Cox-Maze IV Procedure Concomitant with Valvular Surgery In Situs Inversus Dextrocardia: A Single-Center Experience in China

Summary

We summarize the Cox-Maze IV procedure concomitant with valvular surgery performed in patients with situs inversus dextrocardia at this institution.

Abstract

Atrial fibrillation (AF) is the most common cardiac arrhythmia. The use of ablation technologies made the Cox-Maze IV procedure (CMP-IV) technically easier, faster, becoming the gold standard for the surgical treatment of AF. However, the efficacy and safety of CMP-IV in situs inversus dextrocardia are largely unknown. This paper summarizes the CMP-IV procedure performed concomitantly with valvular surgery in patients with situs inversus dextrocardia at this institution.

From February 2016 to September 2020, three dextrocardia patients with persistent AF and valvular diseases were referred to this institution for valvular and CMP-IV surgery. CMP-IV was performed using either cryoablation with a nitrous oxide (N₂O)-based cryoprobe or a bipolar radiofrequency clamp and bipolar radiofrequency pen. Mechanical valve replacement or mitral vavuloplasty was performed in another patient in addition to tricuspid annuloplasty. Transmurality of the ablated atrial tissues was evaluated by electron microscopy. Heart function was assessed by transthoracic echocardiography. Cardiac rhythm was monitored by 24 h Holter at 3, 6, 12, 18, 24, and 48 months follow-up.

All the AF was successfully eliminated in the ablation procedure without recurrence or other complications during hospitalization. The mean bypass and crossclamp times were similar in all the patients. The postoperative ventilator support time, the duration of stay in the ICU, and postoperative residence time were also not significantly different among the patients. Transmural atrial necrosis was detected in the ablated atrial tissues. Sinus rhythm maintenance was achieved at 3, 6, 12, 18, 24, and 48 months follow-up in all the patients. All valve protheses switched freely; no tricuspid regurgitation was observed. The results of the present study demonstrate that the CMP-IV is safe and effective in eliminating AF in dextrocardia patients concomitant with valvular surgery.

Introduction

Dextrocardia is a rare, congenital cardiac malformation in which the axis of the heart is indexed to the right side of the thoracic cavity. Dextrocardia with situs inversus totalis refers to all visceral organs, including the heart, being mirrored and is extremely rare^1,2. Atrial fibrillation (AF) is the most common arrhythmia that affects millions of people and causes substantial morbidity and mortality, especially with respect to the increased risk of stroke³.

A literature survey was unable to demonstrate a definitive approach for the concomitant Cox-Maze procedure (CMP) and valve surgery in dextrocardia with situs inversus. There are only a few reports of mitral valve replacement in cases of dextrocardia with situs solitus and even less in situs inversus^4,5,6,7,8,9. However, those strategies are not applicable to tricuspid valve surgery, not to mention the complex CMP-IV in dextrocardia.

This paper reports the surgical techniques and experience in three cases concerning the biatrial lesion set of the CMP-IV operation using cryoablation or radiofrequency ablation concomitantly with valve surgery in situs inversus dextrocardia. All surgeries succeeded in the maintenance of sinus rhythm (SR) at 12 months follow-up to each patient and at 48 months follow-up to the previous two. Electron microscopy was used to investigate the transmurality of the atrial cryoablation.

CASE PRESENTATION:

Patients and preoperative examination
From February 2016 to September 2020, a 48-year-old female patient, a 55-year-old male patient, and a 39-year-old male patient were successively admitted to the cardiac center with similar complaints of palpitation, dyspnea, and easy fatigability on exertion lasting for years (Table 1). They all denied any familiar history of situs inversus dextrocardia or other cardiac health comorbidities. All patients were referred to electrocardiography (ECG), chest roentgenography (Figure 1), computed tomography (CT), and Doppler transthoracic echocardiography (TTE) routinely for preoperative examination.

Case 1: A 48-year-old woman presented with complaints of palpitation, dyspnea, and easy fatigability on exertion lasting for years. The anamnesis was unremarkable. During the physical examination, a grade 3 systolic blowing murmur was heard in the fifth intercostal space outside the midline of the right clavicle. X-ray plain film and CT scan showed that the contour of the dextrocardia was enlarged and situs inversus totalis. Transesophageal echocardiography revealed moderate to severe mitral regurgitation and mild tricuspid regurgitation after moderate mitral valve prolapse and tricuspid annular dilation. There was no thrombosis, and the diameter of the left atrium was 5.3 cm. AF with a rapid ventricular rate was detected by ECG.

Case 2: A 55-year-old man presented with similar symptoms for years. There was no history of cardiac health comorbidities; however, he had had a stroke about six months ago. On physical examination, a diastolic blowing murmur was heard at the left second intercostal space, radiating to the neck. Plain X-ray and CT scan revealed dextrocardia with an enlarged contour and situs inversus totalis. Transesophageal echocardiography showed moderate aortic valve regurgitation and mild to moderate tricuspid regurgitation following mild aortic prolapse and tricuspid annular dilation. The diameter of the left atrium was 4.5 cm without atrial thrombosis. AF with a rapid ventricular rate was detected by ECG.

Case 3: A 39-year-old male presented with progressive exertional dyspnea and intermittent palpitation without any history of situs inversus dextrocardia or other cardiac health complications. During the physical examination, a grade 3 systolic blowing murmur was heard in the fifth intercostal space outside the midline of the right clavicle. X-ray plain film and CT scan revealed that the contour of dextrocardia was enlarged and situs inversus totalis. Transesophageal echocardiography showed severe mitral valve regurgitation and tricuspid regurgitation after annular enlargement. There was no atrial thrombosis, and the left atrium diameter was 5.8 cm. A 24 h ambulatory ECG demonstrated paroxysmal AF with a total load of 165 min.

Diagnosis, assessment, and plan
Case 1: A biatrial cryo-Cox-Maze IV procedure (cryo-CMP-IV) with mechanic mitral valve replacement and tricuspid annuloplasty were simultaneously performed.

Case 2: A biatrial cryo-CMP-IV procedure with concomitant mechanic aortic valve (AV) replacement and tricuspid annuloplasty was performed.

Case 3: A biatrial CMP-IV procedure, mitral valvuloplasty, and tricuspid annuloplasty were performed simultaneously.

Protocol

The Institutional Review Board approved the study protocol, and samples of the dilated left atrium (LA) tissues in the dextrocardia cases were collected for electron microscopy after written informed consent had been obtained.

1. Surgical procedure and ablation

1. Perform a median sternotomy and suspend the left lateral pericardium after opening.
   1. Cannulate the ascending aorta and the superior and inferior vena cava (SVC, IVC) to establish mild hypothermic cardiopulmonary bypass (CPB).
   2. Have the operator switch position from the right side to the left of the operating table after establishing the bypass.
   3. Give antegrade cold blood cardioplegia intermittently from the aortic root to achieve cardioplegic arrest.
   4. Perform the right atrial (RA) incision on the left side of the heart, parallel to the atrioventricular sulcus, providing exposure for subsequent RA ablation and tricuspid valve surgery. Ensure the left-sided left atriotomy is located parallelly under the interatrial groove.
   5. Place a retractor on the wall of LA for sufficient exposure to perform LA ablation and approach the mitral valve (MV).
   6. Make an aortic incision via a transverse aortotomy performed specially for selective antegrade cardioplegia into the left and right coronary orifices and subsequent AV surgery.
      NOTE: This was done for the second patient.
2. Cryoablation
   NOTE: In the previous two patients, cryoablation was performed exclusively using a flexible, 10 cm long, metal cryoprobe (see the Table of Materials). The cryoprobe uses nitrous oxide (N₂O) gas to achieve rapid atrial tissue freezing to a target of -60 °C¹⁰.
   1. Design the cryolesion set to replicate the mirror image of the CMP-IV lesion set. Set the duration of the LA cryoablation for each lesion at -60 °C for 2 min.
      1. Ensure the posterior LA box lesion is composed of the LA incision and the cryolesion encircling the left and right pulmonary veins.
      2. Apply a cryolesion line to connect the left superior pulmonary vein with the left atrial appendage (LAA).
      3. Form an ice ball to mark the coronary sinus using cryoablation from the epicardium (Figure 2). When performing the mitral isthmus line, place the cryoprobe at the inferior aspect of the left atriotomy and direct it to the mitral annulus at the 8 o'clock position, across the posterior LA and coronary sinus, as marked with the ice ball (Figure 3A).
      4. Apply right-sided LAA amputation.
      5. After the LA cryoablation, sample 4 x 8 mm tissue of the cryoablated LA for electron microscopic examination. In addition, sample a similar, large, nonablated tissue from the margin of the LA incision for the control test.
         NOTE: Nonablated tissue was sampled in the second case.
3. Perform prosthetic valve replacement surgery with a 27 mm mechanical MV using a 2-0 polypropylene running suture. Replace a 23 mm mechanical AV with 2-0 polypropylene running sutures.
   NOTE: The mechanical MV replacement surgery was performed on the first patient, whereas the replacement with the mechanical AV was done for the second patient.
4. Perform the RA cryoablation during the CPB, with the heart warm and beating, for 2 min at -60 °C for each ablation lesion.
   1. Create the linear cryoablation lines from the inferior aspect of the left-sided right atriotomy up onto the SVC and down to the IVC (Figure 3B).
   2. Make the tricuspid isthmus linear cryolesion from the midportion of the right atriotomy, directed endocardially toward the tricuspid annulus at the 10 o'clock position (Figure 3B and Figure 4).
   3. Make a lateral cryolesion from the midportion of the right atriotomy up to the tip of the right atrial appendage (RAA).
5. Perform three-dimensional (3D) printing of the heart in advance, using the derived cardiac CT data (Figure 5)¹¹.
   NOTE: This was done for the third patient.
   1. Access the left atrium through the interatrial groove during the operation. Extend the mitral isthmus lesion to the posterior mitral annulus for the left atrial lesion sets and ablate the coronary sinus in the endocardium and epicardium with a bipolar radiofrequency pen.
      1. Make other lesions using bipolar radiofrequency clamps: (i) bilateral pulmonary vein isolation; (ii) ablation lines connecting the left atrial appendage and the left superior pulmonary vein; (iii) ablation lines connecting the right and the left superior pulmonary veins; (iv) ablation lines connecting the right and the left inferior pulmonary veins, and (v) mitral line lesions (Figure 3A).
      2. Dissect the Marshall ligament, and separate the left atrial appendage using an epicardial atrial clamp closure device. Use bipolar radiofrequency forceps to ablate the entire right atrial lesion sets, including the annular tricuspid valve lesions, superior and inferior vena cava lesion lines, and lesion lines connecting the right atrium incision to the right atrial appendage (Figure 3B).
   2. Resect the A1 ruptured chordae, implant a single, flexible, artificial chord with 4-0 expanded polytetrafluoroethylene in situ (see the Table of Materials), and close the residual leak of the anterior commissure and the A2 leaflet cleft.
      1. Implant a 32 mm, rigid mitral ring to stabilize the annulus. Ensure that the coaptation height is 9 mm after the mitral valve reconstruction. After de-airing and closure of the interatrial sulcus incision, remove the aortic clamp, then make a longitudinal incision on the surface of the right atrium.
6. Perform the tricuspid annuloplasty with a 30 mm tricuspid ring or with a 28 mm band, implanting them in an "upside-down" and particularly "mirror-image inversion" manner using 2-0 polyester interrupted sutures (Figure 6). Remove the holder before fixation of the annuloplasty ring.
   NOTE: Tricuspid annuloplasty was performed in the previous two patients, while the band was used in the third case.
7. Ensure that sinus rhythm is restored in all patients without any atrioventricular block before cardiopulmonary bypass weaning. Fix temporary epicardial pacing wires after the cardiac surgery.

2. Postoperative management and follow-up

1. Monitor all patients by continuous ECG recordings during hospitalization to ensure no early AF recurrence occurs.
2. Administer antiarrhythmic drugs (AADs) orally, with 200 mg/day of amiodarone routinely, for the first 3-6 months to prevent recurrence of AF.
3. Administer warfarin for oral anticoagulation and test prothrombin time (PT) regularly.
4. Perform chest roentgenogram, TTE, ECG, and 24 h Holter before discharge.
5. After hospital discharge, follow all patients with clinical examination, PT test, TTE, ECG, and 24 h Holter at 3, 6, 12, 18, 24, 36, and 48 months after surgery.
   NOTE: The third patient was followed during a 12-month follow-up period.

Representative Results

Surgical procedure and early postoperative period
A mechanic MV replacement, tricuspid annuloplasty, and concomitant cryo-CMP-IV were performed simultaneously for the first patient. The second had undergone surgery of mechanic AV replacement, tricuspid annuloplasty, and concomitant cryo-CMP-IV. In the third patient, a biatrial CMP-IV procedure was performed simultaneously with mitral valvuloplasty and tricuspid annuloplasty. All operations were smooth, and each beating heart restored SR after resuscitation (Table 2).

The postoperative course was uneventful. AF did not recur during the hospital stay. The temporary pacemaker was not indicated as atrioventricular block did not develop. No other complications occurred in any patient. TTE revealed no valve regurgitation, and all implanted valvular prostheses worked well. The New York Heart Association (NYHA) class improved from class III preoperatively to class II before discharge. Each patient was discharged in normal SR by ECG and 24 h Holter on postoperative day 12 and day 16, respectively (Table 2).

Follow-up
All patients were followed up for 1-4 years. At the 3, 6, 12, 18, 24, 36, and 48 months follow-up in the first two and at 3, 6, and 12 months follow-up in the third patient, the maintenance of SR and atrial contractility were demonstrated by 24 h Holter and TTE. All heart functional capacities were improved to NYHA class I by 3 months after surgery (Table 2). To date, all patients have an improved quality of life, and no heart failure, ischemic or hemorrhagic stroke, or other postoperative complications occurred in any patient at the last follow-up visit.

Electron microscopy
Tissue necrosis was observed by electron microscopy in the full-thickness of the endocardium and almost full-thickness muscularis from the cryoablated left atrium. However, only edema and degeneration were observed in the epicardium and neighboring muscularis. The control sample from the nonablated left atrial tissue showed eumorphism in electron microscopy-normal cell morphology (Figure 7).

Figure 1: Chest roentgenogram of the dextrocardia. Please click here to view a larger version of this figure.

Figure 2: Coronary sinus lesion in the mirror-image dextrocardia. The ice ball was formed using cryoablation epicardially. Please click here to view a larger version of this figure.

Figure 3: Cryo-CMP-IV lesion set in the mirror-image dextrocardia. (A) Left atrial lesion set. The mitral isthmus cryolesion was directed toward the 8 o'clock position of the mitral annulus endocardially. The white spot represents the ice ball. (B) Right atrial lesion set. The tricuspid isthmus cryolesion was directed toward 10 o'clock position of the tricuspid annulus endocardially. Abbreviation: Cryo-CMP-IV = cryo-Cox-Maze IV procedure. Please click here to view a larger version of this figure.

Figure 4: Right atrial cryoablation in the mirror-image dextrocardia. The tricuspid isthmus cryolesion was directed toward 10 o'clock position of the tricuspid annulus endocardially. Please click here to view a larger version of this figure.

Figure 5: 3D printed heart model. (A) Preprinting 3D model digital file embedded with designated ablation lines. (B) View of the 3D printed model. Please click here to view a larger version of this figure.

Figure 6: Tricuspid annuloplasty in the mirror-image dextrocardia. The tricuspid ring was implanted in an upside-down and mirror-image inversion manner by interrupted sutures. The holder was removed before implantation of the annuloplasty ring. Please click here to view a larger version of this figure.

Figure 7: Electron micrographs of cryoablated left atrium. (A, B) Myonecrosis adjoins the endometrium from the female and male patients, respectively. (C, D) Myodegeneration near the epicardium from the female and male, respectively. Scale bars = 5 µm (A, B), 10 µm for C, 20 µm for D. Please click here to view a larger version of this figure.

	Patient 1	Patient 2	Patient 3
Sex	Female	Male	Male
Age (years)	48	55	39
NYHA class	III	III	II
Anamnesis	No	Stroke	No
AF pattern	Long-standing, persistent	Long-standing, persistent	Paroxysmal
AF duration (years)	5	3	2
TTE	Mirror-image dextrocardia	Mirror-image dextrocardia	Mirror-image dextrocardia
Left atrial diameter* (mm)	53/84	45/69	58
Left ventricular diameter (mm)	67	61	54
Ejection fraction (%)	46	49	68
Mitral regurgitation	Moderate to severe	No	Moderate
Aortic regurgitation	No	Moderate	No
Tricuspid regurgitation	Mild	Mild to moderate	Mild
CT	Situs inversus totalis	Situs inversus totalis	Situs inversus totalis
* Left atrial diameter is demonstrated as antero-posterior / left-right diameter.

Table 1: Patient preoperative characteristics. Abbreviations: NYHA = New York Heart Association; CT = computed tomography; AF = atrial fibrillation.

		Patient 1	Patient 2	Patient 3
Concomitant procedures		Mitral valve replacement	Aortic valve replacement	Mitral valvuloplasty
		Tricuspid annuloplasty	Tricuspid annuloplasty	Tricuspid annuloplasty
Aortic cross-clamping time (min)		95	92	140
Cardiopulmonary bypass time (min)		155	147	203
NYHA class before discharge		II	II	II
NYHA class at 3, 6, and 12 months follow-up		I	I	I
NYHA class at 18, 24, and 36 months follow-up		I	I	-
Early AF recurrence		No	No	No
Complications		No	No	No
Temporary pacemaker		No	No	No
TTE
Left atrial diameter* (mm)		37/63	43/55	36
Left ventricular diameter (mm)		55	53	51
Ejection fraction (%)		53	68	68
Valvular prosthesis function		Normal	Normal	-
Mitral regurgitation		-	-	No
Tricuspid regurgitation		No	No	No
Sinus rhythm restoration
3 months follow-up		Yes	Yes	Yes
6 months follow-up		Yes	Yes	Yes
12 months follow-up		Yes	Yes	Yes
18 months follow-up		Yes	Yes	-
24 months follow-up		Yes	Yes	-
36 months follow-up		Yes	Yes	-
* Left atrial diameter is demonstrated as antero-posterior / left-right diameter.

Table 2: Operative and postoperative characteristics of cryo-CMP-IV. Abbreviation: Cryo-CMP-IV = cryo-Cox-Maze IV procedure; AF = atrial fibrillation; NYHA = New York Heart Association; TTE = transthoracic echocardiography.

Discussion

Dextrocardia is a group of rare heart defects in which the heart is situated on the right side of the thoracic cavity instead of on the left side. One-third of all dextrocardia cases are mirror-image cases, which means the orientation of the cardiac chambers is a mirror image to levocardia (normally situated heart)¹². It is estimated that situs inversus dextrocardia associated with situs inversus totalis occurs with an incidence of much less than 1 in 10,000-50,000 births^1,2. Exposing and reaching the intracardiac structures was difficult for the three patients in this study presenting with situs inversus dextrocardia and situs inversus. The malposition made it impossible to perform the classic atriotomy incision on the right. Hence, the best method for intracardiac surgery was via the left-sided atriotomy by an operator standing on the left, which is opposite to the normal situation.

AF is the most common cardiac arrhythmia related to systemic or pulmonary thromboembolism and is associated with substantial morbidity and mortality³. The CMP has proven to be the most effective therapeutic method in SR restoration and maintenance^13,14. Over a decade of evolution, the modern conception of the Maze procedure was redefined by Damiano, with the new, facilitated iteration termed as the Cox-Maze IV procedure (CMP-IV)¹⁵. A prospective study conducted over a decade demonstrated that the CMP-IV gave excellent results and can achieve high success rates in the therapy of AF, with 90-93% freedom from AF and 82-84% freedom from AF off AADs¹⁶. The CMP-IV is considered the gold standard for the surgical therapy of AF¹⁷. The Society of Thoracic Surgeons 2017 Clinical Practice Guidelines for the surgical treatment of AF recommend CMP-IV with radiofrequency (RF) and cryothermal energy at the time of concomitant cardiac valvular operations to restore SR¹⁸. The optimal scheme of ablative energy sources applied for CMP-IV is either cryothermia alone or combined bipolar RF and cryothermia^18,19,20.

Cryoablation can be used adjacent to coronary arteries and valve tissue without causing injury, maintaining the structural integrity of the atrial tissue and leaving a smooth endocardial surface²¹. Moreover, cryoablation allows for the completion of full LA lesion sets via only a left atriotomy, which simplifies the operating steps compared with bipolar RF ablation. Along with its safety and the above features that help replace bipolar RF with cryoablation, cryoablation facilitates establishing the biatrial lesion set of CMP-IV^22,23,24. A recent study by Ad and colleagues demonstrated that cryo-CMP achieved a high success rate with 93% SR restoration and 85% SR off-AADs at 2 years after surgery²⁵.

In 2013, our cardiovascular surgery center introduced cryo-CMP-IV in China and has accumulated the largest series of 161 cases to date. Liu and colleagues carried out a retrospective study on the first 62 cases, which included many patients associated with giant LA, and many underwent a second operation. The study resulted in a successful restoration rate of 83.3% of SR off-AADs at the 18-month follow-up²⁶. Recently, the center reached a high annualized volume of CMP of approximately 400 patients per year, with a satisfactory rate of 89.58% freedom from AF at 2 years after surgery²⁷.

In this study, all patients were diagnosed as mirror-image dextrocardia, which means the anatomy of all intracardiac and extracardiac structures is mirror-imaged versus normal, such as the distribution of coronary artery, location of the conducting system, and the geometry of the cardiac valvular structure. The anatomic malposition of situs inversus dextrocardia impacted all technical aspects of the surgical procedure in the intracardiac operation. It made it inconvenient to perform tricuspid annuloplasty and challenging to establish the sophisticated lesion set of CMP-IV. After extensive preoperative evaluation and discussion, we chose cryothermal energy to generate the biatrial lesions of CMP-IV for the first two cases, as it was an energy source capable of producing reliable transmural lesions in a safer and more convenient manner.

However, to accurately understand the anatomical structure and guide surgical ablations in the third case, a 3D printing heart model was made for dynamically displaying the spatial relationship between the specific ablation lines and the key anatomical references, such as the coronary sinus, mitral isthmus, posterior mitral annulus, and right coronary artery. In addition, the rehearsal process provided an intuitive perspective on feasible ablation strategies, including the position, direction, and length for each clamping, to ensure continuous lesion sets and avoid potential damage to the surrounding structures.

We marked the coronary sinus by epicardial cryoablation during the LA lesion set in the first two cases. To protect the circumflex coronary artery, the mitral isthmus lesion is usually adjacent to the P3 cusp of the posterior leaflet of the MV, at about 4 o'clock position on the mitral annulus in the majority of patients^21,28. As far as the mirror-image dextrocardia was concerned, we displaced the mitral isthmus lesion in a mirror-image inversion manner to the 8 o'clock position on the mitral annulus for each case in this study (Figure 3A). Similarly, the tricuspid isthmus lesion was displaced from the 2 o'clock to the 10 o'clock position on the tricuspid annulus in these dextrocardia cases (Figure 3B).

Consistent with the experience of others, we had learned that integrity, continuity, and transmurality of CMP-IV are critical for successful cryoablation of AF²⁹. In these rare cases, we operated in a mirror-image inversion manner to integrate the biatrial lesions of CMP-IV and exclusion of LAA. To guarantee the continual lesions, it is important to stretch the atrium to flatten the atrial folds, so that the cryoprobe can adhere closely to the atrium wall during ablation. Transmural ablation was done at -60 °C for 2 min (cooled by nitrous oxide) for each cryolesion.

Additionally, electron microscopy revealed almost full-thickness tissue, except for necrosis of the epicardium of the cryoablated left atrium. Cox and colleagues proclaimed that transmural lesions are ensured with cryothermy at -60 °C for 2 min on an arrested heart, whereas epicardial cryothermy on a beating heart does not guarantee a transmural lesion³⁰. Our experience is consistent with that of Ad and others that it is important to give particular attention to keep an endocardial, bloodless, surgical field during cryoablation for better effect²⁹, especially in the RA ablation while the heart is beating. However, the major disadvantage of using cryothermal energy to ablate remains that there is no qualitative method to detect with certainty whether a given lesion is transmural simultaneously during the cryoablation procedure.

Experience suggests that the surgeon simply had must look at the cryolesion to see when it has become transmural at the time of cryoablation^16,30. Thus, during the cryoablation of the first two cases, we waited until the entire desired lesion was frozen transmurally at -60 °C and then counted 2 min by the clock. However, the incomplete or non-full-thickness transmural atrial necrosis in this study may be due to the cryoablation LA epicardium immediately encountering the ice water in the pericardial cavity during mild hypothermic CPB. The heat sink effect of the ice water can limit the epicardial cryolesion formation. Hence, drainage of the ice water during LA cryoablation will be helpful to achieve transmural necrosis. Overall, cryoablation allows for the more convenient achievement of a complete CMP-IV lesion set, and it was efficacious in eliminating AF in these reported cases of situs inversus dextrocardia.

The intraoperative findings in the first two patients revealed that repair of the MV and AV was difficult and infeasible because of chordal fusion and thickened leaflets; hence, prosthetic valve replacement surgeries were performed. We also delineated an optimal method of tricuspid annuloplasty in this study. The Sovering ring, designed asymmetrically according to tricuspid features, was placed elaborately in a mirror-image inversion manner in compliance with tricuspid valve anatomy in each situs inversus dextrocardia (Figure 5). Attention must be paid to remove the holder before fixing the annuloplasty ring. The intraoperative regurgitation water test showed good coaptation of the tricuspid leaflets without leakage. The TTE demonstrated no tricuspid regurgitation before discharge and at mid-term follow-up.

In conclusion, we reported three cases of patients with situs inversus dextrocardia. CMP-IV appeared to be effective in eliminating AF and preserving atrial function in these cases. CMP-IV was performed concomitantly with valvular surgery, safely and effectively. Moreover, the 3D printed heart model helps simulate and modify the CMP-IV procedure, especially in patients with rare malformations, and supports preoperative planning and training for surgical ablation of AF.

Materials

Name	Company	Catalog Number	Comments
CryoICE	AtriCure, Cincinnati, Ohio	CRYO2	Cryoablation in case 1 and case 2 was performed exclusively using it with a flexible 10cm in length metal cryoprobe.
Medtronic Open Pivot Standard mechanical MV	Medtronic, Minneapolis, Minn	709291 / MHV 500DM27 STD MITRAL	A 27-mm MV was adopted in case 1.
Medtronic Open Pivot Standard mechanical AV	Medtronic, Minneapolis, Minn	646871 / MHV 500FA23 STD AORTIC	A 23-mm AV was adopted in case 2.
bipolar radiofrequency pen	AtriCure Inc., Cincinnati, OH		Maze-IV in case 3
bipolar radiofrequency clamps	AtriCure Inc., Cincinnati, OH		Maze-IV in case 3
Goretex	W.L. Gore & Associates, Inc., Elkton, Maryland		A surgical suture made of polytetrafluoroethylene.
rigid mitral ring	Kingstron Bio, Suzhou, China	Element Force ARM32	A 32 mm ring was adopted in case 3.
Tricuspid Sovering Band	Sorin Group Italia S.r.l., VC, Italy	SBG0730 / SB30T	A 30 mm ring was adopted in case 1.
Tricuspid Sovering Band	Sorin Group Italia S.r.l., VC, Italy	SQB0240 / SB30T	A 30 mm ring was adopted in case 2.
Tricuspid Sovering Band	Sorin Group Italia S.r.l., VC, Italy	SBF0930 / SB28T	A 28 mm band was adopted in case 3.