Optimizing Internal Mammary Artery Harvest and Preparation

LIMA and spasm

First, accepting the fact that every harvested LIMA undergoes severe spasm shall be a universal admission. A study by Yavuz et al. calculated that the mean blood flow in the LIMA was 60.7 ± 6.0 mL/min before papaverine application.^[2] Post papaverine application in various subgroups, the mean blood flow in those receiving intraluminal papaverine rose to 129.3 mL/min, it was 87.7 mL/min in the subgroup of topical spray while 130.6 mL/min in those receiving periarterial papaverine on transit time flow measurement analysis. Francesco et al. evaluated LIMA topical free flow and intraluminal free flow measurements in a study of over 180 patients and found that standard untreated LIMA flow was roughly 31.6 ± 19.9 mL/min overall study subgroups which increased to 45.4 ± 38.9 mL/min in those treated with papaverine while it was 38.6 ± 25.2 among those treated by glycerylnitrate-verapamil offering statistically significant (P = 0.1) difference.^[3]

Skeletonized versus pedicled IMA harvest

While obvious drawn advantages exist in favor of skeletonized LIMA harvest ranging from longer, lengthy, better skeletal supply to sternum, it is associated with increased time consumption and much more technical expertise in the harvest. In terms of flow measurement, a randomized trial by Puslecki et al. found no statistically significant difference between both subgroups of pedicled versus skeletonized IMA under evaluation in microscopic as well as inflammatory marker changes in both subgroups of IMA.^[4]

However, another prospective study of 357 patients conducted by Deja et al, compared no skeletonized IMA with skeletonized ones and found that free left internal thoracic artery blood flow was 66.3 ± 7.42 mL/min in no skeletonized vessel versus 100.3 ± 14.84 mL/min in skeletonized (P = 0.04).^[5] Furthermore, in a review analysis conducted by Erden et al., analyzing 17 papers providing the best clinical evidence summarized that graft patency was comparable in both the pedicled as well nonpedicled group, offering no statistically significant difference.^[6] Thus, a skeletonized IMA shall be recommended but would not follow a strict dictum of protocol and shall be individualized based on patient and comorbidities as well as a surgeon.

The ideal vasodilator

In a comparative study by Cooper et al., the authors compared normal saline, papaverine, nifedipine, glyceryl trinitrate, and sodium nitroprusside (SNP) agents as treatment for IMA.^[7] Free flow in each subgroup was measured. While saline produced a small increase in flow gain by 10 mL/min (from a median of 23 mL/min to 38 mL/min) (not significant), a significant increase was observed with papaverine, with a flow gain of 18 mL/min (from 25 mL/min to 43 mL/min). Nifedipine and glyceryl trinitrate raised free flow by 48 mL/min (from 23 mL/min to 71 mL/min) and 39 mL/min (from 23 to 62 mL/min), respectively. SNP, on the other hand, increased inflow by 82 mL/min (from 26 to 108 mL/min). Thus, they recommended the use of SNP as an ideal dilator. SNP, being a potent vasodilator, releases Nitric oxide, and induces hypotension in high dosage. With a half-life of only 2 min, it is commonly used to treat hypertensive crises with typical infusion rates ranging from 0.5 to 4 mcg/kg/min, which is then titrated to the desired effect. Typical infusion concentrations for adults are 200 mcg/mL or 400 mcg/mL. Thus, for local administration in IMA harvest, it is considered safe in regulated doses under the anesthetic’s guidance. In a randomized trial conducted by Francesco et al., 100 patients were randomly divided into three subgroups of glyceryl-trinitrate/verapamil (GV) solution group, papaverine group, and normal saline group where dilators were administered intraluminal and flow rates were studied.^[3] While the papaverine subgroup had maximal flow, it did not reach statistical significance when compared to the GV subgroup. However, intraluminal free flow in group GV and papaverine subgroup was higher than the normal saline group (P = 0.004 and 0.001, respectively).

A randomized trial to explore ideal vasodilator was conducted by Battaloglu, et al. comparing four vasodilators, namely, nitro-glycerine, diltiazem, papaverine, and adenosine.^[8] They found no significant differences among the five groups’ pre-treatment flow rates (P = 0.526) or post-treatment flow rates (P =.194). The mean ratio values were 1.74 ± 0.17 with nitro-glycerine, 1.77 ± 0.49 with diltiazem, 1.82 ± 0.59 with papaverine, and 1.57 ± 0.54 with adenosine. Thus, no ideal vasodilator exists. While few studies point to SNP as an ideal agent, most of the studies hail papaverine as the single most common drug to be used as a dilator based on cost, availability, and robust data support.

Intraluminal, topical spray, or injection to adjacent tissue-the ideal delivery

Gowda et al. studied papaverine delivery through topical spray and perivascular injection into LIMA pedicle in forty randomized undergoing coronary revascularizations.^[9] In analyzing data, they found that LIMA flows were identical in both groups before the papaverine application. However, LIMA blood flow after papaverine application in the topically sprayed group was 87.20 ± 13.46 mL/min, while it was 104.7 ± 20.19 mL/min in those who received a perivascular injection of papaverine to LIMA pedicle. It was hypothesized that the perivascular injection of papaverine exposed IMA to prolonged duration to dilator in comparison to spraying. A study conducted by Yorgancioğlu et al. involving 86 patients was divided into two subgroups – one receiving SNP spray while the other subgroup was given perivascular injection of SNP.^[10] Statistically significant differences were noted in flow measurement (P < 0.05) between the two groups, where SNP injection to the pedicle provided a better flow than simple spraying of the same agent. In a similar trial conducted by Dregelid, et al., involving 78 patients undergoing coronary revascularization, intraluminal papaverine solution injection provided a better blood flow rate and distal dilation than mere submersion in papaverine solution but at a considerable risk of mechanical wall injury which was reported in 8 of 52 internal mammary arteries treated with intraluminal papaverine.^[11]

An interesting comparative study was conducted by Bahcivan et al. randomizing 75 patients into three subgroups, namely, group 1 had papaverine injected into the endo thoracic tissue around the internal thoracic artery before dissection, group 2 had papaverine injected into IMA pedicle, and group 3 had intraluminal papaverine injected.^[12] Mean blood flow was 56.3, 21.1, and 20.9 mL/min in groups 1, 2, and 3, respectively. Thus, they proposed that papaverine injected into endo thoracic fascia not only facilitated rapid harvesting by creating a plane of dissection, but it also gave better flow to LIMA. However, the said practice was associated with more episodes of bleeding in multiple studies due to dilatation of IMA branch vessels as well and thus not routinely recommended. Considering the research, perivascular papaverine injection is recommended for optimal and prolonged topical action of vasodilators. While intraluminal injection occasionally yields better results, the associated risk discourages its regular use.^[13-16]

In a recent RCT published by Rezk et al., the authors randomized 100 patients into intrapleural LIMA harvest versus extrapleural IMA harvest to follow up for variation in outcomes in two groups. The study mainly found lesser respiratory complications with better improvement in forced expiratory volume in the first and second sec (FEV1%), forced vital capacity (FVC%), and FEV1/FVC in the extrapleural approach.^[17]