Vasodilator drug effects on internal mammary artery and saphenous vein grafts

The sources of calcium for noradrenaline-induced contraction in the human thoracic internal artery

The aim of the present study was to examine the contribution of intracellular and extracellular calcium sources in contraction caused by noradrenaline (NA) of the human internal thoracic artery (ITA) in vitro. Distal segments of ITA were obtained from 20 patients (aged 38-73, at the time of routine coronary artery surgical revascularization (CABG)). Contractile responses to 10^-6 mol/L NA in the physiological salt solution and in Ca²⁺-free solution without and after incubation with 10^-6 mol/L thapsigargin (TSG) were recorded under isometric conditions. Responses of ITA rings to 1 μM NA without incubation with TSG accounted (% of reaction to 80 mM KCl) 224.70 ± 14.06% in PSS solution, 141.30 ± 8.66% in Ca²⁺-free solution, and 80.03 ± 1.71% after PSS restoration and were statistically significantly different (p < 0.0001, one-way ANOVA). Responses of ITA rings to 1 μM NA with 1 μM TSG accounted (% of reaction to 80 mM KCl) 114.50 ± 2.79% in Ca²⁺-free solution and 36.70 ± 2.38% after PSS restoration. Responses in Ca²⁺-free solution and after PSS restoration without and with TSG were statistically significantly different (p = 0.0257 and p < 0.0001, respectively-t test). ITA contraction is caused by calcium derived not only from the SR and the extracellular matrix. The delivery of calcium to the space surrounding tissue does not immediately deliver calcium to the myofilaments.

Antispastic Management in Arterial Grafts in Coronary Artery Bypass Grafting Surgery

Arterial grafts have long-term patency superior to vein grafts but have a tendency to develop spasm that can lead to potentially life-threatening complications. A perfect antispastic protocol should include advanced surgical technique and adequate pharmacologic methods. All pharmacologic vasodilator drugs relax the vessel through specific mechanisms, and therefore, there is no perfect, single best vasodilator to prevent or treat spasm of the arterial graft against all mechanisms of contraction. One of the choices is to use a combination of pharmacologic vasodilators targeting different mechanisms of spasm to obtain the reliable and best effect.

Potassium induced contraction of the internal thoracic artery in vitro is time related: the potential consequences in the analysis of the mechanism of the spasm after coronary artery bypass grafting and in the analysis of the results of in vitro studies

The aim of the present study was to examine how, under in vitro conditions, the human left internal thoracic artery (LITA) reacts to contractile agonist:potassium chloride (KCL) as a function of time, as well as to examine whether a change in the LITA reactivity can correlate with the occurrence of the refractory vascular spasm (RVS). Distal segments of LITA obtained from 33 patients aged 38–73, at the time of routine coronary artery surgical revascularization (CABG). Contractile response to 80 mmol K⁺ was recorded under isometric conditions. In 16 (48,5 %) LITA segments, contractile reaction to K⁺ after experiments ranging 1–10 h were registered. No contractile response even after 10 h of incubation was observed in 17 (51.5 %) LITA segments. Between 120 and 300 min after the beginning of the experiment, the reaction was maximum and amounted up to 300 % control reaction, then decreased. First, with respect to in vitro research isolated by LITA rings, while analyzing the results of the research, one should take into consideration the possibility that during the research, the functional state of the tissues changes and in particular its sensitivity to depolarization of the cell membrane. Second, the change in the sensitivity to depolarization of the cell membrane of the smooth muscles’ LITA might be the potential mechanism causing the occurrence of the postoperative spasm after the CABG treatment.

Bilateral internal mammary artery grafting: rationale and evidence

Coronary artery bypass graft (CABG) surgery remains the preferred mode of revascularization in patients with complex multi-vessel coronary artery disease. The left internal mammary artery (IMA) and saphenous vein are the most commonly utilized conduits in CABG surgery and are still considered to be the gold standard by most surgeons. However, there is emerging evidence that use of bilateral IMAs is associated with significantly better long-term outcomes and the benefit increases with time from surgery. In spite of this incremental beneficiary effect, most surgeons are reluctant to use both IMAs, because it is technically more demanding, time-consuming and is associated with marginally higher sternal wound infection rates. This review highlights the histological features, physiological characteristics and genomics of IMAs that provide the basis for the use of these vessels during CABG surgery. Additionally, the superiority of the bilateral IMAs with regard to patency and long-term outcomes is also discussed in detail. Furthermore, the safety of using bilateral IMAs with regard to early postoperative outcomes with special reference to deep sternal wound infections has been addressed. The present review provides enough evidence to convince more surgeons about the advantages of bilateral IMA grafting.

Internal thoracic artery: anatomical and biological characteristics revisited

The left internal thoracic artery has become the conduit of choice for coronary artery bypass grafting, due to its superior patency rates at 10 or more years with little or no evidence of atherosclerotic changes. Recent evidence indicates that a second internal thoracic artery graft provides improved results relative to overall survival and major cardiac and cerebrovascular event-free survival, and reduces the need for repeat revascularization. However, the routine use of bilateral internal thoracic arteries is limited due to a perceived higher incidence of deep sternal wound infection. The surgical anatomy, collateral blood supply to the sternum, and biological characteristics of internal thoracic artery conduits are reviewed.

The haemodynamic and metabolic effects of epinephrine in experimental hyperdynamic septic shock

OBJECTIVE

To study the effect of epinephrine (EPI) infusion on vital organ blood flow and metabolic variables during sepsis.

DESIGN AND SETTING

Randomised placebo-controlled animal trial in an animal laboratory.

ANIMALS

Seven merino cross-ewes.

INTERVENTIONS

Chronic implantation of flow probes (aorta, renal, mesenteric and coronary artery and sagittal sinus). Induction of sepsis by intravenous injection of E. coli. Random allocation of sheep to EPI (0.4 microg kg(-1) min(-1)) or vehicle for 6 h.

MEASUREMENTS AND RESULTS

E. coli induced hypotension and hyperlactataemia and increased cardiac output, renal, mesenteric and coronary blood flows. Compared to vehicle, EPI restored mean arterial blood pressure (69 vs. 86 mmHg) and further increased cardiac output (6.4 vs. 7.1 l/min). EPI, however, decreased renal blood flow (330 vs. 247 ml/min) and renal conductance. EPI also reduced mesenteric and coronary conductance without changes in flows. Compared to vehicle, EPI increased urine output (293 vs. 544 ml/6 h) but not creatinine clearance. EPI increased lactate (1.8 vs. 15.7 mmol/l) with accompanying acidosis (serum bicarbonate: 25.2 vs. 15.7 mmol/l), hyperglycaemia (2.6 vs. 13.5 mmol/l) and hypokalaemia (4.3 vs. 3.0 mmol/l).

CONCLUSIONS

Hyperdynamic sepsis increased blood flow to heart, gut and kidney. Although EPI infusion further increased cardiac output, blood pressure and myocardial performance, it was also associated with potent metabolic effects, decreased mesenteric, coronary and renal conductance and a significant reduction in renal blood flow.

The vasodilator effects of clevidipine on human internal mammary artery

Endothelial dysfunction and platelet activation with thromboxane release may contribute to spasm or alterations in internal mammary artery (IMA) graft flow during coronary artery surgery. Clevidipine, an ultrashort-acting dihydropyridine calcium channel blocker, is undergoing clinical development, but there are little data regarding its effects on human vasculature. We investigated the effects of clevidipine on human IMA obtained during surgery. After precontracting IMA segments with an analog of thromboxane (U46619, 10(-8) mol/L), acetylcholine and nitroglycerin were added cumulatively to examine endothelial function. Concentration-response curves to clevidipine were cumulatively obtained during submaximal contraction to the U46619 (10(-8) mol/L) in rings with and without endothelium. In the IMA samples with endothelium, acetylcholine did not completely reverse the U46619-mediated contraction, which implies impaired endothelial function (40% +/- 6% maximal response). Both clevidipine and nitroglycerin completely reversed U46619-induced contraction (clevidipine (50% effective concentration [EC50] = 3.88 +/- 0.84 x 10(-6) mol/L, nitroglycerin EC50 = 4.84 +/- 2.76 x 10(-8) mol/L). The responses to clevidipine were similar in preparations with or without intact endothelium. Clevidipine is an endothelium-independent arterial vasodilator that offers a potential therapeutic option in the treatment of perioperative arterial graft vasospasm and/or hypertension.

IMPLICATIONS

Clevidipine is a new ultrashort-acting dihydropyridine calcium antagonist. In human internal mammary arteries precontracted with a thromboxane A2 analog, clevidipine was an effective vasodilator on vessel segments in the presence and in the absence of endothelium.

Preserved vasodilatory response to nitroglycerin in saphenous vein bypass grafts

BACKGROUND

Uncertainty exists regarding the effects of nitroglycerin on atherosclerotic segments of coronary arteries, and information on vasoreactivity of saphenous vein bypass grafts is sparse. Intravascular ultrasound enables identification of atherosclerosis in angiographically normal segments and allows continuous determination of alterations in cross-sectional lumen areas.

METHODS AND RESULTS

Patients with documented coronary atherosclerosis were studied. Vessel morphology and lumen area at baseline and after 100 to 200 micrograms nitroglycerin were assessed at 10-second intervals for 60 seconds in vessel segments without angiographically apparent lesions. Coronary artery saphenous vein bypass grafts from 11 patients were compared with native coronary arteries in 16 different patients. Atherosclerosis was present in all vessel segments studied. There was a rapid increase in lumen area compared with baseline after intravascular nitroglycerin in both native coronary arteries and saphenous vein bypass grafts. Maximum lumen area dilatation was 19.6 +/- 12.2% in saphenous vein bypass grafts and 19.7 +/- 13.1% in native coronary arteries. An earlier peak response in saphenous vein bypass grafts (34.5 +/- 6.9 seconds) compared with native coronary arteries (44.7 +/- 8.5 seconds; P = .003) was found. Vessel wall area remained constant during vasodilation, but there was a significant reduction in measured wall thickness (P = .034).

CONCLUSIONS

In patients with documented coronary artery disease, intravascular ultrasound reveals substantial atherosclerosis in angiographically normal vessel segments. In these vessel segments, both native coronary arteries and saphenous vein bypass grafts exhibit prompt vasodilation with the intravascular administration of nitroglycerin. The vasodilatory capacity in response to nitroglycerin seems to be preserved in transposed, denervated, and devascularized saphenous veins.

Effects of graded reductions in internal mammary artery bypass flow on left ventricular function

This study investigated the controversial relationship between reduction in internal mammary artery (IMA) graft blood flow and left ventricular function in a canine model. Ten dogs underwent IMA grafting to the left anterior descending coronary artery. The left anterior descending coronary artery proximal to the IMA graft was intermittently occluded while IMA flow was mechanically controlled for 5-minute periods to produce four IMA flow groups representing 100%, 75%, 50%, and 25% of unoccluded IMA graft blood flow. As a control, the left ventricle was reperfused with native left anterior descending coronary artery flow between each IMA graft flow period to allow return to steady state. Sonomicrometry was used to obtain stroke work end-diastolic dimension relationship data for regional and global left ventricular function for each of the four flow groups. The global pressure recruitable work area relationship showed a significant rightward shift at 25% of unoccluded IMA flow, whereas the regional pressure recruitable work area relationship shifted at 50% of unoccluded IMA flow. Thus, regional myocardial function is more sensitive to reductions in IMA blood flow than is global left ventricular performance, and there is a significant IMA flow reserve for global left ventricular function.