Emerging importance of alpha-adrenergic coronary vasoconstriction in acute coronary syndromes and its genetic background

Reprint of: the paradox of α-adrenergic coronary vasoconstriction revisited

Activation of coronary vascular α-adrenoceptors results in vasoconstriction which competes with metabolic vasodilation during sympathetic activation. Epicardial conduit vessel constriction is largely mediated by α(1)-adrenoceptors; the constriction of the resistive microcirculation largely by α(2)-adrenoceptors, but also by α(1)-adrenoceptors. There is no firm evidence that α-adrenergic coronary vasoconstriction exerts a beneficial effect on transmural blood flow distribution. In fact, α-blockade in anesthetized and conscious dogs improves blood flow to all transmural layers, during normoperfusion and hypoperfusion. Also, in patients with coronary artery disease, blockade of α(1)- and α(2)-adrenoceptors improves coronary blood flow, myocardial function and metabolism. This article is part of a Special Issue entitled "Coronary Blood Flow".

Handgrip-enhanced myocardial fractional flow reserve for assessment of coronary artery stenoses

BACKGROUND

Fractional flow reserve (FFR) may yield false-negative results in up to 12% of lesions tested, and there is a zone of uncertainty at borderline values.

METHODS

Forty-eight patients were investigated by means of dobutamine stress echocardiography (DSE), coronary angiography, and FFR assessment of 48 coronary lesions before, during, and immediately after handgrip exercise.

RESULTS

Mean FFR values were lower during and immediately after handgrip exercise as compared with baseline (0.86 +/- 0.09 vs 0.87 +/- 0.08 vs 0.88 +/- 0.08, P < .05, respectively). The sensitivity of FFR < or = 0.75 for predicting myocardial ischemia on DSE was 17.6% before handgrip exercise, 52.9% during, and 35.5% immediately after exercise. The specificity of FFR < or = 0.75 before, during, and immediate after exercise was 100%, 93.5%, and 96.8%, respectively. In 10 patients, FFR values > 0.75 before handgrip became < or = 0.75 during or immediately after handgrip exercise (P = .01). All these patients had angina and/or DSE indicating ischemia in the territory of the vessel studied, and underwent coronary intervention. At 6 months follow-up, all patients were asymptomatic with negative DSE tests.

CONCLUSIONS

The addition of handgrip exercise can significantly lower the FFR and potentially improve its ability to detect physiologically significant stenoses.

Relevance of the NOS3 T–786C and G894T variants for cholinergic and adrenergic coronary vasomotor responses in man

OBJECTIVE

We investigated the impact of the -786C allele at the promoter and the 894T allele in exon 7 of the gene encoding the endothelial nitric oxide synthase (NOS3) on coronary vasomotor responses to exogenous and endogenous stimuli.

METHODS

In 47 individuals undergoing coronary angiography for chest pain, but without significant stenosis in the left anterior descending artery (LAD), nitroglycerine and acetylcholine were infused intracoronarily, and a cold pressor test (CPT) was performed. Coronary blood flow (CBF) in the LAD was calculated from quantitative coronary angiography and intracoronary Doppler measurements. Aortic and coronary sinus lactate levels were determined in 18 individuals. To analyze the impact of NOS3 genotypes, a logistic regression model was used.

RESULTS

In response to acetylcholine (p = 0.002) and CPT (p = 0.015) CBF reduction was associated with homocygosity for the -786C allele. Myocardial lactate uptake was reversed into net lactate production in CC homocygotes. No independent effects of the G894T polymorphism were observed in the present study. Haplotype analysis revealed a significant linkage disequilibrium between both polymorphisms (p < 0.001).

CONCLUSIONS

Our findings suggest a pathophysiologically relevant role for the T-786C polymorphism in human coronary vasomotion. The observed linkage disequilibrium between both NOS3 genotypes deserves further research in future studies.