Page 97 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answers 30, 31 ECG Cases

Answer 30
VetBooks.ir 1 ECG 30 shows sinus arrhythmia and criteria for atrial enlargement.

2 • The heart rate is 90 bpm. There are wide and notched (bifid) P waves in leads II, III, and aVF. The
P wave duration in lead II is 60 ms (normal: <40 ms). A wide and notched P wave is also referred
to as “P mitrale” despite the fact that tall P waves can be detected in cases of both left or right atrial
enlargement.
• Atrial enlargement is associated with volume overload and increased atrial size, as for example
occurs with degenerative mitral or tricuspid valve disease or cardiomyopathy. ECG detection of atrial
enlargement is relatively insensitive but usually specific in both cats and dogs. This patient had severe
left atrial enlargement due to advanced degenerative mitral valve disease.

Answer 31

1 ECG 31 shows sinus bradycardia and QT interval prolongation.
2 • The heart rate is ~45 bpm. The PR interval is mildly prolonged at 140 ms, indicating first-degree
AV block. The P wave is notched and low voltage in lead II. The QRS duration is normal, but the QT
interval is markedly prolonged at 360 ms (normal: 150–250 ms, depending on heart rate). The QT
interval is measured from the beginning of the QRS complex to the end of the T wave and represents
the total duration of electrical depolarization and subsequent repolarization of the ventricular
myocardium. The QT interval is inversely related to the heart rate.
• Long QT syndromes are caused by abnormal ionic current flow during repolarization. Various
drugs are a common cause of a long QT interval, including the class IA antiarrhythmic agents,
including quinidine, procainamide, and disopyramide, and class III antiarrhythmic agents, including
sotalol and amiodarone. A number of noncardiac drugs have also been reported to prolong QT
interval, including cisapride, phenothiazines, haloperidol, tricyclic antidepressants, antimicrobial
agents (erythromycin, chloroquine, and trimethoprim–sulfamethoxazole), and antifungal agents
(ketoconazole and itraconazole).
• Long QT intervals predispose to the development of polymorphic ventricular arrhythmias, (torsade
de pointes; see ECG 4, p. 48).

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