Document Type

Presentation

Publication Date

Fall 10-5-2026

Abstract

Background: Myocardial protection strategies employed in cardiac surgery and transplantation have centered around in situ cardioplegic arrest combined with hypothermic cooling to mitigate myocardial damage and reperfusion injury. The cardioplegic solution is delivered directly to the myocardium at 4°C, producing electromechanical silencing and reduced metabolic demand, while the patient is typically cooled systemically to ~33°C. In transplantation static cold storage at ~4°C has been the standard method for preserving donor hearts for the past 60 years. A handful of cardiac surgical reports have examined warm-ischemic myocardium, but the molecular trajectory of myocardium receiving neither protection (mimicking infarction or the warm ischemic interval preceding donation after circulatory death) has been minimally characterized at the transcript level in human tissue. None have employed serial, paired-sample design. Objectives: To elucidate the underlying molecular consequences of warm and cold ischemia over a clinically relevant time course and evaluate molecular changes in a paired sample design. Method: Six donor hearts (50% male and 50% female, mean age of 44 yrs, mean LVEF 55%) were procured following the standards of transplantation, receiving in situ cold cardioplegia and timely excision. The left anterior descending artery (LAD) was ligated in situ prior to cardioplegia to create a region of warm ischemia without cardioplegic flow. Left ventricular myocardial tissue samples were maintained under static cold storage (cooler with ice; 50mL cold saline-containing conical, 4 °C) or warm static storage (50 mL warm saline-containing conical maintained in a 37 °C water bath). Sampling occurred at nine serial timepoints; T0 (on average 10 minutes (min) post cross-clamp), T1 (15 min post), T2 (30 min post), T3 (45 min post), T4 (60 min post), T5 (90 min post), T6 (120 min post), T7 (180 min post), and T8 (240 min post). At each timepoint, samples were flash frozen, with parallel 4% paraformaldehyde and glutaraldehyde fixation, and internal/external temperatures were recorded. Results: Internal and external tissue temperatures diverged over time. Cold-sampled tissue cooled from 37°C baseline to a median of ~7°C at T0, reaching 2–4°C by T3–T4 and remained hypothermic thereafter. Warm-sampled tissue remained at 28–32°C throughout the observation period. RNA integrity and transcripts were stable over time in cold-ischemic tissue (RIN ~8 across all timepoints; R² = 0.08), but declined progressively under warm ischemia, from RIN ~8 at T0 to ~4.5 by T7–T8 (R² = 0.84). Unsupervised clustering separated samples primarily by phenotype (cold vs. warm) rather than by donor or collection time (Figure 5). Cold-ischemic samples showed a quiescent transcriptome under cold ischemic conditions, whereas warm ischemic samples showed immediate induction and transcriptional changes (Figure 6). Conclusions: Cardioplegic arrest with hypothermic storage preserved RNA integrity and limited differential expression of transcripts over a four-hour window, while unprotected warm ischemia produced progressive transcriptional changes, RNA degradation, and loss of transcript integrity. These findings characterize the transcriptional trajectories of ischemic injury and suggest cardioplegic arrest with hypothermia helps retain transcriptomic molecular integrity across a clinically meaningful window. This study points toward a dynamic, molecular framework for staging ischemia and elucidating the molecular targets for biomarker discovery for extended myocardial preservation strategies.

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