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D. RICHENS#, R.S. JUTLEY*, M. BAKER+ and M. SHAJARF€
#Consultant Cardiac Surgeon, *Specialist Registrar, Trent Cardiothoracic Rotation, +Chief Perfusionist, €Cardiac Anaesthetist, Nottingham City Hospital, UK
Keywords: Minimally invasive, mitral valve, endoclamp, trans-oesophageal echocardiography, double lumen tube
Minimally invasive mitral valve surgery has recently been advocated as an alternative to the conventional median
sternotomy approach. It has serval documented advantages and requires a close relationship betweeen the surgeons,
anaesthetist and perfusionist for a successful outcome. This article demonstrates our surgical technique for replacement
of the mitral valve. The various aspects of the specialised equipment used are also described
J.R.Coll.Surg.Edinb., 47, October 2002, 676-680
Surgery to the mitral valve has traditionally been performed through the median sternotomy.1 However, this approach is associated with complications such as infection, dehiscence, mediastinitis and neurological problems, some of which have an unacceptably high mortality rate. 2-4 As a speciality, cardiac surgery arguably has been one of the slowest to adopt the minimally invasive or limited access surgical approach. However, since the mid-1990’s it has rapidly gained popularity, led by pioneers such as Hugo Vanermen in Aalst, Belgium. 5-7 There are now several studies that demonstrate such techniques offer patients a shorter intensive therapy unit (ITU) and in-patient stay, lowers blood transfusions rates, is associated with less wound discomfort and facilitates a more rapid return to work. 8-11 On balance, although the technique has a higher disposable items and revenue cost, intensive care and hospital stay is shorter. This, along with a more rapid rehabilitation has a lower cost for the community. This article describes our minimally invasive technique for replacement of the mitral valve using the Port Access SystemTM (Heartport, Redwood City, CA).
This approach is particularly useful for its cosmetic result and may be applied to either mitral stenosis or incompetence, atrial septal defects and atrial myxomata. It is also useful in re-operations to avoid the inherent complications with re-sternotomy and dissection of pericardial adhesions necessary to obtain adequate surgical exposure of the mitral valve. The approach may be also used in a heavily calcified aorta where application of the conventional cross-clamp carries a risk of embolism and vessel wall trauma. There are some relative contraindications to the minimally invasive approach. These include a previous right thoracotomy with an adherent right lung, severe mitral valve annulus calcification, a dilated ascending aorta greater than 4.5 cm in diameter and severe pulmonary hypertension. However, each patient must be assessed on his or her own individual merit prior to surgery.
The patients must be made aware that the potential risks of the procedure are similar to those expected by the conventional approach. Specifically, they are counselled about the risks of peri-operative myocardial infarction, cerebro-vascular events and bleeding along with the complications of cardiopulmonary bypass and anaesthesia. In addition, consent is obtained for conversion to sternotomy or thoracotomy in case of operative difficulty or complications.
Patient Anaesthesia
The procedure is performed under a general anaesthetic. Radial arterial lines are placed in both arms to monitor inadvertent occlusion of the innominate artery by the endoclamp balloon. A double-lumen endotracheal tube is used to allow single left lung ventilation. An 8.3-Fr percutaneous endopulmonary catheter is then floated through the right internal jugular vein to the pulmonary artery and used as a vent during the procedure. This allows a bloodless surgical field. The vent position is initially checked with the pressure waveform but later confirmed with the trans-oesophageal echocardiography (TOE) (Figure 1). A single intravenous dose of 1.5 g of cefuroxime is administered on induction of anaesthesia and a urinary catheter passed.
A TOE probe is inserted and an initial inspection of the mitral valve is performed to evaluate mitral anatomy and function for the possibility of repair or replacement. As the delivery of anterograde cardioplegia depends on the competency of the aortic valve, the valve morphology is also assessed with the TOE probe. Any significant aortic regurgitation would preclude anterograde cardioplegia delivery necessitating the placement of a retrograde cannula into the coronary sinus through the right internal jugular vein. Trans-oesophageal echocardiography measurement of the proximal aorta determines the amount of saline to be used in filling the balloon that isolates the heart. For example, a 3 cm diameter aorta would require 30 mls of contrast for balloon filling maintained at a filling pressure of 300 mmHg. Moreover, assessment of the shape of the aorta gives an indication whether the occluding balloon is likely to be effective. In our experience, a fusiform and tortuous aorta can make balloon siting difficult.
Anaesthesia is maintained prior to and during cardiopulmonary bypass (CPB) using total intravenous anaesthesia (TIVA). Prior to transfer to the operating room, external pads are placed across the chest wall to allow both external defibrillation and pacing, if required, at the end of the procedure.
Patient Set-up
The patient is placed supine on the operating table. Adequate exposure is usually achieved by placing a rolled up towel between the scapulae (Figure 2). The patient is prepped with an iodinebased solution from mid-thigh to the neck. The groin is always prepped last. The patient is draped exposing the anterior and right lateral chest wall and both groin areas. An Iodoban adhesive strip is then applied to the exposed areas, thus, minimising the risk of infection and contamination.
Surgical Incisions and Cardiopulmonary Bypass
The mitral valve is exposed through a 6cm right anterior thoracotomy (working port) through the fourth intercostal space. The incision is positioned such that 25% is medial to the midclavicular point and 75% lateral to it. A soft tissue retractor, usually of medium size, is then inserted (Figure 3). A 5mm port is then placed in the seventh intercostal space in the mid-axillary line. This port is used initially for CO2 gas insufflation and later for cardiotomy suction. Carbon dioxide is used to fill the pleural cavity because of its high solubility. Any residual air in the left side of the heart following the procedure, therefore, is easily absorbed thereby minimising the risk of air embolism. The port is connected to CO2 gas, which is run at 3-4 l/min. A second 5mm port is then introduced for the videoscope through the fourth intercostal space in the mid-axillary line. Left single-lung ventilation is commenced only after these ports are in place. A 2mm incision is made medial to the working port in the fourth intercostal space. Under direct vision with a 30° videoscope the handle of the customised atrial retractor is introduced into the right pleural cavity. Direct visualisation avoids injury to the right internal mammary artery that courses 1-2 cm lateral to the sternal edge.
Figure 1: Mid-oesophageal short axis bi-caval view during TOE. The pulmonary artery catheter (arrow) may be seen in the right atrium as it is floated into the pulmonary artery through the superior vena cava (SVC).
Figure 2: Positioning of the patient in theatre. A trans-eosophageal echocardiogram is seen in place along with an endopulmonary vent positioned via the right internal jugular vein.
Figure 3: A medium sized soft tissue retractor is seen inserted into the 6cm working port. The right lung may be seen in the incision.
Figure 4: The wire tip over which the venous cannula is threaded (arrow) can be seen in the right atrium having been introduced through the inferior vena cava.
Figure 5: The 28-F venous catheter with the introducer and sharper, stiffer mandril.
Figure 6: The 28-F venous catheter is introduced over the guide wire into the right atrium (arrow) taking care that the stiffer mandril is withdrawn before full placement.
Figure 7: The 23-F arterial cannula with the Y-connector for passage of the endoclamp into the aortic root.
Once the various ports are in place, a 4cm transverse incision is made in the right groin and the femoral artery and vein dissected free in preparation for cannulation. The patient is heparinised and the vessels cannulated after 4/0 PTFE purse strings are in place to secure the cannulae. The venous cannula is inserted first but in each case the Seldinger technique is used under guidance with the TOE. With the venous cannula insertion, once the guide wire is seen in the right atrium (Figure 4) the track is gently dilated. The 28-F cannula (Figure 5) is then gently threaded into the atrium over a mandril. However, before its final and full placement in the atrium the mandril is withdrawn to avoid puncturing the thin-walled right atrial appendage. A TOE image of a satisfactory positioning may be seen in Figure 6. Similarly, the 23-F arterial cannula (Figure 7) is only inserted once the guide wire is visualised in the descending aorta, thereby, excluding the possibility of intimal dissection. With the cannula in place, a specialised balloon-tipped endoaortic catheter (Figures 8 and 9) is introduced through an arm of the Y-connector of the femoral arterial cannula, (EndoclampTM, Heartport, Redwood City, CA) and positioned in the aortic root. The triple-lumen 10.5-Fr catheter is designed to occlude the aorta, deliver the cardioplegia and vent the aortic root. Placement is again performed under TOE guidance and over a guide wire. In our unit, we prefer to leave the guide wire in place but withdrawn into the endoaortic catheter tip in cases of accidental balloon rupture. The final positions of the various catheter and cannulae may be seen in Figure 10.
The patient is then placed on cardiopulmonary bypass and cooled to 26-28°C using a standard membrane oxygenator and roller pump. Venous drainage may be assisted by an additional pump.
Mitral Valve Exposure and Surgery
Using a 0° videoscope, the pericardium is opened using an upside down T-shaped incision placed 1 cm anterior to the phrenic nerve. The left flap is sutured back onto itself while the right flap is sutured to the underside of the soft tissue retractor. The lower edge of the incision is retracted with the aid of stay sutures brought out through the skin in the fifth intercostal space.
The incision with its retraction gives an excellent view of the left and right atria. The endoaortic balloon is then inflated gently under TOE vision. The amount of contrast for filling and the balloon pressure is determined by the aortic root size as previously described. It is important that the root pressure falls to less than 10 mmHg with a cardiopulmonary bypass perfusion pressure of greater than 40 mmHg. The pressures in both radial artery catheters must also be equal to exclude inadvertent balloon inflation at the level of the neck vessels. Diastolic arrest of the heart is then achieved by a single dose of cold crystalloid cardioplegia delivered anterogradely into the aortic root as seen in Figure 11. Once the heart has stopped, the aortic root is vented while at the same time monitoring the root pressure.
The mitral valve is exposed by opening the left atrium just posterior to the intra-atrial groove and anterior to the right pulmonary veins. A cardiotomy sucker is placed in the chamber through the 5-mm CO2 port to evacuate blood from the pulmonary veins for return to the venous reservoir. The blade of the trans-thoracic customised atrial retractor (Figure 12) is attached to the handle and the roof of the left atrium lifted. The mitral valve is now fully exposed with the anterior leaflet hanging free like a curtain. The mitral valve apparatus is inspected and assessed using long-handled single-shafted instruments that minimise visual obstruction of the surgeon. Mitral valve replacement is then performed using standard techniques (Figure 13). In our unit we use interrupted 2/0 Ethibond pledgted sutures with the Teflon pledgets placed on the inflow side. We also preserve the sub-valvular apparatus, demonstrated to result in improved left ventricular haemodynamics.12 Due to the limited surgical incision and distance of the mitral annulus from the chest wall, it is usually necessary to use a knot pusher.
Figure 8: The 10.5-Fr endoaortic catheter that is positioned through an arm of the arterial return line in the femoral artery has three lumens. Lumen A is used for antegrade cardioplegia delivery, aortic root venting and active suctioning during de-airing prior to termination of CPB. Lumen B is used to inflate the balloon and monitor pressure. Lumen C continuously monitors the aortic root pressure via a port distal to the balloon.
The left atriotomy is closed under direct vision with continuous 4/ 0 polypropylene suture. As the surgeon ties the suture, the anaesthetist inflates the left lung to fill the atrium and aid in de-airing the chamber. With the endoclamp balloon still inflated, the aortic root is then placed on active suction to allow thorough de-airing. The TOE probe allows the surgeon to observe the process in the realtime. Once all the air is removed, the balloon is slowly deflated to re-perfuse the heart. During re-perfusion a left atrial catheter is inserted for post-operative fluid management and temporary atrial and ventricular pacemaker wires placed. The function and movement of the prosthetic mitral valve is assessed as the heart recovers. After rewarming the patient is separated from CPB and the arterial and venous cannulae removed after heparin has been reversed with protamine. Haemostasis is secured after which the right lung is inflated and two 30-F chest drains are placed, one through the videoscope port site. The chest, groin and port incisions are then closed in layers. A note is taken of the bypass time and balloon inflation time and the patient transferred to the ITU, ventilated and sedated with a propofol infusion.
Figure 9: The arterial and venous lines are seen in the right groin. The arterial line has a Y-connection that allows the endoaortic catheter to be positioned in the aortic root. The white arrow demonstrates the oxygenated arterial return from the CPB machine through the second arm of the arterial line.
Figure 10: The various lines placed in the heart during the minimally invasive mitral valve replacement approach. The endoaortic balloon catheter is seen threaded up the aorta with its final position in the ascending aortic arch (A). With the balloon inflated cardioplegia is delivered into the coronary arteries through one of the lumens. Venous drainage is through a cannula in the right atrium (B). The endopulmonary vent is positioned in the pulmonary artery after passage through the tricuspid and pulmonary valve (C). For retrograde cardioplegia delivery an additional catheter can be passed into the coronary sinus via the internal jugular vein under TOE control (D). Illustration courtesy of Heartport, Redwood City, CA.
Figure 11: Mid-oesophageal aortic valve long axis view. The balloon inflated in the aortic root shown illustrated within the circle. Cardioplegia is being delivered in anterograde fashion. The aortic valve is seen closed allowing passage of the cardioplegia into the coronary arteries.
Figure 12: The customised atrial retractor. The handle is screwed onto the blade after it is introduced into the chest cavity through a 2mm incision. The blade lifts the roof of the atrium exposing the mitral valve.
Figure 13: Mitral valve replacement using a mechanical valve seen held on a specialised valve holder. Interrupted non-absorbable 2/0 sutures are used to secure the valve. Due to limited access a knot pusher is used.
After transfer to ITU, blood is obtained for arterial gas analysis, clotting studies, haematology and biochemistry. The patient is extubated in ITU once there is no excessive bleeding from the drains, he or she is warm, has a stable haemodynamic status and appropriate level of oxygenation. The drains are usually removed the following day if there is less than 100 mls drainage in the previous 4 hours and there is no air leak. Central venous and arterial monitoring lines are also removed the day following surgery.
Anti-coagulation is commenced at this point to achieve a target INR of 2.5 - 3.5 by discharge. The patient is then gently mobilised with the ward physiotherapist aiming for the patient to climb a flight of stairs by the 3rd to 4th post-operative day. Discharge is typically on day 4 with surgical review planned 6 weeks after surgery.
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Copyright: 12 August 2002
Correspondence: D. Richens, Nottingham City Hospital, Hucknall Road, Nottingham, NG5 1PB, UK