In treating patients with atrial fibrillation (AFib), the restoration and maintenance of sinus rhythm has long been a mainstay of clinical therapy. Several different methods for converting AFib to normal sinus rhythm can be used. Pharmacologic conversion provides at best moderate success rates and is associated with the potential risks of adverse drug reactions in particular ventricular proarrhythmia. The standard method of cardioversion, originally introduced by Lown in 1962, is high energy electric cardioversion delivered externally to the thorax. This method, which has success rates reported from 61 to 90 percent for paroxysmal AFib, requires a significant degree of patient anesthesia, may have reduced efficacy in patients with severe obesity, and may produce a significant incidence of skin and muscle trauma. In addition, the efficacy is significantly reduced in chronic AFib. Because of these inherent limitations, alternative therapies can play a role and have been sought.  

Internal Cardioversion 

Internal cardioversion has been investigated for over 2 decades. In 1974, Mirowski demonstrated the efficacy of internal low energy cardioversion of AFib in an animal model. Subsequent studies have determined that two electrode systems positioned in the coronary sinus and the right atrium produced the lowest defibrillation thresholds in animal models. Using the two catheter, two electrode system, multiple small studies have demonstrated high cardioversion success rates, notably in traditionally low success groups such as chronic AFib, with average energies required for conversion ranging from 2-4 J. Only rare and minor complications were reported. 

A single study of 187 patients offers a direct, prospective comparison between internal and external cardioversion. In this study, primary internal cardioversion was successful in 65/70 patients (93%) as compared to 92/117 (79%) for external cardioversion. Furthermore, internal cardioversion was also successful in 22/25 (88%) of the external failures and had a significantly lower failure rate in obese patients. The average energy required for successful internal cardioversion was 3 J. Of note, only one patient in this group developed a complication, a femoral hematoma which required no follow-up treatment, compared to 46 patients receiving external cardioversion who developed skin burns or pectoral myalgias requiring analgesia. 

Single Catheter System 

Recently, EPMed Systems has developed the Atrial Low Energy Reversion Therapy (ALERT) catheter to simplify the internal cardioversion procedures. The ALERT catheter is balloon-tipped, for positioning in the pulmonary artery, and equipped with two defibrillating electrodes which lie in the pulmonary artery and the right atrium. The catheter also has ports for right atrial and right ventricular pacing as well as for hemodynamic measurements. A single preliminary study comparing this single catheter technique to standard two catheter internal cardioversion demonstrates promising results. Similar cardioversion success rates were noted in both groups (30/32 or 92% using the ALERT catheter as compared to 39/42 or 93% using two catheters); likewise similar low levels of energy were used in both groups. However, catheter placement time and fluoroscopy time were significantly shorter in the ALERT group. In addition, no complications occurred in the ALERT group as compared to one patient who developed a major femoral hematoma in the two-catheter group. 

Presently, studies are ongoing to compare the efficacy and safety of the ALERT catheter internal defibrillation system to standard external cardioversion. The Arrhythmia Service at St. Luke's-Roosevelt is participating in this trial, which will recruit over 150 patients throughout the US and Canada.  

Summary 

Multiple studies have demonstrated high success rates and excellent safety records with low energy internal cardioversion. The technique may offer a significant advance in cardioversion therapy, especially in patients who have failed or are at high risk to fail traditional methods of external cardioversion.

References Alt E et al, Eur Heart J 1997;18:1796-1804. Alt E et al, Amer Heart J 1997; 134:419-425.  

ARRHYTHMIA CONFERENCE SET FOR MAY 8 

 The annual Diagnosis and Management of Clinical Arrhythmias Symposium will be held on Saturday, May 8, 1999 at the Conference Center at Roosevelt Hospital, located at 1000 Tenth Avenue (at 59th Street) in Manhattan. In addition to faculty from the Arrhythmia Service at St. Luke's-Roosevelt Hospital, guest faculty will include Dr. Ramon Brugada from Baylor Medical Center in Houston, who will discuss the genetic basis of atrial fibrillation, and Dr. N. A. Mark Estes, from Tufts University in Boston, who will discuss radiofrequency catheter ablation for atrial fibrillation.

The conference, designed for the practicing internist and cardiologist, is sponsored by the Arrhythmia Service of St. Luke's-Roosevelt Hospital . For more information contact the Service at 212-523-4017.  

Reproduced with permission. Published by the Arrhythmia Service of St. Luke's-Roosevelt Hospital Center, New York, New York.