Page 16 - VetCPD Jnl Volume 7, Issue 4

VETcpd - Cardiology Electrical cardioversion
Synchronized electrical cardioversion (transthoracic, transeosophageal or intracardiac) can be successful (Bright et al. 2005; Sanders et al. 2014; Jung et al. 2017). Due to equipment requirements, this procedure is mostly performed in a referral setting under the supervision of
a cardiology specialist.With the routinely used transthoracic approach, defibrillation pads with conductive gel are placed on either side of the chest wall, over the heart and an electric shock is delivered under general anesthesia (Pariaut 2017).When the shock is successful, the electrical activity of the atrial cells is reset and the sinus node regains control of the rhythm (Pariaut 2017).This procedure has a
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are two-fold: first, by improving diastolic filling and subsequently boosting cardiac output; second, reducing the risk of tachycardia-induced cardiomyopathy and subsequent heart failure. It is important to note that in cases with concurrent CHF, symptomatic treatment of CHF will contribute to HR reduction, by decreasing sympathetic nervous system activation.
Several anti-arrhythmic drugs are used to control HR in AF. A combination
of digoxin and diltiazem is an effective regime to reduce the ventricular response rate (Gelzer et al. 2009).This has been reported to have a more pronounced negative chronotropic effect than either of the drugs used as monotherapy (Gelzer et al. 2009; Jung et al. 2016).
treatment (aiming for trough levels 6-8 h post-pill of 0.6-1.0 ng/L, higher serum levels may increase the risk of toxicity with no additional rate control benefit).
Alternatives to consider in cases where the diltiazem, digoxin or both fail or are unsuitable or ineffective include class III anti-arrhythmic drugs, such as amiodarone and sotalol (Saunders et al. 2006; Pedro
et al. 2012).A 20% decrease in HR was observed in 76% of dogs with AF receiving amiodarone (Saunders et al. 2006). Sotalol, or pure class II anti-arrhythmic drugs (beta-blockers) can also help controlling the ventricular response rate in AF; however their use is controversial in dogs with uncontrolled CHF (common at the time of AF diagnosis).
Diltiazem is a calcium channel blocker whose negative chronotropic effect results from the slower impulse conduction through the AV node, resulting in reduced
has been reported that 50% of dogs with an underlying heart disease will have recurrence of the arrhythmia within two months; 70% of dogs with lone AF will have recurrence of the arrhythmia within three months and virtually all within five months (Bright and zumBrunnen 2008; Pariaut 2017).This means cardioversion is not expected to maintain a sinus rhythm long-term, and owners should
be counselled about the benefit of this procedure. Pre-treatment with oral amiodarone appears to be beneficial at delaying the recurrence of AF (mean
265 days vs 87 days) (Bright et al. 2005), but this requires further investigation. Considering this high recurrence rates, cardioversion is recommended only in few specific cases, where the heart is structurally normal, the patient continues to show clinical signs despite good rate control or if rate control is not achieved despite all efforts.
Rate control
In the vast majority of dogs diagnosed with AF, the goal is to achieve adequate rate control, by using negative chronotropic anti-arrhythmic drugs to reduce the HR. The advantages to this
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Hayes 2018).This makes it a valuable choice for most patients with fast HR that tolerate oral administration.An intravenous formulation exists, however it has to be ordered on special import license to the UK. One of the main potential side effects
with atrial fibrillation
When managing patients with AF using a rate control strategy, the clinician is aiming to reduce the ventricular response rate.This tends to be higher in dogs with ongoing CHF where the sympathetic system is activated (Menaut et al. 2005), therefore concurrent CHF treatment is essential and should not be overlooked.
While ventricular rate reduction is
an overall easy therapeutic strategy, managing these patients over time may
be challenging as a clear target for the degree of HR control lacks consensus.
In addition, at-home HR assessment
is important, because the sympathetic drive of a dog in the hospital setting is increased (Uechi et al. 2002) and therefore HR in-clinic is not a reliable indicator
of true daily HR.This has recently been confirmed by Gelzer et al. who showed that the HR based on an ECG trace was not useful to predict the HR in the home environment (Gelzer et al. 2015).
It has been suggested that the lowest ventricular rate achievable without hemodynamic compromise is desirable and a Holter-determined 24-hour mean HR of ≤140 bpm could be indicative of
92% immediate success rate, independent
of concurrent structural disease or
pre-treatment with amiodarone (Bright
et al. 2005; Bright and zumBrunnen,
2008). However, pre-procedure treatment
with amiodarone is common practice number of impulses reaching the ventricles among many cardiologists as it may (i.e. reduced number of QRS complexes). lead to a pharmacological cardioversion, Two different formulations are currently avoiding a general anesthetic and electrical available: modified released (three times
Dogs with severe clinical signs (for example if the HR is too fast, or if
the patient is collapsed), may require a more aggressive and urgent approach. Intravenous diltiazem, amiodarone or esmolol (beta-blocker) are options to consider. Alternatively, lidocaine can also be attempted. Not many general practices will have ready access to all these drugs on the shelf and referral may be necessary. Fortunately, urgent intravenous treatment
and recurrence of AF may be identified to onset of action that can vary between
within 120 days (Bright et al. 2005). It 25 mins and one hour (Kittleson 2002; Treatment goals for patients
ers
cardioversion. daily administration) and sustained release When cardioversion is successful, (twice daily administration). Diltiazem
maintaining
sinus rhythm
is not eas
y is r
apidly ab
sorbed in d
ogs, wi
th a ti
me
is rarely required.
Only
associated with th
humans is its negative inotropic effect. In dogs, this has not yet been proven to be clinically relevant, although anecdotal reports of dogs with severe DCM not tolerating diltiazem are known (Cooke and Snyder 1998).
Digoxin reduces AV node conduction
by increasing parasympathetic and inhibiting sympathetic tone (Fox et al. 1999), a mechanism of action that makes
it extremely useful in cases where CHF
is present . It is however unlikely to be enough as monotherapy (Gelzer et al. 2009). It is crucial to closely monitor for potential toxicity side effects (inappetence, vomiting, diarrhoea, development of ventricular arrhythmias, etc.), and to note that these may be more pronounced if hypokalemia is also present.Toxicity side effects may require dose reduction or discontinuation. Digoxin serum levels should be checked once week after starting
e use of dil
tiazem
in