To the Editor:
The interesting and timely paper by Cain et al.1, in
press in the Journal of Cardiac Surgery , provides important
details concerning the devastating consequences of Mycobacterium
chimaera (MC ) infection. In their patient extreme fragility of
the mediastinal tissues was observed after repair of an acute aortic
dissection; during follow-up multiple reoperations were required to
treat recurrent dehiscence of the aortic grafts. Despite repeat
explantation of foreign materials infection persisted with mediastinitis
and eventual systemic diffusion with fatal outcome.
MC infection after open cardiac surgery using cardiopulmonary
bypass has been recently reported as a clinical outbreak worldwide and
identified as originating by contaminated water in heater-cooler
units2. Current experience shows that MC causes
a slow-growing and extremely difficult to treat infection with an
incubation period which has been recently demonstrated to be as long as
>12 years3.
We have recently treated a patient, quite similar to that reported by
Cain et al.1, who presented with a pseudoaneurysm of
the distal suture line twelve years after repair of type A aortic
dissection4. At first operation replacement of the
ascending aorta and hemiarch using of a Djumbodis®dissection system (Saint Come-Chirurgie, Marseille, France) was
performed. At reoperation extremely fragile tissues were noted and,
after removing the metallic stent, the aortic arch was replaced with a
frozen elephant trunk technique. Cultures of the excised material grewMC . In this case we hypothesized that the stent played an
important role in the onset of infection for at least 2 reasons:
presence of foreign material in the blood stream and injury to the
aortic wall by the edges of the stent. The case described by Cain et
al.1 also supports our belief that extreme fragility
of the aortic tissues caused by MB was a further important factor
in the occurrence of this complication.
Interestingly, a delayed diagnosis occurred in both cases; this most
likely played a critical role in favouring development of extra‐cardiac
manifestations of the disease, in reducing the effectiveness of
antibiotic therapy due to immunologic impairment and causing a negative
outcome in both patients.
MB infection may have different locations ranging from
single-organ to systemic manifestations5. When it
involves the mediastinum and particularly the major vascular structures
often results in life-threatening complications despite proper
antimycobacterial treatment. An early diagnosis, even with significantly
extended surveillance, appears extremely difficult due to slow-growing
and long incubation period of MB .
Although no specific guidelines are so far available, intra-operative
prevention with improvement of setting and development of heater-cooler
units is mandatory and should be based on specific
recommendations5.