Page 249 - Clinical Small Animal Internal Medicine

21 Supraventricular Arrhythmias 217

metabolism and elimination in the presence of ascites, as for treatment of SVT has only been reported recently. It
VetBooks.ir well as decreased hepatic and renal blood flow that has been shown to terminate episodes of SVTs in the
presence or absence of an accessory pathway. Lidocaine
accompany heart failure. Moreover, drug selection may
depend on the level of certainty regarding the nature of
of paroxysmal atrial fibrillation initiated by elevated
the arrhythmia. Indeed, it may be challenging to deter­ has also been used successfully to terminate recent onset
mine the origin of wide‐complex tachycardias, which are vagal tone in large‐breed dogs with normal cardiac func­
characteristic of ventricular tachyarrhythmias but on tion. One to two boluses of lidocaine restored sinus
occasion correspond to SVTs with aberrant intraven­ rhythm within 30–90 seconds, while causing mild self‐
tricular conduction. For example, drugs used for rate‐ limited hypotension following the intravenous bolus.
control management of SVTs, in particular calcium
channel blockers, may cause hemodynamic collapse if Sotalol
given in the presence of rapid ventricular tachycardia Although availability of the IV formulation of sotalol is
and would persist at a fast rate despite treatment. Besides limited, the oral formulation can be used for acute man­
the drugs used for chronic management, paroxysmal agement of SVTs, as most of them are not immediately
SVTs may require emergency intervention when they life‐threatening. Sotalol has potassium channel and mild
cause hemodynamic instability. beta‐blocking properties, which make it a good option to
terminate and prevent/decrease the recurrence of focal
Acute Management atrial tachycardias, atrial flutter, and AV reciprocating
Antiarrhythmic drug administration should always be pre­ tachycardia. Conversion of those arrhythmias back to
ceded by attempts to identify and eliminate potential trig­ sinus rhythm usually occurs 2–4 hours after oral admin­
gers for the arrhythmia. This includes correcting electrolyte istration of the drug.
disturbances, hypoxemia, hypovolemia, and acidosis.
Common drugs used for the management of SVTs Long‐Term Management
include calcium channel blockers (diltiazem), beta‐ Termination of the arrhythmia and maintenance of sinus
blockers (esmolol), sodium channel blockers (procaina­ rhythm is the preferred approach for the long‐term man­
mide, lidocaine), and drugs that combine several agement of SVTs (rhythm‐control strategy). It is more
antiarrhythmic properties (sotalol). likely to succeed when limited structural cardiac changes
are present. However, rate‐control strategies used for the
Diltiazem management of atrial fibrillation can also safely be
On occasion, diltiazem terminates SVTs if the arrhythmia applied to the control of most sustained SVTs.
mechanism is dependent on the AV node. Diltiazem can Among various antiarrhythmic medications, sotalol
be administered as intravenous boluses and constant rate has proven to be the most effective rhythm‐control drug.
infusion for acute management of tachyarrhythmias. Conversion to sinus rhythm usually occurs just a few
hours after oral administration, but it can take up to a
Esmolol few days to observe a response. Sotalol is also effective at
Esmolol is a short‐acting intravenous beta‐1‐selective preventing arrhythmia recurrence. The negative ino­
blocker that is rapidly metabolized by blood esterases. It tropic effect of sotalol is modest compared to other beta‐
is used for rate‐control and termination of AV node‐ blockers. Nonetheless, dogs with myocardial failure
dependent SVTs. However, it may be less effective than should be closely monitored while receiving sotalol.
intravenous diltiazem. Atrioventricular reciprocating tachycardia usually
responds well to sotalol, which alters the electrophysio­
Procainamide logic properties of all the cardiac structures necessary for
Procainamide has been used for the management of the maintenance of this arrhythmia, including the acces­
SVTs. It is also indicated for acute management of broad‐ sory pathway, the atrial myocardium, the AV node, and
complex tachycardias, when discrimination between the ventricular myocardium. In dogs that fail to respond
SVT and ventricular tachycardia is difficult, as it is also to monotherapy, sotalol can be combined with mexile­
very effective in terminating ventricular arrhythmias. tine (5–7 mg/kg q8h) with better results.
Unfortunately, it is no longer available in an oral formu­
lation and the IV formulation has limited availability Nonpharmacologic Treatment of Supraventricular
outside the United States. Arrhythmias
Synchronized DC cardioversion and radiofrequency
Lidocaine catheter ablation have been successfully used to treat
While lidocaine is extensively used as first‐line therapy supraventricular arrhythmias. In particular, dogs with
for acute termination of ventricular tachycardia, its use AV reciprocating tachycardia show the best results with