A Bridge Beyond Pacemakers

UHN team generates cardiac-like cells that could replace electronic pacemakers after AV block.

Image Caption: The cover image of Cell Stem Cell depicts the heart’s conduction system as a highway, with cars symbolizing electrical signals. The cars are crossing a damaged AVN bridge representing AV block. A new innovation using heart cells grown in the lab acts as a bandage to restore this passage. Illustration by Maggie Kwan; Cover Cell Stem Cell ©2026.

A research team from UHN’s McEwen Stem Cell Institute (McEwen) has grown heart cells in the lab that mimic the atrioventricular node (AVN), the part of the heart that carries electrical impulses from the atria to the ventricles. This innovation could offer individuals with a dysfunctional AVN a novel treatment option—called a biological conduction bridge—that may one day replace standard pacemaker implants.

As the “electrical bridge” between the atria and ventricles, the AVN is responsible for maintaining the pace of the ventricles’ contractions and, thus, efficient blood flow. An improperly functioning AVN can lead to a life-threatening condition called atrioventricular (AV) block, which is typically treated by implanting an electronic pacemaker (EPM) to take over the AVN’s function. Although lifesaving, EPMs are not without limitations, including the need for surgery to replace their batteries every 10 to 15 years and their inability to respond to physiological changes. These limitations underscore the need for alternative approaches that more closely mimic native cardiac conduction.

In pursuit of an alternative, cell-based therapy for AV block, Dr. Stephanie Protze, a McEwen Scientist, and her team used a specialized lab process that turns stem cells into specific cell types to create cardiac pacemaker cells that behave like those in the AVN (AVNLPCs). The team then assessed gene expression and functional properties to confirm the cells’ identity as AVNLPCs.

The AVNLPCs showed the same key biological markers as AVN pacemaker cells in developing human hearts. For example, the cells showed high expression of key AVN genes, including TBX3, MSX2, RSPO3, and low expression of genes such as SCN5A, GJA1, GJA5, which are characteristic of other cell types, such the heart muscle cells.

When integrated into a 3D–heart tissue model, the AVN-like pacemaker cells’ responses to electrical signals were comparable to those observed in the human heart. This includes slow electrical impulse conduction and blocking conduction of fast atrial rates, such as those seen in atrial fibrillation, which would be life-threatening in the ventricles.

Importantly, when the researchers implanted their AVNLPCs into a preclinical model of SAN and AVN dysfunction, the cells remained functional and continued to display the same electrophysiological properties observed in the 3D–heart tissue model.

Overall, this work establishes a foundation that could be used to further develop a biological conduction bridge. The McEwen team’s work offers the first evidence that AVNLPCs are functional in multiple model types, both in vitro and in vivo. Importantly, they demonstrate that AVNLPCs mimic the key safety features of AVN conduction in humans—namely, the ability to block fast atrial rates from reaching the ventricles, which is a key safety feature of the AVN.

Although additional studies are required to replicate these results and test the efficacy of AVNLPCs in additional lab models, and eventually in humans, this work represents an important step toward a more biologically relevant and durable alternative to electronic pacemakers for patients with AV block.

The first author of this study is Dr. Michelle Lohbihler, a former graduate student at UHN’s McEwen Stem Cell Institute in the Protze Lab.

The senior author of this study is Dr. Stephanie Protze, a Scientist at UHN’s McEwen Stem Cell Institute and an Assistant Professor of Molecular Genetics at the University of Toronto’s Temerty Faculty of Medicine.

Drs. Sara Nunes Vasconcelos, Michael Laflamme, and Kumaraswamy Nanthakumar, who are Senior Scientists at UHN, also contributed to this study. Dr. Laflamme is also a Tier 1 Canada Research Chair in Cardiovascular Regenerative Medicine.

This work was supported by the Canadian Institutes of Health Research, the Canadian Foundation for Innovation, the Government of Canada’s New Frontiers in Research Fund, the Canada Research Chairs Program, BlueRock Therapeutics, and UHN Foundation. 

Dr. Laflamme receives funds as a consultant for and is also a scientific founder of BlueRock Therapeutics. Drs. Laflamme and Protze also share a patent for materials related to this study. 

Lohbihler M, Lim AA, Massé S, Kwan M, Mourad O, Mastikhina O, Murareanu BM, Elbatarny M, Sarao R, Qiang B, Dhahri W, Chang ML, Xu ALY, Mazine A, Khattak S, Nunes SS, Nanthakumar K, Laflamme MA, Protze S. Human pluripotent stem cell-derived atrioventricular node-like pacemaker cells exhibit biological conduction bridge properties in vitro and in vivo. Cell Stem Cell. 2026 Mar 23. doi: 10.1016/j.stem.2026.02.012. 

New Models of Cardiac Rehabilitation

Hybrid and virtual care models are expanding access and improving patient-centred cardiac care.

Image Caption: The COVID-19 pandemic transformed how cardiac care was delivered worldwide, highlighting the need to understand its impact on program delivery and care models.

Before the COVID-19 pandemic, cardiac rehabilitation programs were traditionally delivered in person. However, when the pandemic began, programs rapidly shifted to virtual formats to maintain patient care. In a new study from UHN’s KITE Research Institute (KITE), researchers examined how this transition reshaped cardiac rehabilitation across Canada, expanding access and supporting more patient-centred models of care. 

The research team surveyed 108 representatives from 150 cardiac rehabilitation programs to understand the barriers and benefits of in-person, virtual, and hybrid program models. Compared to programming before the pandemic, they found a significant decline in in-person programming and an increase in virtual and hybrid models. Close to 50% of rehabilitation programs now offer two or three delivery models. 

The integration of hybrid and virtual models helped programs reach more participants. Virtual programs require fewer operational resources than in-person programs, which allow programs to support more patients without exceeding capacity. At the same time, virtual programs reduce financial or logistic barriers for patients who face challenges attending in-person, such as transportation costs, limited mobility, or restrictive schedules. 

By directing lower-risk patients to virtual or hybrid formats, programs can allocate limited in-person resources to high-risk patients who require more supervised, onsite care, addressing long-standing eligibility restrictions. Ultimately, program selection was based on patient preference and collaborative discussions between patients and clinicians, enabling more tailored, patient-centred decision making.

However, in-person models remain important for social connectedness and peer support. Participants noted that patients are generally less satisfied with fully virtual formats. Researchers also found that patients with language or communication barriers face challenges across all models, particularly in person, where translation services were not consistently available. 

With continued improvements in technology and better translation services, these evolving models could strengthen Canada’s cardiac rehabilitation system and enable more equitable, patient-centred care.

Dr. Susan Marzolini, lead author of the study, is a Scientist at UHN’s KITE Research Institute. At the University of Toronto, Dr. Marzolini is an Associate Professor at the Rehabilitation Sciences Institute and an Assistant Professor in the Faculty of Kinesiology & Physical Education. 

This work was supported by UHN Foundation.

Marzolini S, Ocampo G, Hébert AA, Barbieri R, Cotie L, Barry-Hickey D, Martinuzzi M, Konidis R, Oh P. The Evolution of Cardiac Rehabilitation Since COVID-19. Heart Lung Circ. 2026 Feb 5. doi: 10.1016/j.hlc.2025.09.006. 

Rehumanizing Classroom Care

Human-centred clinical letters can help schools better support children with disabilities.

Image Caption: Many children with disabilities require individualized school supports, yet disjointed communication between clinicians and educators can make that support difficult to obtain.

Children with disabilities often struggle to access appropriate school supports. Clinical letters are commonly used by clinicians to communicate medical information, management plans, and care recommendations to schools. A new study from The Institute for Education Research (TIER) at UHN highlights the importance of using a critically reflective approach when writing clinical letters to improve communication and collaboration between clinicians, families, and schools. 

Clinical letters are a key form of communication between clinicians and schools. However, clinicians may be unaware of the everyday challenges that shape school-based care, such as limited resources and rigid policies, which can hinder how effectively schools apply clinicians' recommendations.

A critically reflective approach encourages clinicians to reflect on their assumptions and consider the systemic barriers that families and schools face. It also supports writing in a more collaborative, human-centred way, guiding clinicians to describe each child by highlighting strengths and goals, not just challenges, and to use team-oriented language, such as “We would like to work with you to…”.

To investigate the impact of critically reflective writing, the research team interviewed 17 parents and educators across Ontario and assessed their responses to clinical letters written by clinicians after completing training in this approach. 

Participants felt that the critically reflective letters rehumanized children with disabilities and promoted stronger communication and collaboration. Shifting from challenge-focused descriptions to highlighting the children’s strengths and abilities changed how educators perceived them. Participants felt this made it easier to understand children’s needs and could support more trusting, open communication between families and educators. Improved communication and collaboration could also create new opportunities for shared advocacy by helping families and educators build a common understanding of challenges and identify where change is needed. 

Overall, more thoughtful, human-centred clinical writing can help bridge communication gaps between health and education systems, ultimately improving support for children with disabilities. 

Dr. Victoria Boyd, first and corresponding author of the study, is a Scientific Associate at The Institute for Education Research (TIER) and the Centre for Advancing Collaborative Healthcare & Education (CACHE) at UHN.

Dr. Nicole Woods, co-author of the study, is a Senior Scientist and Director of TIER. Dr. Woods is also a Scientist at The Wilson Centre at UHN as well as an Associate Professor in the Department of Family and Community Medicine, the Department of Surgery, and the Institute of Health Policy, Management and Evaluation at the University of Toronto (U of T). 

Dr. Stella Ng, senior author of the study, is a TIER Scientist, Scientist at The Wilson Centre, and Director of CACHE at UHN. At U of T, Dr. Ng is an Associate Professor in the Department of Speech-Language Pathology and a Faculty Member of the Rehabilitation Sciences Institutes. 

This work was supported by UHN Foundation, the Spencer Foundation, the Social Sciences and Humanities Research Council, Dr. Boyd’s Kimel-Schatzky Fellowship, and Dr. Ng’s Ontario Ministry Early Researcher Award and Arrell Family Chair in Health Professions Teaching. 

Boyd, VA, Woods, NN., Campbell, WN, Kumagai, AK, & Ng, SL. (Re)humanizing clinical documentation for disabled children: a cascade of potential outcomes of critically reflective practice. Disability & Society. 2026 Feb 01. DOI: 10.1080/09687599.2025.2536587 

Smartwatches for Heart Health

New study highlights how smartwatches can detect early signs of worsening heart failure.

Image Caption: Wearable technology, such as a smartwatch, is effective at gathering physiological data (like heart rate) from people passively, in their daily lives. This makes these technologies good candidates for monitoring symptoms of heart failure that are difficult to measure in traditional clinical settings. Illustration by Katie Yost ©2025

A new study from UHN, featured on the cover of Nature Medicine, shows that wearable technologies such as Apple Watch can help monitor heart failure by providing early signs of deteriorating health where medical attention may be needed.

Heart failure—when the heart does not pump blood adequately to meet the body’s needs—is a global health crisis that leads to hospitalizations, increased use of health care services, and reduced life expectancy. Despite recent medical advances, patients with heart failure still face a high risk of poor outcomes. This highlights the need to improve risk assessment and better guide timely interventions.

“For patients with heart failure, periods of stability are often interspersed with flare-ups of symptoms such as shortness of breath or fatigue. These episodes may require medical attention to prevent hospitalization and improve quality of life,” says Dr. Heather Ross(link is external), Clinician Investigator at UHN and co-senior author of the study. “However, risk assessments for heart failure patients often rely on scheduled clinical visits or evaluation tools that take measurements at only one point in time. They don’t account for the changing, episodic nature of heart failure.”

Therefore, doctors and clinicians need to find better ways of monitoring heart failure symptoms and predicting when medical intervention may be needed. Wearable technology, such as Apple Watch, can continuously track important health and fitness measures, such as heart rate and blood oxygen levels, making it an excellent candidate for monitoring. However, until recently, it has been unclear how these measurements might be used to understand day-to-day changes in people living with heart failure.

To investigate this, the research team, led by researchers at UHN’s Peter Munk Cardiac Centre and the Ted Rogers Centre for Heart Research, initiated the Ted Rogers Understanding Exacerbations of Heart Failure study (TRUE-HF) in collaboration with Apple in the fall of 2020. The study examined whether biometric data from Apple Watch could be used to predict peak oxygen uptake (pVO₂) in patients with heart failure in their daily lives for a three-month period. PVO₂ is the highest amount of oxygen the body uses during intense exercise, serving as a key indicator of cardiorespiratory fitness. It is typically measured in a clinical setting using Cardiopulmonary Exercise Testing (CPET), where patients are evaluated while exercising to maximal capacity.

“We created an AI model, called TRUE-HF, trained on data from 154 patients and then validated on 63 patients, to estimate individuals' daily peak oxygen uptake using measurements from Apple Watch,” says Dr. Chris McIntosh, Senior Scientist at UHN and co-senior author of the study. “We found that when participants went about their daily routines while wearing an Apple Watch, our smartwatch-based pVO₂ estimates strongly correlated with lab-derived ones from CPET.”

What’s more, they found that each 10% drop in the TRUE-HF–estimated fitness measure (pVO₂) was linked to a more than threefold higher risk of an unplanned medical event. These events typically occurred approximately a week after the drop first appeared. A modified version of the model also predicted unplanned use of medical services around 21 days after the first drop in predicted pVO₂. These results were further validated in a public cross-platform FitBit dataset from the National Institutes of Health (NIH) All of Us Research Program.

These results suggest that daily smartwatch measurements can provide early warning signs of worsening health and help predict when unplanned medical care may be needed for people living with heart failure. Identifying real-time changes in health through wearable technology, without requiring additional tests or added effort from patients, could enable faster, better care.

Yuan Gao is a doctoral candidate at UHN and co-first author of the study.

Dr. Yas Moayedi is a Clinician Investigator at UHN and co-first author of the study.

Dr. Christopher McIntosh, Senior Scientist at UHN and Dr. Heather Ross, Clinician Investigator at UHN, are co-senior authors of the study. Dr. McIntosh is an Assistant Professor in the Department of Medical Biophysics at the University of Toronto (U of T). Dr. Heather Ross is a Professor at the Institute of Medical Sciences at U of T.

Other study authors from UHN include Farid Foroutan, Bhavish Verma, Ben Kim, Enza De Luca, Margaret Brum, Darshan H. Bhrambhatt, Joe Duhamel, and Anne Simard.

This work was supported by the Ted Rogers Centre for Heart Research, the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Institutes of Health Research (CIHR), the University of Toronto, and UHN Foundation.

Dr. Ross is the Loretta Rogers Chair in Heart Function.

Apple Incorporated provided 200 iPhones and Apple Watch devices for the study, provided feedback on the manuscript, and collaborated with all authors to build the study-specific mobile application. All authors are investigating patenting the TRUE-HF model described in the manuscript.

Information Needs in Cancer Care

Patients and caregivers seek more inclusive, tailored resources for cancer care decisions.

Image Caption: Patients and caregivers are increasingly taking an active role in managing cancer care. To make informed decisions, they need clear, trustworthy, and accessible information. But many still face persistent challenges finding and using the health information they need.

Many people diagnosed with breast cancer rely on health information to understand their diagnosis and make decisions about their treatment.  A new study from The Institute for Education Research at UHN shows that patients and caregivers often feel overwhelmed by the amount and complexity of health information and face persistent gaps in timely, inclusive, and tailored resources. 

The research team interviewed 16 patients with breast cancer and caregivers to understand their experiences with accessing, evaluating, and using health information during diagnosis, treatment, and follow-up. Despite high education levels and digital literacy, many participants said they felt unprepared and overwhelmed by the volume and complexity of information presented to them. During the interviews, participants highlighted three main challenges: 

● Mixed feelings about guidance from health care providers: Some participants felt reassured when clinicians cautioned against independent online research. Others, however, felt it limited their ability to actively participate in decision-making about their care.

● Information overload: Participants described difficulty navigating large amounts of information and finding resources that were timely, relevant, and appropriate for their specific stage of care. 

● Need for more tailored and inclusive resources: Participants noted gaps in information, especially for male patients and people from racialized or cultural minority groups, who often could not find materials that reflected their experiences.

Participants emphasized the importance of connecting with other patients and caregivers. They also expressed strong support for a curated digital library that would bring trustworthy information together in one easy-to-access place.

These findings highlight opportunities for health care systems to strengthen information and resources available to support informed decision-making, promote patient participation, and create more equitable cancer care. Future research should explore the needs of patients who face additional barriers to accessing health information, including those with lower health literacy or limited support networks.

Mohamed Ugas, first author of the study, is a research analyst at the Princess Margaret Cancer Health Literacy Research Centre. 

Dr. Janet Papadakos, senior author of the study, is a Scientist at The Institute for Education Research at UHN and the Co-Director of the Princess Margaret Cancer Health Literacy Research Centre. At the University of Toronto, Dr. Papadakos is an Assistant Professor at the Institute of Health Policy, Management, and Evaluation. 

This work was supported by The Princess Margaret Cancer Foundation, with operational support provided by UHN Foundation.

Ugas M, Giannopoulos E, Tan J, Cil TD, Croke J, Forbes R, Giuliani ME, Koch A, Papadakos T, Quartey NK, Snow M, Westergard S, Papadakos J. Exploring the information needs of breast cancer patients and families in a large, urban, academic hospital: perceived barriers and facilitators to finding relevant and credible information. Support Care Cancer. 2026 Jan 23. doi: 10.1007/s00520-026-10344-3.

Mapping Models of Liver Disease

Researchers map liver cells in a key hepatitis B model, enhancing research into new treatments.

Image Caption: Hepatitis B infection can lead to end-stage liver disease and cancer. However, studying liver disease has been challenging due to a lack of well-understood models, molecular tools, and limited human tissue availability.

Treatment options for liver diseases, including hepatitis B, remain limited, and many patients ultimately require a liver transplant. New ways to study the liver are critical for developing therapeutic interventions and filling this treatment gap. Researchers at UHN have created the first comprehensive atlas of liver and immune cells in a widely used preclinical model of chronic Hepatitis B Virus (HBV) infection—a development that could accelerate research into the disease and its progression to liver cancer.

The liver is a vital organ that regulates chemicals in the blood. HBV is a virus that can cause a lifelong (chronic) infection that leads to serious illnesses such as liver scarring and liver cancer (hepatocellular carcinoma, HCC). In end-stage liver disease, the liver can no longer regenerate after injury, making transplantation the primary treatment option. 

Studying HBV infection, including disease progression and treatment, remains challenging because there are few experimental models and limited human tissue availability. To address this, researchers sought to characterize a commonly used preclinical model of HBV at a cellular level. 

The team generated an atlas of single-cell gene expression data that also includes information on which genes are expressed in which parts of the liver. This atlas captures how tens of thousands of liver and immune cells behave in both healthy conditions and during chronic viral infection in the HBV model.

Using this atlas, the researchers found that the cell population in this preclinical model is comparable to human livers and the immune cells trigger the same kinds of inflammatory responses. The liver atlas also showed that HBV infections in this model lead to gene expression and cellular changes similar to those in the human liver. HBV infections in both the model and in humans activate certain immune cells, called dendritic cells, in the same area of the liver, and T cells become “worn out” over time.

This study highlights that HBV infection affects this well-known preclinical model in similar ways to humans, confirming the model’s importance in liver disease research. This atlas, therefore, offers a powerful new tool for understanding HBV and developing better treatments.

Zoe Clarke, Jawairia Atif, and Xinle Wang are co-first authors of the study. Zoe Clarke is a PhD Candidate at the University of Toronto (U of T), Dr. Jawairia Atif is a PhD graduate at UHN, and Xinle Wang is a former research student at UHN and a current medical student at U of T.

Dr. Ian McGilvary, Senior Scientist at UHN and Dr. Gary Bader, Affiliate Scientist at Princess Margaret Cancer Centre are co-senior authors of the study. Dr. McGilvary is also a Professor in the Department of Surgery at U of T. Dr. Bader is also a Professor in the Department of Molecular Genetics at U of T.

Dr. Sonya MacParland, a Senior Scientist at UHN, the Research Director of the Ajmera Transplant Centre,  and a Professor in the Department of Laboratory Medicine and Pathobiology at U of T, is the co-senior and corresponding author of the study.

This work was supported by the University of Toronto McLaughlin Centre, Canadian Liver Foundation, the Natural Sciences and Engineering Research Council, the Canadian Institutes for Health Research, and UHN Foundation.

Sonya MacParland is a Tier 2 Canada Research Chair in Liver Immunobiology. 

Clarke ZA, Atif J, Wang X, Liu LY, Wood L, Camat D, Liu Y, Shiwram A, Hyduk SJ, Chung S, Ma XZ, Manuel J, Lok S, Lau TNH, Thoeni C, Michalak TI, McGilvray ID, Bader GD, MacParland SA. A single-cell atlas of the woodchuck liver reveals cellular programs conserved in human HBV infection. J Hepatol. 2026 Jan 22:S0168-8278(26)00019-X. doi: 10.1016/j.jhep.2025.12.030. Epub ahead of print. 

Co-first authors of the study (L to R): Zoe Clarke, a PhD Candidate at the University of Toronto, Dr. Jawairia Atif, a PhD graduate at UHN, and Xinle Wang, a former research student at UHN and a current medical student at U of T.

Digital Clues in Dementia Care

Real-time location systems reveal sleep and activity patterns to support better dementia care.

Image Caption: Real-time location system technology is increasingly used in dementia units to help locate residents and monitor wandering. These systems provide continuous location data that can offer valuable insight into residents’ activity patterns during the day and at night. (Photo by Tim Fraser/KITE Studio)