Page 173 - Problem-Based Feline Medicine

10 – THE CAT WITH TACHYCARDIA, BRADYCARDIA OR AN IRREGULAR RHYTHM 165

● The authors use procainamide at 5–10 mg/kg slow
SUPRAVENTRICULAR PREMATURE BEATS
IV bolus. This bolus can be repeated once if neces-
(SVPBS)***
sary.
● Esmolol at 250–500 μg/kg IV bolus given slowly
Classical signs
over 1 minute. The bolus can be followed with a con-
stant rate infusion at 50–200 μg/kg/min. Esmolol is ● Pulse deficits.
compatible with 5% dextrose. ● Interruptions of rhythm regularity.
● Propranolol at 20 μg/kg slow IV bolus. Repeat
boluses can be given up to a total maximum dose of
100 μg/kg. Pathogenesis
DO NOT USE LIDOCAINE IN CATS. Severe neu- Premature beats result from two mechanisms, alter-
rotoxicity can occur. ations in impulse formation and alterations in impulse

If patient is not symptomatic for the arrhythmia: conduction.
● Atenolol 6.25–12.5 mg/cat PO every 12 hours. Alterations of impulse formation depend on the
● Propranolol at 2.5–5 mg/kg PO every 8 hours. intrinsic automaticity of diseased cardiac cells.
● Sotalol 10–20 mg/cat PO every 12 hours. ● Diseased myocardial cells outside the specialized con-
● Procainamide 10–20 mg/kg PO every 8–12 hours. duction system can acquire automaticity because of
changes in the resting membrane potential.

Prognosis Alterations of impulse conduction result from re-
entry and by-pass tracts.
Most cats with sustained ventricular tachycardia have ● Re-entry, is a self-sustaining electrical circuit that
severe myocardial damage and are at high risk of sud- repeatedly depolarizes surrounding tissue.
den death. ● By-pass tracts alter the normal pathway of conduc-

The prognosis is fair. tion by providing an alternative pathway around
the AV node.

PREMATURE BEATS
Clinical signs
The following are definitions of electrocardiographic
findings necessary to understand the distinguishing fea- Most patients show no evidence of clinical signs.
tures between supraventricular and ventricular prema-
In some cases panting, restlessness and anxiety may be
ture beats:
seen.
● A fusion beat occurs when the ventricles are
activated by two different wave fronts, resulting
in abnormal/aberrant appearance of the QRS Diagnosis
complex.
The heart rate is normal and the cardiac rhythm is irregu-
● An interpolated beat is when a ventricular beat
lar because of the premature beats (Figure 10.4).
occurs between two normal beats without disturb-
ing the cardiac rhythm. The ectopic P wave is premature, the configuration may
● The re-setting or non-resetting of the sinoatrial be different from normal sinus beats.
node refers to the influence of the premature beat
The morphology of the QRS complex is similar to a
on the basic sinus rhythm.
normal sinus beat.
● If the rhythm is disturbed by the premature beat
then the rhythm is reset. Resetting of the basic The QRS complex is usually narrow, but in very pre-
rhythm is also referred to as non-compensatory mature beats it may be wider (longer duration) than
pause. normal.