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| Journal of the New Zealand Medical Association,
11-May-2012, Vol 125 No 1354
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Are two internal thoracic artery grafts as safe as
one? Experience from Green Lane Hospital
Arul Baradi, Paget F Milsom, Alan F Merry
The value of coronary artery bypass graft (CABG) surgery in
the treatment of coronary artery disease has been well established over the last
50 years, but few randomised trials have been conducted concerning any of the
variations in this type of surgery.1 The
currently accepted standard (using a single internal thoracic artery graft for
the left anterior descending artery with supplemental vein grafts for bypassing
lesions in other vessels) is based on evidence derived from large observational
studies rather than randomised controlled
trials.2,3 While this strategy provides
excellent short to medium-term results, its long-term success is limited by
progressive vein graft failure.3
There have been no randomised trials comparing SITA to BITA
grafts. However, several large observational studies have compared the two
techniques. Lytle et al conducted a retrospective, non-randomised, long-term
(mean follow-up interval of 10 postoperative years) study of patients undergoing
elective primary isolated coronary artery bypass surgery who received either
single (8123 patients) or bilateral ITA grafts (2001 patients), with or without
additional vein grafts.1
Various statistical methods (including propensity matching)
were used to address the issues of patient selection and heterogeneity. The
study showed better survival (84% vs 79% at 10 years, p <0.001) and
reoperation rates (1% vs 3%, p <0.01) for BITA grafting. Kurlansky et al have
recently published their retrospective 30-year follow-up experience with 4584
patients receiving BITA (2215 patients) or SITA (2369 patients)
grafts.4 They demonstrated a long-term survival
benefit in propensity matched groups receiving BITA grafts (p=0.001).
Early studies regarding the safety of BITA grafting
suggested an increased perioperative risk in patients offered BITA
grafts.5 The major concern was the risk of
sternal wound infection, particularly in obese, diabetic females of advanced
age.5-7 More recent studies have disputed this,
suggesting no increased risk with BITA grafting in diabetic
patients.8 However, many surgeons continue to
reserve BITA grafting for patients with low surgical risk. According to the
Society of Thoracic Surgeons (STS) National Adult Cardiac Surgery Database, only
4% of CABG operations in the USA involve BITA
grafts.9
The objective of this study on primary isolated coronary
artery bypass surgery was to compare short-term mortality and major morbidity
between patients undergoing primary CABG with BITA or SITA grafts at our
institution.
MethodsThis was a retrospective observational study. Ethics
approval was provided by the Northern Ethics Regional Committee.
Table 1. Outcomes assessed and included in our
composite endpoint
We identified all 8004 patients who underwent coronary
artery bypass graft surgery involving either single or bilateral internal
thoracic artery grafts (with or without additional vein / radial artery grafts)
by the Green Lane Cardiothoracic Surgical Unit between 1990 and 2004. 1412
patients who had emergency surgery, concurrent valvular surgery or redo-cardiac
surgery were excluded from the study. We made no distinction in our analyses
between patients who received pedicled or skeletonized grafts.
Data were collected from the Green Lane Cardiothoracic
Surgical Database (which records patient information based on hospital records,
catheterization, echocardiography and operative reports, including follow up
information following discharge regarding mortality and readmission to hospital
within the first 30 days of operation).
Patients receiving BITA grafts (637 patients) were
case-matched with patients of similar surgical risk receiving SITA grafts (total
5955 patients). Patients were matched for major risk factors known to
significantly affect surgical risk and the risk of
mediastinitis11 in particular (see Table 2). To
avoid confounding due to operator selection bias, experience of the operating
surgeon was also matched. Conditional logistic regression models were used to
estimate the odds ratios for different outcome measures between patients
receiving BITA grafts relative to patients receiving SITA grafts.
Table 2. Matching criteria
ResultsWe found 6592 patients who met our inclusion criteria, 637
with BITA grafts and 5955 with SITA grafts. After case-matching, the groups for
further analysis were well balanced (Table 3):
Table 3. Baseline data
There was no significant difference in our composite primary
endpoint between patients receiving BITA grafts and those receiving SITA grafts
[odds ratio 0.84 (95% CI 0.59, 1.21)], nor in any of the component outcomes
(Table 4).
Table 4. Outcome data
*all p-values > 0.1.
DiscussionIn our patients, there was no statistically significant
difference in the risk of death or in specified major morbidities in the
short-term between patients receiving BITA versus SITA grafts [odds ratio 0.84
(95% CI 0.59, 1.21)]. In particular, there was no difference in rates of
reoperation for sternal wound complications [odds ratio 1.00 (0.29,
3.44)].
Our findings are consistent with published data regarding
the perioperative risks of BITA grafting. The systemic review conducted by
Taggart et al.12 revealed an operative
mortality with BITA grafting of 1%-2%, which was no higher than the operative
mortality associated with SITA grafting.
Other studies have shown that risks of sternal wound
complications are minimal in the absence of factors which increase the risk of
sternal wound morbidity (diabetes, morbid obesity, female gender, respiratory
impairment).11,13-14
Although our study did not distinguish between pedicled and
skeletonized techniques of ITA harvesting, there is evidence that harvesting of
the ITA using the skeletonized rather than pedicled technique further diminishes
the risk of sternal wound
complications.15
Our study’s primary limitation is that it is
retrospective, with the inherent potential for selection bias. This is also a
limitation of previous research on the topic, including the large observational
study conducted by Lytle et al.1 No prospective
randomized controlled trials comparing the clinical outcomes of BITA to SITA
grafting have yet been published.
The Arterial Resvascularization Trial (ART) is a large
randomized controlled trial designed to provide a definitive comparison of the
two techniques that has recently completed recruitment of
patients.16 However, 10-year follow up data
from this study will be available only in 2017 (the authors of the ART trial
have stated an aim to publish preliminary 5-year data in 2012).
Evidence-based medicine implies making clinical decisions
for each patient on the basis of the best evidence currently available, and
until the results of ART become available surgical decisions regarding BITA
versus SITA grafting will necessarily be informed by observational evidence
alone.17 Our data demonstrate that surgeons in
our unit have been able to utilise BITA grafts in selected patients without
increased risk of perioperative adverse outcomes, including sternal wound
complications. Given the suspected long-term clinical benefit of BITA grafting
over SITA grafting, we would recommend increased utilization of BITA grafting in
selected patients.
Competing interests: None
declared.
Author information: Arul Baradi, Medical
Registrar, Department of General Medicine, Auckland City Hospital, Auckland;
Paget F. Milsom, Clinical Director, Cardiothoracic Surgical Unit, Auckland City
Hospital; Alan F. Merry, Professor of Anaesthesiology, University of Auckland
and Specialist Anaesthetist, Auckland City Hospital
Acknowledgements: We thank Irene Zheng and
Mildred Lee (Biostatisticians, Auckland City Hospital) for their assistance.
Correspondence: Professor Alan F. Merry,
Head of Department, Anaesthesiology, University of Auckland, Private Bag 92019,
Auckland, New Zealand. Tel: +64(9) 3737599 ext 89301; Fax: +64(9) 3737970;
email: a.merry@auckland.ac.nz
References:
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