Meet our Care Team!
Dale Yoo
MD, FACC, FHRS
Managing Partner and President, Board Certified Cardiologist and Electrophysiologist
Dr. Yoo started Heart Rhythm Specialists in 2019 in order to integrate state of the art science and technologies with the personalized approach to clinical medicine. With his extensive background in engineering and research he has been able to create a new kind of practice to cater to the specific needs of the human condition. He enjoys playing golf and tennis as well as traveling the world teaching and sharing knowledge.
David Singh
MD
Provider
Dr. David Singh is a board-certified cardiac electrophysiologist
with over 13 years of experience in treating complex heart rhythm disorders. He
currently practices at Heart Rhythm Specialists in Plano, Texas. Previously,
Dr. Singh served as Director of Electrophysiology at The Queen’s Medical Center
in Honolulu, Hawaii from 2011 to 2024, where he also held leadership roles as
Chief of Cardiovascular Diseases and Chief Quality and Safety Officer.
Dr. Singh completed his medical training at Georgetown University, followed by residency at UCSF and fellowships in cardiology and
electrophysiology at Cedars-Sinai Medical Center and UCSF respectively. He has
held academic appointments as Professor of Medicine at the University of Hawaii
John A. Burns School of Medicine.
An active researcher and educator, Dr. Singh has authored numerous
peer-reviewed publications and book chapters in cardiology and
electrophysiology. He has been principal investigator on multiple clinical
trials and is recognized for his expertise in complex arrhythmia management and
minimally fluoroscopic ablation techniques.
Dr. Singh also serves as CEO of the Melvin Scheinman Educational Rhythm Foundation, a non-for-profit organization devoted to increasing access
to electrophysiology care in low- and middle-income countries around the world.
Dr. Singh is dedicated to advancing the field of electrophysiology
through research, education, clinical innovation and service.
Mary Susan Williams
MSN, APRN, ANP-BC
Advanced Care Nurse Practitioner
Clinical & Device Lead
Mary Susan received her Master of Nursing degree and Nurse Practitioner certification from Texas Women’s University in 2011. She began her nursing and nurse practitioner career at Parkland Hospital. It was there, that she discovered her love of cardiology.
She has worked for Heart Rhythm Specialists since its beginning in 2019 and has worked with Dr. Yoo in EP Cardiology since 2014.
She enjoys caring for and educating her patients and their families about electrophysiology and their specific conditions.
Outside of the office, she enjoys spending time with her husband and 3 kids, Arkansas Razorback Sport, and traveling.
Amanda de Avillez
MSN, APRN, AGACNP-BC
Acute Care Nurse Practitioner
Hospital Lead
“BIO COMING SOON”
Erin Sheffield
Office Manager
Erin joined Heart Rhythm Specialists on March 12, 2024, bringing with her over a decade of experience in the healthcare and medical administration fields. Her career began in 2012 as a File Clerk at an OBGYN office, and since then, Erin has gained extensive experience across various sectors of the healthcare industry.
Before joining HRS, Erin worked at a dental insurance company, managing onboarding and new hire training. She also served as a Surgical Financial Counselor at an Oral Maxillofacial Surgery practice for two years. Erin then transitioned to an urgent care facility, where she worked in the billing department and later took on the role of DOT Clinical Educator and Occupational Medicine Administrator. In this role, she was responsible for answering clinical staff questions, managing workers’ compensation claims, and collaborating with employers to ensure a smooth process while their employees were under care.
Erin holds a degree in Medical Coding and Billing, which has further enhanced her expertise in managing medical office operations. Her knowledge and leadership skills led her to the role of Office Manager at HRS, where she now leads the exceptional staff in delivering top-tier care to patients. Erin is dedicated to providing a seamless experience for both patients and staff and contributing to the overall success of the team.
Outside of work, Erin is a proud mother to two beautiful sons, Theodore and Franklin, and enjoys spending quality time with her family.
Erin has been with Heart Rhythm Specialists for almost a year and looks forward to continuing her growth and supporting the team’s success.
Autumn Lopez
Surgery Coordinator/Assistant Manager
Autumn joined the Heart Rhythm Specialists team in March 2020. She ventured into the healthcare industry to help and teach others. At the clinic, she does it all! She manages the MA’s/Assistants, creates schedules, and monitors all clinic practices. She also oversees all surgical procedures and schedules them.
She accurately documents any and all cardiac and sleep apnea diagnostic reports. She assists the practice in managing all tasks of record keeping and reconciliation. She stays busy exploring Holter monitoring devices and stays up to date with current technology. Her EP interests include: arrythmia management and studying cardiovascular diagnostics; all while being a living witness to the healing process of excellent patient care.
Outside of the clinic, you might find her at the lake with her friends and family, enjoying the water and sun. However, the majority of her time is spent with her 2 sons and grandbabies!
Ashley Worthington
Medical Assistant
Ashley joined the HRS team at the beginning of January 2022. Her background begins assisting in labor & delivery, exploring the world of ophthalmology with Lasik care, to her current adventure into electrophysiology.
Ashley began in administration but successfully transitioned to the clinic as the newest medical assistant. She spends time accurately computing extended cardiac monitoring reports & explaining treatment procedures and medication therapy with patients. Her day to day duties include documenting vitals, medication verification, and performing all preliminary intake prior to exams with providers. She holds education in nutrition therapy and manages/operates the clinic’s patient and provider communication system.
Her interests in EP include arrhythmia management & studying cardiovascular diagnostics. She spends her time away from the clinic volunteering with her church, spending time with family at parks, and roller skating.
Marisol Valdez
Medical Assistant
Marisol joined the Heart Rhythm Specialists team in search of development opportunities to help her grow as a professional individual. She has 20 years of experience in the medical field, which includes being a Certified Pharmacy Technician. She is always eager to contribute her skills as a Medical Assistant, utilizing her excellent communication abilities to effectively interact with patients and provide quality care under the guidance of Dr. Yoo. She is a highly motivated individual who is always eager to apply new skills that she has learned from being a part of the team at HRS.
Marisol is also a Yellow Belt Lean Six Sigma & a Certified Spanish/Bilingual Assistant. This allows her to help identify problems, develop solutions, and improve the efficiency of our clinic processes. Her bilingual certification gives her the ability to bridge cultural gaps, enhance communication with diverse clients, and provide better customer service in multiple languages.
Outside of work, Marisol enjoys spending quality time with her 2 children. She is most proud of overcoming her own personal health challenges, which includes being in remission for the last 5 years!
Brianna “Bri” Graham
Medical Administrator
Brianna came to HRS with six years of experience in the medical field focusing on administrative work. She brings a strong foundation in healthcare operations. Her journey to HRS began with a desire to return to the DFW area after living in East Texas, where she was introduced to Dr. Yoo. After her first interview, she knew that she wanted to join the team.
Professionally, she holds certifications in medical billing/coding, CPR, and is a licensed notary. She also has an associate degree in healthcare administration and is currently pursuing her bachelor’s degree in the same field.
Outside of work, she is a proud parent to an almost six-year-old son, who enjoys football and basketball. Together, they share a love for adventure, whether it’s hiking, visiting parks, exploring new dessert shops, or playing board games.
Leeza Bertucci
Medical Administrator
Leeza is a mother of two, a 17 year old daughter and a 12 year old son. She has 16+ years of medical field experience and has spent the last year working for Dr. Yoo. Fate brought her to Heart Rhythm Specialists. Before HRS, she mainly worked in oncology until one of her makeup clients referred her to Autumn. A few months later, Autumn reached out for an interview out of the blue! HRS has been her family ever since.
Leeza began doing front desk for Dr. Yoo and now does check out/scheduling and is currently learning billing.
She is very thankful for Dr. Yoo, Autumn, Erin, and really all of the staff here at HRS. Everyone is like family outside of family!
