Bypass conduit vessel wall biology substantially influences downstream myocardial contractile response to injury from ischemia and reperfusion

Impact of purely internal thoracic artery T-graft technique on the mode and quality of surgical myocardial revascularization evaluated by early postoperative coronary angiography

BACKGROUND

The use of the internal thoracic artery for coronary artery bypass has improved the results of such surgery. However, bypass using only the internal thoracic arteries sometimes requires a T-graft. This purely internal thoracic artery T-graft technique has progressively become part of our surgical protocol for coronary artery bypass surgery.

AIMS

The aim of the study was to analyse the impact of this surgical technique on the degree and quality of coronary revascularization using early postoperative angiography.

METHODS

Between January 2004 and December 2006, 148 patients underwent coronary artery bypass surgery exclusively using both internal thoracic arteries in a T-graft configuration. Systematic postoperative angiography was offered to all 148 patients; it was accepted by 108 patients and refused by 40 patients.

RESULTS

There were no statistically significant differences between the two groups. In-patient mortality was 2.02% (n=3) for the whole population studied, and 1.49% (n=2) for the 134 patients who received only coronary artery bypass grafts. The revascularization rate was 89% and 3.46 coronary anastomoses were constructed per patient (range 2-6). Angiography was performed on 108 right internal thoracic artery to left internal thoracic artery anastomoses, 374 anastomoses of internal thoracic arteries to coronary arteries and 382 inter-anastomosis segments: 98% of the anastomoses and segments were patent.

CONCLUSION

The exclusive recourse to the purely internal thoracic artery T-graft technique meant that it has been possible to dispense with other types of graft while achieving complete and effective revascularization of the coronary artery.

Morphology and histology of human and canine internal thoracic arteries

BACKGROUND

We evaluated human and canine internal thoracic arteries (ITAs) to determine whether the latter is valid for studies relevant to clinical use.

METHODS

We studied 19 human ITAs obtained from 1 female and 14 male victims of recent fatal accidents who had no evidence of cardiovascular disease (mean age = 39+/-19 years; range = 15 to 79 years), and ITAs of 21 randomly-selected mongrel dogs of both sexes, weighing 18-40 kg (average = 24.3+/-5.7 kg). Specimens were fixed in formalin at a controlled pressure of 120 mm Hg, before extensive assessment that included intimal thickening, condition of the internal elastic lamina, and number of medial elastic lamellae and vasa vasorum.

RESULTS

The canine morphology and histology were similar to the human ITAs, but there was no intimal hyperplasia, and the media and adventitia were thinner (ITAs of humans older than 40 years had significant increases in medial thickness, as well as in overall length). Morphologically and histologically, the left and right canine ITAs were almost completely the same.

CONCLUSIONS

Canine ITAs are valid for bilateral comparative studies and are a useful tissue source and model for clinically-relevant experimental studies.

Venous myogenic tone and its regulation through K+ channels depends on chronic intravascular pressure

In this study, we compared the level of myogenic tone and its negative-feedback control through specific K+ channels in two types of human veins (saphenous [SV] and cephalic [CV] veins), which experience different ranges of pressure in vivo. We also investigated whether an experimental model of increased venous pressure in rats exposed to head-up tilt for 2 weeks produced changes similar to those observed in the human veins. Cylindrical vein segments were cannulated, their diameters were measured, and the intraluminal pressure was set at different levels (2 to 30 mm Hg) in vitro. Acetylcholine test showed that during the regular harvesting process 76% of the human SVs exposed for coronary bypass grafts had no functional endothelium. We found significant myogenic tone in the human SV, where the in vivo pressure is high, but it was not present in the human CV, where the in vivo pressure is low. The nonspecific K+ channel antagonist, tetraethylammonium (TEA), decreased the diameter of the human SV but not the CV. Iberiotoxin and 4-aminopyridine, blockers of the Ca(2+)-sensitive (KCa) and voltage-gated K+ (KV) channels, also decreased the diameter of the human SV by 10.2 +/- 4.8% and 19.5 +/- 4.7%, respectively. In the rat SV, significant myogenic tone was found, but TEA had no effect, even after 2 weeks of in vivo pressure increase in the hindlimb by head-up tilt. We conclude that (1) an increased venous myogenic tone correlates with higher chronic intraluminal pressure loads, (2) KCa and KV channels counterregulate the myogenic tone in human, but not in rat, saphenous vein, (3) the counterregulatory effect is more effective at high than at low intraluminal in vitro pressure levels, and (4) its development is probably a long-term process.