Page 16 - Journal of Structural Heart Disease Volume 3, Issue 4

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Original Research Article
to-left shunt across the defect. For these reasons, patients with unrepaired ASDs are often referred for cardiac catheterization to assess pulmonary vascular resistance (PVR) and shunt fraction (Qp:Qs) followed by transcatheter device closure of the defect should there be favorable anatomy and hemodynamics.
Not all patients with unrepaired ASDs develop PAH. Although older age and defect size are independent predictors of PAH in patients with ASDs [5, 6, 7], other risk factors are unknown. One possible risk factor may be living at higher altitude. Living at higher elevations may increase a person’s risk of developing PH/PAH due to lower oxygen tension, contributing to more substantial oxygen saturation variability, pulmonary vasoconstriction, and pulmonary vascular remodeling irrespective of the presence of structural heart defects [8, 9]. In patients with unrepaired ASDs, little is known about these e ects of elevation. Speci cally, how much does living at a moderately high altitude raise pulmonary artery pressures, and is this associated with pulmonary vascular remodeling? Thus, we aimed to determine whether living at moderate altitude (4500–6000 ft or 1372–1829 m) is associated with a greater likelihood of developing PAH among patients referred for transcatheter device closure of ASDs.
Materials and Methods
PCWp ≤ 15 mmHg. The secondary outcome was the presence of PH, de ned as mPAp ≥ 25 mmHg without elevated PVR and/or with PCWp > 15 mmHg.
Patients aged 18 to 99 years with an ASD or ASD physiology (i.e., partial anomalous pulmonary venous return) were included. Patients with a patent foramen ovale, ASD < 4 mm (in any one imaging plane), resid- ual ASD after prior surgical or transcatheter device clo- sure, or other types of congenital heart disease were excluded. Raw catheterization data were collected, and Qp:Qs and PVR were independently calculated for each patient (reported values were not used). In cases in which catheterization data were incomplete, such as in reports lacking pulmonary vein and/or sys- temic arterial saturations, a value of 95% was used. Oxygen consumption (VO2) was derived from the LaFarge equation and table, which provides an esti- mated VO2 based on the patient’s age and heart rate.
Study data were collected and managed using REDCap electronic data capture tools hosted by the University of Colorado [10]. Data were tested for nor- mality using Shapiro-Wilk tests. Non-normally distrib- uted continuous data are presented as median (inter- quartile range), and categorical data are presented as frequency (percentage). Comparative statistics were calculated using Wilcoxon rank-sum or Chi- square tests, as appropriate. As pulmonary pressures are known to increase with age, catheterization data were further analyzed for di erences between eleva- tion categories using logistic regression controlling for age. All analyses were performed with Statistical Analysis Software (SAS Institute, version 9.4, Cary, NC).
Results
Thirty-seven moderate altitude and 126 low alti- tude patients were identi ed. Baseline patient char- acteristics are outlined in Table 1. Elevations of pa- tients’ zip codes of residence ranged from 74 to 7110 ft above sea level, with a median elevation of 246 ft in the low-altitude group (74–839 ft) and 5334 ft in the moderate altitude group (4983–5633 ft, p < 0.0001).
Defect size and PCWp were similar between groups as shown in Table 2. Despite the lack of di er- ence in Qp:Qs between groups (median Qp:Qs 1.5 vs. 1.6, p = 0.07), there was a trend toward higher pulmo- nary artery pressures in the moderate altitude group
This was a multicenter, retrospective cohort study of adult patients who were referred for transcathe- ter device closure of an ASD during a 10-year period (2003–2013). Catheterization databases and records from three academic centers were reviewed after in- dividual institutional review boards approved the study. Variables extracted from records were demo- graphic information including the patient’s zip code of residence, presence of other risk factors for PH such as lung disease or sleep apnea, use of PH/PAH medi- cations, and catheterization measurements including mean pulmonary artery pressure (mPAp), pulmonary capillary wedge pressure (PCWp), PVR, Qp:Qs, and defect size (balloon-sized or pre-procedure size mea- sured by echocardiography). Elevation was de ned as ‘moderate altitude’ if the zip code elevation was ≥ 4500 ft. Otherwise, elevation was considered ‘low altitude’. The primary outcome was the presence of PAH, de ned asmPAp≥25mmHg,PVR>3Woodunits×m2,and
Nicolarsen, J. et al.
Altitude and Pulmonary Arterial Hypertension