Rural Cardiology Desert Atlas

Purpose

The Rural Cardiology Desert Atlas maps the cardiology access gap across US counties using exclusively public, aggregate data. It was built alongside the HEARTLAND Protocol — an implementation toolkit for primary care–led heart failure management in rural and resource-limited settings — and is freely available for policy makers, researchers, hospital administrators, and journalists.

Data sources

NPPES NPI Registry (CMS, monthly dump). Every licensed individual provider whose primary taxonomy code indicates a cardiology subspecialty: Cardiovascular Disease, Interventional Cardiology, Clinical Cardiac Electrophysiology, Advanced Heart Failure and Transplant Cardiology, Adult Congenital Heart Disease.
CMS Hospital General Information (Provider Data Catalog). Source of hospital counts and Critical Access Hospital designation per facility.
CDC Interactive Atlas of Heart Disease and Stroke. Age-adjusted heart disease mortality per 100,000 (adults 35+).
US Census Bureau ACS 5-year estimates for county population and median household income.
USDA Economic Research Service — Rural-Urban Continuum Codes 2023 (RUCC). A county is flagged as rural when its RUCC ≥ 4.
HRSA HPSA designations — primary care Health Professional Shortage Area status per county.
US Census ZCTA↔County relationship file (2020) — maps each ZIP Code Tabulation Area to the county that covers most of its residential population.
US Census TIGER gazetteer (2023) — internal latitude/longitude points for counties and ZCTAs.

Distance calculation

For each county, we compute the great-circle distance between the county centroid and the nearest cardiologist’s ZIP centroid. This is done with a k-d tree built in 3D unit-vector space over all unique provider practice locations nationwide, so a county with zero in-county cardiologists still reports the distance to the nearest provider in a neighboring county. ZIP centroids understate distance variability within very large urban ZIPs; at the county level this approximation is appropriate.

Update cadence

Underlying datasets refresh at different cadences: NPPES monthly, CMS hospitals weekly, Census ACS annually, USDA RUCC every 10 years (most recent release 2023), CDC mortality every few years. A GitHub Action re-runs the pipeline monthly and opens a pull request when counties.json changes.

Limitations

Provider counts reflect the number of licensed cardiologists whose primary practice ZIP code falls within the county. They do not reflect part-time, locum tenens, or telehealth availability.
A single cardiologist with multiple practice locations is counted at their primary practice ZIP only.
Hospital-based practice ZIPs may pull specialists into a different county than their patient population.
ZCTA↔County crosswalks are an approximation; ~1-2% of ZIPs span more than one county, in which case we assign to the county with the greatest population overlap.
This atlas does not contain patient health information.

Citation

Muller Ferreira V. Rural Cardiology Desert Atlas [Software & dataset]. 2026. Available from: https://atlas.heartlandprotocol.org

Related publication: Muller Ferreira V. "HEARTLAND Protocol: Heart failure Evidence-based Access in Rural Treatment, Linking Advanced Network Delivery." Cureus, 2026.

License

Source code and derived data are released under the MIT License. Upstream sources retain their own licenses — all public-domain US government datasets except the Census ZIP centroid file (CC BY 4.0 Census). Please cite this atlas and its source datasets when reusing.

Author

Vicky Muller Ferreira, MD. ORCID 0009-0009-1099-5690.