Cardioplegia flow dynamics in an in vitro model.

Area of Science:

• Cardiovascular Surgery
• Biomedical Engineering
• Fluid Dynamics

Background:

• Extracorporeal circuits deviate from Poiseuille mechanics, complicating cardioplegia (CP) flow distribution calculations.
• Understanding CP flow dynamics is crucial for effective myocardial protection during cardiac surgery.

Purpose of the Study:

• To quantify cardioplegia (CP) flow dynamics in a simulated coronary atherosclerosis model.
• To assess flow distribution across varying degrees of lumen reduction (51%, 81%, 98%).

Main Methods:

• An in vitro model simulating coronary atherosclerosis with paired restrictions was used.
• Hydraulic fluid movement was assessed under variable flow, temperature, viscosity, and pressure.
• Cardioplegia solutions (4:1 and crystalloid) were delivered via 14- and 18-gauge conduits at 8°C and 100 mmHg.

Main Results:

• Both 4:1 and crystalloid CP solutions showed significantly less total flow through the 14-gauge conduit compared to the 18-gauge (p < 0.0001 and p < 0.001).
• Four-to-one CP at 8°C demonstrated the most favorable fluid dynamics, delivering higher percentages of flow through the smaller lumen conduit.
• Blood CP resulted in the least homogeneous fluid distribution at all tested parameters, irrespective of temperature (8°C vs. 37°C).
• Increased cardioplegic solution hematocrit led to inhomogeneous fluid distribution, independent of delivery temperature or infusion pressure.

Conclusions:

• Cardioplegia delivery in simulated atherosclerotic models is sensitive to conduit size and solution properties.
• Four-to-one cardioplegia at 8°C may offer improved flow distribution in certain conditions.
• Elevated hematocrit in cardioplegic solutions significantly impairs homogeneous flow distribution, posing a risk for uneven myocardial perfusion.