Using MRI to Find and Close Gaps in Repeat Atrial Fibrillation Ablation

Table of Contents

• Key Points
• Why This Research Matters
• Who Was Included in the Study
• What Happened During the First Ablation
• How the MRI Scans Were Performed
• Key Findings: Where the Gaps Were Found
• Key Findings: Gap Size and Ablation Time
• What These Findings Mean for Patients
• Study Limitations: What This Research Could Not Prove
• Recommendations for Patients
• Frequently Asked Questions
• Source Information

Key Points

• In a 15-patient study, DE-CMR identified gaps in old ablation lines before repeat atrial fibrillation ablation.
• Right-sided pulmonary veins had significantly more large gaps than left-sided veins.
• Gap counts differed significantly among the four pulmonary veins, supporting personalized imaging.
• Up to 33% of gaps were left untreated or incompletely ablated, highlighting the need for complete closure.
• The study was small and observational, so it cannot prove DE-CMR improves long-term outcomes.

Why This Research Matters

Atrial fibrillation (AF) is the most common type of heart rhythm disorder, affecting millions of people worldwide. Instead of the heart's upper chambers (the atria) beating in a coordinated way, they quiver chaotically, which can lead to symptoms like palpitations, fatigue, and shortness of breath—and, more seriously, an increased risk of stroke.

For many patients, one of the most effective treatments is catheter ablation, a procedure in which a doctor threads a thin, flexible tube through blood vessels to the heart and delivers heat (radiofrequency energy) or extreme cold (cryoenergy) to create tiny scars. These scars are deliberately placed around the openings of the pulmonary veins—the four veins that carry oxygen-rich blood from the lungs back to the heart. The goal is to create a "wall" of scar tissue that blocks the abnormal electrical signals triggering AF.

However, ablation doesn't work perfectly for everyone. In some patients, AF comes back because the scar tissue is not complete—small gaps remain in the ablation lines, allowing stray electrical signals to slip through. In these cases, a second, repeat ablation procedure may be needed.

This study addressed a key clinical challenge: how to find those gaps quickly and precisely before a repeat ablation. The researchers tested whether a specialized MRI technique, DE-CMR, could create a detailed "map" of scar tissue in the heart's left atrium (the upper left chamber), highlighting exactly where the gaps were located.

Who Was Included in the Study

The study involved a small but carefully selected group of 15 patients who had previously undergone ablation for atrial fibrillation and were now scheduled for a repeat procedure.

• 12 of the 15 patients had their first ablation performed at the same hospital as this study, meaning their full medical records and procedure details were available.
• The other 3 patients had their initial ablation at another hospital, according to records that reported successful pulmonary vein isolation in all 3 procedures.
• Each patient underwent a DE-CMR scan within 30 days before their repeat ablation.

This is a relatively small group, but it allowed the researchers to perform a detailed, patient-by-patient analysis of scar patterns, gap locations, and ablation results.

What Happened During the First Ablation

Understanding the initial ablation technique is important because it explains why the gaps appeared in the first place. For the 12 patients treated at the study hospital, the original procedure followed a specific protocol:

1. 3D mapping: A computer system called CARTO (Biosense Webster, Diamond Bar, CA, USA) was used to construct a detailed three-dimensional electrical map of the heart. This map was then merged with a CT or MRI image (a CMR or CT angiography) of the left atrium to show doctors exactly where to deliver energy.
2. Circumferential lesions around each pulmonary vein: Continuous radiofrequency lesions (tiny burns) were delivered around each of the four pulmonary veins using a 3.5-mm open-irrigation tip catheter (Navistar, Biosense Webster) at 40 watts of power. These encircling lesions were designed to completely isolate each vein from the rest of the atrium.
3. Additional ablation lines: In 8 patients, extra lines were created to connect the right and left encircling lesions along the roof of the left atrium. In 3 patients, similar connecting lines were placed on the posterior (back) wall of the atrium.
4. Targeting complex signals: In 2 patients, doctors also targeted areas with complex fractionated electrograms—chaotic, fragmented electrical signals that are believed to help sustain AF.
5. Verification: The endpoint of the procedure, achieved in all pulmonary veins, was the absence of a local electrogram (no electrical activity) inside the entire surrounded region, together with confirmed "exit block" by pacing within the pulmonary vein opening. In plain terms: doctors confirmed that no electrical signals could travel out of the vein into the atrium.

The situation was different for the 2 patients who underwent cryoablation. Instead of heat, they were treated with a 28-mm cryoballoon catheter (Arctic Front, Medtronic, Montreal, Quebec, Canada), which freezes tissue at the vein opening. For the 3 patients treated elsewhere, records reported successful pulmonary vein isolation in all 3 procedures, and 1 of those patients also received an additional mitral isthmus line—an ablation line along the area between the mitral valve and the left inferior pulmonary vein.

How the MRI Scans Were Performed

The imaging technique in this study was highly advanced, so here's a step-by-step explanation of how it worked:

1. Timing: Each patient's CMR scan was performed 30 days or less before the repeat ablation procedure.
2. Equipment: Scans used a 3T scanner (Magnetom Trio, Siemens Healthcare, Erlangen, Germany)—a very powerful MRI machine—with a 32-channel cardiac coil (a special receiver placed around the chest to capture clear heart images).
3. Heart rhythm requirement: All scans had to be performed while the patient was in normal sinus rhythm (a normal, regular heartbeat). If a patient was in AF at the time of the scan, doctors first performed electrical cardioversion—a procedure that delivers a controlled shock to reset the heart's rhythm—under deep sedation with propofol (at a dose of 1 mg/kg).
4. Contrast injection: Each patient received an intravenous (IV) bolus of 0.2 mmol/kg of gadobutrol (Gadovist, BayerSchering, Berlin, Germany). This is a contrast agent ("dye") that accumulates in scarred tissue and makes it appear bright on the scan.
5. Waiting period: The contrast agent was given 25 to 30 minutes before scanning to allow it to wash out of healthy tissue and remain visible in scarred areas—this is what creates the "delayed enhancement" effect that gives DE-CMR its name.
6. Scanning sequence: Images were acquired using a free-breathing 3D navigator technique (meaning the patient did not need to hold their breath consistently) with electrocardiographic (ECG) gating (so images were taken at the same point in each heartbeat) and an inversion-recovery gradient-echo sequence. The imaging was done in the axial orientation.
7. Image detail: The acquired voxel size was 1.25 x 1.25 x 2.5 mm—a voxel is the 3D equivalent of a pixel, so this represents a very fine level of detail. Other typical sequence parameters included: repetition time/echo time of 2.3/1.4 milliseconds, flip angle of 11 degrees, bandwidth of 460 Hz/pixel, and inversion time (TI) of 280 to 380 milliseconds. A "TI scout" sequence was used to nullify the left ventricular signal (making the heart muscle appear dark) and determine the optimal imaging time.
8. Breathing instructions: Patients were instructed to maintain steady, shallow breathing during the scan to minimize chest movement that could blur the images.
9. Scan duration: The typical scan time for the DE-CMR sequence was about 15 minutes (range 11 to 18 minutes), depending on the patient's heart rate and breathing patterns.

Once the scans were completed, the images were processed into 3D models of the left atrium showing areas of scar tissue as "bright" regions, which allowed doctors to visualize the ablation lines from the previous procedure and identify any gaps along them.

Key Findings: Where the Gaps Were Found

The core of the study was a detailed analysis of the gaps in the previous ablation lines. Here is what the researchers found, with all the numbers intact:

Overall gap frequency. The mean number of gaps per pulmonary vein was 1.29 ± 0.41. In other words, on average, each vein had a little more than one area where the ablation line was broken.

Differences between the four pulmonary veins. When the researchers looked at each vein separately, they found a statistically significant difference in the number of gaps:

• Left superior pulmonary vein (LSPV): 1.4 gaps
• Left inferior pulmonary vein (LIPV): 0.67 gaps
• Right superior pulmonary vein (RSPV): 1.53 gaps
• Right inferior pulmonary vein (RIPV): 1.07 gaps

These differences were statistically significant at p = 0.048, meaning there is less than a 5% probability that the differences were due to random chance. In plain language, the location of the vein genuinely mattered for how many gaps were found.

Right side versus left side. Comparing the right-sided pulmonary veins to the left-sided veins, the total numbers of gaps were similar: 1.20 versus 1.03 gaps per vein, respectively. This difference was not statistically significant (p = 0.427), meaning the total gap count was roughly comparable on both sides.

Big gaps favored the right side. However, an important difference emerged when the researchers looked at the size of the gaps. They classified "big gaps" as any gap longer than the overall mean gap length of 13.3 mm (about half an inch). The findings:

• Right-sided pulmonary veins: 46.2% of gaps were "big"
• Left-sided pulmonary veins: 21.4% of gaps were "big"

This difference was statistically significant at p = 0.043. So, even though the two sides had a similar number of gaps, the right-side veins tended to have larger gaps—a finding that could be clinically important, since larger gaps may be more likely to conduct abnormal electrical signals.

Average gap length by vein. The researchers also calculated the average gap length for each vein. Although the right-sided veins tended to have longer gaps, these differences did not reach statistical significance:

• LSPV: 10.4 mm
• LIPV: 8.8 mm
• RSPV: 15.2 mm
• RIPV: 16.4 mm

The overall p-value was 0.240, meaning the trend toward longer gaps on the right side could not be definitively confirmed in this small study. Still, the data pointed in a consistent direction.

Key Findings: Gap Size and Ablation Time

The researchers also examined whether the total length of the gaps was related to how much radiofrequency (RF) time was needed during the repeat procedure. RF time is the total amount of time the ablation catheter delivered energy to the heart tissue.

Overall correlation. A linear regression analysis looking at the association between total gap length (across all veins) and RF time per patient showed a non-significant correlation: R = 0.350; p = 0.220. This means there was a weak-to-moderate trend in the expected direction—patients with longer gaps did tend to require more RF time—but the relationship could not be confirmed statistically.

Why wasn't the correlation stronger? The authors offered two possible explanations:

1. The small number of patients (15) limited the statistical power to detect a real correlation.
2. A complete ablation was not performed in all gaps. In fact, up to 33% of the identified gaps were not ablated or were only incompletely ablated during the repeat procedure. Because such a large proportion of the gap length was left untreated, the "dose" of RF energy delivered did not correspond perfectly to the amount of gap detected—weakening the correlation.

Roof-line analysis. In a separate analysis focused on the 7 patients who had a roof line (the connecting line along the top of the left atrium) from their prior ablation, the correlation between gap length and RF time was stronger: R = 0.776; p = 0.071. Again, this failed to reach statistical significance—likely because only 7 patients were included—but a strong positive relationship (R nearly 0.78) suggests the CMR-detected gaps were indeed guiding the ablation efforts in these patients.

What These Findings Mean for Patients

If you or a loved one is preparing for a repeat atrial fibrillation ablation, these findings are directly relevant. Here's why:

• DE-CMR can provide a roadmap. The study suggests that a DE-CMR scan before a repeat ablation can reveal precisely where the previous ablation lines have breaks, allowing the electrophysiologist to focus energy only on the gaps rather than re-ablating the entire pulmonary vein region. The visual correlation between ablation points from the prior procedure and the scar pattern on DE-CMR was good, giving doctors confidence in the technique.
• The right side may deserve special attention. Because right-sided pulmonary veins had a significantly higher proportion of large gaps (46.2% vs. 21.4%), doctors may want to pay extra attention to the right superior and right inferior veins when planning a repeat procedure. A large gap may be more likely to permit electrical conduction and therefore more likely to be the culprit behind recurrent AF.
• Individual vein differences matter. The significant difference in gap counts among the four veins (p = 0.048) underscores that every patient's scar pattern is different. A "one-size-fits-all" approach to repeat ablation is not sufficient; personalized imaging is valuable.
• Complete gap closure matters. Notably, up to 33% of gaps were not ablated or were only partially ablated during the repeat procedures in this study. For patients, this highlights the importance of having a detailed imaging-guided approach that allows the doctor to systematically close every gap found—not just the easy ones.

Study Limitations: What This Research Could Not Prove

It is important to interpret these results with appropriate caution. The study had several limitations:

• Small sample size. With only 15 patients, the study lacked the statistical power to confirm several trends. The non-significant correlation between total gap length and RF time (R = 0.350, p = 0.220) and the roof-line correlation (R = 0.776, p = 0.071) might well become statistically significant in a larger study.
• Incomplete gap ablation. Because not all detected gaps were actually ablated during the repeat procedures, the true relationship between gap burden and ablation time could not be fully assessed.
• Mixed ablation techniques. The patient group included different initial ablation approaches (radiofrequency, cryoablation, operations at other hospitals). This variation could influence scar formation patterns and gap characteristics.
• Observational design. This was not a randomized control trial comparing DE-CMR-guided ablation with standard care, so the study cannot definitively prove that this imaging approach improves long-term outcomes like freedom from AF recurrence.
• Timing of the scan. Scans were performed up to 30 days before the repeat procedure, and scar tissue may evolve slightly during that interval, so the gaps seen on the scan might not perfectly match the gaps present at the time of ablation.

Recommendations for Patients

Based on this research and current clinical guidelines (including the 2012 HRS/EHRA/ECAS Expert Consensus Statement on catheter and surgical ablation of atrial fibrillation referenced in the study), here is practical advice for patients facing a repeat ablation:

1. Ask about advanced imaging. If you are scheduled for a repeat AF ablation, ask your electrophysiologist whether delayed-enhancement CMR (DE-CMR) is available and appropriate for you. This scan can provide a detailed map of existing scar tissue and reveal gaps that need to be closed.
2. Make sure the scan is done correctly. As this study shows, the quality of the DE-CMR depends on several factors: being in sinus rhythm during the scan (which may require cardioversion beforehand), receiving the correct dose of contrast agent (here, 0.2 mmol/kg of gadobutrol), and having the scan on a powerful 3T MRI system. If your clinic offers this technique, ask about their imaging protocol.
3. Discuss the full closure of all gaps. This study found that up to one-third of gaps were left untreated or partially treated. Before your repeat ablation, discuss with your doctor whether the plan includes verifying that all gaps identified on the scan have been successfully closed, using the same endpoints described in this study—absence of local electrograms inside the isolated region and confirmation of entrance/exit block with pacing.
4. Understand the procedure endpoints. A successful ablation is defined by electrical isolation, not just by "burning" tissue. The research used specific verification methods (pacing from within the pulmonary vein to confirm exit block), which represent the gold standard for confirming that no signals can pass through. Ask your doctor to explain how they will verify success during your procedure.
5. Pay attention to right-sided veins. Given the higher proportion of large gaps on the right side, a careful check of the right superior and right inferior pulmonary veins is especially important—even if the total number of gaps on the right seems similar to the left.
6. Be aware of recovery and follow-up. After a repeat ablation with a CMR-guided approach, patients should still expect standard post-procedure monitoring and follow-up appointments, including regular ECG checks to detect any return of arrhythmia.

As with any medical procedure, the decision to undergo a repeat ablation—and the technique used—should be made in close consultation with your heart rhythm specialist, who can weigh your individual anatomy, ablation history, and overall health.

Frequently Asked Questions

What is DE-CMR, and how does it help before a repeat atrial fibrillation ablation?

DE-CMR is a special MRI technique that uses dye to show scar tissue. In a study of 15 patients, scans before repeat ablation clearly revealed gaps in old ablation lines around the pulmonary veins. This gave doctors a detailed roadmap, allowing them to target only those breaks instead of re-ablating healthy tissue.

How common were gaps in the old ablation lines, and did they differ between veins?

In a study of 15 patients, each pulmonary vein had, on average, about 1.29 gaps. Gaps were not evenly spread: the researchers found a statistically significant difference among the four veins, with the right superior vein averaging 1.53 gaps and the left inferior vein averaging 0.67.

Does this study prove that DE-CMR-guided repeat ablation leads to better outcomes?

No. This was a small, observational study of 15 patients, not a randomized trial comparing DE-CMR guidance with standard care. It cannot prove the technique improves long-term freedom from atrial fibrillation. Larger studies are needed to confirm any real benefit for patient outcomes.

What should I ask my doctor about if I am scheduled for a repeat ablation?

Ask whether delayed-enhancement MRI is available and appropriate for you, how the scan will be performed, and whether the plan includes verifying that all gaps found are closed. Also ask how success will be confirmed, such as checking for electrical block, since this study noted that up to one-third of gaps were left untreated.

Is there a link between the size of gaps and how long the repeat ablation takes?

The study found only a weak-to-moderate relationship that was not statistically significant. One likely reason: up to one-third of gaps were not ablated or were only partially ablated. A separate analysis of patients with roof lines suggested a stronger correlation, but the number of patients was too small to be conclusive.

Can a second opinion help me decide whether MRI-guided gap closure is needed for my repeat atrial fibrillation ablation?

Before a repeat atrial fibrillation ablation, a second opinion can be valuable because success depends on precisely closing the gaps left by the first procedure. In a study of 15 patients, DE-CMR MRI identified gaps along previous ablation lines, with right-sided pulmonary veins showing a higher proportion of large gaps (46.2% vs 21.4%). Notably, up to 33% of detected gaps were not ablated in that study. A specialist can review your prior ablation records and imaging to assess whether DE-CMR-guided targeting is appropriate for your repeat procedure. Diagnostic Detectives Network provides independent expert second opinions.

Source Information

This patient-friendly article is based on peer-reviewed research. The original scientific content is an online appendix and methods supplement from a study titled "Supplemental CMR-Guided Approach to Localize and Ablate Gaps in Repeat AF Ablation Procedure."

Key details from the original source:

• Authors: Image Acquisition (listed as the author group in the provided text)
• Imaging platform: 3T MRI scanner (Magnetom Trio, Siemens Healthcare, Erlangen, Germany), with gadobutrol contrast (Gadovist, BayerSchering, Berlin, Germany)
• Ablation systems referenced: CARTO 3D electroanatomic mapping (Biosense Webster, Diamond Bar, CA, USA), Navistar open-irrigation catheter, and Arctic Front cryoballoon catheter (Medtronic, Montreal, Quebec, Canada)

References cited in the original article:

• Tamborero D, Mont L, Berruezo A, et al. Left atrial posterior wall isolation does not improve the outcome of circumferential pulmonary vein ablation for atrial fibrillation: A prospective randomized study. Circ Arrhythm Electrophysiol. 2009;2:35-40
• Bisbal F, Guiu E, Calvo N, et al. Left atrial sphericity: A new method to assess atrial remodeling. Impact on the outcome of atrial fibrillation ablation. J Cardiovasc Electrophysiol. 2013;24:752-759
• Calkins H, Kuck KH, Cappato R, et al. 2012 HRS/EHRA/ECAS expert consensus statement on catheter and surgical ablation of atrial fibrillation: Recommendations for patient selection, procedural techniques, patient management and follow-up, definitions, endpoints, and research trial design. Europace. 2012;14:528-606

Note: This article is intended for educational purposes and is not a substitute for professional medical advice. Always consult a qualified healthcare provider about your specific condition and treatment options.