Real-world cardioversion results

MAASTRICHT, THE NETHERLANDS. Cardioversion is used to convert a patient experiencing highly symptomatic or persistent atrial fibrillation (AF) to normal sinus rhythm (NSR). Conversion can be achieved by oral administration of antiarrhythmic drugs like amiodarone or propafenone, or by the infusion of drugs like ibutilide (Covert), dofetilide (Tikosyn) or flecainide (Tambocor) in a hospital setting (chemical conversion). Chemical conversion is most effective if started within a couple of hours of the onset of the episode and becomes less effective as time goes by. In cases where an episode has lasted longer than 7 days drug-induced conversion is not effective and electrical conversion (cardioversion) must be used to regain NSR, either alone or in combination with antiarrhythmic drugs. Cardioversion is also sometimes used instead of drugs in an attempt to convert an AF patient who has just arrived in hospital if the patient suffers severely (fainting, dizziness, breathlessness, etc).

Electrical cardioversion (also known as direct-current or DC cardioversion) is a procedure whereby a synchronized electrical current (shock) is delivered through the chest wall to the heart through special electrodes or paddles that are applied to the skin of the chest and back. The purpose of the cardioversion is to interrupt the abnormal electrical circuit(s) in the heart and to restore a normal heartbeat. The delivered shock causes all the heart cells to contract simultaneously, thereby interrupting and terminating the flutter or AF without damaging the heart. The heart’s electrical system then restores a normal heartbeat controlled by the sinus node.

Skin burns and ischemic stroke are the most common adverse effects accompanying the procedure. Patients with a low blood serum level of potassium or a toxic level of digoxin may experience life-threatening ventricular fibrillations when undergoing cardioversion. Thus potassium levels should always be checked prior to cardioversion and corrected if necessary.

Cardiologists/electrophysiologists at Maastricht University Medical Center now report the results of a study aimed at determining the immediate and medium-term (1 year) outcome of cardioversion in a group of 1800 AF patients who underwent cardioversion prior to enrolment in the Euro Heart Survey on AF. The patients included in the study were generally not in good health with 64% having hypertension, 31% having coronary artery disease, and 25% having valvular heart disease or heart failure. The average age of the patients was 64 years, 59% were male, and the average length of time that the participants had been suffering from AF was relatively short ranging from 4 days (24%) to 11 months (21%). For 27% of patients cardioversion was for their first episode, while 35% had previously been diagnosed with paroxysmal AF and 37% with persistent AF.

Forty percent of patients (primarily persistent afibbers) underwent electrical cardioversion (ECV), 36% (primarily paroxysmal afibbers or those experiencing their first episode) were treated with intravenously administered antiarrhythmic drugs (63% with amiodarone and 13% with propafenone), and the remaining 24% (primarily paroxysmal afibbers or those experiencing their first episode) underwent oral administration of antiarrhythmic drugs (mainly amiodarone and flecainide) or non-antiarrhythmics (digitalis, beta-blocker, verapamil, diltiazem). Acute success of chemical conversion was defined as restoration of sinus rhythm within 24 hours after the onset of pharmacological treatment. Acute success of ECV was defined as maintaining NSR for at least 10 minutes after the final shock.

Outcomes and complication rates for the three cardioversion approaches are summarized below.

-
Electrical
Intravenous
Oral
Acute success
88%
71%
75%
NSR at 1-year*
70%
72%
64%
Major complications
4.3%
5%
5%

* NOTE: 63% of study participants used an antiarrhythmic drug during follow-up

The most common complications in the chemical conversion groups were transient ischemic attack (TIA) at 1.3% and heart failure at 1.0%, while the most common complications in the ECV group were heart failure at 1.1% and ventricular tachycardia at 0.8%. No patients died prior to discharge from hospital. The main factors predicting acute success of ECV were:

  • Absence of chronic obstructive pulmonary disease (COPD)
  • Paroxysmal AF
  • Use of biphasic defibrillator.

Factors predicting acute success of intravenous administration of antiarrhythmics were:

  • Paroxysmal AF
  • Absence of valvular heart disease
  • Absence of heart failure
  • Presence of hypertension
  • Presence of coronary artery disease.

Paroxysmal AF and a smaller left atrial diameter favourably influenced the results of cardioversion with orally administered drugs.

The following factors were predictive of being in NSR at the one-year follow-up:

  • Paroxysmal AF
  • Shorter total AF history
  • Use of amiodarone or Class 1C antiarrhythmics during follow-up
  • Absence of COPD
  • Younger age
  • Smaller left atrial diameter.

The researchers noted that a significant number of patients treated with non-antiarrhythmics converted to NSR within 24 hours and ascribe this to the known phenomenon of spontaneous conversion. They conclude that, “Contemporary conversion of AF is routinely successful and safely performed with a high proportion of patients in NSR at 1-year follow-up”.

In an accompanying editorial Drs. Rene Tavernier and Mattias Duytschaever of the University Hospital Ghent take issue with the conclusion that a major complication rate of 4.5% can be considered a safe procedure. They also question that 70% of study participants really were in NSR at the 1-year follow-up since this conclusion was based on just a single ECG. Most other studies have found a success rate of 50% or less. Finally, they suggest that cardioversion be delayed a reasonable amount of time to allow spontaneous cardioversion to occur.
Pisters, R, et al. Clinical correlates of immediate success and outcome at 1-year follow-up of real-world cardioversion of atrial fibrillation. Europace, Vol. 14, 2012, pp. 666-74
Tavernier, R and Duytschaever, M. Cardioversion for atrial fibrillation in the real world: there is room for improvement. Europace, Vol. 14, 2012, pp. 617-18

Editor’s comment: I agree with the Belgian editorialists that a 1-year cardioversion success rate of 70% is unrealistic. My own study of electrical cardioversion revealed that a typical 1-year success rate is more like 40% or less. It is interesting that the Maastricht group measured serum potassium levels of all patients and took steps to correct low levels prior to proceeding with electrical cardioversion.