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Medical City Healthcare


Learn more about our leadership team at Medical City Healthcare and our commitment to delivering premier healthcare services to communities across North Texas.

Allen Harrison


Allen Harrison serves as president of Medical City Healthcare, HCA Healthcare’s North Texas Division. Medical City Healthcare is one of the largest divisions in the HCA Healthcare portfolio and includes 19 North Texas hospitals and Rapides Regional Medical Center in Louisiana.

Before joining Medical City Healthcare in January 2023, Harrison served for five years as president and CEO of Methodist Healthcare in San Antonio. Previously, he served as CEO at Methodist Hospital and Methodist Children’s Hospital in San Antonio; CEO at St. David’s Healthcare in Austin; and COO of Presbyterian/St. Luke’s Medical Center in Denver, Colorado. Allen started his career as a clinical engineer, responsible for overseeing a service line delivering custom medical equipment to persons with disabilities.

Harrison holds a Master of Business Administration from the University of Colorado at Denver, a Master of Engineering and Biomedical Engineering from the University of Virginia and he graduated magna cum laude from Oral Roberts University with a Bachelor of Science in Biomedical Engineering.

Joseph Parra, MD

Chief Medical Officer

Joseph Parra, MD, serves as chief medical officer (CMO) of Medical City Healthcare, bringing extensive medical and leadership experience to this role. Dr. Parra provides senior clinical direction and collaborates closely with physicians, clinicians, colleagues and leadership to ensure the successful implementation of the division’s vast and multi-faceted patient care initiatives. He focuses on ensuring outstanding clinical care through exceptionally effective and compliant quality management programs, including patient and employee safety initiatives.

Dr. Parra previously served as CMO for HCA Healthcare’s North Florida Regional Medical Center. Before that role, he served as CMO of Orange Park Medical Center, achieving Level II Trauma status and starting a graduate medical education program, among other initiatives.

A hospitalist by training, Dr. Parra holds multiple medical board appointments and is involved in several philanthropic organizations. He earned a Master in Business Administration from Fort Hays University in Kansas and a Doctor of Medicine from the University of Kansas.

Zach Mueller, DNP, RN, NEA-BC

Chief Nursing Executive

Zach Mueller, DNP, RN, NEA-BC, serves as chief nursing executive (CNE) of Medical City Healthcare. In this role, he oversees the nursing practice, education, informatics, research and operations for nurses at all Medical City Healthcare hospitals in North Texas.

Mueller brings a wealth of healthcare experience to his role, having worked in nursing for over 20 years, starting at the bedside as an RN primarily in the emergency department. Mueller joined Medical City Dallas and Medical City Children’s Hospital in 2011 and was promoted to senior vice president and chief nurse in 2015. He has also served in a variety of leadership roles, including as director of education, director of pediatrics and director of cardiovascular services.

Mueller is active in several professional organizations, including the Emergency Nurses Association (ENA) and the American Organization of Nurse Executives (AONE). His career achievements include speaking nationally and internationally on a variety of nursing and healthcare topics. In 2014, he was named among the prestigious Dallas–Fort Worth “Great 100 Nurses.”

Mueller earned a Doctor of Nursing and a Doctor of Nursing Practice from the University of Colorado. He also has a master’s degree in nursing and two undergraduate degrees. He is board-certified by the American Nurses Credentialing Center as a nursing executive, advanced.

Kristin Dyer

Chief Financial Officer

Kristin Dyer, MCH, serves as the chief financial officer (CFO) of Medical City Healthcare and is directly responsible for the strategic planning and oversight of all accounting and financial operations for the division.

Dyer has been part of HCA Healthcare, the parent company of Medical City Healthcare, since 2013. Prior to her role at Medical City Healthcare, which she began in January 2023, she served as CFO of the HCA Healthcare North Florida Division, where she oversaw the financial efficiency and risk management for 15 hospitals and more than 120 additional sites of care. She previously held CFO roles at Chippenham and Johnston-Willis Hospitals, a 758-bed, two-campus organization in HCA Healthcare's Capital Division in Richmond, Virginia and at Capital Regional Medical Center in Tallahassee. She also performed controller duties at Portsmouth Regional Hospital in New Hampshire.

Dyer served eight years in the U.S. Navy, where she achieved the final rank of lieutenant in the Medical Services Corps and acted as CFO/Comptroller at the Naval Hospital Twentynine Palms, CA.

She earned a Master of Healthcare Administration, Health Policy Certification and a Bachelor of Science in Health Services Administration from Ohio University in Athens.

Vince Doyle

Chief Information Officer

Vince Doyle serves Medical City Healthcare as Chief Information Officer. In this role, he delivers technology solutions that solve business challenges and support superior, patient-centered care.

Doyle most recently served as CIO of HCA Healthcare’s South Atlantic Division, where he oversaw two large acquisitions, implemented innovative technologies for patients and caregivers, and created efficiencies through Lean Six Sigma processes. Previously, he held IT leadership positions in HCA Healthcare’s North Florida and South Atlantic Divisions.

Prior to joining HCA Healthcare, Doyle held leadership positions within a large Level 1 Trauma hospital in Denver and a nationwide management-consulting firm specializing in outpatient diagnostic imaging centers.

Doyle holds an MBA in Strategic Management from Regis University and a bachelor’s degree in Management Information Systems from Southern Methodist University. He is also a graduate of the HCA Healthcare Emerging Leaders Program.

John Thresher

Chief Development Officer

John Thresher serves as chief development officer for Medical City Healthcare. In this role, he leads strategic growth initiatives, including physician partnerships, service line development, network integration and other efforts to improve healthcare programs in the communities served by Medical City Healthcare and CareNow Urgent Care.

Thresher brings decades of executive business development, strategy and operations leadership. He has worked in high-level executive and sales roles across multiple healthcare sectors. Prior to this role, he served as senior vice president of strategy and development for Medical City Healthcare.

Thresher is a proud graduate of the U.S. Military Academy in West Point where he graduated with a Bachelor of Science in Engineering Management. A distinguished honor graduate of the U.S. Army Flight School, he served as a Senior Army Aviator and Instructor Pilot. He earned several military awards and service medals, including a Bronze Star.

Jenifer Tertel

Regional Vice President of Human Resources

Jenifer Tertel serves as regional vice president of human resources for Medical City Healthcare, a role she has held since 2015. In this role, Tertel oversees human resources functions including recruitment, colleague engagement and relations for all Medical City Healthcare hospitals, ambulatory surgery centers and the CareNow Urgent Care network.

Tertel began her career with HCA Healthcare in 2006 when she joined Medical City Dallas Hospital as director of recruiting and employee relations. She was promoted to vice president of human resources, co–ethics and compliance officer, employee health and volunteer services in 2010 at Medical City Dallas where she served for 9 years.

Under her leadership, Medical City Healthcare has been recognized as one of the “Best Companies to Work for in Texas” by Texas Monthly and a “Top Places to Work in Healthcare” by Becker’s Hospital Review.

Tertel earned a Bachelor of Arts in Political Science and a minor in Economics from Wright State University in Dayton, Ohio. She also holds a Master of Business Administration degree from Northern Kentucky University with an emphasis on strategic marketing. Tertel holds Senior Professional Human Resources (SPHR) and SHRM-SCP certifications.

Mark E Whitley

Senior Vice President of Network Assets and Referral Management

Mark E. Whitley is responsible for network asset development for all Medical City Healthcare hospitals and outpatient centers, a role he has held since 2004.

Whitely began his career with HCA Healthcare in 2004 as the vice president of the outpatient services group. In that role, he was responsible for all of the North Texas Division's outpatient development, including acquisitions and the development of new ambulatory surgery centers, imaging centers and oncology centers. Before joining the division, he worked as a healthcare management consultant.

Whitley earned his Bachelor of Business Administration in finance and management from The University of Texas at Austin and his Master of Science in healthcare administration from Trinity University in San Antonio, Texas.

Brian Hutchinson

Senior Vice President of Strategy and Development

Brian Hutchinson serves as division senior VP of strategy and development for Medical City Healthcare since Feb. 2024.

In this role, Hutchinson is responsible for cultivating and growing physician relationships and service strategies across the HCA Healthcare North Texas division.

Hutchinson previously served as chief executive officer at Plano Orthopedic & Sports Medicine Center since 2016. He also held roles as the regional director of operations, overseeing surgical and primary care practices for a large physician services group in North Texas.

He earned a Master of Business Administration from Southern Methodist University and a Bachelor of Finance from Louisiana Tech University. He also achieved a Certified Medical Practice Executive (CMPE) credential.