Page 87 - WSAVA2017
P. 87

E. Rudloff1
1Lakeshore Veterinary Specialists, Emergency and Critical Care, Glendale, USA
Cardiac function relies on a specialized excitation and conduction system of cardiac muscle and a coordinated contractile process. Alterations of the stimulating nodes, conduction pathway, and myocardial fibers can affect rhythmicity and efficacy of the pump system. Conditions often encountered in the critically ill animal (hypoxia, ischemia, electrolyte imbalances, neuromuscular disease, inflammation, toxemia, medications, etc.) can affect the conduction system, resulting in incomplete or abnormal conduction pathways, chaotic cardiac muscle contraction, and reduced cardiac output and tissue perfusion.
Electrocardiogram (ECG) interpretation is required to characterize a cardiac dysrhythmia, as an adjunct to determining cardiac enlargement, and as an indicator for certain electrolyte, systemic, and metabolic disorders. Treatment of dysrhythmias will be based on the ECG diagnosis and cardiovascular status of the patient.
An aberrant conduction of an electrical impulse
through the heart (dysrhythmia; arrhythmia) can
occur independently and myocardial disease is not required. Virtually any systemic illness, trauma, and situation with inadequate oxygen delivery can result
in tachyarrhythmias. With the severest dysrhythmias, cardiac arrest can occur. Arrhythmias must be distinguished from 60-cycling activity and artifact from improperly placed leads, or patient movement. Good contact must be made between the leads and the patient’s skin. Thick-haired dogs may need to have their hair clipped, and clean clips should be used with secure contacts. Electrode pads can be placed for continuous monitoring, or on the bottom of the digital pads. Contact is enhanced with electrode cream or alcohol. Alcohol should never be used when electrocautery use or defibrillation is anticipated. Arrhythmias are identified by their rate followed by the types of aberrant impulses and by their anatomic origin. A tachyarrhythmia is a rapid rate originating from any region of the conduction system (sinus tachycardia, supraventricular tachycardia), or
from the atrial (atrial fibrillation) or ventricular (premature ventricular contraction, ventricular tachycardia, ventricular fibrillation) muscle. Other common rhythms encountered in the ER include accelerated idioventricular rhythm and electrical alternans.
Sinus Tachycardia: the heart rate is increased (in our hospital we consider this >120 bpm in the dog and >200 bpm in the cat). The most common causes of sinus tachycardia in the ER include hypovolemia and pain.
Atrial Tachycardia: Paroxysms of 3 or more atrial premature contractions constitute an atrial tachycardia, where the p-wave and p-r interval are different than the normal beat. The r-r intervals of the burst are consistent. Causes include atrial enlargement, myocardial disease, systemic disease, trauma, hyperthyroidism, and drug- induced.
Atrial Fibrillation: p-waves are not normal, “f” wave predominate (fibrillation of the atria), with normal qrs complex. The r-r interval is irregular and unpredictable. The qrs rate is generally fast, however slow a-fib can occur. The most common causes of atrial fibrillation in the ER include any disease associated with left atrial enlargement (eg cardiomyopathy, severe chronic mitral regurgitation) and severe systemic disease.
An Urban Experience

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