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Syndrome X and endothelial dysfunction

M F Bellamy1, J Goodfellow, A C Tweddel

  • 1Department of Cardiology, University of Wales College of Medicine, Cardiff, UK.

Cardiovascular Research
|January 20, 1999
PubMed
Summary
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Syndrome X patients exhibit generalized endothelial dysfunction, impacting systemic arteries. Oral L-arginine improved exercise capacity and blood flow, suggesting microvascular improvements.

Area of Science:

  • Cardiology
  • Vascular Biology
  • Exercise Physiology

Background:

  • Syndrome X, characterized by angina with normal coronary arteries and positive exercise tests, presents unexplained features and conflicting evidence.
  • The underlying mechanisms of Syndrome X, including the nature of myocardial defects and the presence of endothelial dysfunction, require clarification.

Purpose of the Study:

  • To investigate generalized flow-related endothelial dysfunction in Syndrome X.
  • To determine if myocardial defects in Syndrome X reflect microvascular or myocardial dysfunction.
  • To assess the efficacy of oral L-arginine in improving endothelial dysfunction and related parameters in Syndrome X.

Main Methods:

  • Flow-mediated brachial artery dilatation was assessed using ultrasonic wall-tracking in 7 Syndrome X patients and controls.

Related Experiment Videos

  • Syndrome X patients underwent a 4-week randomized, double-blind, placebo-controlled crossover trial of oral L-arginine (7 g twice daily).
  • Evaluations included brachial artery studies, exercise tests, and technetium-99m tetrofosmin scans.

    • Main Results:

    • Flow-mediated dilatation was absent in Syndrome X patients compared to controls.
    • Stress imaging revealed similar defects in both technetium-99m tetrofosmin and thallium-201 scans.
    • L-arginine administration significantly increased flow-mediated dilatation, exercise duration, and peak oxygen consumption (VO2max) by approximately 17%, while rate-pressure product (RPP) and imaging defects remained unchanged.

    Conclusions:

    • The findings support generalized endothelial dysfunction in Syndrome X, with coronary microvascular dysfunction being more likely than myocardial dysfunction.
    • Oral L-arginine effectively improved endothelial function, exercise capacity, and VO2max in Syndrome X patients.
    • The observed improvements suggest a nitric oxide-mediated enhancement of skeletal muscle perfusion and microvascular distribution homogeneity.