StarCare Animals
INTRODUCTION
Some abnormalities on the electrocardiogram (ECG) may indicate structural problems in the heart or other nonstructural cardiac pathology. However, the relationship between ECG abnormalities and structural changes in the heart is complex. Often, the combined use of electrocardiography and echocardiography can help to address these specific problems.
Structural Changes in the Pet Heart
Like humans, the heart of mammals such as cats and dogs consists of four chambers separated by valves. Structural changes in the heart, such as myocardial hypertrophy (hypertrophy), ventricular dilatation, valvular stenosis, or valvular regurgitation, can alter normal electrical activity and show up on the electrocardiogram. In addition, pets may experience a variety of structural changes in the heart due to birth defects, age, breed predisposition, or disease, which can have a significant impact on cardiac function. For example, dogs may have enlarged hearts and reduced contractile function due to dilated cardiomyopathy; in cats, hypertrophic cardiomyopathy, characterized by thickening of the heart wall, is more common.
Structural Problems and ECG Abnormalities in the Pet's Heart
By recording the electrical activity of the heart, the pet's ECG can reveal abnormalities of structural heart problems, i.e., they are reflected in the ECG as the following changes:
· Enlarged left atrium: A wide P-wave or notched P-wave in lead II suggests an enlarged left atrium.
· Left atrial enlargement: wide P-waves or notched P-waves in lead II are indicative of left atrial enlargement.
· Left ventricular enlargement: High R waves in specific leads (I, II, and aVF) suggest left ventricular enlargement.
· Ventricular enlargement or conduction disturbances: Wide QRS wave clusters.
Note: These abnormalities are not always seen with enlarged chambers and may be seen in normal hearts. In addition, the ECG is not sensitive to recognizing mild to moderate changes in chamber size.
The Pet Practitioner's Perspective: Synergistic Effects of ECG and Ultrasound
The use of ECG in conjunction with echocardiography is an extremely valuable approach. The ECG provides an easy, non-invasive way to detect electrical abnormalities that can indicate specific structural changes in the heart. Of course, the ECG can also reveal non-structural aspects of the heart, such as arrhythmias, electrolyte balance abnormalities, conduction block, myocardial ischemia, drug effects, etc., and plays an important role in confirming the diagnosis of cardiac problems or in initial screening.
Echocardiography complements ECG information by providing a visual assessment of cardiac anatomy and function. For example, if a dog's ECG shows signs of arrhythmia, echocardiography can help determine if this is caused by a structural abnormality such as an enlarged ventricle or valvular lesion. Similarly, if an ECG shows that a cat may have hypertrophic cardiomyopathy, an echocardiogram can confirm whether the heart walls are thickened and assess the degree of blood flow obstruction. Echocardiography can also demonstrate valvular abnormalities indicated by ECG changes, thus helping to confirm the diagnosis and assess the severity of the condition.
Precautions
When interpreting ECGs, veterinarians should consider the susceptibility of specific breeds to certain heart conditions. In addition, the size and shape of the animal can affect the ECG reading. Therefore, knowledge specific to different species is important.
Summary
In veterinary practice, understanding the changes in the structure of the heart in cats and dogs and their effect on ECG abnormalities is key to the effective diagnosis and management of heart disease. The combined use of electrocardiography and echocardiography can provide a comprehensive view that greatly enhances the veterinarian's ability to develop an accurate assessment and treatment plan.
References
Mark D. Kittleson, Heart Disease: Conduction Abnormalities in Dogs and Cats, 2024 Merck & Co., Inc., Rahway, NJ,
Mustafa Ahmed, Echocardiogram vs. EKG – Explained By A Cardiologist, 2017, https://myheart.net/articles/echocardiogram-vs-ekg-explained-by-a-cardiologist/.
Schwarzman Animal Medical Center, Heart Disease in Dogs and Cats, 2023, https://www.amcny.org/pet_health_library/heart-disease-in-dogs-and-cats/.
