Keywords
aneurysm - thoracic aorta - left heart bypass - aortic valve insufficiency - airway
obstruction - aortic valve replacement
Introduction
Compression of the left main bronchus is an uncommon complication of large aneurysms
of the descending thoracic aorta (DTA). It requires urgent intervention and carries
a risk of perioperative mortality. When concomitant aortic valvular pathology exists,
urgent repair of both lesions presents a surgical challenge. Both the staging and
timing of operation are crucial to achieving a successful outcome. We present a case
of surgical aortic valve pathology coexistent with a DTA aneurysm complicated by left
main bronchus compression. This report outlines a safe and effective method of managing
the simultaneous conditions.
Case Presentation
A 52-year-old man presented to the general practitioner with 6-month history of atypical
chest pain associated with dyspnea, hoarseness, and weight loss. On examination, the
patient had stridor and was immediately referred to the acute medical unit. Computed
tomography (CT) of his thorax showed a 6.5- × 4.5-cm DTA aneurysm effacing the proximal
left main bronchus ([Fig. 1]). A CT aortogram confirmed an anterior saccular aneurysm of the DTA with a maximum
caliber of 5.6 cm, along with left main bronchus compression ([Fig. 2]). There was no evidence of dissection or contrast leak. The patient was referred
to our unit for urgent surgery.
Fig. 1 Transverse section of a contrast-enhanced computed tomography scan demonstrating
compression of the left main bronchus measuring 2.4 mm at its narrowest.
Fig. 2 Sagittal section of a contrast-enhanced computed tomography depicting an anterior
saccular aneurysm of the descending thoracic aorta with a maximum caliber of 56 mm.
On admission, a preoperative transthoracic echocardiogram revealed severe aortic regurgitation
with tricuspid leaflets alongside moderate left ventricular (LV) dysfunction with
an ejection fraction (EF) of 40%. His coronary angiogram was satisfactory with no
flow limiting lesions; however, it demonstrated a right coronary artery (RCA) dominant
system and a very short left main stem (LMS). Pulmonary function tests confirmed an
obstructive defect (forced expiratory volume in 1 second [FEV1] 47% predicted, forced vital capacity [FVC] 66% predicted, FEV1/FVC 75%). His past
medical history was significant for previously undiagnosed hypertension, empiric inhalers
for symptomatic relief of dyspnea which were ineffective, and recent smoking cessation
after a 15 pack year history.
The patient was taken to theater the day following admission for a planned mechanical
aortic valve replacement (AVR) through a superior hemisternotomy followed by DTA repair
through a left thoracotomy. Prior to sternotomy and heparinization for cardiopulmonary
bypass, a spinal drain was inserted to reduce the risk of paraplegia during the anticipated
second-stage DTA surgery. The patient was systemically cooled to 34°C and antegrade
cold (4°C) blood cardioplegia was administered every 20 minutes. Cardioplegia was
initially administered into the aortic root. However, severe AV regurgitation rendered
this method inefficient; hence, it was later selectively administered into the left
coronary artery and RCA ostia. Notably, the short LMS may have resulted in differential
delivery down either the left anterior descending or left circumflex arteries. Owing
to minimal access, it was not possible to administer retrograde cardioplegia.
Intraoperative findings suggested vasculitic changes including a blood-stained pericardial
effusion with vascular adhesions and a thickened edematous ascending aortic wall.
Intraoperative transesophageal echocardiogram showed global LV dysfunction with an
EF of 30%.
The patient initially failed to come off bypass, so a second run of bypass was required
to rest the myocardium and allow longer reperfusion as well as optimization of inotropic
drugs and insertion of a pulmonary artery catheter. He was eventually weaned off bypass
on moderately high inotropic and vasoconstrictor support (cardiopulmonary bypass time
145 minutes, aortic cross clamp time 108 minutes). Prolonged cross-clamp time was
a result of limited access to the AV due to a small incision and a thickened aortic
wall. The decision was made to delay his DTA repair until his LV function returned
to his preoperative state and he was therefore transferred to the postoperative critical
care unit.
On day 2 following AVR, a transesophageal echocardiogram showed recovery of LV function
and the patient was taken back to theater for his second operation. Access was gained
through a left fifth intercostal space thoracotomy, and he was put on left heart bypass
(LHB) with one-lung ventilation to maintain distal aortic perfusion. The aneurysm
was replaced with a rifampicin-impregnated 22-mm Dacron tube graft leaving the native
aneurysm tissue adherent to the left main bronchus as a buttress. Motor evoked potentials
were maintained throughout.
The remainder of his postoperative course was uneventful, and the patient was discharged
home on postoperative day 7. At 6 weeks follow-up, he remains well.
Discussion
Open repair is the procedure of choice for DTA aneurysms in young patients. This is
best achieved using LHB to avoid pulmonary complications of full cardiopulmonary bypass,
especially in the setting of left main bronchus compression and lung atelectasis.
The complexity of this case arises from the fact that the patient had both left main
bronchus compression necessitating urgent intervention on the DTA alongside concomitant
severe aortic valvular regurgitation and LV dysfunction precluding LHB. Management
options included a single-stage approach through a left hemi-clam shell incision,
an immediate staged approach, a delayed staged approach, or a hybrid procedure.
A hemi-clam shell incision provides excellent exposure of the DTA and aortic valve,
permitting a single-stage operation for concomitant DTA and cardiac lesions.[1] However, it is a major incision associated with prolonged and debilitating recovery.
A single-stage repair requires full cardiopulmonary bypass and carries a significant
risk of respiratory complications with prolonged mechanical ventilation and tracheostomy.
In the setting of an atelectatic, potentially infected lung, LHB is more desirable
in view of superior respiratory outcomes.
Although a hybrid approach with thoracic endovascular aortic repair may reduce surgical
morbidity, it risks complete bronchial obstruction by increasing the pressure within
the aneurysmal sac; prevention of this would require a left main bronchus stent that
can be further complicated by the formation of an aortobronchial fistula.[2] Furthermore, surgery is preferable in young patients due to better long-term outcomes.
A staged operation is preferable to a single-stage clamshell incision due to lower
risk of complications. A delayed staged approach is associated with high cumulative
mortality, alongside risk of death from pulmonary complications in the interval between.
In light of the clinical urgency of the situation, this patient was consented for
an immediate staged repair through a superior hemisternotomy and lateral thoracotomy.
DTA repair is done under LHB to minimize the risk of spinal cord ischemia by maintaining
distal aortic perfusion to the intercostal arteries. However, it requires adequate
LV function alongside a competent aortic valve. Therefore, the AVR had to be done
prior to the DTA repair. Aortic cross-clamping against a pumping LV in LHB results
in sudden-onset hypertension proximally and afterload mismatch; in this case, it would
have caused deterioration of the already impaired LV.[3]
The patient had a significant reduction in LV function intraoperatively following
AVR; thus, the decision to proceed immediately with the DTA operation was deemed inappropriate.
Prolonging the operation, anesthesia, and cross-clamp time to complete the DTA repair
would have significantly increased the risks of intraoperative morbidity and mortality.[4]
This case demonstrates that open surgery can be safely performed as a delayed staged
procedure with a short interval for concurrent aortic valve and DTA pathology. In
a noncompetent aortic valve, AVR must be done prior to aneurysm repair of the thoracic
aorta. Based on this case, implications may also be made for immediate staged repair
providing the LV function is adequate.
