Electrosurgery in the EP Lab: A Review

Electrosurgery is an important component of cardiac electrophysiology, enabling the operator to dissect tissue, create pockets, free cardiac leads, and coagulate tissue. The term electrosurgery is described as the application of high frequency electric current into biological tissue to obtain a desired clinical effect (e.g., cutting, sealing bleeding vessels, coagulating tissue). Therefore, electrical current runs through the patient in electrosurgery. In contrast, electrocautery involves an electric current that heats an instrument, which is applied to tissue to produce its clinical effect. 

The standard electricity delivered to households has an oscillating frequency of 60 Hz. At this frequency, there is significant risk for cellular depolarization, ionization, and damage to human tissue. However, when the frequency is ramped up to above 100 kHz,¹ the current alternates so rapidly that the cells do not depolarize or react to the current. Electrosurgical units typically produce alternating currents in the frequency range of 200 kHz to 3.3 MHz.² 

The Electrosurgery Circuit

Current is the flow of electrons, and voltage is the force that drives current through the circuit against the resistance. This is related as: Voltage (V) = Current (I) X Resistance (R).

These variables complete the electric circuit and when high frequency electricity flows in the circuit, the tissue resistance or impedance converts the electric energy into heat energy, which can produce various clinical effects such as cutting, sealing off bleeding vessels, and coagulating tissue. In basic terms, a circuit consists of a generator that provides voltage to drive current, an electrode that delivers the RF current to the target tissue, which provides impedance, and a receiving electrode that returns the current back to the generator. The heat produced while current passes through the tissue is responsible for the clinical effects of electrosurgery.

There are two types of electrosurgical generators: constant voltage and automatic power adjustment. Most conventional electrosurgical generators use a constant voltage output system. In these generators, voltage is constant, irrespective of the tissue impedance. They deliver less power to the tissue with higher resistance compared to the tissue with lower resistance. In contrast, electrosurgical generators with an automatic power adjustment system deliver constant power output and the same clinical effect in a wide range of impedance in the circuit.

Based on the circuit configuration, there are two types of energy delivery electrodes: monopolar and bipolar. In the bipolar system, both the active and receiving electrodes are in close proximity, integrated in the same forceps-like device. Because of this configuration, bipolar systems use a low-voltage waveform and there is little chance for unintended dispersal of current. The monopolar electrode system is more commonly employed in EP device implantation. Current passes from the active electrode through the patient to the receiving or dispersive electrode. The active electrode and receiving electrode are two separate mechanical parts. The receiving electrode is generally much larger in size as a patch, and is applied to a different part of the body as closely to the surgery site as possible. To minimize impedance, the return electrode is usually placed on a large vascular muscle (Figure 1).

Temperature and Lesion Creation

Temperature at the source and tissue is another factor that greatly affects the size of the lesion. At 50^oC, cells lose their structural integrity and tissue damage is irreversible. At 90^oC, tissue fluids evaporate and tissue desiccation occurs.² Tissue is boiled and vaporized at >100^oC, and carbonization and char formation occurs at 150-200^oC. The temperature is highest at the tissue electrode interface and it dissipates as the current spreads, and the line at which the temperature gradient crosses 50^oC defines the lesion radius (Table 1). Thus, the lesion size increases in direct proportion to the temperature at the source and to the contact surface area of the heat source. However, in practice, it is also noted that coagulum and char forms at a high temperature close to the source, which adheres and insulates the electrode, resulting in a smaller electrode surface area available for electrical conduction. Char formation may be particularly unwanted in desiccate mode, which can result in sticking of the electrode to the tissue and subsequent avulsion of the coagulum from the tissue surface. Therefore, desiccation should only be to the point of tissue blanching.

Electrosurgical generators usually deliver energy in two modes: continuous and interrupted. Waveforms can be sinusoidal and sometimes dampened (where peak voltages are decremented to zero within the repeated bursts). Some manufacturers also have proprietary waveforms (Table 2).

Cut Mode

Cut mode involves a low-voltage, continuous, sinusoidal waveform. This mode produces higher tissue temperatures in a shorter time, leading to rapid expansion of the intracellular contents as well as vaporization and division of the tissue under the electrode. It offers clear tissue division with minimal thermal spread. 

Blend Mode

Blend mode involves an interrupted waveform. The current supply is interrupted, and has ‘on’ and ‘off’ cycles. It is capable of varying degrees of cutting and hemostasis depending on the percentage of ‘on’ time, also known as duty cycle. The more time off, the more coagulation effect — therefore, the greater the hemostatic effect. A blend duty cycle of 25% will have greater hemostatic effect than a blend duty cycle of 50%. This mode is selected when hemostasis is desired with cutting, or when low voltage coagulation or desiccation is desired. A blend mode with 50% duty cycle is commonly used on generators.

Coagulation Mode

This mode delivers a high-voltage, modulated waveform with an intermittent duty cycle that is on 6-8% of the time. Tissue is heated with intermittent brief spikes of high voltage. During the remaining 94-92% of the cycle, the cells cool down and form a coagulum. Because the tissue is exposed to current flow for significantly less time, it does not heat to the point at which vaporization occurs. Coagulation mode is applied on larger superficial surfaces and for oozing tissue sites.

There are three modes in coagulation that are programmable. In desiccate mode, direct contact is made with the tissue and current density is lower than in cut mode. Energy is delivered relatively slowly to heat the target tissue, which is then dried. The voltages employed in desiccate mode are higher than cut; however, the frequency is lower and the active ‘on’ time is only approximately 8% of the time. 

In fulgurate mode, the voltages used are more than double that of desiccate, and a damped waveform is commonly used. The high voltages allow the cautery device to be used in a non-contact method. Sparks will arc from the electrode to the tissue and cause a shallow eschar to coagulate tissue. 

Some generators will specify a separate spray mode, which can be considered a high intensity fulgurate mode where the peak voltage is even higher. This mode features the highest crest factor. The crest factor is the ratio of the peak voltage to the average (root mean square) voltage. Cutting modes have a crest factor of ~1.5-2.5, whereas coag modes have a crest factor of ~5-8. Spray mode is used when operators wish to achieve the fastest and broadest hemostasis.  

Factors Affecting Energy and Lesion Size

The amount of heat production and the tissue effect is determined by electrode geometry, current density, impedance of the tissue, distance from the source of energy or the electrode, power setting, and time of application. Muscular patients have lower impedance and will require lower power settings than obese or emaciated patients. Additionally, the smaller the electrode, the higher the current density — therefore, the more heat produced. Long activation time will increase risk for unintended thermal injury, and too short of time may not produce the desired clinical effect. A higher power setting increases the depth of tissue coagulation and/or the incision. 

Electrosurgical Technology

In our practice, we utilize conventional cautery pens for de novo implants. However, we utilize the PhotonBlade (Invuity; Figure 2) for generator changes and lead revisions where lead preservation is paramount, as well as in implants with elevated bleeding risks where illumination is desired to facilitate identification of bleeders. In de novo implants, we utilize Blend Cut 20W and Spray Coag 30-35W as our default settings. However, we utilize Pure Cut at 10W in procedures involving prior leads (Figure 3). This flexibility has allowed us to use the least amount of energy possible with effective cutting around sensitive leads, such as the copolymer lead. 

The PhotonBlade (Figure 2) is a newer electrosurgical device which has insulated coatings that surround the blades, except for an exposed edge, to help reduce collateral damage. The PhotonBlade, which received 510(k) clearance from the FDA in 2016, is the newest monopolar RF device combining an advanced energy delivery tip with illumination for direct visualization. The electrode tip is located at the distal end of a rotatable and extendable shaft, which also has a LED light. The distance from the electrode tip to the LED is approximately 2 cm, and the light makes the deepest crevices of the pockets visible in order to appreciate the sources of bleeding. The tip design focuses energy for directed heat delivery at a controlled level, with the goal of maintaining a relatively low tip temperature during most parts of the procedure. The PhotonBlade is compatible with any commercially available electrosurgical generator, and allows for more flexibility in power and mode selection. A vacuum suction accessory will be available for smoke evacuation.

Wasserlauf et al recently determined that in terms of thermal damage to transvenous cardiac device leads, PhotonBlade had a lower thermal spread³ and lower risk for lead injury. In an ex vivo study, at the commonly used setting of Pure Cut 20W, damage occurred with only 12.7% of treatments using PhotonBlade.⁴ In a separate study, PhotonBlade use at Pure Cut 20W resulted in no visible damage in 54 ex vivo specimens (53/54 no damage, 1/54 damage visible only under microscopy).⁵ Thus, PhotonBlade may be particularly advantageous in device revision procedures where there is a high priority for lead preservation. Patients who are at high risk of bleeding, on anticoagulation, and with deep pockets may also benefit from the illumination feature of the PhotonBlade. 

Practical Considerations

Using monopolar electrosurgery in patients with pacemakers or ICDs should be done with caution to avoid interference with the implants. If the patients have prosthetic conductive joints, efforts should be made to place the prosthesis out of the direct path of the circuit. For example, the return electrode should be placed on the patient’s right if the patient has a left hip prosthesis. 

Cautery performed directly onto device generators should be avoided or limited to avoid the potential for circuitry damage and current concentration in the tips of the leads. Cautery around leads should also be avoided, but is sometimes necessary. Operators may need to free tissue around leads for the purpose of generator changes, pocket revisions, and extractions. It should be noted that copolymer leads are the most susceptible to cautery damage, followed by polyurethane. Silicone leads are most resistant to cautery damage.⁷ 

The lowest possible generator setting that will achieve the desired clinical effect should always be used. The maximum power settings should never be exceeded, as there is a higher chance of arcing and capacitive coupling. Additionally, the electrode tip should be frequently cleaned to avoid any eschar buildup. Eschar increases impedance/resistance, and raises the risk for sparking and flaming of the eschar. Cleaning should be done with a sponge to avoid any scratches onto a coated electrode tip. 

Acknowledgement: The authors would like to thank William Chu, RN for the cautery photos.

Disclosure: Dr. Yang reports that he has received consulting fees from Invuity, Inc. Dr. Shrestha, Kulbak and Dr. Greenberg have no relevant disclosures to report.

References

1. Munro MG. Fundamentals of Electrosurgery Part I: Principles of Radiofrequency Energy for Surgery. In: Feldman L, Fuchshuber P, Jones DB (eds.). The SAGES Manual on the Fundamental Use of Surgical Energy (FUSE). New York, NY: Springer Science+Business Media, LLC; 2012, Page 19.
2. Kneedler J, Pfister J, Watson D, Whalen M. Electrosurgery (An Online Continuing Education Activity). Pfiedler Enterprises, 2016. Available at https://bit.ly/2MSqAvv. Accessed August 27, 2018.
3. Bennett H, Taylor S, Fugett J, et al. Assessment of penetrating thermal tissue damage/spread associated with PhotonBlade, Valleylab Pencil, Valleylab EDGE Coated Pencil, PlasmaBlade 3.0S and PlasmaBlade 4.0 for intraoperative tissue dissection using the fresh extirpated porcine muscle model. Proceedings of SPIE, 10066J. Published 22 February 2017.
4. Wasserlauf J, Esheim T, Jarett N, et al. Damage to Transvenous Leads During Electrocautery - A Comparison of Two Insulated Electrocautery Blades. Heart Rhythm Society Scientific Sessions, Poster Session. Boston, MA, 2018.
5. Wasserlauf J, Esheim T, Jarett N, Chan E, Knight B. Impact of Blade Orientation and Cautery Mode When Delivering Electrocautery to Transvenous Leads Using an Insulated Blade. Heart Rhythm Society Scientific Sessions, Poster Session. Boston, MA, 2018.