Name: Fergie
Age: 10 years
Sex: FS
Breed: DSH

Please review Fergie’s clinical history.

Fergie was presented for evaluation today with a history of inappetence and lethargy for the past 4 days. On physical examination, she appeared to be moderately dehydrated.  Her heart rate was 100 bpm and regular.  Pulse strength was decreased and capillary refill time was prolonged.  Her rectal temperature was 100.2° F.  

View Fergie’s electrocardiogram (the black bar represents one second)

 

 
Discussion:  The combined findings of sinus bradycardia and 1st degree AV block are consistent with increased vagal tone.  The differential diagnosis list for sinus bradycardia in cats includes primary causes (e.g. sinus node disease, rare in cats), but sinus bradycardia more commonly occurs secondary to increased vagal tone due to a variety of non-cardiac abnormalities, including toxicities, hypothermia, and electrolyte abnormalities like hypocalcemia or hypomagnesemia.  Prolonged Q-T segments may be noted in animals with profound bradycardia from any cause (as listed above) but any abnormalities that may directly affect the Q-T interval (hypocalcemia, hypomagnesemia, hypokalemia or ventricular conduction abnormalities like bundle branch blocks) should be considered. Treatment/Management: If no overt reason for sinus bradycardia is identified and the patient has clinical signs of low cardiac output, administration of vagolytic agents (i.e. atropine or glycopyrrolate) may result in increased sinus depolarization rate or development of sinus tachycardia.  If there is minimal or no response to vagolytic agents, there may be primary disease of the sinus node present.  Fergie was diagnosed with sinus bradycardia likely secondary to dehydration and hypokalemia ([K] = 2.2 mmol/L) and was treated with cautious administration of potassium-supplemented fluids until the reason for her inappetence could be identified.