close up of an IV bag

Carnitine may improve heart function in children receiving CRRT

close up of an IV bag

A first-of-its-kind study demonstrated that IV carnitine supplementation is associated with improvement in myocardial strain and repletion of plasma total and free carnitine in children with AKI receiving CRRT.

Supplementation of a special nutrient could help improve heart function in children receiving continuous dialysis in critical care units. The nutrient carnitine plays an essential role in producing energy for use by heart and skeletal muscles. Critically ill children with acute kidney dysfunction often need a continuous dialysis therapy (also known as CRRT, continuous renal replacement therapy) to help remove toxins while kidneys are not working. An unintended consequence of this CRRT is removal of carnitine. Often these critically ill children are unable to eat by mouth and therefore can’t receive carnitine unless it is supplemented. Children’s National Hospital researchers have proven that intravenous carnitine supplementation is associated with repletion of the body’s carnitine supply and may cause improvement in heart function as shown by heart strain analysis (which detects subclinical cardiac dysfunction that may not be apparent by traditional echocardiography).

In a first-of-its-kind study, the Children’s National researchers, Asha Moudgil, M.D., Kristen Sgambat, M.D., and Sarah Clauss, M.D., investigated carnitine deficiency in children receiving CRRT. They demonstrated for the first time that these children become severely deficient in carnitine after being on CRRT for >1 week, and that carnitine supplementation is associated with carnitine repletion and improved heart function. This knowledge can help to guide clinical care, as carnitine can be easily added to the IV nutritional formulations that are typically given to these patients.

Although little was previously known about carnitine status in patients with acute kidney injury (AKI) receiving CRRT, iatrogenic carnitine deficiency related to chronic hemodialysis (HD) in patients with end stage renal disease is a well-known phenomenon. It was theorized that given the continuous removal of solutes by CRRT in combination with lack of dietary intake and impaired production of endogenous carnitine by the kidney in critically ill children with AKI, carnitine would be rapidly depleted.

The latest controlled pilot study (NCT01941823) of 48 children hypothesized that carnitine supplementation would improve left ventricular function in children receiving CRRT. Children ages 1-21 years with AKI requiring CRRT, who were admitted to the pediatric intensive care unit at Children’s National Hospital from 2015 to 2018 were eligible to prospectively enroll in the “CRRT Intervention group,” if they were total parenteral nutrition (TPN)-dependent and not receiving any enteral or IV carnitine prior to enrollment.

The researchers say that “An exciting collaborative effort between nephrology and cardiology made it possible to use a sophisticated technology known as speckle tracking imaging to study the effects of carnitine on heart in this population.” This technology can identify early changes in heart motion, also known as cardiac strain that may not be detected using standard heart imaging techniques.

This is the first study to demonstrate that IV carnitine supplementation is associated with improvement in myocardial strain and repletion of plasma total and free carnitine in children with AKI receiving CRRT. A cohort of pediatric chronic HD patients demonstrated similar benefits in a prior study conducted by Drs. Moudgil and Sgambat. Compared with chronic HD, carnitine is even more rapidly depleted by CRRT, with losses approximating 80% of intake. The effect of carnitine deficiency and supplementation on cardiovascular function in patients receiving CRRT had not been previously investigated.

The pilot study by Drs. Moudgil, Sgambat, and Clauss was single center and limited by small sample size. The small sample size may have limited the ability to detect significant differences in demographics and clinical characteristics and multivariable analyses could not be performed. However, given that it is a pilot study, the findings provide a solid launching point for future investigations to show how supplementation can be best utilized to optimize cardiac outcomes in children receiving CRRT.

Nikki Gillum Posnack

Research team develops new and improved method for studying cardiac function

Nikki Gillum Posnack

While researching how plastic affects heart function in sensitive populations, such as children born with congenital heart defects, Children’s National researcher Nikki Posnack, Ph.D., led a team that developed a new and improved, replicable method of performing simultaneous dual optical mapping to examine electrical activity and calcium for the study of cardiac function.

Since arriving at the Sheikh Zayed Institute for Pediatric Surgical Innovation, researcher Nikki Gillum Posnack, Ph.D., a principal investigator with the institute and assistant professor of pediatrics at the George Washington University School of Medicine and Health Sciences, has been focused on examining how exposure to plastic affects heart function in sensitive populations, such as children born with congenital heart defects. She performs optical mapping to conduct this research, but the industry standard approaches of either using dual cameras or sequential single cameras were cost prohibitive and technically challenging while also diminishing the quality of the imaging results.

Fast forward to July 2019 when Dr. Posnack and her team published “Plasticizer Interaction With the Heart” in the journal Arrhythmia and Electrophysiology, which used imaging techniques to reveal the impact of plastic chemicals on the electrical activity of the heart. Dr. Posnack’s laboratory has since expanded this technique and revealed a new replicable method of performing simultaneous dual optical mapping to examine electrical activity and calcium handling in the heart.

Sharing a new method for studying cardiac function

This groundbreaking method is itself the focus of a new BMC Biomedical Engineering journal article titled “Lights, camera, path splitter: a new approach for truly simultaneous dual optical mapping of the heart with a single camera.”

The article compares and contrasts the current standard for dual camera simultaneous configurations and single camera sequential configurations to Dr. Posnack’s new single camera simultaneous configuration.

Simultaneous dual mapping systems use two probes and dual dyes – one for electrical voltage and the other for calcium. While dual-dye combinations like Di-4-ANEPPS with Indo-1, Di-2-ANEPEQ and calcium green have been developed to separate fluorescence signals by emission, these dye combinations can have spectral overlap, creating the need for non-ideal emission bandpass to negate spectral overlap and/or the inclusion of a calcium probe with an inferior dissociation constant. Additionally, dual-sensor systems require proper alignment to ensure that fluorescence signals are being analyzed from the same tissue region on each individual detector, which could lead to erroneous results. The dual-camera optical setup is expensive, technically challenging and requires a large physical footprint that is often not feasible for basic science and teaching laboratories conducting critical research.

As an alternative, some researchers use a single camera configuration to sequentially image the voltage and calcium probes using excitation light patterning. This approach also has limitations. These single-sensor designs use dual-dye combinations that require two or more excitation light sources, but share a single emission band. Like the dual camera system, this platform design is also technically challenging since the different excitation light wavelengths require light source triggering, camera synchronization and frame interleaving. Due to timing coordination, decreased frame rates, excitation light ramp up/down times and shutter open/close times, single system setups require shorter exposure times compared to dual sensor setups, diminishing the signal-to-noise quality without offering the same temporal fidelity. There is a cost advantage to the single camera system, however, because the additional camera is often one of the most expensive components.

This new single camera, simultaneous dual optical mapping approach is the first multiparametric mapping system that simultaneously acquires calcium and voltage signals from cardiac preparations, using a commercially available optical path splitter, single camera and single excitation light. Using a large field of view sCMOS sensor that is faster and more sensitive, this configuration separates the two emission bands for voltage and calcium probes and simultaneously directs them to either sides of the single, large camera sensor. This protocol employs a commonly used dual-dye combination (RH237 and Rhod2-AM). In contrast, other protocols may require genetically-encoded indicators or fluorescent probes that are not yet commercially available.

The team validated the utility of the approach by performing high-speed simultaneous dual imaging with sufficient signal-to-noise ratio for calcium and voltage signals and specificity of emission signals with negligible cross-talk. Demonstrating the need for simultaneous electrical and calcium sensors, they found that when ventricular tachycardia is induced, there is spatially discordant calcium alternans present in different regions of the heart even when the electrical alternans remain concordant.

Having eliminated the second camera as well as the need for multiple excitation light sources, light pattering and frame interleaving, this system is more cost effective, simpler, and can be easily setup by various types of researchers, not just those with engineering backgrounds.

With a limited research budget and a background in physiology, Dr. Posnack worked collaboratively with her post-doctoral fellow Rafael Jaimes III, an engineer in the Sheikh Zayed Institute for Pediatric Surgical Innovation, to develop a cost-effective system that would enable her to truly study the effects of plastics on the heart.

Multidisciplinary approach

“We’re fortunate to have a multidisciplinary team in the Sheikh Zayed Institute so that I could work with an engineer to develop the technology and system we needed to propel our research,” said Dr. Posnack. “There are so many researchers who have the science background, but not necessarily the technical aptitude, and they get stymied in their research, so we’re proud that this paper will help other researchers replicate the system to study cardiac function.”

The research paper was funded by a grant from the National Institutes of Health as well as support from the Children’s Research Institute, Children’s National Heart Institute and the Sheikh Zayed Institute for Pediatric Surgical Innovation.

The applications for this optical mapping system are significant and Dr. Posnack has been consulted by other research teams looking to implement it in their labs. Additionally, Dr. Posnack has collaborated with several neuroscience teams at Children’s National Hospital, including one that is investigating the effects of hypoxia on brain and heart development, and another that is interested in using image modalities and data processing to analyze calcium as an indicator of neuron firing.

Dr. Posnack continues to use this new dual optical mapping system to further her research as she anticipates the publication of a new article about age-dependent changes in cardiac electrophysiology and calcium handling.