Page 1006 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Cardiovascular system 981

VetBooks.ir Clinical presentation/diagnosis TORSADES DE POINTES
Heart sounds are pounding. Pulsations in the jugular (‘TWISTING OF THE POINTS’)
vein occur when the right atrium contracts during
ventricular systole. Syncope may occur. Persistence Overview/aetiology/pathophysiology
may lead to heart failure due to myocardial fatigue. Torsades de pointes is uncommonly encountered
Trains of abnormal ventricular beats are present during quinidine treatment for AF and is more likely
and the QRS conformation is bizarre. QRS com- in potassium-deficient animals. Sudden death dur-
plexes occur without a preceding P wave and the P ing quinidine therapy may be due to development
wave may be obscured. The T wave is often long. of torsades de pointes, with rapid deterioration into
Capture beats, when a P wave is followed by a QRS, ventricular fibrillation.
may occur. Heart rate is high, often over 100 bpm
(Fig. 8.20). Ectopic complexes may be monoform Clinical presentation/diagnosis
or multiform. Multiform ventricular tachycardia Wide polymorphic ventricular tachycardia, with
is at increased risk of degenerating into ventricular twisting of complexes around the baseline is pres-
fibrillation. ent (Fig. 8.21). This may progress to ventricular
fibrillation.
Management
Correction of any underlying conditions, such as Management
electrolyte imbalances, is critical. If pulmonary Quinidine administration should be ceased imme-
oedema is present, treatment should include the diately. Lidocaine administration may be of ben-
administration of nasal oxygen and furosemide. efit. Magnesium sulphate administration has also
Administration of i/v lidocaine may be correc- been used (Table 8.4). Intravenous sodium bicar-
tive. Excitement and seizure activity have been bonate administration increases protein binding of
associated with lidocaine administration. Other quinidine and decreases the amount of the active
medications, such as quinidine, procainamide, form.
magnesium sulphate and propafenone, have been
used (Table 8.4). VENTRICULAR FIBRILLATION

Overview/aetiology/pathophysiology
The causes of ventricular fibrillation are many and
variable. Ventricular fibrillation precedes death by a
8.20 few seconds. Peripheral pulse and heart sounds are
absent.

Clinical presentation/diagnosis
There are coarse, low-frequency undulations in
the ECG and no recognisable atrial or ventricular
activity.

Fig. 8.20 Ventricular tachycardia. Base–apex Management
electrocardiogram recorded from a horse undergoing Therapeutic options are limited. There is often inad-
treatment for AF with the oral medication quinidine. equate time to respond unless the horse is under gen-
Quinidine intoxication resulted in monomorphic eral anaesthesia, when immediate recognition may
ventricular tachycardia. The ventricular rate is occur. Electrical defibrillation may be attempted,
140 bpm. All the QRS complexes have a similar but success is uncommon. Biphasic defibrillators are
appearance. indicated if treatment is to be attempted.