Submyometrial vasopressin injection before microwave ablation of vascular-rich submucosal myomas: a preliminary case study

Temperature-dependent dielectric properties of human uterine fibroids over microwave frequencies

Microwave ablation is under investigation as a minimally-invasive treatment for uterine fibroids. Computational models play a vital role in the development, evaluation and characterization of candidate ablation devices. The temperature-dependent dielectric properties of fibroid tissue are essential for accurate computational modeling.Objective:To measure the broadband temperature-dependent dielectric properties of uterine fibroids excised during hysterectomy procedures.Methods: The open-ended coaxial probe method was employed for measuring the broadband dielectric properties of freshly excised human uterine fibroid samples (n = 6) obtained from an IRB-approved tissue bank. The dielectric properties (relative permittivity,ε_r, and effective electrical conductivity,σ_eff) were evaluated at temperatures ranging from 23 °C-150 °C, over the frequency range of 0.5-6 GHz. Linear piecewise parametrization with respect to temperature and quadratic parametrization with respect to frequency was applied to characterize broadband temperature-dependent dielectric properties of fibroid tissue.Results: The baseline room temperature values ofε_rvary from 57.5 ± 5.29 to 44.5 ± 5.77 units andσ_effchanges from 0.91 ± 0.19 to 6.02 ± 0.7 S m^-1over the frequency range of 0.5-6 GHz. At temperatures close to the water vaporization point,ε_r, drops considerably i.e. to 12%-14% of its baseline value for all measured frequencies.σ_effvalues initially rise till 98 °C and then fall to 11%-13% of their baseline values at 125 °C for frequencies ≤2.45 GHz. Theσ_efffollows a decreasing trend for frequencies >2.45 GHz and drops to ∼6 % of their baseline room temperature values.Conclusion:The temperature dependent dielectric properties of uterine fibroid tissues over microwave frequency range are reported for the first time in this study. Parametric models of uterine fibroid dielectric properties are also presented for incorporation within computational models of microwave ablation of fibroids.

Transcervical microwave ablation in type 2 uterine fibroids via a hysteroscopic approach: analysis of ablation profiles

Type 2 uterine fibroids are challenging to resect surgically as ≥ 50% volume of myoma lies within the myometrium. A hysteroscopic approach for ablating fibroids is minimally-invasive, but places a considerable burden on the operator to accurately place the ablation applicator within the target. We investigated the sensitivity of transcervical microwave ablation outcome with respect to position of the ablation applicator within 1 - 3 cm type 2 fibroids.Methods:A finite element computer model was developed to simulate 5.8 GHz microwave ablation of fibroids and validated with experiments inex vivotissue. The ablation outcome was evaluated with respect to applicator insertion angles (30°, 45°, 60°) , depth and offset from the fibroid center (±2 mm for 3 cm fibroid and ±1 mm for 1 cm fibroid) with 35 W and 15 W applied power for 3 cm and 1 cm fibroids, respectively. Power deposition was stopped when thermal dose of 40 cumulative equivalent minutes at 43 °C (CEM43) was accrued in adjacent myometrium.Results:Within the range of all evaluated insertion angles, depths and offsets, the ablation coverage was less sensitive to variation in angle as compared to depth and offset, and ranged from 34.9 - 83.6% for 3 cm fibroid in 140 - 400 s and 34.1 - 67.9% for 1 cm fibroid in 30 - 50 s of heating duration. Maximum achievable ablation coverage in both fibroid cases reach ∼ 90% if thermal dose is allowed to exceed 40 CEM43 in myometrium.Conclusion:The study demonstrates the technical feasibility of transcervical microwave ablation for fibroid treatment and the relationship between applicator position within the fibroid and fraction of fibroid that can be ablated while limiting thermal dose in adjacent myometrium.

Assessment of the perioperative effect of vasopressin in patients undergoing laparoscopic myomectomy: A double-blind randomised study

Background and Aims:

Myomectomy is associated with perioperative bleeding. The aim of the study is to evaluate the effect of intramyometrial vasopressin on blood loss and the associated cardiovascular complications during myomectomy.

Methods:

The study included 194 patients classified into two groups- 1) Vasopressin group: the vasopressin was diluted as 0.1 unit/ml and 15 ml was injected by the surgeon in the plane between the myometrium and the myoma. 2) Control group: The patients received an equal amount of normal saline. The monitored parameters included the amount of blood loss, required blood transfusion, heart rate, mean arterial blood pressure, the incidence of hypertension, hypotension, bradycardia, tachycardia, electrocardiogram (ECG) changes and the blood troponin I level.

Results:

The heart rate decreased significantly in both groups, but the decrease was lower with vasopressin than the control group through the time points T3 to T5 (P < 0.05) The mean arterial blood pressure increased significantly in both groups, but the increase was higher with vasopressin than the control group through T3 to T5 (P < 0.05). The amount of blood loss decreased significantly with vasopressin than the control groups (P = 0.001). The number of transfused packed red blood cells was lower with vasopressin than the control group (P = 0.001). The incidence of hypertension, bradycardia and atrial extrasystole was higher with vasopressin than the control group (P = 0.005, P = 0.012, P = 0.033, respectively).

Conclusion:

Intramyometrial vasopressin decreases blood loss and blood transfusion, but it is associated with cardiovascular complications that may be serious as reported in other studies. Therefore, anaesthesiologists and gynaecologists must follow the precautions to avoid and minimise the incidence of complications with intramyometrial vasopressin.