Assessment of endothelial modulation of coronary vasomotor tone: insights into a fundamental functional disturbance in vascular biology of atherosclerosis

Structural Thickening of Medial Layer in Coronary Artery With Spasm in Patients With Myocardial Infarction

Background

The underlying pathophysiology of coronary artery spasm (CAS) remains unclear. We aim to determine whether coronary artery medial layer thickness is associated with CAS using optical coherence tomography.

Methods and Results

A total of 50 patients with previous myocardial infarction underwent optical coherence tomography of the left anterior descending artery: 20 with CAS and 30 without CAS. Intimal and medial layer areas were measured by planimetric analysis of optical coherence tomography images. The medial area/external elastic membrane (EEM) area was significantly greater in patients with than without CAS (0.13±0.01 versus 0.09±0.01, respectively, P<0.01), whereas the intimal area/EEM area was similar in the 2 groups. In patients without CAS, the relationship of intimal area/EEM area with medial area/EEM area and coronary diameter response to intracoronary injection of acetylcholine was characterized by an inverted U‐shaped curve (y=−1.85x²+0.81x+0.01, R²=0.43, P<0.001) and a U‐shaped curve (y=2993.2x²−1359.6x+117.1, R²=0.53, P<0.001), respectively. Thus, the medial layer became thin and the contractile response became weak in coronary arteries with greater intimal area in the non‐CAS patients. In contrast, in patients with CAS, the intimal area/EEM area had no significant relationship with the medial area/EEM area in either linear correlation analysis or quadratic regression analysis. Thus, even when the intimal layer thickened, the medial layer did not thin in patients with CAS.

Conclusions

The structural thickness of the coronary medial layer was increased in patients with CAS, which may provide mechanistic insight into the pathogenesis of CAS.

Registration

URL: https://www.upload.umin.ac.jp; Unique identifier: UMIN000018432.

Relationship of a thinned medial layer to the attenuated contractile response in atherosclerotic coronary arteries

Coronary arteries with advanced atherosclerosis do not necessarily have greater contractile responses than those with early atherosclerosis. This study aimed to clarify the relationship between thickness of the medial layer and the contractile response to acetylcholine (ACh) in coronary artery using optical coherence tomography (OCT). The OCT and the vasomotor response to ACh in the left anterior descending coronary artery were assessed in 32 patients with previous myocardial infarction. The intimal and medial layer areas were measured by planimetric analysis of the OCT images. The coronary contractile response to ACh had a positive linear relationship with medial area (r = 0.61, P < 0.001). In contrast, the relationship between the coronary contractile response to ACh and intimal area was described by an inverted U-shaped curve that was fitted to a quadratic regression model (R² = 0.35, P = 0.002, y-axis, contraction; x-axis, intimal area). The contractile response increased as the intimal layer thickened up to the inflection point; thereafter, the contractile response declined. The relationship between medial area and intimal area was also described by an inverted U-shaped curve that was fitted to a quadratic regression model (R² = 0.41, P < 0.01, y-axis, medial area; x-axis, intimal area). The medial area increased as the intimal area thickened up to the inflection point; thereafter, the medial area thinned. In conclusion, the thinned medial layer was associated with the attenuated contractile response in a coronary artery with greater atherosclerosis.NEW & NOTEWORTHY This is the first clinical study to show the relationship between the contractile response and the thickness of medial smooth muscle layer in coronary artery of patients with previous myocardial infarction using OCT. The contractile response to acetylcholine was attenuated, and medial layer area was thinned in coronary artery with greater atherosclerosis compared with those in coronary artery with mild or moderate atherosclerosis. The coronary contractile response was positively correlated with thickness of the medial layer in coronary arteries with either mild or greater atherosclerosis. Thus, coronary arteries with advanced atherosclerosis do not necessarily have greater contractile responses than those with early atherosclerosis, which could be related to the thinned medial layer.

Influence of calcium antagonists on long-term survival of patients treated with coronary angioplasty

A meta-analysis reported that nifedipine increased mortality dose-dependently in patients with coronary artery disease. However, there have been few studies (specifically in Asians) on the long-term prognosis of patients treated with calcium antagonists after successful coronary angioplasty (PTCA). The subjects consisted of 583 consecutive patients (461 males, aged 59 +/- 10), who underwent successful elective PTCA between 1985 and 1990. First, they were divided into two groups; the calcium antagonist (+) group (n = 560) and the calcium antagonist (-) group (n = 23), and were evaluated in terms of total survival and cardiac events. Second, the calcium antagonist (+) group was further divided into 4 groups according to calcium antagonist type, i.e., short-acting nifedipine group (n = 156), long-acting nifedipine group (n = 203), diltiazem group (n = 184) and the other group (n = 17), and these groups were evaluated in the same way. The primary end-point was set as death from any cause. Secondary end-points were any cardiac events, including non-fatal acute myocardial infarction, coronary artery bypass surgery and repeat PTCA. The mean follow-up period was 4.5 +/- 1.8 years. A multivariate analysis was performed with the Cox proportional-hazard model. The Kaplan-Meier analysis showed that the calcium antagonist (-) group had significantly worse prognoses than the calcium antagonist (+) group (p < 0.05), and that there was no significant difference among the prognoses of the four calcium antagonists groups. The multivariate analysis revealed that the use of a calcium antagonist was one of the independent factors positively contributing to the prognosis. The use of any type of calcium antagonist did not increase mortality in patients who underwent successful elective PTCA, rather, it contributed to a favorable outcome.

Enhanced endothelin-B-receptor-mediated vasoconstriction of small porcine coronary arteries in diet-induced hypercholesterolemia

The coronary vasoconstrictor effects of endothelins, mediated by both endothelin ETA and ETB receptors, may be differentially altered in pathophysiological states associated with endothelial dysfunction and elevated endothelin levels. Experimental hypercholesterolemia is associated with coronary endothelial dysfunction and increased circulating endothelin concentrations. These studies were designed to test the hypothesis that experimental hypercholesterolemia is characterized by a differentially altered coronary contractile response to ETA- and ETB-receptor stimulation, in vitro. Pigs were fed either a normal or a high-cholesterol diet for 10 to 13 weeks. Changes in the intraluminal diameter of pressurized small coronary arteries (< 481 +/- 25 microns in diameter) to cumulative concentrations (10(-10) to 10(-6) mol/L) of endothelin-1 (ET-1), and sarafotoxin 6c (S6c), a specific ETB-receptor agonist, were measured using a video dimension analyzer. The maximal contraction attained with ET-1 was greater than with S6c in both normal (86 +/- 7% versus 47 +/- 7%, P = .001) and hypercholesterolemic (77 +/- 6% versus 37 +/- 7%, P < .001) pigs. At 10(-10) mol/L, vessels from hypercholesterolemic pigs manifested greater contraction to both ET-1 (23 +/- 6% versus 8 +/- 3%, P = .02) and S6c (17 +/- 5% versus 4 +/- 2%, P = .02). Incubation of arteries from hypercholesterolemic pigs with BQ-788 (ETB-receptor antagonist), but not FR-139317 (ETA-receptor antagonist), altered the contractile response to ET-1 at 10(-10) mol/L. Removal of the endothelium abolished the difference in response to S6c between normal and hypercholesterolemic pigs. These studies demonstrate that experimental hypercholesterolemia is characterized by enhanced coronary vasoconstriction to endothelins in vitro, the mechanism of which is mediated mainly through the ETB receptor. Thus, the ETB receptor has a role in regulation of coronary artery tone in both the steady-state and pathophysiological states.