**4. Changing landscape of safety and efficacy of catheter ablation at current era**

AF ablation is a relatively complex procedure with approximately 4.5% risk of a major complication and is only available in specialized centers. But currently, this procedure is being increasingly offered to patients, and even sicker patients. With early recognition and prevention of complications, advances in technology, increased operator experience, AF ablation has become a more widely and frequently performed safe and effective procedure with low complication rates.

An updated worldwide survey on safety and efficacy of catheter ablation of AF in humans was conducted by Cappato et al. [57] between 2003 and 2006 on 20,825 procedures amongst 16,309 patients.

Complications associated with catheter ablation of Atrial Fibrillation (**Table 3**):

Vascular access complications such as hematoma, arteriovenous fistula, pseudoaneurysm etc. are low nowadays due to almost universal use of ultrasound guided vascular access. Various esophageal temperature monitoring probes (e.g. CIRCA) or Esophageal cooling devices are available that has reduced the rate of catastrophic complications like atrio-esophageal fistula.

3-D Electroanatomic mapping (EAM) and high definition (HD) mapping in the modern era has significantly improved efficacy and safety of ablation and has reduced


#### **Table 3.**

*Procedural risks and complication rates with catheter ablation of atrial fibrillation.*

procedural time and fluoroscopy time. There are 3 mapping systems widely available CARTO (Biocense Webster Inc., Diamond Bar, California), EnSite NavX (St Jude Medical, St Paul, Minnesota), Rhythmia (Boston Scientific Inc., Marlborough, MA, USA). Pre procedural imaging, cardiac CT or MRI, integration with 3-D mapping systems further allows for increased procedural accuracy and safety. Phased array Intracardiac Echocardiogram is routinely used to aid in the visualization of cardiac anatomy, esophageal proximity to the posterior LA, pulmonary vein anatomy, catheter navigation, transeptal puncture and even tissue changes during ablation lesion delivery. The CARTO3 mapping system has the advantage of Integrated ICE (CARTOSOUND) allowing for direct integration of ICE images into the EAM system, however ICE is used in conjunction with all three mapping systems. Bidirectional steerable Navigational sheaths such as VIZIGO (Biocense Webster Inc., Diamond Bar, California) which can be visualized with EAM systems have facilitated in safe catheter navigation and reduced fluoroscopy time.

In recent years, mapping catheter technology for AF ablation has improved significantly. HD mapping catheters with unique form factors with small electrode size, spacing and orientation allows for optimized electrogram collection allowing for better assessment of electrical properties of tissue, fractionated potentials, acquire accurate anatomy/geometry, wavefront propagation etc. Deflectable mapping catheters such as PentaRay or OctaRay (CARTO, Biocense Webster), IntellaMap Orion (Boston Scientific, Marlborough, MA, USA), HD Grid (Abbott, St Pail, MN) have their unique advantages each contributing to efficacy and safety of ablation procedure. INTELLAMAP ORION High Resolution mapping catheter is a basket catheter with 64 electrodes that is capable of high definition electro-anatomical mapping providing more accurate and greater resolution. OCTARAY is a novel multielectrode catheter for high-resolution atrial mapping that has proven its utility for mapping ablation gaps and provide high resolution mapping. With improvement in software technology mapping systems are also able acquiring more points in ultrashort time, tissue proximity indicator, wavefront

#### *Recent Advances in Catheter Ablation for Atrial Fibrillation and Non-pharmacological Stroke… DOI: http://dx.doi.org/10.5772/intechopen.106319*

annotation algorithm incorporating unipolar and bipolar electrograms increasing accuracy of map and identify ablation gaps or critical targets for ablation.

With improvement in software technology, new algorithms in the mapping systems enable acquisition of data in automated, efficient, and accurate process that reduces the dependence on the system operator. Future endeavors into HD mapping of AF include the use of novel algorithms, Artifical Intelligence (AI) neural networks and non contact mapping methodologies for the identification of AF triggers and drivers.

Probably, the greatest improvement in catheter ablation has been the rapid improvement in ablation catheter and energy delivery technology. The first RF ablation catheters were non irrigated and hence were associated with risk of coagulation and char formation at the catheter tissue interface resulting in risk of embolism. With development of open irrigated ablation catheter energy delivery has become more efficient and safer. Further development in catheter technologies include the introduction of feedback mechanisms to determine catheter contact including contact force catheters and local impedance technologies. These technologies allow for assessment of catheter tissue contact, tissue proximity, electrical and mechanical coupling and quality of lesion formation.

Equipped with modern imaging, mapping or navigational ability, irrigated ablation catheters, AF catheter ablation is now emerging as a standard of care for rhythm control in modern era with shorter procedural time, reduced fluoroscopic time, low procedural complication rates probably even lesser compared to initially reported complications in the earlier publications. Current literature suggests 60–90% improvement in selected patient with medically refractory AF and 2–3 fold better than achievable with AAD [26].

## **5. Surgical ablation of atrial fibrillation**

As mentioned above Maze III procedure has proven very effective in preventing recurrence of Atrial Fibrillation however has been limited by surgical morbidities and hence a stand alone maze procedure in the absence of any other cardiac surgery indications was difficult to justify. Since then, several other iteration of Maze III procedure has evolved most using linear lines to isolate pulmonary veins and posterior wall, though less efficacious than COX Maze procedure [58, 59]. Results from PRAGUE 12 study showed more patients stayed in sinus rhythm when surgical ablation was added to cardiac/valve surgery in patients with AF. 117 patients were randomized to receive the modified Maze surgical ablation procedure (RF or Cryo based on surgeon's preference) and 107 patients underwent surgery only. 60.2% of patients with surgical ablation were in sinus rhythm at 1 year compared to 35.5% (*P* = 0.002) and interestingly this benefit was entirely driven by improvement in long persistent and permanent AF patient group [26].

Current guideline (2017 HRS/EHRA/ECAS/APHRS/SOLAECE Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation) [45] recommendations regarding surgical ablation for AF is as follows (**Table 4**).

#### **5.1 Hybrid convergent procedure**

Although PVI has shown great efficacy in PAF, endocardial catheter ablation in patients with persistent and long standing persistent AF has reduced success rate. Posterior wall of LA is a complex anatomical structure in terms of atrial myofiber orientation which was demonstrated by Pashakhanloo et al. [60]. There is also

endo-epicardial dissociation with complex 3D wavefront propagation, and endocardial mapping alone may not identify epicardial substrate, similarly endocardial ablation may not be enough to modify epicardial substrate. To overcome this limitation, a newer


#### **Table 4.**

*2017 HRS/EHRA/ECAS/APHRS/SOLAECE expert consensus on surgical ablation for AF.*

**Figure 7.** *Figure adopted from DeLurgio et al. [61].* *Recent Advances in Catheter Ablation for Atrial Fibrillation and Non-pharmacological Stroke… DOI: http://dx.doi.org/10.5772/intechopen.106319*

hybrid convergent approach with endo-epicardial ablation was compared to endocardial ablation alone in the CONVERGENT [61] trial by DeLurgio et al. (**Figure 7**).

One-hundred fifty-three patients were randomized 2:1 to Hybrid Convergent vs. catheter ablation. Epicardial ablation was performed with unipolar radiofrequency device (EPi-Sense, AtriCure, OH). Pericardial access was gained through a transdiaphragmatic or subxiphoid approach, and the radiofrequency device was positioned inside a pericardioscopic cannula with an endoscope. Primary outcome was freedom from AF/AFl/AT without AAD or previously failed AAD without increase in dosage. Study concluded that Hybrid Convergent procedure has superior effectiveness compared to the catheter ablation for the treatment of persistent and long-standing persistent atrial fibrillation.

Both findings from PRAGUE 12 study and CONVERGENT trial provides unique insight into understanding the mechanism of Persistent and long standing persistent AF and offers new treatment options for this variety of AF which is more difficult to tackle with endocardial ablation alone.

#### **6. Device detected atrial fibrillation**

Device detected or subclinical atrial fibrillation (SCAF) is a term that broadly encompasses AT detected by cardiac implantable electronic devices (CIEDs), which include implantable cardiac monitors, dual-chamber pacemakers, dual-chamber implantable cardioverter-defibrillators, and cardiac resynchronization therapy devices. There is no consensus about role of anticoagulation in this unique group of patients, though it is believed to affect as many as one-third of the U.S. population. Current guidelines recommend OAC for stroke and systemic embolism prophylaxis in patients with non valvular atrial fibrillation based on CHADSVasc2 score irrespective of Paroxysmal, persistent/long standing persistent or permanent category. False detection may occur due to oversensing of far field R wave, noise, or runs of Premature atrial complexes (PAC) or undersensing may misdiagnose true AT and hence all device detected Atrial high response events (AHRE) require further verification by physician.

The temporal relationship between atrial fibrillation and stroke is not as well understood, and in some patients, episodes of AF are not detected until months after a stroke. Though studies like CRYSTAL AF [62] and EMBRACE [63] has shown increased trend of anticoagulation prescription by physicians amongst patients with cryptogenic stroke who has AF detected with an implantable loop monitor or an event monitor for 30 days, there was reduced trend towards starting anticoagulation amongst patients with CIED detected AF without cryptogenic stroke [64]. Multiple studies, including MOST, TRENDS, and ASSERT trials have added insight into this unique clinical situation of SCAF. Subgroup analysis of 316 patients from MOST (MOde Selection) trial in patients with sinus node dysfunction showed AHRE (atrial rate > 220 beats/min for 10 consecutive beats) was an independent predictor of mortality or nonfatal stroke and AF, indicating that pacemaker patients with sinus node dysfunction and AHRE were more than 2.5 times as likely to die or have a stroke, and were 6 times as likely to develop AF than those without AHRE [65]. TRENDS [66] study prospectively looked at 2486 patients with pacemakers or defibrillators that monitor AT/AF burden (defined as the longest total AT/AF duration on any given day during the prior 30-day period) and concluded that AT>5.5 h was significantly associated with increased risk of thromboembolic event in patients with ≥1 stroke

risk factor (heart failure, hypertension, age ≥65 years, diabetes, or prior thromboembolic event) and emphasized the notion that Thromboembolism risk is a quantitative function of AT/AF burden. In the ASSERT study, subclinical episodes of AT, defined as atrial rates ≥190 beats/min lasting >6 min, were associated with an increased risk of ischemic stroke [67]. Stroke risk was incremental with longer duration of AT but similar risk between AT of 6–24 h duration, or >24 h duration, stroke risk increased with the number of subclinical AT episodes [68]. IMPACT [69] trial had a predefined anticoagulation plan. Anticoagulation protocol was initiated if AT (defined as ≥200 beats/min for 36 of 48 beats) was detected≥48 h in patients with CHADS2 score ≤2 with discontinuation of anticoagulation if there were no AT recurrences detected for 30 days, CHADS2 scores of ≥3 to 4 would initiate anticoagulation for device-detected AT ≥24 h in 2 days, with discontinuation if there were no AT recurrences detected for 90 days, patients with CHADS2 scores ≥5 to 6, or with a history of prior thromboembolism were prescribed anticoagulant therapy for any AT, without discontinuation, regardless of AT recurrence [68]. Data Monitoring Committee recommended trial termination on the basis of failure to demonstrate a meaningful difference in outcome with the interventional strategy. There was no significant difference between groups in the primary outcome, which was the composite of ischemic stroke, systemic embolic, and major hemorrhagic events, or in all-cause mortality.

Guidelines are unclear about role of anticoagulation in device detected SCAF. One school hypothesizes there is lack of scientific evidence to prove benefit of anticoagulation in SCAF and there is no clear consensus regarding "how much is too much device detected AF" based on varying duration of AF seen in various trials. Other school argues that there is lack of temporal relationship between AF and stroke/thromboembolism reflecting AF is marker for increased risk of stroke or systemic thromboembolism and hence anticoagulation if initiated with detection of AF may prevent stroke. It is accepted that risk of stroke is independent of duration (Paroxysmal or persistent) of AF or symptoms of AF in patients with clinical AF and mostly governed by risk factors for stroke (e.g. CHADSVasc2 risk calculator tool). There is no answer to whether AF-related stroke risk varies on the method of AF detection e.g., 12 lead ECG, Holter monitor, Implantable loop monitor or pacemakerdefibrillator. It is established that SCAF is a common clinical situation and eventually on longitudinal follow up many of these patients eventually develop clinical AF. Thus device detected AF offers an opportunity for closer monitoring of this patient population, and initiation of anticoagulation should be based on risk of stroke guided by tools as CHADSVsac2 score profile after patient-physician discussion based on patient preference and values.
