49. TACHYARRHYTHMIAS

Life theatening tachycardia needs electrical cardioversion regardless of the cause or type of arrhythmia.

Antiarrhythmic drugs are useful if the patient has a stable blood pressure, if cardioversion has failed or after successful cardioversion to stabilize the rhythm.

The patient usually has structural heart disease and a precipitating event has initiated the arrhythmia. These events include, hypoxia, hypercarbia, electrolyte disturbance, myocardial ischaemia and drug toxicity. The anaesthetist must ensure that the patient is oxygenated and adequately ventilating.

Atrial Fibrillation

Atrial fibrillation (AF) is the most common perioperative tachyarrhythmia. The atrial rate is usually 350 to 600 beats/minute with a variable ventricular rate. Patients who have had atrial fibrillation for more than two days are at risk of emboli if they have cardioversion, and should be anticoagulated before cardioversion.

Patients with atrial fibrillation who have a low blood pressure may need synchonised cardioversion (100 to 200J).

Patients with a stable blood pressure and rapid AF need drug treatment to control their heart rate. If they have poor left ventricular function they may require amiodarone 5 to 7 mg/kg over 30 minutes followed by an infusion at 50 mg/h or digoxin 15 micrograms/kg over one hour. If the patient has good left ventricular function the rate can be controlled with amiodarone, digoxin, beta-blockers or verapamil.

Asymptomatic patients may require no treatment. Often spontaneous atrial fibrillation will spontaneously revert within 24 hours.

Atrial Flutter

Atrial flutter is usually a regular rhythm with an atrial rate of 250 to 350 beats/minute and is often resistant to drug treatment and needs cardioversion (50J).

Supraventricular Tachycardia

Most patients with a wide complex QRS tachycardia have ventricular tachycardia (VT). (Patients with SVT and a right bundle branch block will have a wide complex tachycardia).

Most patients with a narrow complex QRS tachycardia have supraventricular tachycardia (SVT).

It is very important to try and diagnose the difference between SVT and VT as the treatment of each arrhythmia is different and VT may progress to ventricular fibrillation (VF) and death. SVT is less dangerous.

Life theatening tachycardia needs electrical cardioversion

Non-life theatening wide complex tachyarrhythmia is best treated with amiodarone (150 mg over 10 minutes then 1 mg/min for 6 hours) or lignocaine (1 to 1.5 mg/kg dose then 1 to 4 mg/min infusion).

Non-life theatening narrow complex tachyarrhythmia is best treated with adenosine (6 mg), amiodarone or digoxin.

Antiarrhythmic Drugs

Adenosine is the drug of choice for AV nodal or AV re-entry tachycardia. It will revert the arrhythmia in more than 90% of cases. If an initial dose of 6 mg is ineffective a second dose of 12 mg may be given. It should be given rapidly into a large vein and flushed with saline. It may cause bronchospasm in asthmatics.

Verapamil is better than beta-blockers. (1mg/minute up to a maximum of 10m). It should not be used if the patient has sinus node abnormalities, 2nd or 3rd degree heart block, VT or AF associated with Wolf Parkinson White syndrome (verapamil will increase the ventricular response).

Amiodarone can be used for both SVT and VT, though adenosine or verapamil are better for SVT.

Beta-blockers don not revert AF or atrial flutter but will slow the ventricular rate.