Comparison of Angio-based Microvascular Resistance (AMR) between coronary microvascular resistance in high altitude and plain regions

Abstract Objective This study aims to compare the differences in coronary microvascular resistance between patients living long-term in high-altitude regions and those in plain areas using a novel Angio-based Microvascular Resistance (AMR) index. Methods This study is a prospective, single-center observational research project aimed at assessing differences in coronary microvascular function among patients from varying altitudes using a pressure-free guidewire and adenosine-free AMR evaluation. It includes patients who underwent coronary angiography for suspected coronary artery disease at our hospital from February 1 to May 1, 2024, with non-obstructive lesions (50% stenosis) and adequate image quality for AMR analysis. Participants must have lived at high altitudes (≥2500 meters) for at least one year without residing below that altitude for over three months prior to the visit. Exclusion criteria encompass significant stenosis, acute coronary syndrome, chronic total occlusion, severe altitude sickness, serious cardiac diseases, and other severe comorbidities. A control group of non-high-altitude patients with suspected coronary artery disease was matched 1: 1 based on age, gender, comorbidities, hemoglobin, and platelet counts. Results A total of 62 patients were included in this study, comprising 186 vessels, with 31 patients (93 vessels) in the high-altitude group and 31 patients (93 vessels) in the plain group. The hemoglobin levels in the two groups were (144 ± 17 vs. 139 ± 18 g/L, P=0. 2062), and platelet levels were (192 ± 50 vs. 196 ± 56 *10⁹/L, P=0. 7932). The Gensini scores (6. 5 ± 6. 0 vs. 5. 8 ± 5. 3, P=0. 658) and SYNTAX scores (4. 707±4. 240 vs. 4. 371±4. 581, P=0. 8280) of coronary angiography showed no significant differences between the two groups. Additionally, there were no statistical differences in age, gender, hypertension, diabetes, hyperlipidemia, and BMI between the two groups. Vessel-level analysis revealed that the AMR value in the high-altitude patients was significantly higher than that in the plain patients (3. 470 ± 0. 690 vs. 3. 251 ± 0. 72, P=0. 0374). Furthermore, AMR values were independently measured by two assessors, showing good consistency between the two groups (r=0. 9283), with minimal inter-observer bias. Conclusion This prospective, single-center, exploratory study found that patients living long-term in high-altitude regions exhibit higher microvascular resistance compared to those residing in plain areas. Further research is needed to determine whether this difference in microvascular resistance leads to adverse outcomes and whether cardiovascular physicians should routinely consider targeted microvascular pharmacotherapy for these patients. Future studies with larger sample sizes and more rigorous designs are required to focus on this clinical issue.