Diagnosis: Flutter

Patients with atrial flutter have been exposed to anticoagulation therapy, cardioversion and drug regimens to control rate and protect them from the symptoms. When these therapies grow old or are no longer effective, they look to their electrophysiologist for a cure, which is ablation therapy. Counterclockwise or Type I isthmus-dependent atrial flutter is one of the most common supraventricular tachycardias seen in electrophysiology labs today. This being true, it is also one of the rhythms that can be cured with radiofrequency ablation in a relatively short time. The methods and equipment vary, but the goal of achieving bi-directional isthmus block is common. Counterclockwise flutter is a macro re-entrant circuit utilizing the intraatrial isthmus to complete the circuit. The isthmus is a band of tissue that extends from the tricuspid valve to the coronary sinus septally and terminates where the right atrium meets the inferior vena cava or the eustachian ridge. These patients will come to the EP lab in atrial flutter or sinus rhythm. If they are in flutter, the diagnosis of counterclockwise flutter can be confirmed as soon as the catheters are in place. If the patient is in sinus rhythm, atrial stimulation protocols will be needed to either put the patient in atrial flutter or to prove there is conduction across the right atrial isthmus.

Techniques

The first step in curing counterclockwise flutter is to correctly diagnose the rhythm; this is achieved with the typical complement of catheters for ablation. A coronary sinus catheter to make sure it is not a left-sided flutter, a HIS bundle catheter to help determine the direction of electrical conduction, a right ventricular catheter for back-up pacing (depending on the physician) and a right atrial catheter for pacing. There are a variety of catheters used to record electrograms from the lateral wall of the right atrium and across the isthmus. Some physicians use a quadrapolar ablation catheter formed against the lateral wall of the right atrium to note conduction direction, with the proximal electrogram coming earlier than the distal signal. Afterward, the catheter is positioned against the atrial septum. Counterclockwise flutter is confirmed by the distal signal being earlier than the proximal signal. Other physicians will use 10- or 20-pole catheters (St. Jude, Livewire, Duo Deca or Cordis Webster Cristacath), which are left in place along the lateral wall of the right atrium during ablation. If one of these catheters is used, the HIS bundle catheter and coronary sinus catheters are used to determine counterclockwise flutter. If the coronary sinus atrial electrogram is earlier than the HIS bundle atrial electrogram and the signals of the lateral wall catheter are earlier in the superior poles and later in the inferior poles, counterclockwise flutter is diagnosed. With a diagnosis confirmed, it is time to ablate the isthmus. There are two methods used to complete isthmus ablation. The first is continual drag back lesions. The catheter operator places the ablation catheter on the septal side of the isthmus and ablation is started. Each minute, the catheter is moved laterally in an organized manner to achieve a linear lesion that concludes when the catheter reaches the IVC. Three to four of these 5- to 10-minute drag back lesions are generally successful to ablate the isthmus and achieve bi-direction isthmus block. The other method is called spot welding. In this method, the catheter operator positions the catheter as with the beginning of a drag back lesion. However, the difference is that every 30 seconds, ablation is stopped and the catheter is repositioned in an organized manner until multiple welds have been achieved along the isthmus. While the methods differ, the electrophysiologist can achieve successful isthmus ablation with either. After the physician completes the isthmus ablation, bi-directional isthmus block must be determined. This is accomplished through pacing of the lateral wall of the right atrium and coronary sinus pacing. While pacing the lateral wall, counterclockwise block is determined by confirming that the HIS bundle atrial electrogram comes before the coronary sinus atrial electrogram. If block has not been completed, the coronary sinus atrial electrogram will be earlier than the HIS bundle atrial electrogram. This tells the electrophysiologist that the paced beat conducts across the isthmus reaching the coronary sinus before the signal conducts over the top of the atrium. Therefore, clockwise isthmus block is determined by pacing from the coronary sinus and documenting that the proximal poles of the lateral wall catheter are earlier than the distal electrograms. Once bi-directional isthmus block is confirmed, the only thing left is to pull out catheters and sheaths and return the patient to their room for recovery.

Roadblocks

With the basics of counterclockwise flutter ablation explained, it is time to explore the roadblocks to a successful ablation. For example, sub-optimal catheter selection and design are the primary roadblocks. Low temperatures are another. We have learned that temperatures near 55 º to 65 º Celsius cause effective tissue dessication, but sometimes during drag backs or spot welds, adequate temperatures are not achieved. In our EP lab, we combat this problem by having three ablation units available. The first line ablation unit for two of our EP physicians is the EPT-1000 unit. This is successful for a majority of cases. For those where this is not applicable, we use the EP Technologies (formerly Cardiac Pathways) ablation unit with either a standard or large curve Chilli catheter. The other two EP physicians choose to start with Chilli catheters. In theory, the saline-cooled Chilli catheter allows deeper lesions in a v shape, versus the contact lens shape lesion created with the EPT-1000. If after multiple attempts with both aforementioned ablation units, we are still unsuccessful, we return to our EP roots and use the non-temperature monitoring American Cardiac Ablation Corporation unit with a non-temperature, large curve, 8 mm peanut-tip ablation catheter. It is very rare that we use non-temperature-controlled ablation, but it is an option if all else has failed. The other roadblock seems to be finding a catheter that allows adequate contact through the whole isthmus ablation. The large curve Chilli catheter works most of the time, except when the interesting secondary curve causes it to skip a small area along the eustachian ridge. In these cases, a second catheter is used and generally completes isthmus ablation. This problem should be solved in November or December 2002, when EPT releases its saline-cooled catheters on a Blazer platform. The right atrial isthmus is the largest area we have to ablate; therefore, we should not expect one catheter to work on every patient.

Conclusion

If we understand the basics of counterclockwise atrial flutter, have the option of more than one ablation unit and have a variety of catheters to complete right atrial isthmus ablation we should be successful in 95% or greater of these cases and in two hours or less.