Page 105 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answers 37, 38 ECG Cases

Answer 37
VetBooks.ir 1 ECG 37 shows a sinus rhythm and criteria for right ventricular hypertrophy.

2 • The heart rate is 215 bpm. The QRS duration is within normal limits and each is preceded by a
normal P wave. There is a shift in the MEA to the right at –100°, indicated by a predominantly
negative QRS morphology in leads I, II, III, and aVF.
• Right axis deviations are associated with either right ventricular hypertrophy or RBBB, with the
discriminating feature being the duration of the QRS complex. QRS durations >60 ms in the cat are
characteristic of RBBB (see ECG 34, p. 87), and durations <60 ms typical of right heart hypertrophy.
• In this cat an echocardiogram revealed marked right ventricular hypertrophy due to pulmonary
hypertension and tricuspid insufficiency.

Answer 38

1 ECG 38 shows sinus arrhythmia with criteria for left ventricular hypertrophy.
2 • The heart rate is ~150 bpm. Note that the ECG was recorded at 5 mm/mV, which results in the
amplitude of the QRS complex as appearing half its actual height. The P wave amplitude is normal at
0.4 mV. The MEA is +80°, which is in the normal range. The R wave amplitude in lead II is
4.4 mV, in lead aVF is 4.6 mV, and in lead I is 1.5 mV, all of which are indicative of left ventricular
hypertrophy.
• Left ventricular hypertrophy increases the magnitude of the electrical wavefront travelling through
the left ventricle, resulting in an increased R wave in leads parallel with this wavefront, primarily
leads II and aVF. Diseases that cause left heart hypertrophy include cardiomyopathy, valve disease,
and a variety of congenital heart defects. The left heart hypertrophy pattern is not specific to any
one disease or cause, and further diagnostics such as thoracic radiography or echocardiography are
warranted.
• In this case, echocardiography revealed congenital subaortic stenosis and resulting concentric left
ventricular hypertrophy.

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