Retrograde Priming During OCS Cardiac Procurement

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Technical Draft and Procedural Overview

Introduction

Retrograde priming during TransMedics Organ Care System (OCS) Heart cardiac procurement is an advanced perfusion maneuver designed to optimize coronary de-airing, improve myocardial washout, reduce embolic burden, and establish controlled myocardial reperfusion prior to normothermic ex vivo perfusion. The technique is particularly valuable in donation after circulatory death (DCD) procurement, marginal donor hearts, prolonged warm ischemic scenarios, and cases involving anticipated coronary microembolic load.

Unlike conventional antegrade-only priming, retrograde priming introduces oxygenated donor blood or preservation solution through the coronary sinus or via controlled retrograde aortic root filling after cross-clamp release, allowing backward perfusion of the coronary venous circulation and myocardial capillary bed. This facilitates enhanced flushing of residual metabolites, thrombotic debris, air microemboli, and ischemic byproducts before the heart is transitioned onto the OCS circuit.

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Physiologic Rationale

The retrograde approach is based on several physiologic principles:

1. Enhanced Coronary De-airing
Retrograde perfusion allows trapped air within coronary arteries and microvasculature to be displaced toward the aortic root and venting sites.
2. Improved Washout of Ischemic Metabolites
Lactate, potassium, inflammatory mediators, and anaerobic metabolites accumulated during warm ischemia can be evacuated more effectively.
3. Homogeneous Myocardial Reperfusion
Retrograde filling may improve distribution to territories with transient antegrade obstruction or vasospasm.
4. Reduction of Endothelial Injury
Gradual controlled reperfusion minimizes abrupt shear stress and reperfusion injury.
5. Protection During DCD Recovery
Particularly important following normothermic regional perfusion (NRP) or direct procurement and perfusion (DPP), where ischemic exposure is unavoidable.

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Indications

Retrograde priming is most commonly considered in:

* DCD heart procurement
* Extended warm ischemic intervals
* Marginal donor myocardium
* Older donors
* Donors with left ventricular hypertrophy
* Suspected coronary microthrombi
* Post-arrest donors
* Hearts requiring prolonged transport
* Re-operative donor sternotomy
* Cases with significant intracardiac air concern

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Contraindications and Limitations

Relative contraindications include:

* Coronary sinus injury
* Severe right atrial trauma
* Congenital coronary sinus anomalies
* Extensive coronary sinus thrombosis
* Severe aortic insufficiency
* Uncontrolled bleeding during reperfusion
* Fragile donor myocardium prone to edema

Potential risks include:

* Coronary sinus rupture
* Myocardial edema
* Inadequate coronary venous drainage
* Arrhythmias during reperfusion
* Excessive perfusion pressures

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Equipment Required

Standard OCS Heart Components

* OCS heart console
* Aortic cannula
* Pulmonary artery cannula
* Venous reservoir
* Oxygenator
* Perfusion tubing set
* Priming blood reservoir

Additional Retrograde Priming Equipment

* Coronary sinus catheter or retrograde cardioplegia catheter
* Pressure monitoring line
* Y-connectors
* De-airing syringes
* Roller clamp system
* Warm oxygenated donor blood
* Preservation solution
* Air evacuation ports