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Interact CardioVasc Thorac Surg 2008;7:222-226. doi:10.1510/icvts.2007.171611 © 2008 European Association of Cardio-Thoracic Surgery
Cardiac surgery in type-1-myotonic muscular dystrophy (Steinert syndrome) associated to Barlow disease
a Experimental Surgery Unit, Cardiac Surgery, Department of Heart and Vessels, Careggi Hospital, Viale Morgagni 85, 50134, Florence, Italy Received 13 November 2007; received in revised form 4 January 2008; accepted 6 January 2008
*Corresponding author. Tel.: +39-055-794-7467; fax: +39-055-794-7628.
No data exist in the English-language literature about patients with Barlow disease associated to Steinert syndrome and little is known about the employment of hypothermic cardiopulmonary bypass (CPB) and hyperkalemic cardioplegia in these patients. We present our experience with six patients affected by myxomatous degeneration associated to Steinert disease undergoing complex mitral valve repair. In all patients we employed mild hypothermic CPB (31 °C) and myocardial protection was achieved, in the entire cohort, by the use of blood hyperkalemic cold cardioplegia. The postoperative course was uneventful in all patients and neither shivering nor generalized muscle contraction were observed. Furthermore, all patients have remained well on an outpatient basis. Hypothermic CPB and hyperkalemic cardioplegia can be safely employed in patients with Steinert syndrome requiring complex cardiac surgery. Further large studies are necessary to confirm our findings.
Key Words: Myotonic muscular dystrophy; Steinert disease; Mitral repair; Barlow disease
Myotonic dystrophy (MD) is the most common form of adult-onset muscular dystrophy. There are currently two known types of MD: myotonic dystrophy type 1 (MD1), also known as Steinert disease [1], and myotonic dystrophy type 2 (MD2), commonly referred to as PROMM or proximal myotonic myopathy [2]. The MD1 is a genetically transmitted (autosomal dominant) multisystem syndrome caused by an abnormal expansion of a trinucleotide cytosine-thymine-guanine (CTG) sequence found on chromosome 19. It affects skeletal, smooth and cardiac muscle causing nervous system abnormalities, ocular diseases and endocrine disorders [1]. Cardiac involvement is an integral part of the disorder, and it is mainly represented by conduction abnormalities, arrhythmias and, less frequently, heart failure [3]. The association of the Steinert syndrome with mitral valve prolapse or with Barlow disease (also known as myxomatous disease) has been described since 1976 [4]. Nonetheless, no data exist in the English-language literature about patients with myotonic dystrophy type 1 and Barlow disease undergoing cardiac surgery. Myxomatous disease associated to MD1 represents a double challenging situation: on one hand, patients with Barlow disease present a complex mechanism of MR with multiple lesions [5] and a complex, time-consuming mitral repair is often necessary to address all these lesions and to restore coaptation [6]. On the other hand, the management of cardiopulmonary bypass is very challenging in MD1 patients as a myotonic crisis can be triggered by several factors including hypothermia, shivering and mechanical or electrical stimulation. Thus, the management of cardiopulmonary bypass and myocardial protection is a critical point in these patients as the employment of systemic hypothermia and hyperkalemic cardioplegia could theoretically cause generalized muscle contraction during heart operations. For this reason the use of normothermic cardiopulmonary bypass and warm blood cardioplegia has been preferred in patients with Steinert disease undergoing cardiac surgery [7, 8]. As far as we know, no data exist about patients with myotonic dystrophy undergoing cardiac surgery with the use of hypothermic cardiopulmonary bypass (CPB) and hyperkalemia. Therefore, we report our experience with MD1 patients affected by Barlow disease successfully undergoing complex mitral valve repair with systemic hypothermia and hyperkalemic cold cardioplegia.
2.1. Patients Patient characteristics are summarized in Table 1. Diagnosis of Barlow disease was obtained preoperatively in all patients by 2-D Doppler echocardiography. All measurements were carried out following The American Society of Echocardiography guidelines. All patients had diagnosis of Steinert disease preoperatively by electromyography (EMG). One patient (patient no. 3) underwent muscle biopsy. Cardiac catheterization was carried out in all patients to exclude coronary artery disease. All subjects underwent intraoperative transesophageal echo Doppler evaluation of the anatomy of the valve after the induction of anesthesia. Posterior LV and septal thickness were increased in all patients. In contrast, LV ejection fraction was almost normal in the entire cohort and LV dimension and volumes were normal (patients 2–6) or slightly increased (patient 1).
2.2. Ethical issues The study was approved by the Institutional Ethics Board. The authors had full access to the data and take responsibility for its integrity. All authors have read and agreed to the manuscript as written. 2.3. Anesthetic management and monitoring Intraoperative monitoring included: five leads electrocardiogram, invasive systemic blood pressure, central venous pressure, pulmonary artery pressure, pulse oximetry, pharyngeal temperature and TEE. Neuromuscular blockade was monitored using the train-of-four (TOF) technique [9].In order to prevent malignant hyperthermia, the anesthetic machine (Dräger Primus, Lübeck, Germany) was flushed with vapor-free fresh gas (10 l min–1) to wash out residual anesthetic agents for 70 min before the induction [10]. A general intravenous anesthesia was induced with remifentanil (0.5 µg kg–1 min–1), and midazolam (0.1 mg kg–1). Neuromuscular blockade was achieved with cis-atracurium (100 µg kg–1). The anesthesia was maintained with remifentanil (0.3 µg kg–1 min–1) and propofol (3 mg kg–1 h–1). The lungs were ventilated with a mixture of oxygen in air (FiO2: 0.5) with a minute volume adequate to maintain a PaCO2 between 4.6 and 5.3 kPa.
At the end of operation, patients were transferred to the post-cardiac surgery intensive care unit (ICU). When the body temperature stably reached 37 °C and the bleeding rate was into normal range, they were extubated according to the following criteria: tidal volume >8 ml/kg, resting minute ventilation Morphine was employed as analgesic agent (1 mg/h) only for a short time postoperatively. Table 2 shows operative data. Mitral valve repair was performed during total cardiopulmonary bypass, through a conventional midline sternotomy. Myocardial protection was accomplished by antegrade cold crystalloid cardioplegia. The mitral valve was accessed through the left atrium after development of the inter-atrial groove.
Four patients underwent quadrangular resection of the posterior leaflet (PML) associated to a sliding plasty to avoid postoperative left ventricular outflow obstruction due to systolic anterior motion (SAM) of the mitral anterior leaflet. Two patients underwent edge-to-edge repair as originally described [11]. In all patients the reconstruction was completed with the implant of a Carpentier–Edwards (C-E) Physio prosthetic ring (Edwards Lifesciences, Irvine, CA) with pledgdgetted-Ethibond 2-0 (Ethicon INC, Sommerville, NJ) interrupted horizontal mattress. The ring size chosen was based on the true size of the AML. This was determined by using standard C-E mitral sizers to measure both the intrecommissural distance and the anterior-posterior leaflet dimension, with a bias to choose the larger size if between sizes. Gore-Tex neochordae (polytetrafluoroethylene; W.L. Gore & Assoc, Inc., Flagstaff, AZ) were implanted in four patients to correct the prolapse of the anterior leaflet (AML). In two patients, prolapse of the commissural area was repaired by paracommissural edge-to-edge repair. Another associated procedure was cleft correction, either of the posterior or anterior leaflet (three patients). At the end of repair the coaptation was checked by a saline testing. After weaning from CPB, a Doppler TEE was performed and no residual mitral insufficiency was detected. The operation was routinely completed.
There was no in-hospital or 30-day mortality. No postoperative complication occurred. Furthermore, there were no cardiac or respiratory complications and neither hypertonia nor shivering were observed. At discharge, patients had no or trace MR and there was no evidence of systolic anterior motion. All six patients were discharged from hospital after an uneventful course on the 5th, 4th, 5th, 8th, 5th and 6th postoperative day, respectively. There were no late deaths. Subjects in our cohort reached 15, 20, 23, 34, 57, 45-month follow-up and all were checked by outpatient visits and transthoracic echocardiography. No complication occurred during the follow-up and patients were asymptomatic and in New York Heart Association (NYHA) functional class I. Finally, transthoracic echocardiography demonstrated no residual MR and there was no evidence of systolic anterior motion in any patient.
Reports of cardiac operation in patients with MD1 have been rare. As far as we know, only four cases have been reported in the English-language literature [7, 8, 12, 13]. In addition, to the best of our knowledge, no case of Steinert syndrome and Barlow disease undergoing cardiac surgery has been published in the English-language literature. This association has been reported to occur in 16–32% of cases [14, 15]. As the Barlow disease occurs in 6% of females and 1% of males in a normal general population [15] and the incidence of MD1 is estimated to be 1 in 8000 births with a worldwide prevalence ranging from 2.1 to 14.3/100,000 inhabitants [2], therefore the incidence of this association cannot be considered negligible and it might have been underestimated in the past. In our series, all patients showed typical features of Barlow disease: billowing valve with bileaflets prolapse, excess tissue and thickened leaflets, thickened and elongated chordae and severe annular dilatation; four patients had chordae rupture while none showed annular calcification, papillary muscle elongation and/or papillary muscle calcification. As no data exist in the literature of a lower durability of mitral repair in MD1 patients, corrections were carried out following our specific sequential approach to Barlow disease: 1) To repair the posterior leaflet by resecting any prolapsing segment; 2) reduce the posterior annular dimension; 3) reconstruct the posterior leaflet; 4) perform a true sized annuloplasty; and 5) repair the prolapse of the AML or commissures after inspecting the line of closure during saline testing. Perioperative and anesthetic management of MD1 patients may pose serious problems [13] and concerns arise with the association between myotonic dystrophy and Barlow disease, the latter requiring a complex, time-consuming mitral repair to address multiple lesions responsible for regurgitation and to restore coaptation [6]. Thus, the management of cardiopulmonary bypass and myocardial protection is a key point in these patients. Theoretically, during cardiac operations, application of systemic hypothermia or hyperkalemic cardioplegia should be avoided in patients with Steinert disease. Indeed, the membrane of dystrophic myotonic muscle is extremely sensitive to changes in extracellular potassium concentration. Normal muscle excitability is usually decreased when there is an elevation of the serum potassium level; however, hyperkalemia initially causes muscle hypotonicity, followed by hypertonicity upon further serum potassium elevation [8]. Furthermore, the impact of hyperkalemic cardioplegia on the heart of a patient with MD1 is not fully understood. For these reasons all previously reported cardiac operations in MD1 patients were performed avoiding hypothermia and hyperkalemic cardioplegia. Sakai and coworkers [7] and Ogawa and coworkers [8] reported a successful repair of an atrial septal defect (ASD) in patients with myotonic dystrophy using systemic normorthermia with an empty beating heart. Furthermore, Tanaka and Tanaka [12] performed an ASD closure in a 41-year-old man with myotonic dystrophy under mild hypothermia (31 °C) but they did not mention their method of myocardial protection. More recently, Klompe et al. [13] reported a 43-year-old man with Steinert disease who had undergone total correction of tetralogy of Fallot needing re-operation. A pulmonary allograft between right ventricle and pulmonary artery was implanted in this patient on beating heart with the use of extracorporeal circulation (54 min) but without cooling. However, the effective safety of hypothermia and hyperkalemia in MD1 patients have still not been fully investigated. We presented our experience with six patients affected by myxomatous degeneration associated to Steinert disease undergoing complex mitral valve repair. In all patients the CPB time was >100 min and in all patients we employed mild hypothermia (31 °C). In addition, myocardial protection was achieved by the use of blood hyperkalemic cold cardioplegia. As far as we know, this is the first report of patients with Steinert disease undergoing cardiac surgery under hypothermic CPB and employing hyperkalemic cold cardioplegia. In our experience, the postoperative course was uneventful in all patients: all were easily weaned from CPB and neither shivering nor generalized muscle contraction were observed. Furthermore, all patients have remained well on an outpatient basis.
Hypothermic CPB and hyperkalemic cardioplegia can be safely employed in patients with Steinert syndrome requiring complex cardiac surgery. Further large studies are necessary to confirm our findings.
We gratefully acknowledge Dr. Judith Wilson for the English revision of the paper.
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Abstract
1. Introduction
10 l, and a respiratory rate <20 breaths/min. Regarding neuromuscular monitor, the set point was a TOF ratio 
70%.