Ablation Energy Sources

radiofrequency

electromagnetic waves generated by alternating currents fed to an antenna; conducted (not radiated), heat

RF current

oscillate between positive and negative

direct current

cause muscle to contract and not relax

RF is similar to ___ in regards to ___ and ___

Low frequency AC/DC, heat generation, lesion formation

do RF oscillations stimulate cardiac and skeletal muscle

no, they are too rapid

what frequency do arrhythmias occur is response to

low frequency (60Hz)

how is RF delivered

unipolar or bipolar

unipolar RF

energy from ablation catheter tip to large dispersive electrode (sink) applied to skin

unipolar RF energy flow

ablation catheter, through myocardium, to electrode

where is highest current density in unipolar Rf

catheter electrode

what is most necessary to prevent burns with unipolar RF

good skin contact and large surface area

lesions with unipolar RF

narrow and deep

where is power also delivered with unipolar RF

blood pool surrounding tissue (good conductor)

Bipolar sandwhich

two ablation catheter tips with myocardial wall sandwiched between

bipolar 2:1

electrodes placed on one side of myocardial wall and transmits power to adjacent electrodes

sandwich vs 2:1 pro

increased transmurality vs long/larger but shallow

when is sandwich adventagous

thicker tissue

example of when to use sandwich

septal at or vt circuits or intramural freewall vt; one catheter epicardially and the other endocardially

how does RF create lesions

ions move in response to alternating current and oscillate; oscillations generate heat due to friction

resistive heating

contact with electrode (2mm) is directly heated; resisting but being forced to move

conductive heating

remainder of tissue heating occurs by heat conduction; cooking steak

how long and what temp RF electrode reaches steady state

10 seconds at 80-90C

how long does RF need to make lesions

30-60sec

how long does conduction of heat to deeper tissue require

1-2min

____ power and ___ tissue temp ___ lesions size with RF

higher, higher, increase

how high can RF get tissue

110C

what happens above 110 tissue temp with RF

tissue vaporization and prevents further heating

what does boiling plasma do

carbonization (char) and produce coagulum on electrode, increasing electrical impedence

what can small piece of coagulum (charr) do

break off and cause stroke

what is ideal tissue temp RF

50-90

alternating current

positive to negative cause ions to oscilate

convective cooling

heat loss due to blood flow around catheter; cools endocardial surface (bad)

where is highest temp seen in convective cooling RF

below endocardial surface because nothing cooling it, less tissue death at surface

limits of convective cooling

power and time

factors affecting convective cooling

unstable catheter position, poor contact, high blood flow

exploiting convective cooling allows

more power to be delivered into tissue (actively cooled)

how does exploiting convective cooling work

increase depth of conductive heating and avoid very high endocardial surface temps (reduce blood boiling and coagulum formation)

actively cooled RF ablation

allows higher amounts of RF power for longer duration; larger lesion formation

where is maximum temp in actively cooled RF ablation

myocardium

two methods of active cool RF ablation

closed-loop catheter and open-irrigation

closed-loop catheter

internal cooling; can achieve slightly larger lesion volumes and depths (not common)

open-irrigation

internal and external cooling; better at cooling electrode/tissue interface; uses saline infusion pump to push saline to cool outside (most common)

open-irrigation catheter considerations

kidney issue and fluid overload

benefits of active coolingq

small electrode with more power or longer electrode more damage, get done fast

how to optimize lesion size

increase electrode temp, increase RF power delivery, increase RF duration, increase electrode length, increase tissue contact

force contact

10g for optimal lesion; too much = perforation

impedance monitoring

determines lesion formation

good catheter contact before heating (RF)

90-120 ohm

proper lesion formation

5-10 ohm reduction in impedance; transferring energy better

coagulum formation

abrupt rise in impedance > 250 ohms

what does high RF power cause

superheating tissue above 100C = steam pops

steam pop

boiling water within tissue under electrode; gas bubble can form with continuous energy application and might burst

what do steam pops cause

crater formation or myocardial perforation (thin tissue perforates)

common procedure to cure AFib

RF or cryo PVI

hyperthermal ablation challenge

difficult to control lesion, unintended injury to nontargeted tissue, close to esophagus and phrenic

electric field effect on cells

allows tissue specificity; every cell has resting voltage and add electricity to it

electroporation

holes opening on membrane of cell

electroporation threshold

different cell types have different electroporation thresholds: nerves most, then esophagus, cardiomyocytes have lowest

pulse duration effect

delivering voltages for different amounts of time impacts effects of cells

millisecond pulses

highest thermal effect with highest occurrence of muscle contraction

nanosecond pulses

lowest thermal effect with lowest occurrence of muscle contractions

reversible electroporation

pore opens but closes and heals (do not want)

irreversible electroporation

ideal; medium pulse duration and electric field strength

thermal (bad)

pfa moving too fast and creating heat; long pulse duration and high electric field strength

irreversible electroporation and lesions

exposes cells to electric fields that break down cell membrane; permeability causes death

what cells resistant to IRE

blood vessels and nerves; good treatment for nonresectable tumors in close proximity to major blood vessels or nerves

goals of PFA

irreversible electroporation aimed at achieving atrial myocardial injury while reducing nontarget injury

RFA hyperthermal lesions may damage

neighboring cells/structures

PFA has no thermal signature

true; isothermal

PFA can specifically create myocardial lesions

true; tissue specificity

PFA energy delivery is on the order of ___ while RFA is ___

milliseconds; minutes

cryoablation

absorbs heat from surrounding tissue ; like AC

extracellular ice formation

ice forms outside in response to mild temps of 0 to sub20 C

hypertonic stress causes cell shrinkage

reversible within 30-60 seconds

intracellular ice formation

tissue cooled sub40C, ice also forms outside and inside

irreversible

propogate from one cell to another from intercellular channels

cryo lesions formation

max tissue damage at electrode, surrounding experiences incomplete hypothermia

thawing intracellular ice damages tissue is good

true

RF max tissue damage depth

below electrode

cryoablation lesion size factors

duration (longer is better)

freezing rate (freezes faster for less area)

thawing rate (faster is more damage)

electrode contact (more contact better)

`cryomapping

performed at -32C to be reversible within 80sec

catheter adhesion

allow program electrical stim to test functionality

cryoablation

after cryomapping, irreversible

cryo advantages

reversible/modify lesions, assess efficieny and safety of ablation site, lower coagulum and charring, cryoadhesion, painless

cryoadherence

super focal lesion

cryo avnrt

no av block but could come back

cryo pvi

cryoballoon (limited to shape of balloon and PV), dont have to make multiple lesions, phrenic nerve injury is common, esophageal fistula