Stroke volume changes during focal pulsed field vs. radiofrequency ablation for ventricular substrate using Sphere-9 catheter assessed by arterial waveform analysis: a prospective case series.

This prospective case series of eight patients demonstrates that while pulsed field ablation using the Sphere-9 catheter causes transient, reversible reductions in left ventricular stroke volume during lesion delivery, it maintains a favorable safety profile comparable to radiofrequency ablation for ventricular substrate modification.

The Gist

The Big Picture: Fixing a "Short-Circuiting" Heart

Imagine your heart is a house with a very complex electrical wiring system. Sometimes, a short circuit develops in the walls (scar tissue), causing the lights to flicker wildly or the whole house to shake. This is what happens in ventricular arrhythmia—a dangerous heart rhythm caused by scarred heart muscle.

To fix this, doctors use a procedure called ablation. Think of this as sending a tiny repair crew (a catheter) inside the heart to burn or zap the bad wiring so the short circuit can't happen again.

For years, the standard tool for this job has been Radiofrequency (RF) energy. It's like using a hot soldering iron: it heats up the tissue to create a scar that blocks the electricity.

Recently, a new tool called Pulsed Field Ablation (PFA) has arrived. Instead of heat, it uses powerful, ultra-fast electrical pulses. Think of this like a "lightning strike" that zaps the cells without burning them. It's supposed to be safer and more precise, especially in tricky spots.

The Question: Does the New Tool Make the Heart "Stun"?

The researchers wanted to know: When we use this new "lightning" tool, does it temporarily knock the heart out of commission?

Since PFA works by zapping cell membranes, the scientists worried that while it fixes the bad wiring, it might also temporarily "stun" the healthy muscle around it, making the heart pump weaker for a few seconds. They wanted to see if this new method was safe enough to use in large amounts (multiple zaps) without causing the heart to fail temporarily.

The Experiment: The "Sphere-9" and the "Heart Monitor"

The team studied 8 patients with heart rhythm problems. They used a special high-tech catheter called the Sphere-9, which can deliver both the old "hot iron" (RF) and the new "lightning" (PFA) energy.

To measure the heart's strength, they didn't just guess. They hooked the patients up to a super-sensitive monitor (like a high-tech fitness tracker for the heart's blood flow) that measured Stroke Volume.

• Analogy: Imagine the heart is a water pump. Stroke Volume is simply how much water the pump pushes out with every squeeze. If the pump gets "stunned," it pushes out less water.

They applied the energy to the scarred areas and watched the "water pump" in real-time.

What They Found: The "Wobble" vs. The "Steady Hand"

Here is the breakdown of what happened:

1. The New Tool (Pulsed Field / PFA):

• The Effect: Every time they fired a "lightning" zap, the heart's pumping power (Stroke Volume) dropped significantly—by about 33%.
• The Analogy: Imagine you are squeezing a stress ball. Suddenly, someone taps it with a magic wand. The ball goes limp for a split second, and you squeeze out less air. But then, immediately after the tap, the ball bounces back to its normal shape.
• The Result: The heart's strength dropped, but it recovered within a minute. It was a temporary "stun," not permanent damage.

2. The Old Tool (Radiofrequency / RF):

• The Effect: When they used the traditional "hot iron" method, the heart's pumping power barely changed at all.
• The Analogy: Using the hot iron is like carefully melting a specific spot of wax. It doesn't make the whole stress ball go limp; it just changes that one spot. The rest of the pump keeps working normally.

The Conclusion: Is it Safe?

The study found that while the new PFA method causes a temporary dip in the heart's pumping power, it is completely reversible. The heart "wakes up" almost instantly.

• Why this matters: Because the effect is so short-lived, doctors can safely use many, many PFA zaps in a row to fix complex scars without worrying that the heart will stop pumping effectively during the procedure.
• The Takeaway: The new "lightning" tool is safe for the heart muscle, even though it gives the heart a brief, momentary "shock" that makes it pause its work for a split second. It's like a temporary glitch that fixes itself immediately, whereas the old method didn't cause a glitch at all but might be less effective in tricky spots.

Summary in One Sentence

Using the new "electric zap" method to fix heart scars causes the heart to briefly lose its pumping strength (like a momentary stumble), but it recovers instantly, proving it is safe to use even when many zaps are needed.

Technical Summary

Title

Stroke volume changes during focal pulsed field vs. radiofrequency ablation for ventricular substrate using Sphere-9 catheter assessed by arterial waveform analysis: a prospective case series.

1. Problem Statement

Catheter ablation is a standard treatment for ventricular arrhythmias (VA), utilizing either Radiofrequency (RF) or Pulsed Field Ablation (PFA). While PFA offers advantages in lesion formation within anatomically challenging regions (e.g., trabeculations or areas with poor catheter stability) due to its tissue selectivity and deeper lesion penetration, the acute hemodynamic impact of PFA on ventricular contractility remains poorly understood.

• The Gap: There is a lack of real-time data regarding how PFA affects left ventricular (LV) contractility during substrate modification, particularly when delivering multiple lesions in scarred myocardium.
• The Question: Does PFA cause significant, potentially dangerous, acute reductions in cardiac output compared to the established thermal mechanism of RF ablation?

2. Methodology

• Study Design: Prospective case series involving 8 consecutive patients undergoing VA ablation.
• Patient Population:
  • 2 patients with Premature Ventricular Complexes (PVCs).
  • 6 patients with Ventricular Tachycardia (VT).
  • Underlying etiologies included Ischemic Cardiomyopathy (ICM) and Non-Ischemic Cardiomyopathy (NICM).
• Equipment & Technology:
  • Catheter: Sphere-9 (Medtronic), a dual-energy lattice-tip catheter capable of delivering both PFA and RF.
  • Mapping: Affera system (Medtronic) for high-resolution 3D electroanatomical mapping.
  • Imaging: Intracardiac Echocardiography (ICE; AcuNav, Siemens) to visualize scar tissue (defined as hyperechogenicity and wall thinning).
  • Hemodynamic Monitoring: HemoSphere platform (Edwards Lifesciences) with a sensor in the radial artery to measure Stroke Volume (SV) via arterial waveform analysis.
• Procedure Protocol:
  • Lesions were delivered only to scarred regions identified by both ICE (hyperechogenicity) and low-voltage areas on 3D mapping.
  • PFA Parameters: 5.5 seconds per application.
  • RF Parameters: 30 seconds per application.
  • Lesion Strategy: Up to three repetitive lesions per site; consolidation of PFA with RF was performed in some cases.
• Data Analysis:
  • SV was measured at baseline, immediately post-lesion, and at the nadir (lowest point).
  • Comparisons were made between PFA and RF effects on SV.
  • Success was defined by post-procedural non-inducibility of clinical VT.

3. Key Contributions

• Real-Time Hemodynamic Assessment: This study provides one of the first real-time assessments of LV contractility (via SV) during focal PFA delivery in humans, using a minimally invasive arterial waveform system.
• Direct Energy Comparison: It directly compares the acute contractile effects of PFA versus RF within the same procedural context using the same catheter platform.
• Safety Profile in Scarred Tissue: It specifically investigates the safety of delivering high burdens of PFA lesions (average ~70 per patient) within scarred myocardium, a critical concern for VT ablation.

4. Key Results

• Lesion Delivery:
  • Total of 317 PFA applications and 41 RF applications were delivered across 8 patients.
  • Average lesions per patient: ~70 for PFA vs. ~9 for RF.
• Hemodynamic Impact (Stroke Volume):
  • PFA: Caused a transient but significant reduction in SV.
    • Average drop: 33.1 ± 8.3 ml (approx. 33% reduction).
    • The reduction was consistent across different lesion locations.
    • Recovery: SV normalized to pre-lesion baseline values in all cases within one minute of delivery.
  • RF: Resulted in minimal change in SV (≤10% reduction from baseline).
• Clinical Outcomes:
  • All 8 patients achieved non-inducibility of clinical VT post-procedure.
  • No sustained contractile dysfunction or hemodynamic instability requiring intervention was observed.

5. Significance and Conclusion

• Mechanism of Action: The transient SV reduction observed with PFA is attributed to acute electroporation-induced myocyte stunning (temporary sarcomere shortening due to calcium influx) rather than irreversible thermal necrosis. This contrasts with RF, which causes thermal injury but does not acutely disrupt contractility in the same manner.
• Clinical Implications:
  • Safety: The rapid reversibility of the SV drop suggests that PFA has a favorable safety profile for ventricular substrate ablation, even when delivering a high burden of lesions in scarred tissue.
  • Application: PFA can be safely used in regions where RF is limited (e.g., trabeculated areas), provided that the operator is aware of the transient hemodynamic dip.
  • Caution: While safe in scar tissue, the authors note that PFA should be applied carefully in viable tissue due to the potential for transient contractile dysfunction.
• Limitations & Future Directions:
  • The study is a small, preliminary case series (n=8).
  • SV was measured via radial artery waveform (a surrogate for contractility) rather than direct intracardiac pressure-volume loops.
  • Long-term outcomes and the cumulative impact of repeated transient stunning require further investigation.

Summary Verdict: The study demonstrates that while PFA causes a significant, immediate, and transient drop in stroke volume (likely due to myocyte stunning), this effect is fully reversible within minutes. This supports the safety of using PFA for extensive substrate modification in scarred ventricles, distinguishing its acute hemodynamic profile from the minimal impact seen with RF ablation.