Method and apparatus for selecting operating parameter values in electrophysiology procedures
Methods of selecting operating parameter values for tissue ablation procedures are disclosed. Energy supply parameters may be selected based on inputs such as fluid flow rate, impedance, and the distance from an ablation electrode surface to a target tissue surface. The distance to place an ablation electrode surface from a target tissue surface may be selected based on various operating parameter values and/or operating condition values. Operating curves, lookup tables, or processors may be used to select operating parameter values.
1. A method of selecting an operating parameter value for supplying energy to an ablation electrode, comprising:
(a) receiving a first signal representing a value of a fluid flow rate;
(b) receiving a second signal representing a value of an impedance;
(c) receiving a third signal representing a value of a positive distance from an ablation electrode surface to a target tissue surface; and
(d) selecting a value for an operating parameter for supplying energy to the ablation electrode as a function of the first, second and third signals;
wherein:
(d) comprises selecting the operating parameter value based on relationships established between (1) values of the operating parameter and (2) fluid flow rate values, impedance values and distance values;
the relationships are established with analyses of a numerical model of transmission of energy to biological tissue by an ablation electrode;
the numerical model comprises a finite element model; and
to model a tissue temperature distribution, the numerical model comprises equations for modeling an electric field created by the ablation electrode, heat generated by the electric field, and a velocity field of the fluid flow.
2. The method according to claim 1 wherein the numerical model comprises the following equations to model tissue temperature distribution:
∇
·
σ
∇
φ
=
0
;
ρ
c
(
δ
T
δ
t
+
U
δ
T
δ
x
+
V
δ
T
δ
y
+
W
δ
T
δ
z
)
=
∇
·
(
k
∇
T
)
+
J
·
E
;
ρ
(
δ
U
δ
t
+
U
δ
U
δ
x
+
V
δ
U
δ
y
+
W
δ
U
δ
z
)
=
-
δ
P
δ
x
+
μ
(
∂
2
U
∂
x
2
+
∂
2
U
∂
y
2
+
∂
2
U
∂
z
2
)
;
ρ
(
δ
V
δ
t
+
U
δ
V
δ
x
+
V
δ
V
δ
y
+
W
δ
V
δ
z
)
=
-
δ
P
δ
y
+
μ
(
∂
2
V
∂
x
2
+
∂
2
V
∂
y
2
+
∂
2
V
∂
z
2
)
;
ρ
(
δ
W
δ
t
+
U
δ
W
δ
x
+
V
δ
W
δ
y
+
W
δ
W
δ
z
)
=
-
δ
P
δ
z
+
μ
(
∂
2
W
∂
x
2
+
∂
2
W
∂
y
2
+
∂
2
W
∂
z
2
)
;
and
δ
U
δ
x
+
δ
U
δ
y
+
δ
U
δ
z
=
0.
3. The method according to claim 1 , wherein the relationships are established with analyses of an in vitro model of transmission of energy to biological tissue by an ablation electrode.
4. The method according to claim 1 , wherein the second signal, representing the value of the impedance, comprises a signal representing an electrode geometry.
5. The method according to claim 1 , wherein the second signal, representing the value of the impedance, represents an impedance into which energy is supplied.
6. The method according to claim 1 , wherein (d) comprises selecting a plurality of values for an operating parameter, each value corresponding to a separate time during the supplying of energy to the ablation electrode.
7. The method according to claim 1 , wherein (d) comprises selecting a value for each of a plurality of operating parameters.
8. The method according to claim 1 , wherein the operating parameter is a maximum temperature allowed for the ablation electrode.
9. The method according to claim 1 , wherein the operating parameter is power applied to the ablation electrode.
10. The method according to claim 1 , wherein the operating parameter is voltage of the energy supplied to the ablation electrode.
11. The method according to claim 1 , wherein (d) comprises selecting the operating parameter value using a processor programmed with an algorithm.
12. The method according to claim 1 , wherein (a) comprises receiving the first signal from a fluid flow sensor.
13. The method according to claim 1 , wherein the first signal is generated by an input entered by a user.
14. The method according to claim 1 , wherein (b) comprises receiving the second signal from an impedance sensor.
15. The method according to claim 1 , wherein (c) comprises receiving the third signal from a distance sensor.
16. A method of supplying energy to an ablation electrode comprising the method of claim 1 and further comprising:
(e) controlling an energy supply such that energy is supplied to the ablation electrode at the selected operating parameter value.
17. The method according to claim 1 , wherein the first signal, representing a value of a fluid flow rate, represents a value of a blood flow rate.
18. The method according to claim 17 wherein (d) comprises selecting the operating parameter value based on relationships established between (1) values of the operating parameter and (2) blood flow rate values, impedance values and distance values.
19. The method according to claim 18 , wherein the relationships are established with analyses of a numerical model of transmission of energy to biological tissue by an ablation electrode.
20. The method according to claim 19 wherein the numerical model comprises a finite element model.