With technological advancements of cardiac surgery and extended lifespans of patients undergoing cardiac surgery, the number of redo cardiac operation continues to increase. Redo procedures usually involve sternal reentry, which has the potential for hazardous injuries to the important structures and subsequent morbidity and mortality. Furthermore, conventional cardiac arrest may predispose the dilated myocardium to ischemia-reperfusion injury and postoperative low cardiac output in the patients who have poor ventricular function and giant left ventricle for a long-standing valve diseases. Against the situation mentioned above, minimally invasive beating heart technique for redo mitral valve surgery in patients with giant left ventricle has emerged in this environment. More and more reports had confirmed that minimally invasive beating heart technique for redo cardic surgery could be safely performed successfully[3–7].
In our study, the intraoperative blood loss, postoperative transfusion ratio, postoperative transfusion amount and postoperative drainage volume were all reduced significantly in minimally invasive beating heart compared to that in median thoracotomy. The greatest potential benefit of a right mini-thoracotomy is the avoidance of sternal re-entry and limited dissection of adhesions, avoiding the risk of injury to cardiac structures or patent grafts, and limiting the amount of postoperative bleeding. With that in mind, it was not difficult to understand that the patients benefited reduced blood loss and less transfusions from minimally invasive beating heart. Moreover, the operation time and the CPB time in minimally invasive beating heart group were significantly shorter, whereas the shorter CPB time also reduced the need for perioperative blood transfusion, which was more important for redo patients. Of course, less CPB time decreased the release of inflammatory cytokines that contributed to a lower incidence of other comorbidities such as renal and liver insufficiency, pulmonary disease. Postoperative acute renal failure, liver dysfunction, MODS and pulmonary complications all declined in the minimally invasive beating heart, while there were no statistical significances. But there was statistical significance in the extubation time, the patients gained an early extubation which had a certain significance in preventing postoperative pulmonary infection and ventilator-induced lung injury. All the advantages we mentioned above significantly shortened postoperative ICU stay and hospital stay time so that accelerated the patients’ faster recovery. Romano and colleaguesconcluded that redo right thoracotomy mitral valve surgery on the beating heart is associated with shorter bypass time, less transfusion requirements, shorter postoperative ventilation, and lower mortality. The mortality of patients with giant left ventricle was very high, the first cardic surgery death rate was 9% through median thoracotomy in the study of D.HAN, the redo cardic surgery mortality would have been higher understandably. In our study, the logistic EuroSCORE predicted risk of operative mortality was high to 15.3% ± 5.4%. Fortunately, the postoperative 30-day mortality was 6.7% in minimally invasive beating heart group that was significantly lower than the expected mortality predicted by the logistic EuroSCORE, and it was less than 14% in median thoracotomy arrested heart group, but there was no significant difference. Botta and colleaguesreported that two patients died in both groups (mortality was 4.5%) from multiorgan failure and CPB time was respectively 166 and 163 minutes, they asserted that there was no difference in biochemical or clinical outcomes from conventional surgery using aortic clamping and cardioplegic techniques. In our study, the six months postoperative echocardiographic parameters (LVEDD, LVEF, cardiothoracic ratio, NYHA functional class) had a marked improvement compared with the preoperative circumstances, but there were no statistical significances between the two groups. Murzi and colleaguesreported that thirty-day mortality was 4.1% and reoperative mitral valve surgery could be safely performed through a right minithoracotomy with good early and late outcomes.
Currently, possible beating heart alternatives are performing the redo mitral valve operation with aortic endoballoon clamp or an unclamped aorta[6, 12, 13] on the empty beating heart or ventricular fibrillation/fibrillating arrest while myocardial protection is achieved through continuous coronary perfusion. The big advantage of this continuous myocardial perfusion procedure is to decrease or eliminate myocardial damage caused by ischemia-reperfusion injury which follows standard manoeuvres of aortic cross clamping and clamp release[6, 8, 20], which may be advantageous particularly in patients with poor left ventricular functions[10–13, 21]. In the animal model, the morphology and function of the myocardial cells in ventricular fibrillation or sinus rhythm beating heart were all better than that in aortic occlusion during CPB. In this study, we initially started to take the beating heart alternative with ventricular fibrillation, subsequently, we adopted beating heart technique with the empty beating heart that temperature was maintained between 32 and 33 oC. Some researchers believed that beating heart alternative with ventricular fibrillation approach was inferior to the empty beating heart owing to its reduction oxygen delivery to the subendocardium and the consequent suboptimal myocardial protection[6, 9, 21]. As normothermic perfusion was maintained, risk of coagulopathy was reduced and blood loss was usually much less than with hypothermic ventricular fibrillation[4, 6].Therefore, this empty beating heart approach would be better helpful in patients with giant left ventricle tend to merge poor heart function. By keeping the heart beating, myocardial edema is decreased and function may be maintained, which may be of particular importance in these patients with already impaired ventricular function. These were good explanations for the postoperative morbidity of LCOS and ventricular fibrillation was lower in the minimally invasive beating heart group. As we all known, LCOS and ventricular fibrillation are leading causes of death in patients with giant left ventricle. This helps to further explain the lower postoperative 30-day mortality.
This beating heart method increased returned blood volume that influenced operation field, and increased cardiac attraction that contributed to corresponding blood damage augment. It might be contraindicated if there was significant aortic insufficiency resulted in difficult to maintain a relatively bloodless operative field and sufficiently coronary perfusion. In our study, the patient had significant aortic regurgitation that the effective regurgitate orifice area greater than 1 cm2 was excluded. In the event of concomitant mild aortic insufficiency, flows on CPB can be decreased and systemic temperature lowered in other studies. Teruya and colleagues used 2 drop-in suckers through the left atrial incision in this particular case, a left ventricular vent via the apex using mini-left thoracotomy was useful in preventing distention of the left ventricle. We obtained satisfactory results through a left ventricular drainage tube that was inserted right pulmonary vein. Meanwhile, we adopted remifentaniland landiololthat were helpful for heart rate reduction to prevent regurgitant blood flow from coming up to the operative field for very slight aortic insufficiency. Though we got a good view of surgery through the unremitting effects, it was difficult to perform MVP relative to MVR while the heart was kept perfused and beating. Therefore we had a very high probability (86.7%) of valve replacement that was similar to other studies. On the other hand, the patients with large left ventricular heart valve disease in general had poor preoperative cardiac function and serious pathological lesion, so the surgery was mostly performed valve replacement or carried out valvuloplasty cautiously.In the implementation of MVR, mitral posterior and subvalvular apparatus should be preserved as far as possible so that maximized to protect the left ventricular tension ring function and avoid the further expansion of the left ventricular transverse diameter.
It was noteworthy that the saline injection test was never been applied because it would pressurize the ventricle especially in valve repair. Another concern is the possibility of air embolism. An aortic vent was always under continuous suction in the ascending aorta and carbon dioxide was continuously insufflated into the chest to displace intracardiac air in this research. Additionally, the left atrium was filled with backflow of blood keeping the prosthetic or native valve open and the lungs were reinsufflated before closing the atriotomy to prevent possible left atrial air embolism. TEE was also used to ensure complete removal of air. We had achieved good results that there were no neurological complications caused by air embolism through using the methods mentioned above, which also had been confirmed in many other reports[7, 26]. In addition, minimally invasive beating heart approach can avoid systemic embolization caused by aortic clamping when severe aortic calcification. Some groups have reported increased stroke rates in patients undergoing the right minithoracotomy approach with retrograde arterial perfusion for redo mitral valve operation, but others hold the contrary opinion.
The limitations to the use of minimally invasive beating heart approach are mainly related to a prolonged learning curve that can increase the risk of patients at new centres and to the cost of the devices. At the beginning, there was one patient who needed to re-exploration for chest wall bleeding due to lack of experience. This kind of stupid mistake no longer occurred with the improvement of operation skill and experience. Although the operation of patient with giant left ventricle is difficult through minimally invasive thoracotomy, we should not ignore the great advantage of this method. As long as the lung function can be satisfied with one lung ventilation, we should try to take this kind of operation for the patients with giant left ventricle undergoing reoperation. In addition, there are several limitations that it is a small sample size and retrospective study at a single center in our study, long-term follow up data are also needed regarding the durability of this technique. Large-scale multi-center randomized controlled clinical trails are warranted to further validate the potential benefits and the limitations of this technique.