The literature on diagnosis and management of cardiac arrhythmias can be detailed and at times confusing. When faced with a patient with a significant cardiac arrhythmia one often needs to work quickly in order to stabilise the patient and administer appropriate medication in a timely manner. There are several key steps in the management of an arrhythmia which can be summarised as follows:

 Clinical identification of an arrhythmia.

 Determination of the type of rhythm disturbance present--this should include interpretation of an ECG.

 Evaluation of the patient for underlying disease processes that may be responsible for the development of the arrhythmia (consider the following--intrinsic cardiac disease, hypoxia, autonomic disturbances, metabolic disease, mechanical interference with the myocardium, electrolyte disturbances and drugs).

 Deciding whether the rhythm disturbance requires direct intervention (as opposed to management of the underlying condition). The more of a patient's clinical signs can be attributed to the arrhythmia, the more it requires intervention.

 Administration of the chosen therapy followed by monitoring of the response of the patient.

In order to allow appropriate management of rhythm disturbances they must be differentiated into one of four categories: (Further information and doses for all the mentioned drugs can be found in the reference below.)

1.  Bradyarrhythmias

2.  Atrial fibrillation

3.  Supraventricular tachyarrhythmias (other than atrial fibrillation)

4.  Ventricular tachyarrhythmias

Bradyarrhythmias

The three most common bradyarrhythmias that require specific intervention are third degree AV block, sinus arrest (as part of sick sinus syndrome) and atrial standstill. Atrial standstill is often a consequence of electrolyte disturbances, and if this is identified serum potassium should always be checked. Although symptomatic bradyarrhythmias may respond to parasympatholytic or sympathomimetic drugs such as atropine, propantheline and terbutaline, their successful long term management usually requires the implantation of a pacemaker.

Atrial Fibrillation

The management of atrial fibrillation differs in three different types of patient: 1) those with a normal size heart and little or no evidence of structural cardiac disease should be considered candidates for synchronous DC cardioversion; 2) those with evidence of cardiac disease or in which cardioversion is not considered an option but not suffering from signs of congestive heart failure are candidates for rate control with agents such as beta-blockers or diltiazem; finally 3) those with advanced heart disease and signs of heart failure are candidates for rate control and the first agent of choice is digoxin. If rate control with digoxin is not adequate then diltiazem can be administered concurrently. Beta-blockers are contraindicated as first line therapy in dogs with a history of heart failure because of their capacity to worsen systolic function.

Supraventricular Tachyarrhythmias

Supraventricular tachyarrhythmias are usually recognisable as narrow complex tachycardias. They are sometimes, but not always, associated with identifiable P-waves. If these are persistent (as opposed to paroxysmal) then a vagal manoeuvre may be tried to terminate them. Drug therapy for acute management can include administration of agents such as diltiazem, lidocaine, esmolol or Sotalol. They can all be given intravenously but all share the disadvantage of being negatively inotropic and should only be given very cautiously in patients in heart failure. Advanced management of some supraventricular arrhythmias is available such as synchronous conversion and radiofrequency ablation.

Ventricular Tachyarrhythmias

Ventricular tachyarrhythmias are the rhythm disturbances of the greatest concern because of their capacity to degenerate into ventricular fibrillation and cause the death of the patient. Therapy is usually administered when the arrhythmia is thought to be leading to signs of compromised perfusion and resulting in clinical signs. Acute management usually requires the administration of lidocaine; if this is not successful in the slowing or termination of the rhythm disturbance other agents may be required including Sotalol. Persistent rapid ventricular tachycardia that is unresponsive to drug therapy may require synchronous cardioversion to terminate it although this is usually only done in exceptional circumstances. Successful chronic oral management may be achieved with mexiletine, atenolol, Sotalol and amiodarone.

References

1.  Dennis SG. Antiarrhythmic therapies. In: Luis Fuentes V, Johnson LR, Dennis SG, eds. BSAVA Manual of Canine and Feline Cardiorespiratory Medicine, 2nd ed. Gloucester: BSAVA; 2010:166-185.