Adv EP Lesson 7: Biophysics of Ablation Energies

pulsed field ablation

The use of pulsed electric fields to ablate cardiac tissues, through the mechanism of irreversible electroporation.

irreversible electroporation

When cells are exposed to high electric field gradients, this induces a permanent hyperpermabilization of the cell membrane, which leads to cell death.

how does coagulum and char affect the catheter electrode?

makes flow of energy inefficient and raises the overall system impedance and limit power delivery

purpose of irrigated catheters

address challenges associated with tissue overheating and inefficiencies to help RF energy and tissue heating deeper into tissue

contact force sensor equipped RF catheters allow for

measurement of real-time contact force between the catheter tip electrode and cardiac tissue

contact force

measurement of pressure of catheter tip against tissue

contact forcing sensing RF catheters (purpose, application, assumptions)

help physicians understand how much pressure needs to be applied to targeted tissue to form an efficacious lesion

open irrigated RF platforms

tensile strength of tissue is constant during energy delivery and tissue thickness is uniform

historical progression of cryoablation

mixture of salt solution and crushed ice to reduce tumor size and pain

introduction of cooling gases

introduction of freezing devices cooled by Joule-Thomson effect

cryogenic agents

liquid nitrogen, argon, nitrous oxide

liquid nitrogen specification

used for direct application

argon specification

surgical applications

nitrous oxide specifications

permitted construction of diverse delivery instruments such as needles, probes, balloons

joule-thomson effect

the change in temperature that happens when a real gas or liquid expands through a valve, regulator, or porous plug without any heat entering or leaving the system

medtronic cryoablation system

liquid nitrous oxide is kept under high pressure until it reaches the tip chamber where it expands and transforms from liquid to gas

reaction is heat drawing not creating so cold is not added to the tissue to create a lesion, instead heat is drawn away

cryo leads with a wave of

hypothermia

extracellular ice destroys cells by

formation of ice crystals in the extracellular space as the temp drops, creating an osmotic imbalance that causes the cell to dehydrate and shrink

creation of high concentration of solutes in the cell which triggers a cascade of biophysiological changes that result in cell death

intracellular ice destroys cells by

rupture of the cell membrane

damage to intracellular structures

recrystallization

overall free energy of the crystalline structure reduced with larger, fewer crystals

necrosis

apoptosis

factors influencing cryo lesions

temp, cooling rate, thawing rate

most beneficial cooling rate for cell death

fast cooling rates because more likely to result in cell death in a short time span

most beneficial thawing rate for cell death

slower warming is best for cell death as ice crystals grow and create shearing destruction

how does repetitive freeze cycles influence cryolesions

enhances irreversible cell death via ice formation

how does tissue contact influence cryolesions

better contact = optimal withdrawal of heat

enhances rate of cooling/ice formation

how does local heat sink influence cryolesions

circulating blood flow warms the area being cryoablated and reduces the ability of the catheter to remove heat

how does freeze duration influence cryolesions

prolonged exposure to hypothermic and sub zero temperatures increases likelihood of permanent injury

RF ablation

cryoablation

RF adds heat causing direct cell injury with

resistive heating

conducting heating

leading to hyperthermic coagulation necrosis

cryoablation removes heat causing direct cell injury with

hypothermia

ice formation

apoptosis

necrosis

sequence of cryoablation for inadvertent AV block

what does cryo preserve in a cell

ECM and doesn’t denature proteins

connective tissue

differences in cryo and RF and what they give less risk to

cryo: thrombus

RF: phrenic nerve palsy

what do we target with PFA

the irreversible electroporation zone

electroporation zone depends on electric pulse parameters

thermal damage

irrerversible electroporation

reversible electroporation

which of the electric pulse parameters does the cell survive in

reversible electroporation

more in-depth parameters of your electroporation zone

A- the amplitude of the waveform

B – the pulse duration of the waveform

C – the interphase delay between pulses

D – the delay before the next positive pulse

monophasic pulses

long, positive pulses delivered to a catheter electrode array.

next step of monophasic pulses and why

monophasic pulse train

unipolar energy vectoring

In a unipolar vectoring configuration, the electric field is vectored from intracardiac electrodes to the skin ground patch on the patient.

biphasic vs bipolar

biphasic refers to the positive and negative components of the waveform, bipolar refers to how the energy is vectored.

bipolar vectoring

In a bipolar vectoring configuration, the electric field is vectored from electrodes that neighbor each other directly on the catheter.