanosis) Impaired forward cardiac output (severe valvular
Ascites insufficiency, dilated cardiomyopathy, myocardial
Small pericardial effusion infarction or inflammation)
Subcutaneous edema Impaired cardiac filling (e.g., cardiac tamponade,
Cardiac arrhythmias constrictive pericarditis, hypertrophic or restrictive
cardiomyopathy, intracardiac tumor, thrombus)
Low Cardiac Output Signs Cardiovascular drugs (diuretics, vasodilators)
Tiring Neurocardiogenic reflexes (vasovagal, cough-syncope,
Exertional weakness other situational syncope)
Syncope
Prerenal azotemia Pulmonary Causes
Cyanosis (from poor peripheral circulation) Diseases causing hypoxemia
Cardiac arrhythmias Pulmonary hypertension
Pulmonary thromboembolism

Metabolic and Hematologic Causes
Hypoglycemia
Hypoadrenocorticism
Electrolyte imbalance (especially potassium, calcium)
Anemia
Sudden hemorrhage
Neurologic Causes
Cerebrovascular accident
Brain tumor
(Seizures)
Neuromuscular Disease
(Narcolepsy, cataplexy)

AV, Atrioventricular.
FIG 1.1
Syncope in a Doberman Pinscher with paroxysmal
ventricular tachycardia. Note the extended head and neck
with stiffened forelimbs. Involuntary micturition also Tests to explore the cause of intermittent weakness or
occurred, followed shortly by return of consciousness and syncope usually include ECG recordings (during rest, exer-
normal activity. cise, and/or after exercise or a vagal maneuver), complete
blood count (CBC), serum biochemical analysis (including
electrolytes and glucose), heartworm testing, neurologic
activity or twitching; however, these convulsive syncopal epi- examination, thoracic radiographs, and echocardiography.
sodes are preceded by loss of muscle tone. Presyncope, where Other studies for neuromuscular or neurologic disease also
reduced brain perfusion (or substrate delivery) is not severe may be valuable. Intermittent cardiac arrhythmias that are
enough to cause unconsciousness, may appear as transient not apparent on resting ECG may be uncovered by ambula-
“wobbliness” or weakness, especially in the rear limbs. tory ECG monitoring, using a 24-hour Holter, event, or