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BIOPHYSICS OF
RADIOFREQUENCY ABLATION
Michael G. Katz, M.D.
Electrophysiology Fellow, University of Rochester
October 18, ...
ABLATION MODALITIES
Hyperthermic

Standard RF
Cooled RF
Focused Ultrasound
Laser
Microwave
Hypothermic

Cryoablation
RADIO FREQUENCY

Resistive / electrical heating
frequency of 500 kHz
RF SYSTEMS AND UNIPOLAR
VS BIPOLAR
P ~ J2
J ~ 1/r2
P ~ 1/r4
}

}

Steady state
Rapid rise

Prog. Cardiovsc. Dis. 1995:37;185
QUIZ
Increasing the size of the tip of an RF catheter ablation while
maintaining a constant power level, duration of power...
THERMAL LATENCY
PCE 1989:12;962
TEMPERATURE AND
POWER

Prog. Cardiovsc. Dis. 1995:37;185
Circ Res 1990:67;124
RF LESIONS - WHAT WE’VE
DISCUSSED SO FAR:
Temperature at the catheter tissue interface is a determinate
of lesion size.
Ab...
IMPEDANCE
RAPID IMPEDANCE RISE
CONVECTIVE COOLING
Pop Quiz
A
B
HOWEVER...
When the power not limited, catheters large distal electrodes create
LARGER lesions
↑ electrode surface area in...
QUIZ

Which catheter will create the larger lesion if all other
parameters are constant (power = 30 W, time = 60 sec,
cont...
cooled, RF c power increase

traditional, non-cooled RF

cooled, RF s power increase
IRRIGATED CATHETER
DESIGN
CONVECTIVE COOLING
Surface cooling
reduces risk of boiling
and coagulum formation
Higher power can be
used
Higher power re...
QUIZ
At regions of high blood flow (as compared to low flow),
using temperature-controlled RF is likely to:
1. Overheat th...
COMPARISON OF
ABLATION ELECTRODES
TISSUE/EP EFFECTS OF
RF
GUIDING LESION
FORMATION AND
MONITORING
ASSSESSMENT OF CATHETERTISSUE INTERFACE
Without good contact, only intracavitary blood will be heated, with insufficient m...
EVIDENCE OF EFFECTIVE
ABLATION
TITRATION
Titration to efficacy: a specified power or loss of electrograms
Titration to safety: avoid complications of exc...
In an irrigated tip catheter...
CONCLUSIONS
Tissue injury occurs reproducibly at a temperature of about
50°C
Heat transfer in tissue is a predictable biop...
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
Biophysics of Radiofrequency Ablation
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Biophysics of Radiofrequency Ablation

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Biophysics of Radiofrequency Ablation

  1. 1. BIOPHYSICS OF RADIOFREQUENCY ABLATION Michael G. Katz, M.D. Electrophysiology Fellow, University of Rochester October 18, 2013
  2. 2. ABLATION MODALITIES Hyperthermic Standard RF Cooled RF Focused Ultrasound Laser Microwave Hypothermic Cryoablation
  3. 3. RADIO FREQUENCY Resistive / electrical heating frequency of 500 kHz
  4. 4. RF SYSTEMS AND UNIPOLAR VS BIPOLAR
  5. 5. P ~ J2 J ~ 1/r2 P ~ 1/r4
  6. 6. } } Steady state Rapid rise Prog. Cardiovsc. Dis. 1995:37;185
  7. 7. QUIZ Increasing the size of the tip of an RF catheter ablation while maintaining a constant power level, duration of power delivery and perpendicular catheter tip orientation to the tissue surface will: 1. Decrease lesion size 2. Increase lesion size ↑ tip size → ↓power density 3. Result in no significant change in lesion size
  8. 8. THERMAL LATENCY
  9. 9. PCE 1989:12;962
  10. 10. TEMPERATURE AND POWER Prog. Cardiovsc. Dis. 1995:37;185
  11. 11. Circ Res 1990:67;124
  12. 12. RF LESIONS - WHAT WE’VE DISCUSSED SO FAR: Temperature at the catheter tissue interface is a determinate of lesion size. Ablation catheter diameter is a determinate of lesion size. Tissue temperature diminishes rapidly as you move away from tissue catheter contact. Power is directly proportional to the degree of resistive tissue heating
  13. 13. IMPEDANCE
  14. 14. RAPID IMPEDANCE RISE
  15. 15. CONVECTIVE COOLING Pop Quiz A B
  16. 16. HOWEVER... When the power not limited, catheters large distal electrodes create LARGER lesions ↑ electrode surface area in contact with bloodstream, resulting in augmented convective cooling effect, and ↑ the volume of tissue directly heated
  17. 17. QUIZ Which catheter will create the larger lesion if all other parameters are constant (power = 30 W, time = 60 sec, contact force 20 gm-force) 1. Non perfused 7 Fr 4 mm tip catheter 2. Perfused 7 Fr 4 mm tip catheter If power held constant → ↓ temp at tip of perfused catheter
  18. 18. cooled, RF c power increase traditional, non-cooled RF cooled, RF s power increase
  19. 19. IRRIGATED CATHETER DESIGN
  20. 20. CONVECTIVE COOLING Surface cooling reduces risk of boiling and coagulum formation Higher power can be used Higher power results in greater depths of volume heating Surface cooling prevents monitoring of lesion formation High power can cause superheating in subendocardial layers and pop lesions If ablation is power limited, power dissipation into the circulating blood pool can yield decreased lesion depth
  21. 21. QUIZ At regions of high blood flow (as compared to low flow), using temperature-controlled RF is likely to: 1. Overheat the tissue ↑ flow → ↑power to maintain temp → ↑ lesion size / depth 2. Less likely to overheat the tissue 3. No difference
  22. 22. COMPARISON OF ABLATION ELECTRODES
  23. 23. TISSUE/EP EFFECTS OF RF
  24. 24. GUIDING LESION FORMATION AND MONITORING
  25. 25. ASSSESSMENT OF CATHETERTISSUE INTERFACE Without good contact, only intracavitary blood will be heated, with insufficient myocardial temperature to cause necrosis of targeted tissue. Parameters used to assess contact: beat-to-beat variability in electrograms baseline electrode impedence changes in impedance and temperature during ablation fluoroscopy visual assessment by echocardiography pacing capture threshold tactile feedback
  26. 26. EVIDENCE OF EFFECTIVE ABLATION
  27. 27. TITRATION Titration to efficacy: a specified power or loss of electrograms Titration to safety: avoid complications of excessive energy delivery. coagulum formation steam pops cardiac perforation collateral damage (coronary arteries)
  28. 28. In an irrigated tip catheter...
  29. 29. CONCLUSIONS Tissue injury occurs reproducibly at a temperature of about 50°C Heat transfer in tissue is a predictable biophysical phenomenon Factors including temperature, power, time, impedance, cooling, and contact force all contribute to lesion size and depth

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