The Electrocardiogram Made Easy for the Avian Veterinarian
Presenting Author: Marla Lichtenberger, DVM, DACVECC, and Larry Tilley, DVM, Dipl ACVIM
Animal Emergency Center, Glendale, WI, VetMed Consultant Inc, Santa Fe, NM (Tilley)
Interpretive Review and comments by Dr. Nemetz:
Electrocardiography (ECG or EKG) is a well established, essential tool when evaluating the veterinary patient with cardiac disease. As demonstrated by Dr. Garner's paper "A Retrospective Study of Atherosclerosis in Birds" (Click here) , more and more current information is pointing to the fact that heart disease DOES exist in our exotic pet birds, however, it is significantly under diagnosed. Another paper in 2000 by Dr. Straub demonstrated that in an examination of 100 deceased psittacine birds, 98% had some microscopic alterations within the cardiac tissue. This did not mean that these findings were the primary cause of death, but illustrated the fact that the avian heart is not immune to cardiac pathology. The top five pathologic changes found in this study: Fat within myocardial cells (45%), Myocardial cell death (necrosis) (25%), Focal chondroid (cartilage) metaplasia (change) within the aortic wall (21%), atherosclerosis (14%), and calcification within the heart (7%). It bears repeating: 45% of the cases demonstrated fat within the myocardial cells!
The most clinically significant electrical ante mortem pathology of the heart is arrhythmias or alteration in the "pace" of the heart beat. This is because arrhythmias can degenerate into malignant beats and may lead to cardiac arrest. The finding of arrhythmias is the hallmark of the ECG recording. Since many arrhythmias are caused by metabolic imbalances within the body and not primary cardiac disease, correction of these disturbances will quickly resolve the arrhythmias and prevent further heart dysfunction. Dr. Lichtenberger wrote this paper to present the "Big Picture" in using the ECG and the diagnosis of early cardiac abnormalities.
Newer ECG machines (Cardiostore and Biolog) have made the recording of avian ECG easier, but more importantly easier for the veterinarian to interpret. A bird's heart rate routinely exceeds 280 beats per minute (BPM) and can reach 800 BPM in some species. This created a problem in not only the recording of these high heart rates compared to humans and dogs and cats, but also made interpretation extremely challenging. Dr. Lichtenberger used the Biolog ECG machine in this study.
The electrical pattern in the heart creates a tracing measuring the depolarization and repolarization of the atrium and ventricles of the heart. This is represented in an ECG tracing as the P-QRS-T complex, each of which produces a deflection in the electrical axis from the horizontal.
5 main areas are interpreted in an ECG tracing.
1. The heart rate and rhythm. The heart rate is either rapid (tachycardia), slow (bradycardia) or normal. The rhythm is either regular or without rhythm (arrhythmia) meaning clinically abnormal rhythm or breaks in a normal rhythm trace.
2. Identification of the P waves. This shows atrial activity.
3. Identification of the QRS Complex. This shows mostly ventricular activity.
4. Relationship between the P waves and the QRS Complexes. Is there a ventricular beat for each atrial beat? Or is the heart working as two independent hearts?
5. Measurement of the P-QRS-T complex. Measurement of heights and intervals in Lead II. There are six electrical axes: Lead I, II, III aVR, aVL, and aVF. There are many variations in these measurements in different species and within the species.
One note: the ST segment is often absent or very short in normal birds.
These measurements and their interpretations assist the clinician to determine the heart's condition at rest. The ECG is also useful in surgical procedures to assist in the proper level of anesthesia. If a bird became hypoxic (lacking oxygen) or its electrolytes became imbalanced, the heart will react and the ECG will detect these abnormalities that can then be corrected, raising the overall level of safety for that patient.
Cardiology often seems complex and even more so in the avian patient. However with new computer technology and breaking down the ECG into its simple components, various cardiac pathologies can be diagnosed and treated.
This paper demonstrated once again that Avian Heart disease is a real phenomenon, but one that is often diagnosed after the patient has died. It appears that the #1 risk for heart disease in the avian patient is a diet high in fats leading to obesity and myocardial damage. With the advances in computer technology and the understanding of how the avian heart acts differently than other animals, more cases can be diagnosed when the patient is alive. Once the condition is realized, various protocols can help to correct or minimize the effects and give the bird a longer, healthier life.