Page 115 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answers 45, 46 ECG Cases

Answer 45
VetBooks.ir 1 ECG 45 shows atrial standstill.

2 • The heart rate is ~105 bpm and the rhythm is regular.
• There is an absence of P waves. The QRS complexes are narrow indicating they are likely
supraventricular in origin.
• The lack of P waves, slow heart rate, and supraventricular QRS complexes are most consistent with
atrial standstill. The QRS complexes are likely junctional escape beats.
• Atrial standstill can be secondary to a degenerative atrial myopathy or secondary to severe electrolyte
abnormalities, such as hyperkalemia.
• The degenerative atrial myopathy is typified by loss of functional atrial myocytes and atrial fibrosis,
and atrial standstill is usually permanent.
• Hyperkalemia can be secondary to metabolic disease (i.e., diabetic ketoacidosis), renal failure,
or reperfusion injury that sometimes accompanies feline aortic thromboembolism. Correction of
hyperkalemia (e.g., diuresis, glucose, insulin, and so on) can restore normal sinus rhythm.

Answer 46

1 ECG 46a shows SVT and a left MEA shift consistent with left anterior fascicular block (LAFB).
2 • The heart rate is 300 bpm and the rhythm is regular. The QRS complexes are narrow; however, the
QRS polarity is predominantly negative in leads II, III, and aVF, while positive in leads I and aVL,
and is consistent with a left MEA shift (see ECG 18, p. 65).
• There are P waves in front of each QRS complex indicating that the origin of the QRS complexes is
supraventricular (rather than ventricular despite the abnormal polarity).
• SVT can be due to underlying cardiomyopathy, hyperthyroidism, cardiac neoplasia, or drug toxicity
(e.g., bronchodilators, chocolate, sympathomimetics).
• In this case, the presence of the left axis shift is confirmed as the SVT suddenly terminates (arrows,
ECG 46b) and two sinus beats (arrowheads) appear at a slower heart rate.

46b

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