Methods: Between August 2014 and May 2016, 33 patients (17 males, 16 females; mean age 63.9 years; range 45 to 82 years) underwent the Maze procedure using cryoablation for the treatment of atrial fibrillation during a concomitant open cardiac operation. Robot-assisted procedures were used in 12 patients. Biatrial or isolated left atrial ablation was performed according to the underlying pathology. The rhythm assessment with 12-lead electrocardiography and 24-hour Holter, and recordings of atrial fibrillation-related medications, stroke or other thromboembolic events were evaluated by the cardiologist at 3 and 12 months postoperatively.
Results: Thirty patients (90.9%) were in sinus rhythm and three (9.1%) were in atrial fibrillation at the time of discharge. Cryoablation failed in three patients (n=2, 8.3% in isolated left atrial and n=1, 11.1% in biatrial group) following the operation in the mid-term. Among the patients, there was no in-hospital mortality and no major postoperative complications such as stroke, sepsis, renal failure requiring dialysis, and prolonged respiratory failure.
Conclusion: Concomitant surgical cryoablation is an effective method for the treatment of atrial fibrillation, when performed concomitantly with other cardiac surgical procedures and results in very low atrial fibrillation recurrence, even in robotic surgery.
In the present study, we aimed to present midterm results of isolated left atrial (LA) or biatrial cryoablation technique for the treatment of AF as a concomitant procedure of open cardiac surgery and to report a structured local follow-up to one year postoperatively.
Table 1: Demographic characteristics
Perioperative data were retrieved from the institutional database. Preoperative AF was defined as intermittent (paroxysmal, persistent) or permanent according to the Heart Rhythm Society/European Heart Rhythm Association/European Cardiac Arrhythmia Society. Additional rhythm related data were collected including presence of AF at the time of surgery, duration of AF, antiarrhythmic medications, and echocardiographic data such as LA size and left ventricular ejection fraction were all retrieved from database.
There was a heterogeneity for the type of procedures and the approach in terms of robotic assistance; however, uniform protocol for ablation and lesion set was used in all patients. If the LA was planned to open alone (n=24), this was achieved through interatrial groove following midsternal approach and central cannulation (ascending aorta and bicaval) in non-robotic assisted patients. The LA appendage was ligated in all patients using a double layered running suture from the inside of LA. Cryoablation was performed using a flexible argon-based device (cryoICE cryoablation probe, AtriCure Inc., West Chester, OH, USA; Cardioblate CryoFlex Surgical Ablation Probe, Medtronic Inc., Minneapolis, MN, USA) and starting with an ablation line extending from the atriotomy to the mitral valve annulus in the region P2/P3. The left and right pulmonary veins were isolated, an inferior and superior ablation line was placed to complete the box lesion for isolation of the posterior atrial wall, and an additional lesion was placed to connect the box to the closure line of the LA appendage. The cryoprobe can be fit to the shape of the atrial wall, either endocardial or epicardial, creating cryolesions of 1 to 10 cm in length. Principally, atrial cryolesions in this series were performed for 90 sec reaching local temperatures of -130°C. Biatrial ablation (n=9, 27.2%) was performed in the patients with atrial flutter or enlarged right atrium (RA) such as existence of atrial septal defect. An additional RA lesion set consisted of an intercaval lesion extending from the superior vena cava (SVC) to the inferior vena cava (IVC); from this lesion to tricuspid valve annulus and finally from the first lesion to RA appendage.
Twenty-four of the patients (72.7%) underwent mitral valve surgery. The types of the concomitant surgeries in addition to LA or biatrial cryoablation were summarized in Table 2.
Table 2: Operative characteristics of patients
Robotic assistance was used in 12 patients, and
the operative technique was detailed previously.[8]
Briefly, in robotic approach, cardiopulmonary bypass
(CPB) was achieved via peripheral cannulation
(femoral artery, femoral vein, internal jugular vein)
under guidance of transesophageal echocardiography
(TEE). The heart was arrested using cold crystalloid
cardioplegia delivered into the aortic root with a
transthoracic cannula through the thoracotomy. The
inferior and superior venae cavae were occluded with bulldog clamps in patients which the RA was opened.
The cryoprobe is flexible and also suitable for creating
ablation during robotic assistance.
The mean duration of follow-up was 18
(range 10 to 30) months among the discharged patients.
Follow-up data were 100% complete for all patients,
and no patients died during this period.
All patients received oral anticoagulation
therapy with warfarin for three months regardless
of postoperative rhythm. The continuation of oral
anticoagulation therapy was decided according to the
CHA2DS2-VASc score. The patients with mechanical
valves received life-long anticoagulation. All patients
were treated with b-blockers and amiodarone after
surgery, unless postoperative bradycardia or junctional
rhythm was detected.
Prospective follow-up protocol was started in August
2014, consisting of outpatient visits to the responsible
surgeon at first month. The rhythm assessment with
12-lead electrocardiography (ECG) and 24-h Holter,
and recordings of AF-related medication, stroke, or
other thromboembolic events were evaluated by the
cardiologist at three and 12 months, postoperatively.
Definition of success for these patients was normal sinus
or pacing rhythm, and freedom from AF at discharge
and during follow-up. The patients were classified as
free from AF, when they were in sinus rhythm, atrial
paced without underlying AF, junctional rhythm or other
regular rhythm. The patients who developed AF or atrial
flutter, and those who were paced, but had underlying
AF were classified as AF patients. The failure of the
cryoablation procedure was defined as AF more than
three months following the procedure.
Statistical analysis
For the statistical analysis, the program NCSS
(Number Cruncher Statistical System) 2007 Statistical
Software (NCSS LLC, Kaysville, Utah, USA) (License
No: 1675948377483; Serial No: N7H5-J8E5-D4G2-
H5L6-W2R7) was used. The mean, standard deviation,
minimum, maximum, range, median, frequency and
ratio calculations from the descriptive statistical
methods were used when the descriptive study data
were evaluated.
Cryoablation failed in three patients (n=2, 8.3 % in isolated LA and n=1, 11.1% in biatrial group) following the operation in the mid-term. Thirty patients (90.9%) were in sinus rhythm and three (9.1%) were in AF at the time of discharge. One of them became AF in the treated group and required permanent pacemaker implantation following cardioversion; however, this patient maintained sinus rhythm in the follow-up. One more patient required a permanent pacemaker implantation in the failure group due to slow-transition AF. During follow-up, 30 patients (90.9%) maintained their sinus rhythm. The patients with permanent AF at the time of surgery (n=31, 94%) had an increased rate of recurrence at discharge (n=3, 9.1%), compared to those with intermittent AF (n=0.0%).
The LA was larger than 55 mm in 1/3 (33.3%) of failure patients; however, by cryoablation 6/7 (85.7%) patients were converted to sinus rhythm among the patients who had LA larger than 55 mm.
Among the patients, there was no in-hospital mortality and no major postoperative complications such as stroke, sepsis, renal failure requiring dialysis, and prolonged respiratory failure.
There is a very limited number of studies showing the results of cryoablation procedure with robotic assistance in the literature.[9] With the use of specialized robotic forceps, the probe can be molded to conform geometrically to an individual atrial anatomy. In our study, 12 patients underwent cryoablation with robotic assistance and 11 of them converted to sinus rhythm in the mid-term follow-up. The combination of dynamic LA retraction, improved dexterity using endowrist technology, and three-dimensional vision allows surgeon for precise placement of the cryoprobe and avoidance of skips caused by folds in the floor of the LA.
When analyzing the results, creating LA lesions in the setting of more chronic AF (long-lasting persistent AF) seems to be less effective, and these patients may derive greater benefit from a more extensive ablation procedure, such as creating biatrial lesion.
Our findings were consistent with Charitos et al.[10] suggesting that the preoperative duration of AF and the use of a box lesion only in patients with longer AF persistence history were independently associated with higher postoperative AF burden recurrence and many patients later required repeated catheter ablation interventions or the need for electrical cardioversion. In a study containing a large number of patients (n=503) with nine years period of observation, the statistically significant predictors for sinus rhythm continuation after one year were LA diameter, AF duration, preoperative paroxysmal AF, immediate postoperative sinus rhythm, and biatrial ablation for persistent AF.[11]
Our data showed that even in patients with large LA diameters, concomitant surgical AF ablation may restore sinus rhythm with negligible AF recurrence up to one year postoperatively, and enlarged LA diameters should not be considered as a contraindication for concomitant surgical ablation of AF.
The correction of severe mitral valve regurgitation was associated with lower AF burdens during the total observation period. In a similar manner, the patients with mild to moderate mitral valve regurgitation who did not undergo mitral valve repair had significantly higher AF burden during follow-up.[10] Similar conclusions have been obtained after catheter ablation which underscores the influence of coexisting mitral regurgitation on the outcomes of AF ablation procedures. In the case of the surgical patient, correction of mild-tomoderate mitral regurgitation in patients undergoing concomitant surgical AF ablation leads to lower rates of AF recurrence and should be strongly considered.[10]
On the other hand, due to the small number of patients and the resulting limited statistical power, none of the randomized trials was able to show a survival benefit for patients receiving concomitant ablation. However, in a recent propensity scorematched analysis by McCarthy et al.,[12] the mid-term survival of patients with AF receiving concomitant surgical ablation was statistically significantly higher, compared to the untreated patients and comparable to those of patients without preoperative AF.
There are several limitations of the present study, such as a non-randomized retrospective study design with a limited number of patients. Furthermore, the present study was a single center analysis, consisting of a wide spectrum of patients undergoing open cardiac surgery.
In conclusion, our study results suggest that the surgical treatment of atrial fibrillation using this flexible argon-based cryoablation device was safe and effective during a wide variety of concomitant cardiac procedures. This procedure takes 10 to 20 min which does not significant prolong the cardiopulmonary bypass duration. On the basis of our findings, all patients with any history of atrial fibrillation undergoing a cardiac surgical procedure may be considered for a concomitant ablation procedure.
Declaration of conflicting interests
The authors declared no conflicts of interest with respect to
the authorship and/or publication of this article.
Funding
The authors received no financial support for the research
and/or authorship of this article.
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