An old-fashioned blood pressure
cuff to the arm protects bypass patients' hearts during
surgery. The technique, which induces transient upper
limb ischemia, is described by a British team in the
August 18 edition of the Lancet.
Coronary artery bypass graft (CABG)
is a common but risky procedure, and ischemia and reperfusion
injuries incurred during revasculatization have been
the focus of intense research. The simple and effective
blood pressure cuff approach could soon become a standard
part of the heart surgeon's CABG protocol, predicts
lead author Dr Derek Hausenloy of London's Hatter Cardiovascular
Institute via email.
DAMAGE
CONTROL
The researchers tested the effects of three five-minute
upper-right arm cuffs inflated to 200mmHG on 27 patients
after anesthesia for CABG surgery.
Serum troponin-t levels were measured
before and up to 72 hours after surgery, in patients
with and controls without the treatment. Indicators
of cardiac necrosis, troponins are released from damaged
myocytes, and their high levels are associated with
adverse outcomes in CABG patients.
A striking difference in troponin-t
levels was revealed: levels were 43% lower over a 72-hour
period in the patients who'd received the remote ischemic
preconditioning (20.58 µg/L versus 36.12 µg/L
in the non-preconditioned patients).
While the effect is clear, how
the inflator cuff protects against tissue death in the
heart remains a mystery. The authors theorize that the
interrupted blood flow in the arm somehow signals the
heart, by either a hormonal or a neuronal mechanism.
GENTLER
APPROACH
The concept of ischemic preconditioning has been around
since the mid-80s. In natural experiments, prodromal
angina seems to predict better survival and reduced
infarct size following MI.
Dr Stephen Fremes, division head
of cardiovascular surgery at Sunnybrook in Toronto,
has done a lot of work in the field and is impressed
by the Lancet study. "There are a number of different
strategies to try and improve myocardial protection,"
says Dr Fremes, "this one preemptively puts the myocardium
in a state so it's resistant to injury."
A big factor that makes the blood
pressure cuff method so attractive is its non-invasive
nature. Dr Fremes says other, more invasive ischemic
preconditioning techniques have been attempted experimentally.
"In early human studies, there's been ischemic preconditioning
with angioplasty balloons, or with cross-clamping of
the coronary artery," he says, "but what they've done
here is remote conditioning, using another 'organ,'
in this case, an arm."
MULTIPLE
USES
"There is no reason why remote preconditioning should
not also protect cerebral and renal functioning post
CABG surgery," says Dr Hausenloy. "In many cases the
injury sustained to these organs arises from acute ischemia-reperfusion
of them. It could also be used in other surgical settings
where ischemia-reperfusion of the organ is sustained
such as hepatic or bowel surgery."
Despite the promising results,
there's a lot left to be learned about remote ischemic
preconditioning. "The study is a green light for another
study in less well-defined patients, and to look at
harder clinical outcomes in addition to troponin-t,
like CKMB levels, and clinical recovery," says Dr Fremes.
That's precisely what Dr Hausenloy's
got in mind. Following on from the current study's success,
a large multicentre trial has been planned. "If it has
a positive effect on clinical outcomes," says Dr Hausenloy,
"then there is no reason why this non-invasive procedure
should not be adopted for all patients undergoing CABG
surgery."
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