continuity index (ci) calculation for prospective cases of atrial fibrillation ablation with proactive esophageal cooling

Assessing Continuity Index in Pulmonary Vein Isolation with Esophageal Cooling 

Pulmonary vein isolation (PVI) using radiofrequency (RF) catheter ablation has become one of the most common methods for restoring sinus rhythm in the rising number of atrial fibrillation (AF) cases worldwide1. Research has shown that indirect lesion quality markers, such as impedance decline, catheter-tissue contact force, catheter stability, and bipolar electrogram amplitude reduction serve as evidence of transmurality, which contributes to the effectiveness of PVI2. Despite these available markers, improving on successful isolation and ultimately, long-term freedom from arrhythmias remains a high priority for electrophysiologists. Clinical data have shown that the placement of adjacent, overlapping, and continuous lesions along the circumferential isolation line is associated with lower recurrence rates and a higher likelihood of achieving transmurality-associated unipolar electrogram (TUE)2,3.
Kautzner et al., in the EFFICAS II Study, developed the Continuity Index (CI) to quantify discontinuous lesion placement in efforts to further understand how the order of lesion placement during an ablation impacts both short and long-term efficacy (Figure 1)3. The CI refers to the number of positions the catheter tip has moved over to place subsequent lesions in non-adjacent positions after stopping RF power early due to local overheating. A higher CI implies more discontinuity in sequential lesion placement. This study suggested that a PVI with a low CI (CI &#60; 6) resulted in a significant increase in successful isolation as a result of contiguous catheter movement allowing more effective electrical isolation compared to a CI &#8805; 63. One possible mechanism for the observed decrease in long-term efficacy associated with a higher CI is the rapid edema formation that occurs around lesions, which has been thought to result in reversible PVI4,5. When subsequent lesions are delayed, rapid edema formation may prevent transmural or contiguous lesion formation at adjacent positions and may significantly alter or conceal local electrograms in the region of stunned tissue2,3. There exists a need to prevent esophageal thermal injury and potentially lethal atrioesophageal fistula (AEF) during PVI; however, the use of traditional luminal esophageal temperature (LET) monitoring often forces cessation of RF energy application as a result of local overheating detected in the esophagus6,7,8. This in turn causes the CI to increase significantly.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/66688/66688fig01.jpg" /> 
Figure 1: Example of continuity index calculation as originally defined for two examples of ablation patterns3.&#160;This figure was taken from Kautzner et al.3. Abbreviation: CI = continuity index. <a href="https://www.jove.com/files/ftp_upload/66688/66688fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
A proactive esophageal cooling device (see the Table of Materials) has been granted marketing authorization by the Food and Drug Administration (FDA) to reduce the likelihood of ablation-related esophageal injury resulting from radiofrequency cardiac ablation procedures, and data from over 25,000 patients suggest a significant reduction in AEF rate with cooling9. Long-term follow-up data also suggest improved freedom from arrhythmia when using cooling as opposed to LET monitoring10,11. The cooling device is a non-sterile, multi-lumen silicone tube placed in the esophagus, much like an orogastric tube, for the purpose of cooling or warming a patient. The tube acts as a heat sink for RF energy inadvertently delivered to the esophagus, thus minimizing esophageal tissue damage, while pericardial tissues prevent significant cooling of atrial tissue12. Device temperature is controlled by connecting the esophageal cooling device to an external heat exchanger that circulates distilled water within the device (Figure 2). The device can be placed by any provider cleared to place a standard orogastric tube (nurses, physicians, paramedics). For ablation procedures, the device is usually placed by the anesthesiologist or CRNA immediately following induction of anesthesia and intubation. Placement is confirmed by visualizing the radiopaque distal tip in the gastric space on fluoroscopy. The device can also be seen on intracardiac echocardiography (ICE) commonly used during ablations. During the procedure, the patient&#39;s temperature can be continuously measured by usual means (Foley, rectal, forehead, axillary, or tympanic membrane temperature probe), but not via esophageal probe.&#160;Recall that axillary temperature is typically 1.5&#176; C lower than core temperature, and adding this to the axillary measurement is necessary to reflect patient core temperature13.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/66688/66688fig02.jpg" /> 
Figure 2: Diagram of the active esophageal temperature management system. The commercially available heat exchange unit generates temperature-controlled water, which is then delivered across standard tubing sets into the device placed in the esophagus. After circulating at a rate of ~1.5 L/min inside the device, the water returns to the heat exchange unit. The independent central lumen allows gastric decompression and suction. The radiopacity of the distal tip of the device allows for fluoroscopic visualization in the gastric space to confirm correct placement. <a href="https://www.jove.com/files/ftp_upload/66688/66688fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Recent burn injury literature has found a strong association between cooling after thermal injury and a reduction in burn injury severity, with the mechanisms of this effect extending beyond dissipation of heat, to include the alteration of cellular behavior through (i) decreasing release of lactate and histamine, (ii) stabilizing thromboxane and prostaglandin levels, (iii) slowing local metabolism, (iv) altering membrane permeability, and (iv) inhibiting kallikrein activity14. The growing understanding of the local effects of hypothermia in burn injury provides a mechanistic underpinning for the significant safety benefit seen with the esophageal cooling device utilized in this study15. Proactive esophageal cooling allows for the contiguous placement of the sequential lesions without interruption and without the need to pause for local overheating conditions or temperature alarms, likely due to the mechanisms described above. This in turn decreases operator cognitive load, reduces procedure time, and allows a reduced CI which can increase long-term PVI success16,17.
Our aim in this protocol is to describe the methods of prospectively calculating a modified CI in real-time cases and describe the methods used to calculate a modified CI retrospectively in recorded cases. We then provide representative results for cases that utilized both real-time observations utilizing proactive esophageal cooling as well as retrospective data prior to the adoption of cooling. An advantage of this approach is that the CI can be measured easily both in real-time as well as retrospectively. By observing the CI in PVI cases with and without cooling, the impact of cooling on long-term efficacy and lesion continuity can be further quantified, and the use of the CI as a PVI quality measure can potentially be further promoted. Continuing research to explore CI and lesion quality in terms of RF ablation and clinical efficacy remains important, especially when pulsed field ablation appears to be associated with the risk of new adverse events without convincingly improving long-term outcomes 18.

Author Spotlight: Improving Lesion Contiguity in Pulmonary Vein Isolation via Proactive Esophageal Cooling

Determination of Continuity Index Values in Atrial Fibrillation Ablation with Proactive Esophageal Cooling

This protocol describes the methods used to determine the continuity index in patients undergoing pulmonary vein isolation procedures using radio frequency ablation, and demonstrates the differences in continuity index between ablation procedures using proactive esophageal cooling, as compared to procedures using luminal esophageal temperature monitoring. Proactive esophageal cooling using a dedicated device has been granted marketing authorization by the Food and Drug Administration to reduce the likelihood of ablation-related esophageal injury, resulting from radio frequency ablation procedures, and long-term follow-up data suggests improved freedom from arrhythmia when using cooling, as opposed to LET monitoring. Ablation and mapping catheters provide a variety of lesion quality markers, including impedance decline, catheter tissue contact force, catheter stability, and bipolar electrogram amplitude reduction, which serve as evidence of transmural contributing to PVI effectiveness.However, continuity index is not a marker provided by current devices and technologies, and currently requires manual assessment. Proactive esophageal cooling allows for a contiguous placement of sequential lesions without interruption or the need to pause for local overheating or temperature alarms. This, in turn, decreases operator cognitive load and procedure time, and allows for increased lesion continuity, or low continuity index, potentially increasing long-term PVI success.Low continuity index as a result of cooling may not only increase the durability of lesions, resulting in a higher freedom from arrhythmia, but also minimizes risks of thermal injury to critical structures that remains when using reactive luminal esophageal temperature monitoring, and eliminates the need for deviation of critical structures.

Continuity Index (CI) Calculation for Prospective Cases of Atrial Fibrillation Ablation with Proactive Esophageal Cooling

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