An approach to catheter ablation of cavotricuspid isthmus dependent atrial flutter

Much of our understanding of the mechanisms of macro re-entrant atrial tachycardia comes from study of cavotricuspid isthmus (CTI) dependent atrial flutter. In the majority of cases, the diagnosis can be made from simple analysis of the surface ECG. Endocardial mapping during tachycardia allows confirmation of the macro re-entrant circuit within the right atrium while, at the same time, permitting curative catheter ablation targeting the critical isthmus of tissue located between the tricuspid annulus and the inferior vena cava. The procedure is short, safe and by demonstration of an electrophysiological endpoint - bidirectional conduction block across the CTI - is associated with an excellent outcome following ablation. It is now fair to say that catheter ablation should be considered as a first line therapy for patients with documented CTI-dependent atrial flutter.     

Ablation of Post Transplant Atrial Flutter and Pseudo-fibrillation Using Magnetic Navigation via a Superior Approach

Ablation of cavotricuspid isthmus flutter and atrial tachycardia in a complex substrate has never been reported using remote navigation via superior approach. Venous access was obtained via right internal jugular for ablation and left subclavian for duodecapolar catheter placement into the coronary sinus. In a posttransplant patient presenting with both regular and irregular tachycardia, both cavotricuspid isthmus flutter in the donor and atrial tachycardia in the recipient was mapped using a two catheter approach. Successful ablation of typical atrial flutter and anastomotic block was achieved. This is the first report of successful ablation of cavotricuspid isthmus flutter and posttransplant atrial tachycardia using magnetic navigation via superior approach. Using only two catheters, this approach is logical and feasible in complex substrates with interrupted inferior venous access.     

Successful Ablation of Cavotricuspid Isthmus-dependent Atrial Flutter Guided by Contact Force Vector in a Patient After a Tricuspid Valve Replacement

A 46-year-old man after a tricuspid valve replacement due to traumatic severe tricuspid regurgitation developed cavotricuspid isthmus-dependent counterclockwise atrial flutter. During a linear ablation using a contact force-sensing irrigated ablation catheter, the flutter could be terminated by a radiofrequency application within a deep pouch just below the bioprosthetic tricuspid valve.     

A re-analysis of our current understanding of isthmus-dependent atrial flutter: some gaps, some hypotheses

The macro-reentrant circuit of isthmus-dependent atrial flutter (AFL) is located in the right atrium around the tricuspid annulus. High acute success and low recurrence rate makes isthmus ablation a definitive therapy for patients with only AFL. However, a review of the literature suggests that, different aspects of this macro-reentrant circuit are still not entirely understood, while new information continues to emerge. The aim of this article is to discuss some gaps in our "complete" understanding of isthmus-dependent AFL. Few hypotheses have been stated which are open to investigation.     

A review of mitral isthmus ablation

Mitral isthmus ablation forms part of the electrophysiologist's armoury in the catheter ablation treatment of atrial fibrillation. It is well recognised however, that mitral isthmus ablation is technically challenging and incomplete ablation may be pro-arrhythmic, leading some to question its role. This article first reviews the evidence for the use of adjunctive mitral isthmus ablation and its association with the development of macroreentrant perimitral flutter. It then describes the practical techniques of mitral isthmus ablation, with particular emphasis on the assessment of bi-directional mitral isthmus block. The anatomy of the mitral isthmus is also discussed in order to understand the possible obstacles to successful ablation. Finally, novel techniques which may facilitate mitral isthmus ablation are reviewed.     

Ablation of atrial flutter: block (isthmus conduction) or not a block, that is the question?

It is important to identify residual slow conduction and minimize the chance of resumption of conduction after right atrial isthmus ablation to reduce the chance of recurrence of atrial flutter (AFL). The aim of this article is to discuss the best possible way of confirming a bi-directional isthmus conduction (BIC) block after ablation of an isthmus-dependent AFL. A combination of activation and double potential mapping seems to be the most practical way of acutely confirming the BIC block.     

Epicardial fat pad within the transverse sinus mimicking a left atrial appendage thrombus

The presence of left atrial thrombus is a contraindication to cardioversion or catheter ablation in patients with atrial fibrillation, due to the increased risk of systemic thromboembolism. Management of this situation includes changes in the anticoagulation regimen and repeat imaging tests. Accurate diagnosis of left atrial appendage thrombus is therefore essential but can sometimes be challenging. Multiple imaging modalities may sometimes be required in the setting of anatomical variations of the left atrial appendage and surrounding structures.We present the case of a patient awaiting ablation for atypical atrial flutter, who underwent a transthoracic echocardiogram that showed an echodense, mobile structure within the vicinity of the left atrial appendage, suggesting a possible thrombus. A cardiac CT demonstrated the image to correlate with an epicardial fat pad within the transverse sinus.     

Isthmus Dependent Atrial Flutter Cycle Length Correlates with Right Atrial Cross-Sectional Area

Background

Right atrial flutter cycle length can prolong in the presence of antiarrhythmic drug therapy. We hypothesized that the cycle length of right atrial isthmus dependent flutter would correlate with right atrial cross-sectional area measurements.

Methods

60 patients who underwent ablation for electrophysiologically proven isthmus dependent right atrial flutter, who were not on Class I or Class III antiarrhythmic drugs and had recent 2-dimensional echocardiographic data comprised the study group. Right atrial length and width were measured in the apical four chamber view. Cross-sectional area was estimated by multiplying the length and width. 35 patients had an atrial flutter rate ≥ 250 bpm (Normal Flutter Group) and 25 patients had an atrial flutter rate < 250 bpm (Slow Flutter Group).

Results

Mean atrial flutter rate was 283 bpm in the normal flutter group and 227 bpm in the slow flutter group. Mean atrial flutter cycle length was 213 ms in the Normal Flutter Group and 265 ms in the Slow Flutter Group (p< 0.0001). Mean right atrial cross sectional area was 1845 mm² in the Normal Flutter group and 2378 mm² in the Slow Flutter Group, (p< 0.0001). Using linear regression, CSA was a significant predictor of cycle length (β =0.014 p = 0.0045). For every 1 mm² increase in cross-sectional area, cycle length is 0.014 ms longer.

Conclusions

In the absence of antiarrhythmic medications, right atrial cross sectional area enlargement correlates with atrial flutter cycle length. These findings provide further evidence that historical rate-related definitions of typical isthmus dependent right atrial are not mechanistically valid.     

Can Right Ventricular Pacing be Useful in the Assessment of Cavo-tricuspid Isthumus Block?

Background

Cavo-tricuspid isthmus (CTI) block is currently assessed by coronary sinus (CS) pacing or low lateral and septal atrial pacing. Occasionally, CS catheterization through the femoral route can be difficult to perform or right atrial pacing can be problematic because of catheter instability or saturation of the atrial electrograms recorded near the catheter.

Objectives

Our aim was to evaluate the feasibility of assessing cavo-tricuspid isthmus block by means of right ventricular (RV) pacing in patients with ventriculo-atrial conduction, comparing it with CS pacing.

Methods

Circumannular activation was analyzed during CS and RV pacing in consecutive patients in sinus rhythm undergoing CTI ablation for typical atrial flutter. Patients without ventriculo-atrial conduction were excluded from the study. The linear lesion was created during RV pacing and split atrial signals on the ablation line were analyzed. CTI block was confirmed by analyzing local electrograms on the line of block and circumannular activation during CS and RV pacing.

Results

Out of 31 patients, 20 displayed ventriculo-atrial conduction (64%) and were included in the study. Before ablation, during RV stimulation, the collision front of circumannular activation shifted counterclockwise in contrast with the pattern observed during CS pacing. After ablation, circumannular activation was similar during CS and RV pacing, showing fully descending lateral right atrium activation, even if double potentials registered on the ablation line were less widely split during RV pacing than CS pacing (111±26 ms vs 128±30 , p=0.0001).

Conclusions

In patients with ventriculo-atrial conduction, tricuspid annulus activation during CS and RV pacing is similar, before and after CTI ablation. The occurrence of split atrial electrograms separated by an isoelectric interval registered on the line of block can be detected during CS or RV pacing. In patients with difficult CS catheterization via the femoral vein, before trying the subclavian or internal jugular route, if retrograde ventriculo-atrial conduction is present, RV pacing can be an easy trick to assess isthmus block.     

High-density activation map of atrial tachycardia within left atrial appendage

Identification of the critical isthmus of the reentrant tachycardia is essential to maximize the effect of catheter ablation (CA) and to minimize the myocardial injury of CA. An 81-year-old woman presented recurrent palpitations after CA of atrial fibrillation (AF) and atrial tachycardia (AT). She had moderate aortic valve stenosis and coronary artery disease. She had received a pulmonary vein isolation, left atrial (LA) posterior wall isolation, and LA anterior linear ablation for atrial fibrillation 1 year prior. At the start of the procedure, she was in sinus rhythm. Atrial burst pacing induced an AT (230msec). High-density mapping revealed a figure-of-eight activation pattern within the LA appendage (LAA), accounting for 99% of the tachycardia cycle length. The critical isthmus was identified at the mid LAA and the local electrogram of the critical isthmus was not fractionated. A single radiofrequency application at the critical isthmus of the AT, terminated the AT. She was free from any ATs for 28 months.Radiofrequency ablation of the localized reentrant AT was usually performed targeting long fractionated electrograms. In our case, the local electrogram at the critical isthmus was not fragmented compared with the LAA distal part. Long fractionated electrograms were recorded at a more distal part of the LAA than the common isthmus and we could avoid the potential risk of a perforation. A recent developed 3-dimensional electro-anatomical mapping system can identify the critical isthmus and allow us to select a new therapeutic strategy for a critical isthmus ablation of an AT within the LAA.     

Atrial Tachycardia Originating from the Cavo-Tricuspid Isthmus May Exhibit Narrow P Waves

An 83-year-old man underwent electrophysiological testing for focal atrial tachycardia (AT) exhibiting narrow P waves with negative deflections in the inferior leads. Catheter ablation at the cavo-tricuspid isthmus (CTI) successfully eliminated the AT. The propagation map during AT and pacing study from the successful ablation site demonstrated that the atrial activation throughout the CTI did not produce significant P wave deflections. Consequently, during AT, the left atrial activation time determined the P wave duration. This case demonstrates that AT originating from the CTI may exhibit narrow P waves which can be misinterpreted as AT originating from the inter-atrial septum.     

Healthcare Utilization and Clinical Outcomes after Catheter Ablation of Atrial Flutter

Atrial flutter ablation is associated with a high rate of acute procedural success and symptom improvement. The relationship between ablation and other clinical outcomes has been limited to small studies primarily conducted at academic centers. We sought to determine if catheter ablation of atrial flutter is associated with reductions in healthcare utilization, atrial fibrillation, or stroke in a large, real world population. California Healthcare Cost and Utilization Project databases were used to identify patients undergoing atrial flutter ablation between 2005 and 2009. The adjusted association between atrial flutter ablation and healthcare utilization, atrial fibrillation, or stroke was investigated using Cox proportional hazards models. Among 33,004 patients with a diagnosis of atrial flutter observed for a median of 2.1 years, 2,733 (8.2%) underwent catheter ablation. Atrial flutter ablation significantly lowered the adjusted risk of inpatient hospitalization (HR 0.88, 95% CI 0.84–0.92, p<0.001), emergency department visits (HR 0.60, 95% CI 0.54–0.65, p<0.001), and overall hospital-based healthcare utilization (HR 0.94, 95% CI 0.90–0.98, p = 0.001). Atrial flutter ablation was also associated with a statistically significant 11% reduction in the adjusted hazard of atrial fibrillation (HR 0.89, 95% CI 0.81–0.97, p = 0.01). Risk of acute stroke was not significantly reduced after ablation (HR 1.09, 95% CI 0.81–1.45, p = 0.57). In a large, real world population, atrial flutter ablation was associated with significant reductions in hospital-based healthcare utilization and a reduced risk of atrial fibrillation. These findings support the early use of catheter ablation for the treatment of atrial flutter.     

Assessment of the Correlation Between Two Defining Criteria for Bidirectional Isthmic Block in the Ablation of Typical Atrial Flutter

Background

A complete, bidirectional conduction block in the cavotricuspid isthmus (CTI) represents the end-point of the typical atrial flutter ablation. We investigated the correlation between two criteria for successful ablation, one based on the atrial bipolar electrogram morphology before and after complete CTI conduction block, compared to the standard criteria of differential pacing and reversal in the right atrial depolarization sequence during coronary sinus (CS) pacing.

Method

We conducted a retrospective study in 111 patients (81 males, average age 62±10 years) who underwent an atrial flutter ablation during September 2007 - July 2009 in the Cardiology - Rehabilitation Hospital, UMF Cluj-Napoca. We assessed the presence of a bidirectional block at the end of the procedure using the standard criteria. We then analyzed the morphology of the bipolar atrial electrograms adjacent to the ablation line, before and after CTI conduction block.

Results

A change from a qRs morphology to a rSr'' morphology when pacing from the coronary sinus and from a rsr'' morphology to a QRS morphology when pacing from the low-lateral right atrium was associated with a CTI conduction block. Sensitivity (Se), specificity(Sp), positive predictive value (PPV), negative predictive value (NPV) were 96%, 89%, 99% and 67% respectively.

Conclusion

Our study suggests that the analysis of the atrial bipolar electrogram next to the ablation line before and after CTI ablation may be used as a reliable criterion to validate CTI conduction block due to its high sensitivity, specificity and positive predictive value.     

A Model for Mechano-Electrical Feedback Effects on Atrial Flutter Interval Variability

Atrial flutter is a supraventricular arrhythmia, based on a reentrant mechanism mainly confined to the right atrium. Although atrial flutter is considered a regular rhythm, the atrial flutter interval (i.e., the time interval between consecutive atrial activation times) presents a spontaneous beat-to-beat variability, which has been suggested to be related to ventricular contraction and respiration by mechano-electrical feedback. This paper introduces a model to predict atrial activity during atrial flutter, based on the assumption that atrial flutter variability is related to the phase of the reentrant activity in the ventricular and respiratory cycles. Thus, atrial intervals are given as a superimposition of phase-dependent ventricular and respiratory modulations. The model includes a simplified atrioventricular (AV) branch with constant refractoriness and conduction times, which allows the prediction of ventricular activations in a closed-loop with atrial activations. Model predictions are quantitatively compared with real activation series recorded in 12 patients with atrial flutter. The model predicts the time course of both atrial and ventricular time series with a high beat-to-beat agreement, reproducing 96±8% and 86±21% of atrial and ventricular variability, respectively. The model also predicts the existence of phase-locking of atrial flutter intervals during periodic ventricular pacing and such results are observed in patients. These results constitute evidence in favor of mechano-electrical feedback as a major source of cycle length variability during atrial flutter.     

Spontaneous demonstration of counterclockwise right atrial activation following successful isthmus ablation

We describe an uncommon case of typical flutter with symptomatic sinus node dysfunction, in which a permanent junctional rhythm developed following ablation of the cavo-tricuspid isthmus. This rhythm activated the right atrium in counter clockwise manner thus providing spontaneous proof of unidirectional isthmus block, a phenomenon that is usually demonstrated by proximal coronary sinus pacing.     

Electrophysiological Features of Atrial Flutter in Cardiac Sarcoidosis: A Report of Two Cases

We report two cases of systemic sarcoidosis with atrial flutter as the clinical manifestation. In one patient, who had symptoms of shorter duration, the arrhythmia was no longer inducible after a course of glucocorticoid therapy. Electroanatomical mapping in the other case revealed patchy fibrosis of the left atrial myocardium and multiple macro-reentrant circuits. Sinus rhythm could be restored with ablation of these reentrant circuits. To our knowledge, this is the first report on the demonstration of atrial scarring in a patient with sarcoidosis using 3-D electroanatomical mapping. These two cases illustrate that the inflammation of atrial myocardium is the primary mechanism of atrial arrhythmias in patients with cardiac sarcoidosis.     

Effect of autonomic neurotransmitters on excitable gap composition in canine atrial flutter

Atrial arrhythmias are believed to be influenced by autonomic nervous system tone. We evaluated the effects of sympathetic and parasympathetic activation on atrial flutter (AF1) by determining the effects of norepinephrine (NE) and acetylcholine (ACh) on the composition of the excitable gap. A model of reentry around the tricuspid valve was produced in 17 chloralose anesthetized dogs using a Y-shaped lesion in the intercaval area that extended to the right atrial appendage. Excitable gap characteristics were determined during AF1 by scanning diastole with a single premature extrastimulus at progressively shorter coupling intervals to define the reset-response curve. Measurements were made during a constant infusion of NE (15 microg/min) into the right coronary artery and repeated during ACh infusion (2 microg/min) following a 15 min recovery period. The excitable gap (27 +/- 1 ms) was significantly (P < 0.001) increased by NE (34 +/- 1 ms) and ACh (50 +/- 2 ms). The fully excitable portion (7 +/- 1 ms) was also significantly (P < 0.001) increased by NE (17 +/- 1 ms) and ACh (43 +/- 2 ms). We conclude that both neurotransmitters increase the safety margin of full excitability ahead of the wavefront, demonstrating that parasympathetic and sympathetic activation can facilitate the persistence of this refractory atrial arrhythmia.     

A mathematical model of the unidirectional block caused by the pulmonary veins for anatomically induced atrial reentry

It is widely believed that the pulmonary veins (PVs) of the left atrium play the central role in the generation of anatomically induced atrial reentry but its mechanism has not been analytically explained. To understand this mechanism, a new analytic approach is proposed by adapting the geometric relative acceleration analysis from spacetime physics based on the hypothesis that a large relative acceleration can translate to a dramatic increase in the curvature of a wavefront and subsequently to conduction failure. By verifying the strong dependency of the propagational direction and the magnitude of anisotropy for conduction failure, this analytic method reveals that a unidirectional block can be generated by asymmetric propagation toward the PVs. This model is validated by computational tests in a T-shaped domain, computational simulations for three-dimensional atrial reentry and previous in-silico reports for anatomically induced atrial reentry.     

Reflected reentry, delayed conduction, and electrotonic inhibition in segmentally depressed atrial tissues

Reflection is a subclass of reentrant cardiac arrhythmias in which reexcitation of the heart occurs as a result of to and fro electrotonically mediated transmission of impulses across a narrow zone of impaired conductivity. Although relatively well characterized in ventricular tissues, the reflection mechanism has not been studied in atrial tissues. In this study we examine the possibility of reflected reentry in segmentally depressed atrial tissues and evaluate conduction characteristics in these preparations. Narrow strips of atrial pectinate muscle or crista terminalis (canine and calf) were placed in a three-chambered bath and the central segment was superfused with an isotonic sucrose solution or an "ischemic" Tyrode's solution. Proximal to distal conduction across the 1.0- to 1.2-mm wide ischemic gap showed step delays as long as 210 ms. Reflected reentry was readily demonstrable when prominent step delays occurred during anterograde conduction of the impulse across the gap. Progressive acceleration of the stimulation rate resulted in progressively greater impairment of anterograde conduction until complete block occurred. The incidence and patterns of reflected reentry were therefore a sensitive function of the stimulation rate. Other features exhibited by these preparations include a slow recovery of excitability following the action potential, postrepolarization refractoriness, and electrotonic inhibition and summation. Our data suggest that the characteristics of conduction and reflection in segmentally depressed atrial tissues are qualitatively similar to those in ventricular tissues. The presence of electrotonic inhibition in atrial may also help to explain the functionally inexcitable zone seen in the vortex of the leading circle model of atrial flutter.     

SUPRASTERNAL NOTCH ECHOCARDIOGRAPHY AND ATRIAL ARRHYTHMIAS

Anterior-posterior single-crystal echocardiography has been used in atrial flutter and in sinus rhythm after cardioversion to demonstrate anterior movement of the posterior left atrial wall, representing the effects of atrial flutter and sinus contractions.(1) This is thought to be the first report of characteristic superior movement of the inferior left atrial wall during atrial flutter, atrial tachycardia, and sinus rhythm by single-crystal suprasternal notch echocardiography.