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.

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 resus...

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 births¹<...

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.