Title: Outcomes of Radial Artery Grafts Without Postoperative Calcium
Channel Blocker Administration
Running Title: Radial Artery Calcium Channel
Zach M. DeBoard, MD1,2, Brian HC Kim,
BS2, James K. Brevig, MD1,2
1. Cardiac & Thoracic Surgery, Providence Regional Medical Center
Everett, Everett, WA
2. Washington State University Elson S. Floyd College of Medicine,
Pullman, WA
Word Count: 2870
Corresponding Author:
Zach M. DeBoard, MD
Cardiac & Thoracic Surgery
1330 Rockefeller Avenue
Suite 400
Everett, WA 98201
Phone: 425-261-4950
Fax: 425-261-4951
Email:
zachary.deboard@providence.org
Sources of Funding & Conflicts of Interest: none
Background: Guidelines encourage oral pharmacologic antispasmodic
therapy for patients receiving a radial artery conduit during coronary
artery bypass grafting. We review our experience with radial artery
conduits without the postoperative use of calcium channel blocker
therapy.
Methods: A single-center, retrospective review patients undergoing
isolated coronary artery bypass grafting with at least one radial artery
conduit over a three-year period was performed. Patient demographic,
operative, and post-discharge data were collected. Development of angina
or angina equivalent symptoms, imaging suggestive of radial conduit
failure, or percutaneous intervention to the territory grafted by a
radial artery was considered to represent graft failure. Patients were
evaluated for primary outcomes through 90 days postoperatively and
followed for 1 year overall.
Results: 264 adult patients underwent first-time, isolated coronary
artery bypass grafting with use of a radial artery conduit. Three
patients were observed to have radial graft occlusions during the first
90 days, all of which were attributed to technical issues. No patients
required addition of a calcium channel blocker & no additional patients
underwent imaging or intervention for radial graft failure during 1 year
of follow up.
Conclusions: Avoidance of postoperative calcium channel blocker therapy
in patients receiving a radial artery graft was not associated with a
high incidence of imaging-confirmed or clinically suggested conduit
failure.
Introduction:
Common approaches to surgical coronary artery revascularization include
using a single arterial conduit (left internal mammary artery) in
addition to the saphenous vein. Multi-arterial grafting has been shown
to improve survival, graft patency, and reduce the need for repeat
revascularization.1-4 Current guidelines for coronary
revascularization encourage a multiple arterial conduit
approach.5
One option for an additional arterial conduit is the radial artery (RA).
Despite the reported benefits of RA conduits there remains modest
adoption of their use.6 One area of concern with RA
conduits is postoperative spasm that can lead to decreased patency.
Preventative maneuvers to limit spasm intraoperatively include topical
application of antispasmodics and vasodilators.7 There
remains debate over the utility of postoperative oral anti-spasmodic
medication administration for RA conduits. Recommendations exist for
oral calcium channel blocking (CCB) agents ranging between 1-3 months
postoperatively in patients receiving a RA conduit.5Nevertheless, additional medications may lend to hypotension, side
effects, or the complications inherent to
polypharmacy.5,8 While reports have suggested there
may be a benefit to patency with postoperative CCB use in patients
receiving a RA conduit, the data is based on a modest cohort of
patients. We present our experience with RA conduits without
postoperative CCB use.
Methods:
The Providence/St. Joseph’s Health System Institutional Review Board
deemed this study exempt. Using the Providence Regional Medical Center
Everett’s electronic medical record (EMR) and our data submitted to the
Society of Thoracic Surgeons all adult (age >18 years)
patients undergoing isolated CABG and receiving at least one RA conduit
between January 1, 2017 and January 1, 2020 were reviewed. Patients were
excluded if they underwent emergency operations, re-operative sternotomy
for CABG, concomitant aortic or valvular procedures, or lacked adequate
follow up of at least 90 days. Ninety days was selected for the primary
evaluation period as most reports of included in the STS recommendations
limit provision of CCBs to this time frame.5
Patient demographics and operative/hospital data including number of
radial arteries used, coronary arteries bypassed, length of stay, and
mortality were reviewed. Discharge medications and outpatient clinic
notes were reviewed to evaluate for the addition of a CCB or nitrate as
well as new cardiac imaging (angiography, echocardiogram, stress test)
for purposes of angina or equivalent symptoms. Any diagnostic imaging
study results pertaining to evaluation of graft patency (angiography,
echocardiogram) were also reviewed. Our EMR facilitated chart review as
it integrates numerous regional hospital and outpatient clinical
throughout our region as well as partner institutions within the
Providence/St. Joseph’s Health System.
Primary outcomes of radial conduit failure over the 90 day follow-up
were determined angiographically if a patient required percutaneous
intervention to either the RA conduit or native coronary distribution
grafted with a RA conduit. Patients with echocardiography or stress
testing revealing ischemia in the territory grafted with a RA conduit
were also considered to have RA graft failure/dysfunction. Initiation of
a CCB or nitrate for angina or new angina equivalent symptoms (dyspnea,
fatigue) was used as a surrogate for angiographically determined graft
failure. Imaging evaluation and percutaneous intervention were evaluated
for 1 year from the date of surgery.
Radial arteries were harvested as a pedicled conduit via an open
technique with ultrasonic shears and/or hemoclips to ligate radial
vessel branches. The artery is further prepared by proximal cannulation
and is then flushed with a solution of 15mg verapamil, 6.8mg
nitroglycerin, 8 mEq sodium bicarbonate, and 1600 units heparin per
liter of lactated ringers. The radial artery is then bathed in the same
solution until it is brought to the field for grafting. End-to-side
anastomoses to the native coronary artery and ascending aorta are
performed using a running 7-0 and 6-0 polypropylene suture for the
distal, and proximal anastomoses, respectively. Sequential anastomoses
were conducted in a side-to-side fashion with running 7-0 polypropylene.
The proximal and distal extents of the parallel veins along the radial
artery pedicle are occluded with hemoclips at the completion of the
anastomoses. Additional cardioplegia is administered via the conduit
upon completion of the distal anastomosis. Trans-sonic flow probe
analyses are conducted after separation from cardiopulmonary bypass.
Results:
496 patients underwent first-time CABG at our institution during the
study period. Of these, 264 patients had at least one radial artery
conduit (53.2% of all first-time CABG performed). Of the 264 patients,
37 had both radial arteries harvested, and 30 had sequential anastomoses
performed. A total of 331 distal anastomoses with radial grafts were
performed. The majority of patients were male and most operations were
performed in the setting of an acute coronary syndrome. Patient
demographic data appears in table 1.
The majority of radial arteries were used to bypass left-sided coronary
lesions. Obtuse marginal vessels were the most commonly bypassed target
(n=132; 39.9% of distal anastomoses) followed the right posterior
descending artery (n=81; 24.5% of distal anastomoses). Radial graft
anastomotic data appears in table 2.
Three patients with preoperative CCB (diltiazem) use were maintained on
the medication postoperatively. Two patients were discharged on a
nitrate (isosorbide) for long-term use in the setting of peripheral
arterial disease. Over the 90-day follow up window, no patients were
initiated on calcium channel blocker or nitrate therapy.
Eighty-three patients (31%) were discharged on dual antiplatelet
therapy (DAPT) of which clopidogrel was the predominant medication in
addition to aspirin. Twenty-one of these patients were on preoperative
DAPT for recent drug eluting stent placement. The remaining patients
were placed on DAPT for poor quality coronary targets. Intra- and
post-operative data appear in Table 3.
Seven patients underwent repeat coronary angiography during the follow
up window. Of these, three were observed to have issues related to the
RA conduit (1.13% of patients, 0.3% of total distal radial graft
anastomoses). One patient within 30 days postoperative had a RA graft
occlusion and two other patients were found to have RA graft occlusions
within the 31-90 day postoperative period. Four internal mammary artery
grafts and three saphenous vein conduits were found to be non-functional
in the angiographic evaluations. No further percutaneous intervention or
echocardiographic evaluation for concern of dysfunctional grafts or
development of angina or equivalent symptoms occurred on any patient
through the 90-day to 1-year post-operative time period.
Angiographically observed RA findings appear in table 4.
The cohort’s 30-day mortality was 0.75% (2/264) and 1-year mortality
was 1.14% (3/264). The 30-day observed-to-expected mortality ratio was
1.05. Causes of in-hospital death included ischemic bowel due to chronic
abdominal visceral arterial disease (postoperative day 27) and acute on
chronic respiratory failure (postoperative day 52). The single out of
hospital mortality was due to respiratory arrest from accidental
overdose of chronic pain medication on postoperative day 56.
Conclusions:
We present a cohort of patients undergoing CABG with RA conduits over a
3-year period. We utilize RA conduits in over 50% of CABG compared to
6-7% at similar programs in the US.6 A category IIa,
level B recommendation by the STS encourages use of a second arterial
conduit for patients undergoing CABG.5 Recent
literature has demonstrated improved survival, reduced need for repeat
revascularization, and fewer major adverse cardiac and cerebrovascular
events (MACCE) in patients receiving an additional arterial graft, of
which the RA is an option.1-4 With regard to the RA,
STS guidelines provide a category IIa, level C recommendation for oral
pharmacologic manipulation (predominantly a CCB)
postoperatively.5 Our group does not prescribe CCBs
postoperatively unless a patient is taking these medications prior to
surgery for pre-existing issues. Many centers however have been
documented to routinely provide CCB therapy.9 The
addition of a CCB may result in patients failing to be up-titrated on
necessary medications such as beta blockers or angiotensin converting
enzyme inhibitors as well as being subject to side effects such as
hypotension, headaches, or flushing.
A recent review of randomized control trials comparing CCB use to no CCB
administration evaluated 732 patients with RA grafts. Angiographic
follow up was available for 443 patients and demonstrated statistically
improved angiographic patency of RA grafts at 36 months for patients
receiving a CCB (99.1% vs. 78.6%).10 Nevertheless,
two of the studies cited in the review failed to demonstrate improved RA
graft patency in patients receiving CCB therapy immediately post CABG,
including those provided CCB therapy for 1 year or
more.11,12 These findings are further supported by the
lack of association with development of an angiographic RA “string
sign” in patients taking CCB or not.13
As routine angiographic evaluation of all patients during a
postoperative time frame is not feasible in our institution we used
addition of a CCB or nitrate as well as angina/angina-equivalent
symptoms and imaging (echocardiography, scintigraphy) suggestive of
ongoing radial-graft territory ischemia as surrogates for
angiographically-determined graft failure. Patients who underwent
angiographic evaluation of or percutaneous coronary intervention to the
coronary artery bypassed with a radial conduit were also reviewed.
During this time, our cohort’s patency rate for radial grafts was 98.8%
of patients. Previous pooled reports of RA patency rates note between
95-100% patency prior to six months and between 87-99% at 6-36
months.14 We consider the failure of our cohort’s RA
conduits to be technical in nature as the lesions were observed at
anastomotic sites and occurred early in the postoperative period.
We believe overall RA patency may be more so influenced by technical and
anatomic factors rather than administration of CCBs postoperatively. We
use an open, pedicled harvest technique employing ultrasonic shears and
striving for minimal conduit manipulation. Gaudino and colleagues
reviewed methods of RA harvest and observed mixed results as to pedicled
versus skeletonized techniques with regards to
patency.15 We also aim use RAs to graft larger targets
and coronaries with significant proximal stenosis
(>80-90%) or those with a chronic total occlusion. Lower
patency of RA grafts to right-sided targets, coronary arteries with
modest lesions, or coronary arteries with poor runoff territory and
heavy disease burden demonstrates the effects of competitive flow and
target selection as contributing factors to poor RA conduit
patency.15-17 In a review by He and Taggart the
authors note that evolution in surgical techniques may be more
contributory to RA graft patency than systemic CCB
use.7
Our group does not routinely prescribe dual antiplatelet therapy (DAPT)
after CABG (31% prescribed DAPT). The majority of DAPT administration
in the current study postoperatively was from a single surgeon. Our
group prescribes postoperative DAPT for patients taking such medications
preoperatively or for heavily diseased coronary targets and modest flow
vein grafts. The effect of DAPT on RA patency remains unknown.
Our study has a variety of limitations. First, the data was
retrospectively collected and does not include a comparison group.
Second, we are unable to obtain universal angiographic evaluation of all
CABG patients with radial conduits at a specific postoperative interval.
Finally, patients may have had angiographic coronary evaluation or
intervention post surgery at another institution not captured by our EMR
review.
In summary our cohort of patients undergoing CABG with RA conduits
without postoperative CCB administration demonstrated expected graft
patency without increased need for intervention or clinical indications
of RA conduit failure over the study period.
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Table 1. Patient Demographics (n=264)