Page 175 - Problem-Based Feline Medicine

10 – THE CAT WITH TACHYCARDIA, BRADYCARDIA OR AN IRREGULAR RHYTHM 167

In some cases with frequent VPBS panting, restlessness fied as ventricular premature beats. Supraven-tricular
and anxiety may be seen. premature beats will usually reset the sinus rate.

Diagnosis Treatment

The heart rate is normal and the cardiac rhythm is irregu- Isolated premature beats do not require therapy
lar because of the premature beats (Figure 10.5). unless present with other more severe arrhythmias.

The morphology of the QRS complex is abnormal/ If there is a large number of ventricular premature beats
aberrant when compared with the normal sinus beat. where the premature QRS falls within the preceding
T wave (R on T phenomenon), therapy should be con-
The QRS complex is wider than normal and has a sidered.
bizarre appearance.
If there is suggestion of hemodynamic compromise
VPBs may occur as a fusion beat. therapy may be considered:
VPBs may occur as an interpolated beat. ● Atenolol at 6.25–12.5 mg/cat PO every 12 hours.
● Propranolol at 0.5–1 mg/kg PO every 8–12 hours.
There is no association between the P waves and the ● Procainamide at 10–20 mg/kg PO every 8–12
QRS complex. hours.
VPBs do not re-set the sinoatrial node. ● Sotalol at 10–20 mg/cat PO every 12 hours.

Prognosis
Differential diagnosis
The prognosis depends on the underlying disease.
Marked respiratory sinus arrhythmia is rare in
cats but may mimic the presence of premature beats. In most cases isolated premature beats are not life
Sinus arrhythmia is rare in cats and only occurs at threatening.
slow heart rates. Increasing the heart rate above 180 When R on T phenomenon is present, patients may be
bpm by excitement or atropine (0.04 mg/kg parenter- predisposed to the development of ventricular tachy-
ally) will abolish sinus arrhythmia. cardia and/or sudden death.
Motion or electrical artifact may mimic premature If VPBs are due to primary heart disease, this likely
beats. Premature beats can be distinguished from motion reflects an advanced stage and may be associated with
artifact because they occur simultaneously in all leads. a less-favorable prognosis.
Supraventricular premature beats with aber- If due to causes other than primary heart disease, the
rant ventricular conduction may be erroneously classi- prognosis is dependent on the underlying disease.

RHYTHM STRIP: II
50 mm/sec; I cm/mV VPC VPC VPC VPC

05-40Hz
Figure 10.5. Ventricular premature contractions.