From radiofrequency ablation to pulsed ablation
For cardiac electrophysiologists, the shift from radiofrequency ablation to pulsed ablation represents not just a change in energy source, but a significant upgrade in ablation philosophy, safety strategies, and surgical procedures.
If radiofrequency ablation is a battle of “thermodynamics,” then pulsed ablation enters a new dimension of “electromagnetic biology” and “tissue selectivity.” You need to systematically master the following five dimensions of knowledge upgrade:
I. Basic Electrophysiology and Physics: A Shift in Thinking from "Heat" to "Field"
Radiofrequency ablation is essentially thermal coagulation necrosis (resistance heating), while pulsed ablation is essentially irreversible electroporation.
1. Electroporation Mechanism: It’s necessary to understand the concept of electric field strength threshold. Cardiac cells have a low threshold, while tissues such as blood vessels, nerves, and the esophagus have higher thresholds. This is the theoretical foundation of the “tissue selectivity” of pulsed ablation.
Distinguish between reversible electroporation (temporary cell membrane permeability for gene transfection) and irreversible electroporation (permanent cell membrane rupture, leading to apoptosis/necrosis).
2. Electric Field Parameters: The focus shifts from single values of radiofrequency power (W), temperature (°C), and impedance (Ω).
Instead, focus on voltage (V), pulse width (μs), pulse interval, the vector direction of catheter contact, and electric field strength (V/cm). You need to understand that the ablation effect no longer depends primarily on “how tightly the pressure is applied,” but rather on “whether the electric field covers the tissue.”
II. Anatomical and Tissue Interactions: From Emphasis on "Approach" to "Adjacent Relationships"
While the “tissue selectivity” of pulsed ablation improves safety, it also introduces new anatomical requirements.
1. Phrenic Nerve and Coronary Arteries: Although pulsed ablation generally does not damage the phrenic nerve and coronary arteries, caution is still needed in areas such as the superior vena cava and pulmonary vein vestibules to prevent acute stimulation of nerves by high voltage (leading to hiccups or diaphragmatic spasms).
2. Esophageal Protection: The incidence of atrial-esophageal fistula, a dreaded condition in the radiofrequency ablation era, is theoretically reduced in pulsed ablation. However, physicians still need to master how to visualize the esophagus using contrast agents when ablating the posterior wall of the left atrium. While thermal damage is less likely, excessively high electric fields can still cause esophageal spasm or delayed effects.
3. Bubbles and Microemboli: Pulsed ablation generates microbubbles (electrochemical effect) during discharge. You need to learn how to avoid microbubbles entering the arterial system and causing stroke risk through proper venting and catheter stability control. This is fundamentally different from the “eschar” risk associated with radiofrequency ablation.
III. Catheter manipulation and surgical procedure: From "point-by-point" to "holistic" macroscopic control
Pulsed ablation catheters are often flower-shaped, basket-shaped, or loop-shaped, which alters the ablation strategy.
1. Catheter Stability and Coaxiality: Radiofrequency ablation allows for point-by-point ablation by “micro-displacement” of the catheter tip. Pulsed ablation typically requires stable contact between the electrode and tissue. If the catheter shifts during discharge, the electric field direction changes, potentially leading to discontinuous ablation or “sparking.”
You need to master coaxiality: Ensure the ablation electrode loop is parallel to or adheres to the myocardial tissue, rather than making point contact.
2. Failure of the Ablation Index (AI): The AI value and pressure monitoring (CF) relied upon in the radiofrequency era are no longer core indicators of ablation depth in pulsed ablation. While some systems still require slight contact, depth is primarily determined by electric field strength, not mechanical pressure.
You need to establish a new habit of immediate verification of “disappearance of electrical conduction”: Pulsed ablation often takes effect extremely quickly (milliseconds), and the immediate disappearance of local potentials at the ablation site can often be observed intraoperatively. You need to learn to identify effective signals under electromyographic interference in real time during the discharge process.
IV. Prevention and Treatment of Complications: From "Thermal Injury" to "Electro-Mechanical Decoupling" and Concern for "Bubbles"
1. Electromechanical Decoupling: This is a phenomenon unique to pulsed ablation. At the moment of discharge, although the myocardial cells are not yet necrotic, sodium channels are inhibited, causing the heart to temporarily lose contraction. You need to be proficient in identifying this transient decrease in cardiac output under general anesthesia or deep sedation via arterial blood pressure monitoring and differentiating it from ventricular fibrillation.
2. Coronary Artery Spasm: When ablating near the coronary sinus or right coronary artery, the pulsed electric field may induce acute coronary artery spasm. You need to be able to identify ST-segment elevation on ECG and manage intraoperative intracoronary nitroglycerin injection.
3. Hemolysis and Kidney Injury: High-energy pulses may cause red blood cell rupture. Although clinically rare, you need to understand the importance of intraoperative fluid management and postoperative renal function monitoring, especially when performing large-area ablation (e.g., pulmonary vein + left atrial posterior wall + superior vena cava) in the same procedure.
V. Imaging and Anesthesia Management: Collaboration from Local Anesthesia to General Anesthesia/Deep Sedation
1. Depth of Anesthesia: Pulsed ablation discharges can cause intense muscle spasms (even with microsecond-level pulses). To ensure catheter stability, most pulsed ablation procedures require general anesthesia or deep sedation (with the assistance of muscle relaxants).
You need to master the workflow for collaborating with anesthesiologists, understand the matching of the onset time of muscle relaxants with the discharge time, and avoid catheter displacement or cardiac perforation due to patient movement.
2. Image Fusion and Navigation: Because pulsed ablation does not rely on the visualization of “thermal lesions” on X-rays, you rely more on the precise modeling of three-dimensional electroanatomical mapping systems (such as Carto and EnSite).
You need to master how to precisely fuse preoperative CT/MRI images with intraoperative electric field navigation, because “anatomical ablation” has become more prevalent than “electrophysiological verification” in the pulsed ablation era.
Recommendation:
In the initial stages of pulsed ablation, it is recommended that you temporarily set aside your experience from the radiofrequency ablation era regarding “how to make deep incisions and how to control temperature,” and instead focus your efforts on the two core aspects: “how to ensure catheter apposition and stability through imaging” and “how to ensure patient immobility through anesthesia management.” Pulsed ablation reduces the risks to the esophagus and phrenic nerve, but it places higher demands on operational precision, teamwork (anesthesia and nursing), and the interpretation of intraoperative electrophysiological signals.