The role of the ECG in preoperative workups for dogs and cats
Before surgery in dogs and cats, even those without symptoms, the veterinary ECG is essential to gauge anesthetic risk and uncover hidden heart disease.
In-depth coverage in the guide: 4 reasons to order a pre-surgical ECG
Introduction
Every veterinarian, whether a cardiologist or a general practitioner, knows how important it is to run a veterinary electrocardiogram (ECG) on dogs and cats before surgery of any kind, even when the patient shows no symptoms. This step is essential to assess anesthetic risk.
If this precaution matters in the preoperative setting, it matters even more in the face of cardiorespiratory signs: an exam like the ECG is the first move toward an accurate diagnosis of the disease affecting the small animal. Good veterinary practice also recommends an annual ECG for dogs and cats from age 6 onward, as a screen for age-related disease.
Cardiorespiratory conditions can arise from many sources, often uncovered during a preoperative workup: trauma after a car accident, a fall, or a fight; breed predisposition; congenital disease; and various tumors.
The veterinary electrocardiogram, which records the heart's electrical activity in the small animal, is essential before surgery and also for detecting and managing heart disease at many points across a dog's or cat's life. It is a noninvasive, painless exam that requires no prior preparation.
The ECG can be seen as the entry point into veterinary cardiology. When ongoing cardiac follow-up is needed, additional studies should follow, such as Doppler echocardiography, Holter monitoring, and thoracic radiographs, among others.
When to use the ECG
A review of the veterinary literature on the ECG in dogs and cats draws on work by specialists such as Guillermo Belerenian ("Afecciones Cardiovasculares en Pequeños Animales"), Larry Patrick Tilley ("Essentials of Canine and Feline Electrocardiography"), Mike Martin ("Small Animal ECGs"), and Stephen J. Ettinger ("Textbook of Veterinary Internal Medicine"), among others, offering guidance on when the ECG should be used.
Heart sounds, the acoustic events produced as blood strikes the various cardiac structures and great vessels, should anchor the physiological assessment in the clinical exam. The catch is that not all of them can be picked up by simply listening to the cardiac cycle.
The cardiac cycle covers the relaxation phase (diastole) and the contraction phase (systole). The sounds that may be present are: closure of the atrioventricular valves (mitral and tricuspid), the sound that precedes systole; closure of the semilunar valves (diastole); rapid ventricular filling; and atrial contraction.
According to the review, when the third and fourth heart sounds combine with the first and second, the result is a "gallop rhythm," which is hard to hear on auscultation. The third heart sound can appear in patients with dilated cardiomyopathy, while the fourth can be identified in patients with hypertrophic cardiomyopathy, a condition characteristic of cats. The third and fourth sounds also cannot be told apart on simple auscultation. The ECG therefore serves as the supporting tool for detecting overloads that auscultation misses.
Reading the electrocardiogram involves measuring several items, above all the heart rate, since counting the number of beats per minute is basic information. According to the authors, the usual reference ranges are: adult dogs, 70 to 160 bpm; giant breeds, 60 to 140 bpm; toy breeds, up to 180 bpm; puppies, up to 220 bpm; and cats, 120 to 240 bpm.
Analyzing this rate and rhythm points toward a range of abnormalities.
Sinus bradycardia
The sinus rhythm is normal, but the rate falls below the accepted reference range.
Sinus block / sinus arrest
The heart rate varies and is often associated with bradycardia. The rhythm is regularly irregular or irregular with a pause. It is common in brachycephalic dog breeds.
First-degree atrioventricular block
Here the P-R interval, the time from when the impulse leaves the sinus node until it reaches the atrioventricular node, is longer than 0.13 s in dogs and longer than 0.09 s in cats, compared with normal sinus rhythm. Among other causes, it is common in older animals, such as Cocker Spaniels and Dachshunds.
Atrial standstill
Low heart rate with a regular rhythm. The ECG shows no P waves, which do not appear even after atropine administration or exercise. Possible causes include Addison's disease (hypoadrenocorticism), kidney failure, or urinary obstruction.
Sick sinus syndrome
The dog presents with severe, persistent sinus bradycardia. This bradycardia alternates with supraventricular tachycardias (bradycardia-tachycardia syndrome). It is common in female Miniature Schnauzers and has a genetic origin. Fitting a permanent artificial pacemaker may be considered.
How the ECG has advanced
If your clinic does not specialize in cardiology, it probably has no electrocardiograph on hand, given the cost and the space the equipment would take up. That is no longer a concern: portable electrocardiographs built exclusively for veterinary use are now available.
One that has gained strong traction in veterinary telemedicine is INcardio. It is a wireless, portable 12-lead electrocardiograph developed exclusively for veterinary use in small animals. The device runs software that can monitor, capture, and analyze the electrical tracing produced by the exam, along with a cardiology telemedicine module for sending those tracings and receiving the corresponding reports.
We live in the era of apps, tablets, smartphones, and laptops. Technology is part of everyday life, built to make things simpler through bundles of convenience, and veterinary medicine is no exception to that wave.
Portability, size, weight, practicality, and applicability are the baseline requirements when developing solutions and products for the veterinary field, and these are precisely the qualities of the portable ECG device developed and sold by INpulse Animal Health.
Notably, INcardio meets diagnostic needs not only in dogs and cats but has also been tested for use in manatees, horses, ponies, and monkeys. For those cases there is an aluminum version of INcardio, likewise portable and wireless, that can operate up to 6 meters away from the computer.
The reality is that the advance of veterinary telemedicine is making fast, reliable diagnoses easier for veterinarians at a compelling cost-benefit ratio, both for preoperative cases and for everything else that comes up over a dog's or cat's life.