Discussion
In this study we report an overall incidence of perioperative stroke of
1.99% in a large cohort of contemporary patients undergoing the breadth
of adult cardiac surgery. A diagnosis of stroke had a significant impact
on outcomes. Patients required prolonged hospital stays, experienced
greater complications and experienced a 3-fold higher in-hospital
mortality compared with matched controls. The 1-year survival was almost
28% lower.
The incidence of stroke varies significantly depending on the nature of
the surgery, being most prevalent following major aortic surgery
(8.14%) and lowest following isolated CABG (0.85%). The high
prevalence following aortic surgery likely reflects the significant
aortic manipulation that occurs and possible manipulation of the
proximal carotid arteries leading to embolization of atherosclerotic
material. It is also important to highlight that 55.7% of these
patients had undergone emergency repair of type A aortic dissection.
Other studies have also identified this association with aortic
surgery7, and they also note higher incidence
following double procedures, presumably related to longer CPB times and
greater likelihood of atherosclerotic embolisation. In some centres,
epi-aortic scanning is performed to assess the ascending aorta prior to
cannulation. This is not currently available at our centre but may
facilitate reduced intraoperative embolisation. It is notable that the
incidence of stroke following thoracic surgery at our centre over the
same period was only 0.2%, highlighting that patients undergoing
cardiac surgery are at a substantially greater risk, presumably related
to factors specific to cardiac surgery and cardiopulmonary bypass.
In our series, over ¾ of the strokes were early, detected on waking from
anaesthesia – likely reflecting an intra-operative event. In keeping
with this, the vast majority of strokes were ischaemic. A meta-analysis
reported almost equal incidence of early and delayed stroke across a
large number of studies2. Many of the included studies
were from the early 2000’s and our lower proportion of delayed strokes
– which are thought to be related to pre-existing cerebrovascular
disease (chronic small vessel disease and carotid atherosclerosis) and
atrial fibrillation3, may reflect better pre-operative
assessment and optimisation and improved anaesthetic management in the
modern era leading to lower risk of stroke despite operating on higher
risk patients8.
As could be expected, risk factors for atherosclerotic disease were
prevalent in our population of patients experiencing stroke including
diabetes, smoking history, peripheral vascular disease and end stage
renal impairment. We performed propensity matching in order to compare
these patients to similar individuals undergoing similar procedures
rather than comparing to the entire cohort as most other studies have.
In terms of the atherosclerotic risk factors, there were no significant
differences between those patients going on to experience a stroke,
likely reflecting the similar pathophysiology for their cardiac disease
and predisposition to stroke, making it challenging to use these factors
to predict preoperatively patients at risk of developing stroke,
although some have attempted to create risk scores. The relatively small
number of patients in our study provided insufficient power to generate
a scoring system from our data. The notable difference between the
groups was that there was a significantly higher prevalence of previous
TIA in the patients going on to experience a stroke. Interestingly, the
authors of the meta-analysis discussed above, performed a
meta-regression and identified previous neurological event as being the
only factor significantly associated with development of perioperative
stroke2.
Carotid atherosclerosis is thought to be an important risk factor for
perioperative stroke. However, there has been much debate on routine use
of carotid doppler to diagnose significant carotid stenosis
preoperatively, and this is not currently routinely used at our centre,
although is used in selected cases. The prevalence of significant
carotid stenosis in unselected patients is found to be low, and the
incidence of stroke in patients with severe carotid stenosis is found to
be too low to warrant widespread screening and is not recommended by
current guidelines9-12. Some suggest selective
screening (for example, patients >70 years with previous
TIA/stroke) may be useful as there is some evidence that severe carotid
stenosis is a significant predictor for perioperative stroke following
cardiac surgery in these patients13. It is notable
that even in studies describing preoperative carotid screening there is
a low rate of carotid intervention even when severe stenoses are
detected. The options include pre- or simultaneous carotid
endarterectomy or carotid artery stenting. However, knowledge of carotid
atherosclerosis is useful as it can lead to interventions to attempt to
reduce the incidence of cerebrovascular ischemia, for example by
ensuring high pressures and pulsatility whilst on CPB.
The reason for interest in identifying patients at risk preoperatively
is reinforced by examining patient outcomes following stroke. In our
patients, there was significant prolongation of ICU and hospital length
of stay and patients experienced much greater incidence of common
complications including AKI and respiratory tract infections. The
in-hospital mortality was 3-times higher than the matched controlled
patients, at 17.0%, and significantly inferior longer-term survival was
observed. It is worth emphasising that even when the significant early
mortality is excluded, by imposing 30-day conditional survival, the
survival of patients who suffered a stroke remains significantly
inferior highlighting that the impact of stroke on mortality is not
simply in the early phase but persists long-term. In addition to the
financial burden placed on our institution, it is notable that 59.4% of
these patients were transferred to their local hospital for ongoing
stroke rehabilitation. It is also worth highlighting that the ICU and
hospital stays refer to duration at our centre, and not the full
inpatient stay which would be even greater considering the number being
transferred. These outcomes are similar to other series reporting on
patients following perioperative stroke. The 1- and 3-year survival rate
from the meta-analysis were 80.2% and 73.0%
respectively2. Our rates were significantly lower at
61.5% and 53.8%. We believe that this reflects the increase in older
patients with more comorbidities undergoing cardiac surgery. Indeed, our
matched cohort had survival rates of 89.4% and 86.1% which are
significantly inferior to those presented in the meta-analysis of 99.5
and 99.2%.
The challenge of managing perioperative stroke has in part been due to
the limited treatment options traditionally available, since
thrombolysis is contraindicated in this population. There only option
has been to administer high-dose anti-platelet medication and refer the
patient for stroke rehabilitation. Recently though, mechanical
thrombectomy has emerged as an important development in stroke
management. Mechanical retrieval of thromboemboli from the cerebral
arteries by neurointerventional radiology has been demonstrated to
result in significantly greater neurological recovery in selected
patients14,15. This is not contraindicated in surgical
patients and there are now many reports of early postoperative patients
undergoing mechanical thrombectomy with good clinical outcomes both in
cardiac surgery and other surgical specialties16-18.
Mechanical thrombectomy may offer cardiac surgical patients experiencing
perioperative stroke an opportunity to achieve much greater neurological
recovery than has been observed in the past.