ECMO and coronary artery bypass grafting
Post-cardiotomy cardiogenic shock (PCCS) has an incidence of 2-6% in
patients undergoing cardiac surgery and of these, an estimated 0.5-1%
are refractory to maximal-dose inotropic support and IABP
support4-6. Refractory PCCS rapidly leads to
multi-organ failure and has an almost 100% mortality rate which makes
it fatal without the use of MCS using devices such as VA-ECMO; thus,
there is a clinical indication for its use in this cohort.
A range of retrospective studies have looked at outcomes including
survival to weaning from ECMO and survival to hospital discharge for
patients who have undergone cardiac surgery, but only a few of these
have looked at outcomes in patients who underwent coronary artery bypass
graft (CABG) surgery specifically6, 9-11. The largest
cohort of these studies analysed outcomes and survival in 517 patients
treated with ECMO for PCCS, of which 37% had undergone isolated CABG
and 16.8% CABG in combination with valve surgery6.
The study results showed that undergoing isolated CABG was associated
with better survival, with an in-hospital mortality rate of 44% which
was better when compared to that of other cardiac procedures (95%
Confidence Interval (CI) 0.29-0.68; P< 0.001). A similar
association was shown in another study looking at 31 patients (28% of
total cohort) who were treated with ECMO following isolated CABG which
demonstrated that undergoing isolated CABG was associated with improved
in-hospital mortality on EMCO when compared to other cardiac procedures
(41.3% vs 18.8%)9.
By contrast, a 2010 retrospective study looking at 233 patients who had
undergone cardiac surgery and required ECMO post-operatively over an
11-year period, reported an increased hospital mortality which was
associated with having undergone isolated CABG (P= 0.0015), among
other factors10. This was also demonstrated in another
retrospective study involving analysis of outcomes for 101 patients who
received central VA-ECMO at a single centre over an 8-year period which
reported the survival rate for isolated CABG as 17.2%, a figure lower
than the overall survival rate of 27.7% at 1-year follow-up and is
lower than survival rates reported in similar
studies11. Additionally, patients requiring VA-ECMO
following isolated CABG had a significantly increased mortality risk
(Odds Ratio (OR) 3.23; 95% CI 1.1-9.4; P=0.021) compared to patients
who did not undergo coronary surgery. Outcomes in ECMO following CABG
from the included studies are summarised in Table 3.
Whilst there is no consensus on outcomes for patients requiring ECMO
following isolated CABG, the aforementioned studies all demonstrated
that in patients who had undergone CABG in combination with another
cardiac procedure, namely valve surgery, was associated with a decreased
survival rate with some studies quoting survival rates as low as
12.5%6,9-11.
Given that mortality rates for refractory PCCS without ECMO are almost
always 100% this demonstrated the survival benefit of ECMO in post-CABG
patients even though reported survival rates are variable. None of the
studies included looked at the effect of differing ECMO initiation times
on mortality and morbidity rates making it difficult to ascertain the
best timing for starting ECMO for patients undergoing CABG surgery. In
the studies which reported survival rates greater 40%, ECMO was
instituted either intra-operatively during the primary cardiac procedure
or within 24 hours following surgery6, 9. Whilst in
studies that reported lower survival rates, there was no standardisation
for when ECMO was instituted with ECMO being used as late as after the
sixth post-operative day or data for when ECMO was instituted was
missing completely. This would seem to suggest that ECMO should be given
within the first 24 hours to maximise the survival benefit, though more
research analysing the effect of when to start ECMO is required going
forward.