For the last four years, Thomas G. Diacovo, MD, division chief of the UPMC Newborn Medicine Program, and director of Neonatal Cardiovascular Research at the Heart Institute at UPMC Children’s Hospital of Pittsburgh, has been leading new studies to combat the development of acute thromboembolic events (ATE) in neonates who require surgical repair for complex congenital heart conditions.
Rates of thrombosis in postoperative neonatal cardiac patients, and in particular those requiring placement of a systemic to pulmonary artery shunt, are the highest of all pediatric patients treated in specialized centers. The current literature on the subject shows ranges of shunt thrombosis anywhere from 17 to 34 percent, with corresponding morbidity and mortality reflective of such high rates of blood clots. For Dr. Diacovo and his study companions, these rates of thromboembolic disease have been, and continue to be, completely unacceptable.
“There have been many anticoagulation agents developed for adults over many decades, going all the way back to the synthesis of aspirin in the mid-1800s, that have proven to be extremely successful in preventing clot formation in adults and saving lives. However, virtually none of these agents has ever been tested or confirmed in pediatric and neonatal patients to understand their efficacy, safety, pharmacodynamics, and optimal dosage,” says Dr. Diacovo.
Platelet function in neonates also has been understudied, and the availability and development of technologies to rapidly assess platelet response in pediatric patients to various agonists and antagonists has lagged in development.
However, Dr. Diacovo’s research has begun to upend this suboptimal treatment paradigm with new findings, technological advances, and animal models that are now leading to important new clinical trials in human subjects.
In 2017 in the Journal of the American College of Cardiology, Dr. Diacovo and colleagues outlined their novel and groundbreaking process analyzing responses to single agents and combinations of platelet agonists and antagonists, and their findings of the efficacy and optimal usage of cangrelor on P2Y12 receptor function in neonatal and pediatric congenital heart disease (CHD) patients.1
Using a novel mouse model created by the Diacovo lab while at Columbia University, and microfluidic devices by colleagues at the University of Pennsylvania capable of assessing clotting using 20-times less blood than in standard testing platforms (a significant advancement and desirous approach, particularly in neonates where blood draw amounts are limited for safety concerns), the researchers were able to not only show efficacy of the entire testing platform for determining platelet reactivity in these subjects, but they were also able to show the in vivo efficacy of cangrelor, setting the stage for the first trial in neonatal cardiac patients.
“A major success of our work during the first three years was our ability to go from our basic science studies to preclinical and then rapidly translate it into a phase 1 clinical trial that we are in the process of finishing,” says Dr. Diacovo.
The types of studies Dr. Diacovo and colleagues are engaged in are providing the framework and foundation for a new paradigm of treatment determination to combat the scourge of arterial thromboembolic disease. By providing sound, evidence-based guidance and real-time analysis of platelet function in individuals, the most appropriate course of pharmacologic therapy to mitigate clot formation risk may be predicted.
“A large part of our research agenda from the outset has been to test these novel drugs in animal models in order to make better predictions of how these pharmaceutical agents will actually work before introducing them into a child. Just looking at laboratory values has little bearing on actual function. This functionality is a crucial part of the equation we must work to understand,”
says Dr. Diacovo.
The existing methodologies and dearth of evidence to support treatments to combat arterial thromboembolic disease have relied mainly on extrapolation.
“Our preliminary work shows a vast difference between the two age groups, which you may understand intuitively, but because no one has been able to do these studies in the past we lack basic, concrete knowledge of how these agents work in the very young. Knowing what the true pharmacokinetics or pharmaco-dynamics are of these drugs in our neonatal patients, again, is the crux of our entire research endeavor,” says Dr. Diacovo.
Cangrelor Use in Neonates
This investigator-initiated study (ClinicalTrials.gov Identifier: NCT02765633) being conducted at UPMC Children’s and led by Dr. Diacovo is assessing the pharmacodynamics and pharmacokinetics of cangrelor in neonatal patients who are at risk for thrombosis related to the use of pulmonary arterial shunting.
Dr. Diacovo and his study collaborators seek to enroll up to 20 participants who are up to 28 days in age in this trial to analyze the safety and mechanistic properties of cangrelor in four discrete doses. The trial will start with a cohort of four subjects receiving the lowest dose and progress over time to additional cohorts of four — each receiving subsequently larger doses of the agent.
Apixaban and Heart Disease in Children
UPMC Children’s is participating in a multicenter, randomized study investigating the use of apixaban to prevent thrombo-embolism in pediatric patients with congenital heart disease or an acquired version of heart disease (ClinicalTrials.gov Identifier: NCT01707394).
Sponsored by Bristol-Myers Squibb in collaboration with the Pediatric Heart Network and Pfizer, the study — titled “Safety and Pharmacokinetics of Apixaban Versus Vitamin K Antagonist or LMWH in Pediatric Subjects with Congenital or Acquired Heart Disease for Thromboembolism Prevention” — is a badly needed examination of how this antithrombotic functions in pediatric patients, and how it compares in usage and efficacy with low molecular weight heparin (LMWH) or
vitamin K antagonist (VKA).
Dr. Diacovo is serving as the site primary investigator for this study, and is collaborating internally with colleagues from the UPMC Heart Institute at UPMC Children’s Hospital of Pittsburgh.
This apixaban study is being conducted in pediatric patients from age 3 months to 18 years. Various aspects of pharmacokinetics and safety will be examined, as well as outcomes related to bleeding events, fatal bleeding, and bleeding that requires some form of medical or surgical intervention to restore hemostasis.
References and Further Reading
1Kaza EA, Egalka MC, Zhou H, Chen J, Evans D, Prats J, Li R, Diamond SL, Vincent JA, Bacha A, Diacovo TG. P2Y12 Receptor Function and Response to Cangrelor in Neonates With Cyanotic Congenital Heart Disease. J Am Coll Cardiol. 2017; 2(4): 465-476.
Neonatal and Pediatric Platelet Function and Pharmacology.
NIH Project Number: 7R01HD081281-04.
Principal Investigator Thomas G. Diacovo, MD.