(H-303) Quantifying 3D Temperature Distribution Evolution Within the Heart During Heart Transplantation

Introduction:: Organ storage and transportation are critical steps for the success of organ transplantation. Static cold storage (SCS) of hearts for heart transplantation (HTx) remains the standard approach. However, SCS may involve damage to the tissue resulting from extended hypothermic preservation, potentially affecting organ viability. Moreover, the temperature distribution on and within the heart is unknown during heart transplantation. Therefore, there is an interest to study different stages of the heart transplantation process towards determining the 3D temperature distribution on and within the heart. There could be a possibility of having a hypothermic injury in different parts of the heart due to the temperatures that are being used currently in specific parts of the heart transplantation process such as SCS icebox storage and transport.


Materials and Methods:: The heart transplantation process were divided into four stages: (i) when the heart is cooled within the donor via cardioplegia. (ii) when it is extracted from the donor and checked outside the body. (iii) when it is stored and transported via SCS Icebox and (iv) when it is implanted within the recipient. To determine the 4D (3D + time) temperature distribution for each of the above stages, we utilize a custom-developed heat transfer and computational fluid dynamic simulation of the heart using COMSOL Multiphysics. The transient Bioheat transfer equation was solved using time-dependent simulations on an anatomically accurate 3D model of the heart with empirically obtained thermal properties for the cardiac muscle and surrounding tissues. Stage 1 was modelled using transient conduction and advection by the cardioplegia fluid flow for several initial temperature conditions. For the second stage of the process, the heart simulation was performed by using the equilibrium temperature reached in the first stage as an initial condition. Stage 3 was modelled for several hours of transport using transient conduction within the icebox.


Results, Conclusions, and Discussions:: Stage 1 results indicated a heterogeneous cooling behaviour of the heart during cardioplegia. Due to anatomical differences including wall thickness variations, the left heart takes around 2-3x longer to cool down compared to the right heart. Different cardioplegia temperatures between 1 degree Celsius and 10 degrees Celsius demonstrated that around 25 minutes are needed to effectively cool the heart down to temperatures between 5 degrees Celsius and 8 degrees Celsius. The heart warms up heterogeneously during Stage 2 (examination outside the body), before cooling down again via transient conduction within the icebox. Portions of the heart near the ice had a greater tendency to cool below 2 degrees Celsius, indicating a risk of hypothermic injury.

The results obtained suggest that the thermal environment on and around the heart plays an important role in 3D temperature distribution during heart transplantation. The cooling of the heart using cardioplegia depends strongly on the initial temperature of the cardioplegia solution, circulation flow rate and time. The equilibrium temperature from Stage 1 provides the initial conditions for Stage 2 (and so on for each subsequent stage). Depending on the time taken to examine the heart for Stage 2, the heart undergoes heterogeneous warming prior to Stage 3 (icebox). If the heart is cooler after stage 2 (between 4 and 6 degrees Celsius) then portions of the heart could approach zero degrees Celsius in the icebox, which could lead to hypothermic injury.


In conclusion, our study revealed that the temperature distribution inside the heart has a heterogeneous nature due to anatomy and variations in each stage of the heart transplantation process. Furthermore, the interconnected nature of each stage and the temporal variations can result in sub-optimal cooling, especially during the transporting stage. Further analysis is required to optimize these processes.








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