The CMP has been the gold standard in the treatment of AF with the highest late success rates of any single-interventional procedure.10,22,23
This surgical approach was developed at our institution and has gone through various iterations to improve and simplify the procedure.7,19,24,25
The original CMP-III was empirically designed to interrupt the macroreentrant circuits in both atria which were thought to be responsible for AF.7,26,27
However, it is now known that there are multiple mechanisms responsible for AFand this complex arrhythmia is still not thoroughly understood in many patients.28–30
With the anticipated goal to preserve the high success rates of the CMP-III and to decrease invasiveness, the CMP-IV was designed to simplify the operation by using bipolar radiofrequency energy to replace most of the traditional incisions. This energy source was chosen after extensive investigation in our laboratory that demonstrated its ability to reliably create discrete and transmural lesions.15,16
By achieving complete lines of ablations in a matter of seconds it overcame the major limitations of other energy sources. Furthermore, the focused application of energy within the jaws of the clamp minimized the risk of collateral damage to surrounding tissue that had been reported for unipolar energy sources.31
Because invasiveness is a major concern, the ability to reduce cross-clamp time and enable a minimally invasive approach made the CMP-IV more attractive to patients with lone AF.21
This report of 212 consecutive patients undergoing a CMP for lone AF over almost 20 years demonstrated excellent long-term success rates with 93% freedom from AF and 82% freedom from AF off antiarrhythmic medication. Only one late stroke occurred over a total of 763 patient-years of follow-up, with 80% of patients being free from anticoagulation therapy with Warfarin. Considering the side effects of Warfarin, including the higher risk of anticoagulation-associated intracranial hemorrhage, this is important in improving quality of life.32
However, in few patients other indications for anticoagulation therapy were present or developed despite restored sinus rhythm. The technical complexity of the CMP-III kept it from a wide adoption, while its invasiveness made catheter ablation the preferred choice of treatment for most patients with drug-refractory, symptomatic lone AF. Based on isolating the PV (PVI), the results of catheter ablation have been variable with single-procedure success rates between 16 – 84%.6,11,33,34
A recent report from Haïssaguerre’s group, who pioneered PVI, reported a single-procedure success rate as low as 29% after 5 years.35
Certain patient subgroups have done particular poorly, such as patients with longstanding persistent AF and large atria.36,37
A recent review suggested a success rate for a single-procedure ranging from 22% to 45% in patients with persistent or longstanding persistent AF.11
Our experience with the CMP defines the long-term results with this procedure. The CMP-III had excellent freedom from symptomatic AF at 10 years. The less invasive CMP-IV has showed significantly shorter operating times and lower complication rates while resulting in equivalent early freedom from AF, despite more rigid definitions of success and improved follow-up. At the present time, the cut-and-sew CMP-III is no longer performed at our institution. The results of this study confirm the efficacy of the CMP-III lesion set. Moreover, the CMP was equally effective for paroxysmal and longstanding persistent AF. It was also very effective in patients who had failed previous catheter ablation. These results can be achieved with minimal operative risk. Our data would suggest that more patients should be referred for the CMP, particularly symptomatic patients who have either failed a catheter ablation or belong to a subgroup who have poor results with catheter ablation.
The need of pacemaker remains a problem following the Cox-Maze procedure. Although the CMP-IV lesion set might cause a sinus node dysfunction, it is not the only possible mechanism. The majority of patients requiring pacemakers presented with preexisting sick sinus syndrome. Moreover, AF is known to induce sinus node dysfunction. Although sinus node recovery time seems to normalize after termination of AF, the time course of reversing this electrical remodeling is variable, and the risk for pacemaker implantation can not be eliminated completely. It is possible that eliminating right atrial ablations would decrease the need for postoperative pacemaker implantation, however, this also would likely result in a lower cure rate. There are several limitations to this report. While follow-up in the historical series was longer and showed a freedom from symptomatic AF and antiarrhythmics of 83%, few of these patients had electrocardiographic or Holter monitoring at 12 or 24 months. With constantly improving follow-up, recent guideline requirements have been met since 2006.5,11,38
The lack of electrocardiographic or Holter follow-up likely resulted in an underestimation of the long-term failure rate in the CMP-III group. However, the recent CMP-IV cohort has been well monitored with 24-hour Holter or pacemaker interrogation. This cohort reflects the current standard of surgical treatment and shows excellent success rates that compare favorably to our CMP-III experience. This was particularly true for patients who had an isolation of the entire posterior LA. Our success rate off antiarrhythmic drugs at one year in this group was 86%. Moreover, 69% of patients presented preoperatively with persistent or longstanding persistent AF and 40% had previously failed catheter ablation, reflecting a more difficult cohort for successful treatment than the CMP-III group. However, a comparison of the two groups remains difficult. A Kaplan-Meier analysis was most suitable to present the results of the entire series because of the difference in follow-up. However, AF is a dynamic endpoint and reconversion to sinus rhythm after an episode of AF was still shown as permanent failure. To take this into account, we presented the recent CMP-IV results as % of freedom from AF at various time points. In a previous study, patient-specific variables were adjusted by a propensity analysis and we showed similar results with the CMP-III and -IV.19
Finally, the mechanisms for AF recurrence were not well defined. The question remains unanswered whether our failure rate was due to technical difficulties, untreated atrial pathology or a focal mechanism of the recurrent ATAs.
This report gives a benchmark for the excellent long-term success rate of a stand-alone CMP and will provide a useful comparison for the myriad of procedures that are presently performed surgically, including left atrial lesion-sets and PVI, as well as for new and less invasive approaches currently under development.