Allen Harrison


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 16 hospitals, 12 ambulatory surgery centers, more than 45 CareNow Urgent Care centers, more than 5,000 active physicians, 6,000 nurses and 17,000 employees in the North Texas area. The division boasts 6 Magnet® hospitals on 10 campuses recognized for nursing excellence by the American Nurses Association, 11 trauma centers and three accredited comprehensive stroke centers. Rapides Regional Medical Center in Louisiana is also part of the HCA North Texas system.

Prior to joining Medical City Healthcare in January 2023, Allen served for five years as president and CEO of Methodist Healthcare in San Antonio, part of a unique partnership with equal ownership between HCA Healthcare and Methodist Healthcare Ministries. 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.

Allen 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

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. His focus is to ensure outstanding clinical care through exceptionally effective and compliant quality management programs, including patient and employee safety initiatives.

Dr. Parra served previously as CMO for HCA Healthcare’s North Florida Regional Medical Center, where he oversaw operational improvements that resulted in increased quality scores and physician satisfaction. Prior to that role, he served as CMO of Orange Park Medical Center for four years, 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

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 joined Medical City Dallas and Medical City Children’s Hospital in 2011 and was promoted to senior vice president and chief nurse in 2015. Under his leadership, patient satisfaction scores for women’s services and the neonatal intensive care unit increased significantly and Medical City Dallas received an unprecedented third Magnet® designation for nursing excellence. In 2014, he was named among the prestigious Dallas-Fort Worth “Great 100 Nurses.”

Known for his innovation, Mueller created the Compassion Campaign, a multiphase patient and employee experience initiative designed to create compassionate connections between nurses and patients. The campaign contributed to the highest registered nurse (RN) employee engagement in five years and notable improvements in patient satisfaction.

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. 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.

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.

James H. Burrell III, MD

Chief Medical Informatics Officer and Chief Medical Officer

James H. Burrell III

James H. Burrell III, MD, serves Medical City Healthcare as chief medical informatics officer and chief medical officer of its employed medical group.

Previously, he was the chief medical officer for Cigna’s staff model HMO in Arizona, a Level III patient-centered medical home with 25 clinics and 200 physicians, which operated a Medicare Advantage Plan and a commercial ACO.

Prior to that and after retiring from 18 years in clinical practice, Dr. Burrell developed a professional association that employed 180 physicians who worked in clinics in 22 communities in western Texas and eastern New Mexico. A Catholic hospital system acquired this organization from Dr. Burrell and appointed him as its chief executive officer and chief medical officer, positions in which he served for 14 years.

Dr. Burrell’s undergraduate education was at Texas Tech University. He attended the University of Texas Medical Branch for medical school and for his internal medicine residency.

Kristin Dyer

Chief Financial Officer

Kristen Dyer

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

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

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

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, employee engagement and colleague relations for 17,000 colleagues across 16 hospitals, 11 ambulatory surgery centers and 40+ CareNow urgent care locations.

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. Her proven success with employee engagement, talent acquisition strategies and process improvement innovation has helped Medical City gain a reputation as an employer of choice in the North Texas area. Under Tertel’s leadership, Medical City Dallas was recognized by the Alfred P. Sloan Foundation for Workplace Flexibility and Excellence, Best Companies to Work for in Texas by the Texas Association of Business and Society for Human Resource Management and Best Place to Work in Dallas by the Dallas Business Journal.

Prior to joining HCA Healthcare, Tertel was the regional recruiting director and executive recruiter for Mercy Health (Catholic Healthcare Partners) in Cincinnati, Ohio. Before working in human resources, Tertel spent ten years in the property and casualty insurance business working in litigation, with a strong emphasis on case mediation.

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

Mark E. Whitley is responsible for network asset development and referral management for the hospitals and outpatient centers of Medical City Healthcare. He began his career with HCA in 2005 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. Prior to joining HCA, he worked for nine years as a healthcare management consultant with Arthur Andersen and Ernst & Young and spent one year at Tenet Healthcare in outpatient development.

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.