INTRODUCTION
To avoid a high risk redo sternotomy in patients
undergoing mitral valve surgery with patent bypass grafts, an
alternative is the right thoracotomy with moderate-deep hypothermia and
fibrillatory arrest without aortic cross-clamping. This technique has
been reported as safe and effective [1-5] and was therefore
successfully used in our case report in order to avoid injuring a very
dilated patent saphenous vein graft to the left anterior descending
artery.
CASE REPORT
We report a case of a 61-year-old woman with worsening dyspnea and
history of an ALCAPA (Anomalous Left Coronary Artery from Pulmonary
Artery) syndrome having undergone coronary artery bypass grafting
(saphenous venous graft to left anterior descending artery) 30 years
before. Transesophageal echocardiography revealed severe mitral
regurgitation due to prolapse of both very thickened leaflets. Coronary
angiography showed patency of the graft responsible for the perfusion of
the left anterior descending and circumflex arteries. (Figure 1). Even
though not mandatory in planning such cases but useful to potentially
prevent procedural complications, computed tomography revealed a dilated
vein running across the front of the ascending aorta (Figure 2). In
order to avoid injuring the graft, we performed the mitral valve
replacement (MVR) through a right minithoracotomy approach under
ventricular fibrillation (VF) without aortic cross clamping.
Informed consent was obtained from the patient for the procedure and for
future publication of the case report.
SURGICAL TECHNIQUE
A double lumen endotracheal tube was used for intubation and
transesophageal echocardiography was placed for cardiac monitoring. The
chest was opened through a right minithoracotomy (skin incision ≤ 7 cm)
under one lung ventilation at the 4th anterolateral intercostal space.
The endoscopic port was placed at the right 3rd anterior intercostal
space and used as a CO2 port. Cardiopulmonary bypass was
instituted through peripheral cannulation (right femoral artery and
vein) using vacuum-assisted venous drainage. A 20mm diameter arterial
cannula was used to ensure a mean blood pressure of 70mmHg. After
cooling to 22°C in order to induce VF, a left atriotomy between the
phrenic nerve and pulmonary veins was performed. MVR was performed in
standard fashion using instruments for minimally invasive mitral
surgery. After a prosthetic biologic St Jude #33
valve was sewn into place (Figure 2), the left atriotomy was closed with
slow filling and de-airing. When rewarming was completed, cardioversion
was performed. After recovery to sinus rhythm, cardiopulmonary bypass
was terminated and the femoral cannulas removed. A right pleural chest
tube was positioned, and the incision was closed. Fibrillation time,
cardiopulmonary bypass time and total operation time were 37, 59, and 83
minutes, respectively.
No intraoperative complications were registered. The patient had good
in-hospital progression and discharge on postoperative day seven.
DISCUSSION
Conventional re-operative MVR by median sternotomy has several
challenges as it requires dissection to the apex, aortic clamp and
myocardial protection. [1-2] In the presence of adhesions, this
approach carries increased risk of injury of major cardiac structures
(right ventricle, innominate vein and bypassed grafts). [1-2] This
case revealed a very dilated vein running close to the sternum and
across the front of the ascending aorta. (Figure 1) These anatomical
proximities and the fact that this graft is responsible for the
perfusion of all left coronary territory, are high predictive factors of
surgical risk and mortality in a re-sternotomy.
Minimally invasive mitral surgery is associated with a mortality rate
similar to that for sternotomy but reduced length of intensive care unit
and hospital stays, fewer blood transfusions, earlier recovery of daily
activities, and improved quality of life and a comparable risk of
stroke. [1-3] The right minithoracotomy approach can achieve an
excellent operative view of the mitral valve without requiring
dissection of adhesions and has demonstrated to be safe and with similar
results to re-sternotomy. [1-2] By performing the procedure under VF
with systemic hypothermia, aortic cross-clamping and interruption of the
graft flow is unnecessary, not necessarily compromising myocardial
protection, thus, avoiding dangerous dissection around the aorta and the
dilated patent graft. [1-2] Even though myocardial protection can
still be a concern to surgeons, by ensuring hypothermia and a mean
arterial pressure of 70mmHg, safety of MVR under VF is assured, as it
has been documented in cases of functioning grafts. [4] Aortic
insufficiency can make this technique unfeasible because of retrograde
flow obstructing the operative field and inefficient prevention of air
embolism. With a competent aortic valve and by keeping the left heart
empty and vented to the atmosphere, blood in the left ventricle is
preferentially expelled across the mitral valve because atmospheric
pressure is much lower than the aortic root pressure and thus air emboli
are avoided. Additionally, further actions such as Trendelenburg
(head-down tilt) positioning of the patient, CO2insufflation and careful deairing procedures throughout surgery until
the termination of cardiopulmonary bypass were implemented to avoid air
emboli.
Another well reported alternative, that can also be used when there is
absence of aortic insufficiency is beating heart normothermic mitral
valve surgery. This technique has also been demonstrated to be an
effective and safe alternative to prevent aortic manipulation. [5]
When compared to the technique under VF, it has the advantage that it
can be performed under normothermia and it can be speculated that it
provides lower cardiac injury due to constant coronary perfusion.
Nevertheless, in this case, by cooling to 22ºC and ensuring a constant
mean arterial pressure of at least 70mmHg we assured suitable myocardial
protection and simultaneously facilitated surgical technique and
consequently reduced surgical time, as surgery under VF seems to be less
challenging than under a beating heart.
Current knowledge and the success of our case suggest that reoperative
MVR under VF without aorta cross clamping through a right
minithoracotomy is a safe, reproducible and effective option for
patients requiring redo mitral valve surgery, especially when presenting
anatomical characteristics that increase the risk of re-sternotomy such
as coronary bypass grafts.