Study type: Medical/biological study (experimental study)

Pulsing microwave energy: a method to create more uniform myocardial temperature gradients. med./bio.

Published in: J Interv Card Electrophysiol 1997; 1 (1): 57-65

Aim of study (acc. to author)

To study the effects of pulsing microwaves on the temperature gradient in an in vitro ovine endocardial model.

Background/further details

Microwave energy is a possible technique to create large myocardial lesions (e.g. for catether ablation). Microwave ablation may result in prolonged and excessive heating of the endocardium, resulting in thrombus formation.
The authors hypothesized that pulsing of microwave energy might cool the endocardium sufficiently to create a surface temperature similar to the temperature at depth.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 915 MHz
Modulation type: CW
Exposure duration: continuous for 30 s
Exposure 2: 915 MHz
Modulation type: pulsed
Exposure duration: intermittent for 30 min, 1 s on/1 s off
Exposure 3: 915 MHz
Modulation type: pulsed
Exposure duration: intermittent for 30 min, 3 s on/3 s off
Exposure 4: 915 MHz
Modulation type: pulsed
Exposure duration: intermittent for 30 min, 5 s on/5 s off

Exposure 1

Main characteristics
Frequency 915 MHz
Type
Exposure duration continuous for 30 s
Modulation
Modulation type CW
Exposure setup
Exposure source
Setup Each section of tissue was placed on an apparatus that secured the myocardial tissue while allowing the endocardial surface to be exposed.The antenna was placed parallel to the endocardial surface. The assembly was placed in a plexiglass tank containing circulating saline maintained at 37°C.
Parameters
Measurand Value Type Method Mass Remarks
power 9.88 W mean measured - forward power
power 0.59 W mean measured - reflected power

Exposure 2

Main characteristics
Frequency 915 MHz
Type
Exposure duration intermittent for 30 min, 1 s on/1 s off
Modulation
Modulation type pulsed
Pulse width 1 s
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 9.96 W mean measured - forward power
power 1.27 W mean measured - reflected power

Exposure 3

Main characteristics
Frequency 915 MHz
Type
Exposure duration intermittent for 30 min, 3 s on/3 s off
Modulation
Modulation type pulsed
Pulse width 3 s
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 9.95 W mean measured - forward power
power 1.19 W mean measured - reflected power

Exposure 4

Main characteristics
Frequency 915 MHz
Type
Exposure duration intermittent for 30 min, 5 s on/5 s off
Modulation
Modulation type pulsed
Pulse width 5 s
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 9.92 W mean measured - forward power
power 1.27 W mean measured - reflected power

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

Maximum temperatures at 0.5 mm were significantly lower at 63.2 +/- 5.89°C for the 1-second pulse compared with 83.5 +/- 7.31°C for the continuous energy delivery.
Pulse configurations "3 seconds on-3 seconds off" and "5 seconds on-5 seconds off" also resulted in a significantly lower surface temperature than continuous energy delivery. However, temperatures at the 2.0 mm and 3.5 mm depth generated by the pulsing delivery were similar to those temperatures achieved during continuous energy delivery.
These techniques may prevent the excessive endocardial damage that may result in an increased risk of thrombus formation and embolization.

Study character:

Study funded by