Page 65 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answers 7, 8 ECG Cases

Answer 7
VetBooks.ir 1 ECG 7 shows sinus rhythm with evidence of left ventricular hypertrophy.

2 • The average heart rate is 210 bpm. The rhythm is regular.
• The amplitude of the R wave in lead II is 1.9 mV (normal <0.9 mV) suggesting left ventricular
hypertrophy. The caudal limb leads III and aVF, which are similar in orientation to lead II, also
display R wave amplitudes similar to lead II.
• Left ventricular enlargement is often due to cardiomyopathy or, less commonly, hyperthyroidism
or systemic hypertension. Based on the ECG findings as well as the presence of a heart murmur,
underlying changes in cardiac structure and function are likely, and further diagnostics, such as
radiographs or echocardiography, are warranted.

Answer 8

1 ECG 8 shows sinus rhythm with ST segment elevation.
2 • The heart rate is 150 bpm. The ST segment is markedly elevated (arrows) in leads II, III, and
aVF and depressed in lead aVR. The Q waves are notched in leads II, III, and aVF.
• ST segment elevation or depression occurs secondary to myocardial hypoxia/ischemia in dogs and
cats. In humans, the discrete location of a recent myocardial infarction can often be inferred based
on ST segment changes. The mechanisms underlying ST segment changes are complex. Hypoxic
conditions in the myocardium leads to diminished intracellular concentrations of adenosine
triphosphate (ATP), and thus decreased activity of ATP-dependent ion transport systems. These
systems play an important role in maintenance of the resting cell membrane as well as action
potential propagation. In cases of myocardial hypoxemia, neighboring regions of myocardium will
have different electrical properties and a small electrical current (current of injury) flows from the
depolarized ischemic regions to more normal regions, resulting in ST segment elevation or depression.
• In this case, pulmonary thromboembolism secondary to glomerulonephritis and loss of antithrombin
III resulted in severe hypoxemia.

8 I

II

III

aVR

aVL

aVF

52