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Interesting Cases – Heart Disease (Sick Sinus Syndrome)

By November 1, 2009 December 13th, 2011 Interesting Cases

Pico is a 12 year old, male neutered, Miniature Schnauzer. Pico began to have episodes of weakness and collapse that seemed to worsen over a period of 2 weeks. Although he would recover quickly after an episode of collapse, his owner felt Pico should be examined.

Pico was diagnosed with a condition called Sick Sinus Syndrome. In the heart is an area called the sinus node that is responsible for forming the stimulus for the heart to beat. If the sinus node is not stimulating heart contractions properly it is termed as “sick”. Miniature Schnauzers, West Highland White Terriers, Cocker Spaniels and Dachshunds are predisposed to the syndrome. In the Miniature Schnauzer and the West Highland White Terrier, Sick Sinus Syndrome may be a condition that they could inherit.

Picture of the heart showing the S-A (Sinus) Node in the upper left where the stimulus originates to beat the heart


Sick Sinus Syndrome is a condition that affects the heart rate. The heart rate may be very slow (bradycardia), very fast (tachycardia), or there may be a break/stoppage in the heart rhythm (sinus arrest). The diagnosis is made on history, physical examination, a holter monitor reading (ECG machine worn by the pet for 24 hours while he goes about his normal activities) and an ultrasound. Bloodwork and urinalysis is recommended to be sure that there are no other health problems present.

Pico wearing his Holter Monitor that is recording his heart beats.


Pico appearing quite comfortable while the Holter Monitor is working.


The monitor revealed that Pico had a heart rate that varied from 28 beats per minute to up to 229 beats per minute. The normal heart rate for a dog is 70-120 beats per minute. There were stoppages in the heart rhythm of up to 6.85 seconds long.

Normal ECG reading showing a regular heart beats with regular intervals


Sick Sinus Syndrome showing a long delay in between heart beats


Treatment involves medication (in Pico’s case Propantheline Bromide and Theophylline) or if necessay the placement of a pacemaker. Fortunately, Pico has been improving on his medications alone. He used to have 10-20 episodes of weakness and collapse an hour, but has improved to 10 or so much milder episodes a day (no collapse – Pico just pauses for a minute and then carries on doing what he is doing). Although quieter, Pico is enjoying his normal activities and hopefully will continue to do so for some time.