Asian Cardiovasc Thorac Ann 2007;15:225-228
© 2007 Asia Publishing EXchange Ltd
Minimally Invasive Aortic Valve Replacement in Left Ventricular Dysfunction
Minoru Tabata, MD,
Sary F Aranki, MD,
John A Fox, MD1,
Gregory S Couper, MD,
Lawrence H Cohn, MD,
Prem S Shekar, MD
Division of Cardiac Surgery
1 Division of Cardiac Anesthesia, Brigham and Women’s Hospital, Boston, USA
For reprint information contact: Prem S Shekar, MD Tel: 1 617 732 7678 Fax: 1 617 975 0848 Email: pshekar{at}partners.org, Division of Cardiac Surgery, Brigham and Women’s Hospital, 75 Francis Street, Boston, MA 02115, USA.
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ABSTRACT
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The safety and benefit of minimally invasive aortic valve replacement in patients with left ventricular dysfunction has not been well investigated. We conducted a retrospective review of 140 patients with ejection fraction 
40% who underwent isolated aortic valve replacement between July 1996 and March 2005. Aortic valve replacement was performed via an upper hemisternotomy in 73 patients and via a full sternotomy in 67. Two matched cohorts of 41 patients each were constructed using propensity score analysis, and the outcomes were compared. There was no significant difference in operative mortality (hemisternotomy, 2.4% vs 4.8% for full sternotomy), incidence of postoperative complications, blood transfusion requirement, length of hospital stay, or discharge to home rates. Aortic valve replacement via an upper hemisternotomy can be performed safely, even in patients with left ventricular dysfunction, with morbidity and mortality outcomes similar to those of a full sternotomy.
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INTRODUCTION
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Minimally invasive aortic valve surgery was introduced in 1996 and has been gaining acceptance for the last decade.1 In our institution, more than 900 patients have undergone minimally invasive aortic valve surgery since July 1996, with excellent outcomes.2,3 Many studies have shown that it can be performed safely, with mortality and morbidity similar to conventional aortic valve surgery via a full sternotomy.3–11 Some studies have also revealed that it leads to faster postoperative recovery.3,4,10,11 However, the effect of a minimally invasive technique in patients with left ventricular (LV) dysfunction has not been investigated. It is also unclear which subgroup of patients with aortic valve disease derives the greatest benefit from a minimally invasive technique. Left ventricular dysfunction is well known to increase operative risks and length of hospital stay in aortic valve replacement (AVR).12 The aim of this study was to analyze the benefits, safety, and feasibility of minimally invasive AVR via an upper hemisternotomy in patients with LV dysfunction.
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PATIENTS AND METHODS
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We conducted a retrospective review of 140 patients with ejection fraction (EF) 40% undergoing isolated AVR between July 1996 and March 2005. The mean EF was 31.2% ± 7.5%. Aortic valve replacement was performed by a minimally invasive technique in 73 patients (group M) and by a full sternotomy in 67 (group F). Patients undergoing aortic valve repair, aortic root replacement, enlargement of the aortic annulus, homograft or stentless bioprosthetic valve implantation were excluded. Parasternal and thoracotomy approaches were also excluded. Two matched cohorts of 41 patients each were constructed by propensity score analysis. Matched variables included age, sex, EF, New York Heart Association functional class, chronic obstructive pulmonary disease, renal insufficiency, urgency of operation, and valvular pathophysiology. All preoperative data, in-hospital and post-discharge outcomes were collected from the medical records and the Brigham cardiac surgery database, according to The Society of Thoracic Surgeons definitions. Predictors of blood transfusion requirement, early discharge (< 7 days), and discharge to home were revealed by multivariate analysis of the data of all 140 patients. Operative variables, blood transfusion requirement, operative morbidity and mortality, length of hospital stay, and discharge destination were compared between the 2 matched groups. This study was approved by the institutional review board of Brigham and Women’s Hospital (Protocol #2005P000249).
Our minimally invasive approach involved an upper hemisternotomy from the sternal notch to the level of the 4th intercostal space. Cardiopulmonary bypass (CPB) was established by direct ascending aortic cannulation and percutaneous femoral venous or direct right atrial cannulation. An aortic cross clamp was applied through the incision. Antegrade cold blood cardioplegia was delivered through the aortic root and coronary orifices after aortotomy, retrograde cardioplegia (especially in patients with significant aortic insufficiency) was delivered through a coronary sinus cannula placed via the right atrial appendage using transesophageal echocardiographic guidance, and an LV vent was placed through the aortic valve or right superior pulmonary vein. Transesophageal echocardiography was used to assess LV distension during antegrade cardioplegia delivery. Mechanical valves were mostly seated in the intra-annular position with pledgeted everting mattress sutures, and stented bioprosthetic valves were inserted in the supra-annular position using pledgeted non-everting mattress sutures. In re-operations, CPB was established via femoral or axillary arterial cannulation and femoral venous cannulation before sternotomy. In the setting of a patent left internal mammary artery (LIMA) graft, we used moderate hypothermia (20°C – 25°C) and systemic hyperkalemia (serum potassium > 6.0 mEq·L–1) in addition to antegrade and retrograde cardioplegia. When collateral flow from the LIMA graft to the coronary ostia obscured the operative field, CPB flow was reduced temporarily to 500 to 1,500 mL·min–1. Our detailed strategy for minimally invasive AVR in re-operations has been described previously.13
Values of continuous variables are expressed as mean ± standard deviation. Propensity score matching was used to minimize selection bias between the groups. The unpaired t test was used to analyze continuous variables. The chi-squared test was used to analyze categorical variables. A stepwise logistic regression model was used to find predictors of blood transfusion requirements, early discharge, and discharge home. A value of p < 0.05 was considered statistically significant. Statistical analysis was performed with SPSS version 11.5 software (SPSS, Inc, Chicago, IL, USA).
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RESULTS
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Preoperative characteristics of all patients are shown in Table 1
. Group M had higher EF, lower New York Heart Association class, fewer patients with renal insufficiency, more with chronic obstructive pulmonary disease, and fewer with aortic stenosis than group F.
Preoperative characteristics of the patient-matched groups are shown in Table 2. All preoperative variables were well matched. Group F had more re-operations than group M, but the difference was not significant. The operative outcomes of the matched patients are listed in Table 3. The logistic regression model revealed that age ( p = 0.018) was an independent predictor of blood transfusion requirement. Five patients died within 30 days after surgery or before discharge. Hospital mortality was 2.7% (2/73) in group M and 4.5% (3/67) in group F. Mortality and morbidity in the patient-matched groups are shown in Table 3. There were no significant differences in these parameters between groups. Logistic regression revealed that age ( p < 0.001) was an independent negative predictor of early discharge (< 7 days), and that age ( p < 0.001) and renal insufficiency ( p = 0.004) were independent negative predictors of discharge to home.
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DISCUSSION
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We believe this is the first study investigating the effects of minimally invasive AVR in patients with LV dysfunction. The results indicate that minimally invasive AVR can be performed safely with excellent outcomes, even in this high-risk subgroup. No patient suffered perioperative myocardial infarction, and only 3 (4.1%) with EF 25% required an intraoperative intra-aortic balloon pump. Dogan and colleagues7 investigated postoperative cardiac enzyme levels and showed that the limited surgical access of an upper hemisternotomy does not affect the efficacy of myocardial protection. They used only antegrade cardioplegia through an aortic root cannula and selective coronary cardioplegia, and routinely placed an LV vent through the right superior pulmonary vein. We used a combination of antegrade, ostial, and retrograde cardioplegia in our patients, with an LV vent through the right superior pulmonary vein or the aortic valve.
In the setting of a patent LIMA graft, myocardial protection is more complicated because LIMA graft flow cannot be interrupted during aortic cross clamping. We used moderate hypothermia and systemic hyperkalemia. Byrne and colleagues14 have shown that moderate to deep hypothermia provides adequate myocardial protection. There were 13 re-operations via a hemisternotomy for AVR in patients with a patent LIMA graft. The mean patient age was 73.2 ± 7.2 years and the mean EF was 29.6% ± 7.8%. One patient had patent bilateral internal mammary artery grafts. Operative mortality was 7.7% (1/13). Adequate myocardial protection in the setting of a patent LIMA graft can be obtained using our method, even for patients with LV dysfunction.
Adequate exposure was obtained in all minimally invasive operations, and no patient required conversion to a full sternotomy at primary surgery. One patient who needed re-intervention for bleeding from an injured right internal mammary vein required a full sternotomy at re-operation. There was no significant difference in CPB time and cross clamp time between the 2 groups. All surgeons in our institution have now completely changed over to the minimally invasive approach for isolated aortic valve surgery, unless specific contraindications exist (e.g., patients less than 5 feet tall or morbidly obese).
In this series, there was no significant difference in length of hospital stay and discharge to home rate, which indicates that minimally invasive AVR does not contribute to faster postoperative recovery in the subgroup of patients with LV dysfunction. In 2004, Mihaljevic and colleagues3 reported our cumulative experience of 526 cases of minimally invasive aortic valve surgery, mainly with an upper hemisternotomy, and showed faster postoperative recovery, shorter length of stay, and more patients discharged to home than those who had a full sternotomy. This benefit has been reported in some other studies.4 Sharony and colleagues11 described their experience of 438 minimally invasive AVR procedures, mostly with a right minithoracotomy, and showed that the minimally invasive group had a shorter length of hospital stay and higher discharge to home rate than those who had a full sternotomy. They also demonstrated that minimally invasive AVR had the same effect in patients aged over 65 years.10 Other advantages of an upper hemisternotomy for AVR include less incisional pain, shorter duration of ventilation, reduced blood loss, and less blood transfusion.4,5,7,15 In our study, neither incisional pain nor amount of blood loss were evaluated, and no significant difference was found in blood transfusion requirements between the groups, as reported by Stamou and colleagues.9 Some studies have shown that AVR via an upper hemisternotomy is not associated with any particular benefit other than cosmesis.6,9
One of the important limitations is that this study was undertaken on a retrospective series. A prospective randomized study is necessary to assess the reproducibility of our findings. Also, we did not investigate incisional pain, quality of life, or postoperative pulmonary function, all of which might be improved by a minimally invasive technique. It was concluded that minimally invasive AVR can be performed safely in patients with LV dysfunction, but it was not associated with faster postoperative recovery in this subgroup of patients.
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REFERENCES
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ABSTRACT
INTRODUCTION
