Page 107 - Small Animal Internal Medicine, 6th Edition

CHAPTER 4 Cardiac Arrhythmias and Antiarrhythmic Therapy 79

BOX 4.2
VetBooks.ir Factors Predisposing to Arrhythmias Degenerative valvular disease with myocardial fibrosis

Atrial Arrhythmias
Cardiac Ischemia
Mitral or tricuspid insufficiency Trauma
Dilated cardiomyopathy Cardiac neoplasia
Hypertrophic cardiomyopathy Heartworm disease
Restrictive cardiomyopathy Congenital heart disease
Cardiac neoplasia Ventricular dilation
Congenital malformation Mechanical stimulation (intracardiac catheter, pacing wire)
Accessory AV nodal bypass tract(s)
Myocardial fibrosis Extracardiac
High sympathetic tone Hypoxia
+
Ischemia Electrolyte imbalances (especially K )
Intra-atrial catheter placement Acidosis/alkalosis
Thyrotoxicosis
Extracardiac Hypothermia
Catecholamines Fever
Electrolyte imbalances Sepsis/toxemia
Digoxin toxicity Trauma (thoracic or abdominal)
Other drugs (anesthetic agents, bronchodilators) Gastric dilation/volvulus
Acidosis/alkalosis Splenic mass or splenectomy
Hypoxia Hemangiosarcoma
Thyrotoxicosis Pulmonary disease
Severe anemia Uremia
Electric shock Pancreatitis
Thoracic surgery Pheochromocytoma
Other endocrine diseases (diabetes mellitus, Addison
Ventricular Arrhythmias disease, hypothyroidism)
Cardiac High sympathetic tone (pain, anxiety, fever)
Congestive heart failure Central nervous system disease (increases in sympathetic
Cardiomyopathy (especially Doberman Pinschers and or vagal stimulation)
Boxers) Electric shock
Myocarditis Drugs (digoxin, sympathomimetics, anesthetics,
Pericarditis tranquilizers, anticholinergics, antiarrhythmics)

are infrequent or underlying cardiac function is normal, Pulse deficits (see p. 6) and an irregular, weak pulse with
adverse hemodynamic effects may be negligible. However, heart sounds of varying intensity and regularity may be
hemodynamic impairment can be severe in dogs or cats with detected on physical examination. Premature contractions
underlying heart disease, rapid ventricular rates, or myocar- interrupt ventricular filling and reduce stroke volume, some-
dial depression stemming from a systemic disease. times to the extent that there is no ejection at all for that cycle
Factors such as underlying hypoxia, electrolyte or acid- (Fig. 4.1). Rapid atrial fibrillation (AF) and premature con-
base imbalances, and abnormal hormone concentrations tractions of any origin often cause such pulse deficits. VPCs
(e.g., hyperthyroidism) can exacerbate arrhythmias. There- can cause audible splitting of the heart sounds because of
fore, correcting these improves arrhythmia control. Because asynchronous ventricular activation. Ventricular and supra-
some drugs can provoke arrhythmias, reducing dosage or ventricular tachycardias (SVTs) and AF cause more severe
discontinuing the medication may be necessary. hemodynamic compromise than do isolated premature
contractions, especially in patients with underlying heart
CLINICAL PRESENTATION disease.
Box 4.3 lists common arrhythmias according to a clinical
description of the heartbeat. Rapid Regular Rhythms
Rapid regular rhythms include sinus tachycardia, sustained
TACHYARRHYTHMIAS SVT, and sustained ventricular tachycardia. Sinus tachy-
Rapid Irregular Rhythms cardia is caused by high sympathetic tone or drug-induced
Irregular heart rhythms are common. The ECG is important vagal blockade. Underlying factors include anxiety, pain,
for differentiating abnormal rhythms and sinus arrhythmia. fever, thyrotoxicosis, heart failure, hypotension, shock, the