Page 66 - Basic Monitoring in Canine and Feline Emergency Patients

Table 3.6. Continued.
VetBooks.ir Drug General indications Dose (dog) Dose (cat)
IV/IM/SQ: 0.01–0.02 mg/kg
Glycopyrrolate
Hemodynamically relevant
IV/IM/SQ: 0.01–0.02 mg/kg
bradyarrhythmias
Theophylline Long-term treatment of SSS; PO: 10 mg/kg q12h PO: 10 mg/kg q12h
bronchodilation
Propantheline Long-term treatment of SSS PO: 0.25–0.5 mg/kg q8-12h –
Hyoscyamine Long-term treatment of SSS P: 0.003–0.006 mg/kg q8h –
Other anti-arrhythmic medications
Magnesium Adjunct treatment of VT/VPCs IV: 0.3 mEq/kg over 15 min IV: 0.3 mEq/kg over 15 min
chloride
(or sulfate)
Digoxin Heart rate reduction in AF IV: loading protocol of 2.5 μg/kg PO: 5 μg/kg q48h
(especially if concurrent CHF) slow bolus repeated hourly ×
4 hours (total 10 μg/kg)
PO: 3–5 μg/kg q12h
AF, Atrial fibrillation; CHF, congestive heart failure; CRI, continuous rate infusion; IM, intramuscular; IV, intravenous; PO, by mouth;
SQ, subcutaneous; SNS, sympathetic nervous system; SSS, sick sinus syndrome; SVPC, supraventricular premature complex; SVT,
supraventricular tachycardia; VPC, ventricular premature complex; VT, ventricular tachycardia.

also occur in patients with noncardiac diseases, Therefore, P waves of normal morphology may be
including electrolyte derangements (hypokalemia, noted intermittently between ventricular QRS
hypomagnesemia), splenic disease, gastric dilata- complexes, with no consistent temporal relation-
tion-volvulus, and sepsis. Another variant of ven- ship to QRS complexes (see arrows in Fig. 3.9).
tricular ectopy is called accelerated idioventricular Most P waves are not visible because they occur
rhythm (AIVR). AIVR, sometimes oxymoronically simultaneously with QRS complexes and are thus
called ‘slow VT,’ refers to a ventricular rhythm that ‘hidden’ on the ECG. VT is often most often seen
occurs at heart rates close to the sinus rate of the as an intermittent rhythm; that is, the patient has
patient (e.g. <140 bpm in the dog). AIVR most an underlying normal sinus rhythm with frequent
commonly occurs in patients with noncardiac VPCs and paroxysms of VT. If a sinus beat and
causes of ventricular ectopy (see above) or in VPC occur at the same time, wave fronts from
patients under general anesthesia/sedation. both stimuli may cause the ventricle may depolar-
Because the heart rate in AIVR is similar to the ize from both ‘above and below’ simultaneously,
sinus rate for that patient, AIVR does not lead to leading to an abnormal QRS complex that is a
hemodynamic compromise and generally does not morphologic hybrid of the patient’s ventricular
require treatment. and sinus complexes. Such complexes are called
Isolated VPCs are typically easy to recognize fusion beats and can be helpful in confirming the
because QRS morphology differs from the sur- diagnosis of VT.
rounding sinus beats; however, sustained VT may Ventricular ectopy warrants treatment if the
be more difficult to identify without normal sinus ventricular arrhythmias lead to hemodynamic
beats present for comparison. VT is perfectly reg- compromise (hypotension) or place the patient at
ular (identical R–R intervals) unless there are risk for sudden cardiac death. The first-line emer-
multiple ventricular foci involved, in which case gency treatment for VT in dogs is intravenous
QRS morphology also varies between beats (poly- lidocaine; adjunctive treatments if lidocaine is
morphic VT; see Fig. 3.10). Because the ectopic unsuccessful include procainamide or amiodarone
beats originate within the ventricles, the presence (see Table 3.6). In cats, lidocaine is generally
of VT does not affect the firing of the SA node; the avoided or used at much lower doses due to
atria and ventricles are controlled by two inde- adverse effects. Hypokalemia and hypomagne-
pendent ‘pacemakers’ (termed AV dissociation). semia should also be corrected if present. Long-

58 J.L. Ward