Radiofrequency catheter modification of sinus pacemaker function guided by intracardiac echocardiography

Three-dimensional functional anatomy of the human sinoatrial node for epicardial and endocardial mapping and ablation

The sinoatrial node (SAN) is the primary pacemaker of the human heart. It is a single, elongated, 3-dimensional (3D) intramural fibrotic structure located at the junction of the superior vena cava intercaval region bordering the crista terminalis (CT). SAN activation originates in the intranodal pacemakers and is conducted to the atria through 1 or more discrete sinoatrial conduction pathways. The complexity of the 3D SAN pacemaker structure and intramural conduction are underappreciated during clinical multielectrode mapping and ablation procedures of SAN and atrial arrhythmias. In fact, defining and targeting SAN is extremely challenging because, even during sinus rhythm, surface-only multielectrode mapping may not define the leading pacemaker sites in intramural SAN but instead misinterpret them as epicardial or endocardial exit sites through sinoatrial conduction pathways. These SAN exit sites may be distributed up to 50 mm along the CT beyond the ∼20-mm-long anatomic SAN structure. Moreover, because SAN reentrant tachycardia beats may exit through the same sinoatrial conduction pathway as during sinus rhythm, many SAN arrhythmias are underdiagnosed. Misinterpretation of arrhythmia sources and/or mechanisms (eg, enhanced automaticity, intranodal vs CT reentry) limits diagnosis and success of catheter ablation treatments for poorly understood SAN arrhythmias. The aim of this review is to provide a state-of-the-art overview of the 3D structure and function of the human SAN complex, mechanisms of SAN arrhythmias and available approaches for electrophysiological mapping, 3D structural imaging, pharmacologic interventions, and ablation to improve diagnosis and mechanistic treatment of SAN and atrial arrhythmias.

Structural and Functional Properties of Subsidiary Atrial Pacemakers in a Goat Model of Sinus Node Disease

Background

The sinoatrial/sinus node (SAN) is the primary pacemaker of the heart. In humans, SAN is surrounded by the paranodal area (PNA). Although the PNA function remains debated, it is thought to act as a subsidiary atrial pacemaker (SAP) tissue and become the dominant pacemaker in the setting of sinus node disease (SND). Large animal models of SND allow characterization of SAP, which might be a target for novel treatment strategies for SAN diseases.

Methods

A goat model of SND was developed (n = 10) by epicardially ablating the SAN and validated by mapping of emergent SAP locations through an ablation catheter and surface electrocardiogram (ECG). Structural characterization of the goat SAN and SAP was assessed by histology and immunofluorescence techniques.

Results

When the SAN was ablated, SAPs featured a shortened atrioventricular conduction, consistent with the location in proximity of atrioventricular junction. SAP recovery time showed significant prolongation compared to the SAN recovery time, followed by a decrease over a follow-up of 4 weeks. Like the SAN tissue, the SAP expressed the main isoform of pacemaker hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) and Na⁺/Ca²⁺ exchanger 1 (NCX1) and no high conductance connexin 43 (Cx43). Structural characterization of the right atrium (RA) revealed that the SAN was located at the earliest activation [i.e., at the junction of the superior vena cava (SVC) with the RA] and was surrounded by the paranodal-like tissue, extending down to the inferior vena cava (IVC). Emerged SAPs were localized close to the IVC and within the thick band of the atrial muscle known as the crista terminalis (CT).

Conclusions

SAN ablation resulted in the generation of chronic SAP activity in 60% of treated animals. SAP displayed development over time and was located within the previously discovered PNA in humans, suggesting its role as dominant pacemaker in SND. Therefore, SAP in goat constitutes a promising stable target for electrophysiological modification to construct a fully functioning pacemaker.

An anatomical approach to determine the location of the sinoatrial node during catheter ablation

INTRODUCTION

The sinoatrial node (SAN) should be identified before superior vena cava (SVC) isolation to avoid SAN injury. However, its location cannot be identified without restoring sinus rhythm. This study evaluated the usefulness of the anatomically defined SAN by comparing it with the electrically confirmed SAN (e-SAN) to predict the top-most position of e-SAN and thus establish a safe and more efficient anatomical reference for SVC isolation than the previously reported reference of the right superior pulmonary vein (RSPV) roof.

METHODS AND RESULTS

The e-SAN was identified as the earliest activation site in the electroanatomical map obtained during sinus rhythm. The anatomically defined SAN, the cranial edge of the crista terminalis (CT) visualized with intracardiac echocardiography (CT top), and the RSPV roof, which was obtained from the overlaid electroanatomical image of SVC and RSPV, were tagged on one map. The distance from the e-SAN to each reference was measured. Among 77 patients, the height of the e-SAN from the CT top was a median (interquartile range) of -2.0 (-8.0 to 4.0) mm. The e-SAN existed from 10 mm above the CT top or lower in 74 (96%) patients and from the RSPV roof or below in 73 (95%) patients. The reference of 10 mm above the CT top is more proximal to the right atrium than the RSPV roof and can provide longer isolatable SVC sleeves (30.0 [20.0-35.0] vs. 24.0 [18.0-30.0] mm, p < .001). The e-SAN tended to be found above the CT top when the heart rate during mapping was faster (adjusted odds ratio [95% confidence interval] per 10-bpm increase: 1.71 [1.20-2.43], p < .01).

CONCLUSION

The CT top is useful for predicting the upper limit of the e-SAN and can provide a better reference for SVC isolation than the RSPV roof.

The expanding phenotypes of cohesinopathies: one ring to rule them all!

Preservation and development of life depend on the adequate segregation of sister chromatids during mitosis and meiosis. This process is ensured by the cohesin multi-subunit complex. Mutations in this complex have been associated with an increasing number of diseases, termed cohesinopathies. The best characterized cohesinopathy is Cornelia de Lange syndrome (CdLS), in which intellectual and growth retardations are the main phenotypic manifestations. Despite some overlap, the clinical manifestations of cohesinopathies vary considerably. Novel roles of the cohesin complex have emerged during the past decades, suggesting that important cell cycle regulators exert important biological effects through non-cohesion-related functions and broadening the potential pathomechanisms involved in cohesinopathies. This review focuses on non-cohesion-related functions of the cohesin complex, gene dosage effect, epigenetic regulation and TGF-β in cohesinopathy context, especially in comparison to Chronic Atrial and Intestinal Dysrhythmia (CAID) syndrome, a very distinct cohesinopathy caused by a homozygous Shugoshin-1 (SGO1) mutation (K23E) and characterized by pacemaker failure in both heart (sick sinus syndrome followed by atrial flutter) and gut (chronic intestinal pseudo-obstruction) with no intellectual or growth delay. We discuss the possible impact of SGO1 alterations in human pathologies and the potential impact of the SGO1 K23E mutation in the sinus node and gut development and functions. We suggest that the human phenotypes observed in CdLS, CAID syndrome and other cohesinopathies can inform future studies into the less well-known non-cohesion-related functions of cohesin complex genes. Abbreviations: AD: Alzheimer Disease; AFF4: AF4/FMR2 Family Member 4; ANKRD11: Ankyrin Repeat Domain 11; APC: Anaphase Promoter Complex; ASD: Atrial Septal Defect; ATRX: ATRX Chromatin Remodeler; ATRX: Alpha Thalassemia X-linked intellectual disability syndrome; BIRC5: Baculoviral IAP Repeat Containing 5; BMP: Bone Morphogenetic Protein; BRD4: Bromodomain Containing 4; BUB1: BUB1 Mitotic Checkpoint Serine/Threonine Kinase; CAID: Chronic Atrial and Intestinal Dysrhythmia; CDK1: Cyclin Dependent Kinase 1; CdLS: Cornelia de Lange Syndrome; CHD: Congenital Heart Disease; CHOPS: Cognitive impairment, coarse facies, Heart defects, Obesity, Pulmonary involvement, Short stature, and skeletal dysplasia; CIPO: Chronic Intestinal Pseudo-Obstruction; c-kit: KIT Proto-Oncogene Receptor Tyrosine Kinase; CoATs: Cohesin Acetyltransferases; CTCF: CCCTC-Binding Factor; DDX11: DEAD/H-Box Helicase 11; ERG: Transcriptional Regulator ERG; ESCO2: Establishment of Sister Chromatid Cohesion N-Acetyltransferase 2; GJC1: Gap Junction Protein Gamma 1; H2A: Histone H2A; H3K4: Histone H3 Lysine 4; H3K9: Histone H3 Lysine 9; HCN4: Hyperpolarization Activated Cyclic Nucleotide Gated Potassium and Sodium Channel 4;p HDAC8: Histone deacetylases 8; HP1: Heterochromatin Protein 1; ICC: Interstitial Cells of Cajal; ICC-MP: Myenteric Plexus Interstitial cells of Cajal; ICC-DMP: Deep Muscular Plexus Interstitial cells of Cajal; If: Pacemaker Funny Current; IP3: Inositol trisphosphate; JNK: C-Jun N-Terminal Kinase; LDS: Loeys-Dietz Syndrome; LOAD: Late-Onset Alzheimer Disease; MAPK: Mitogen-Activated Protein Kinase; MAU: MAU Sister Chromatid Cohesion Factor; MFS: Marfan Syndrome; NIPBL: NIPBL, Cohesin Loading Factor; OCT4: Octamer-Binding Protein 4; P38: P38 MAP Kinase; PDA: Patent Ductus Arteriosus; PDS5: PDS5 Cohesin Associated Factor; P-H3: Phospho Histone H3; PLK1: Polo Like Kinase 1; POPDC1: Popeye Domain Containing 1; POPDC2: Popeye Domain Containing 2; PP2A: Protein Phosphatase 2; RAD21: RAD21 Cohesin Complex Component; RBS: Roberts Syndrome; REC8: REC8 Meiotic Recombination Protein; RNAP2: RNA polymerase II; SAN: Sinoatrial node; SCN5A: Sodium Voltage-Gated Channel Alpha Subunit 5; SEC: Super Elongation Complex; SGO1: Shogoshin-1; SMAD: SMAD Family Member; SMC1A: Structural Maintenance of Chromosomes 1A; SMC3: Structural Maintenance of Chromosomes 3; SNV: Single Nucleotide Variant; SOX2: SRY-Box 2; SOX17: SRY-Box 17; SSS: Sick Sinus Syndrome; STAG2: Cohesin Subunit SA-2; TADs: Topology Associated Domains; TBX: T-box transcription factors; TGF-β: Transforming Growth Factor β; TGFBR: Transforming Growth Factor β receptor; TOF: Tetralogy of Fallot; TREK1: TREK-1 K(+) Channel Subunit; VSD: Ventricular Septal Defect; WABS: Warsaw Breakage Syndrome; WAPL: WAPL Cohesin Release Factor.

Three-dimensional mapping and intracardiac echocardiography in the treatment of sinoatrial nodal tachycardias

Three-dimensional mapping and intracardiac echocardiography are important tools for the study of the site of origin of an arrhythmia and its substrate. This review examines the application of these techniques in the diagnosis and treatment of sinoatrial tachycardias with a special focus on the syndrome of inappropriate sinus tachycardia. The use of these techniques in electrophysiologic mapping and interventions such as catheter ablation is discussed. Three-dimensional mapping provides unique insights into the generation of normal and abnormal sinus impulses in man and their propagation in the atrium. It permits precise placement of ablation lesions and assessment of real-time electrophysiologic impact of these interventions. Intracardiac echocardiography provides delineation of important anatomic structures in the vicinity of the sinoatrial node complex and monitors the safety of interventions such as catheter ablation.

'Inappropriate' sinus tachycardia: does the 100 beats per min cut-off matter?

Sinus tachycardia is commonly encountered in clinical practice and when persistent, can result in significant symptoms and impaired quality of life, warranting further evaluation. On the other hand, a growing body of epidemiological and clinical evidence has shown that high resting heart rate (HR) within the accepted normal range is independently associated with increased risk of all-cause and cardiovascular mortality. However, higher HR as a risk factor for adverse cardiovascular outcomes is frequently underappreciated. In this review, we focus on two challenging problems that span the spectrum of abnormally fast sinus HR. The first section reviews inappropriate sinus tachycardia, a complex disorder characterized by rapid sinus HR without a clear underlying cause, with particular emphasis on current management options. The latter section discusses the prognostic significance of elevated resting HR and reviews clinical evidence aimed at modifying this simple, yet highly important risk factor.

Computer three-dimensional anatomical reconstruction of the human sinus node and a novel paranodal area

We have previously shown in rabbit that the pacemaker of the heart (the sinus node) is widespread and matches the wide distribution of the leading pacemaker site within the right atrium. There is, however, uncertainty about the precise location of the pacemaker in human heart, and its spatial relationships with the surrounding right atrial muscle. Therefore, the aim of the current study was to investigate the distribution of the sinus node tissue in a series of healthy human hearts and, for one of the hearts to construct a computer three-dimensional anatomical model of the sinus node, including the likely orientation of myocytes. A combination of experimental techniques--diffusion tensor magnetic resonance imaging (DT-MRI), histology, immunohistochemistry, image processing and computer modelling--was used. Our data show that the sinus node was larger than in previous studies and, most importantly, we identified a previously unknown area running alongside the sinus node (the "paranodal area"), which is even more extensive than the sinus node. This area possesses properties of both nodal and atrial tissues and may have a role in pacemaking. For example, it could explain the wide spread distribution of the leading pacemaker site in human right atrium, a phenomenon known as the wandering pacemaker observed in clinics. In summary, a novel 3D anatomical reconstruction presents a new picture of the distribution of nodal cells within the human right atrium.

The anatomy and physiology of the sinoatrial node--a contemporary review

The sinoatrial node is the primary pacemaker of the heart. Nodal dysfunction with aging, heart failure, atrial fibrillation, and even endurance athletic training can lead to a wide variety of pathological clinical syndromes. Recent work utilizing molecular markers to map the extent of the node, along with the delineation of a novel paranodal area intermediate in characteristics between the node and the surrounding atrial muscle, has shown that pacemaker tissue is more widely spread in the right atrium than previously appreciated. This can explain the phenomenon of a "wandering pacemaker" and concomitant changes in the P-wave morphology. Extensive knowledge now exists regarding the molecular architecture of the node (in particular, the expression of ion channels) and how this relates to pacemaking. This review is an up-to-date summary of the current state of our appreciation of the above topics.

Echocardiography-guided interventions

A major advantage of echocardiography over other advanced imaging modalities (magnetic resonance imaging, computed tomographic angiography) is that echocardiography is mobile and real time. Echocardiograms can be recorded at the bedside, in the cardiac catheterization laboratory, in the cardiovascular intensive care unit, in the emergency room-indeed, any place that can accommodate a wheeled cart. This tremendous advantage allows for the performance of imaging immediately before, during, and after various procedures involving interventions. The purpose of this report is to review the use of echocardiography to guide interventions. We provide information on the selection of patients for interventions, monitoring during the performance of interventions, and assessing the effects of interventions after their completion. In this document, we address the use of echocardiography in commonly performed procedures: transatrial septal catheterization, pericardiocentesis, myocardial biopsy, percutaneous transvenous balloon valvuloplasty, catheter closure of atrial septal defects (ASDs) and patent foramen ovale (PFO), alcohol septal ablation for hypertrophic cardiomyopathy, and cardiac electrophysiology. A concluding section addresses interventions that are presently investigational but are likely to enter the realm of practice in the very near future: complex mitral valve repairs, left atrial appendage (LAA) occlusion devices, 3-dimensional (3D) echocardiographic guidance, and percutaneous aortic valve replacement. The use of echocardiography to select and guide cardiac resynchronization therapy has recently been addressed in a separate document published by the American Society of Echocardiography and is not further discussed in this document. The use of imaging techniques to guide even well-established procedures enhances the efficiency and safety of these procedures.

Intracardiac echocardiography and acoustic radiation force impulse imaging of a dynamic ex vivo ovine heart model

Intracardiac echocardiography (ICE) has demonstrated utility in providing high-resolution cardiac ultrasound images for guidance of numerous catheter-based interventions, including radiofrequency ablations (RFA). However, the training of interventionalists and refinement of procedures involving intracardiac catheters is costly and time consuming due to necessary clinical and animal studies. As a result, research and development of ICE for other purposes is gradual and deliberate. Intracardiac acoustic radiation force impulse (ARFI) imaging has been demonstrated to be a suitable modality to monitor the progress of RFA procedures; however, a clinical protocol has been slow to develop due to the expense and demands of clinical experiments. We report on the development and use of an ex vivo heart model to evaluate ICE and intracardiac ARFI imaging. The ability of this model to provide clinically-relevant intracardiac imaging angles was investigated by inserting an intracardiac probe into the heart and imaging it from various positions and orientations. ARFI images of all four chambers also were formed. RFAs were also performed to create stiffer lesions within the right and left ventricles. Upon completion of the ablation, ARFI imaging was used to visualize the lesion and compared with images taken from pathology.The results show the ovine heart model to be a suitable apparatus for recreating several clinically-relevant intracardiac viewing angles of the heart. Also, the results indicate the potential of the heart model to be a valuable tool in the future development and refinement of a clinical protocol for intracardiac ARFI imaging based guidance and assessment of cardiac radiofrequency ablations.

Sinus Node Disease: An Idiopathic Right Atrial Myopathy

Sinus node disease was previously thought to be a disease limited to the sinus node and its atrial connections. However, recent reports have demonstrated sinus node disease as a disease of the entire right atrial myocardium. These patients have widespread electrophysiological abnormalities of their atria, including prolonged refractory periods and slowed conduction. In addition to these electrical changes, there are significant structural changes, such as fibrosis and fatty infiltration, which can be detected endocardially as regions of fractionated signals, low-voltage electrograms, and electrically silent areas. In most cases, the etiology of these changes is unknown. These changes may contribute to the high prevalence of atrial fibrillation seen in patients with sinus node disease.

Challenges and implementation of radiation-force imaging with an intracardiac ultrasound transducer

Intracardiac echocardiography (ICE) has been demonstrated to be an effective imaging modality for the guidance of several cardiac procedures, including radiofrequency ablation (RFA). However, assessing lesion size during the ablation with conventional ultrasound has been limited, as the associated changes within the B-mode images often are subtle. Acoustic radiation force impulse (ARFI) imaging is a promising modality to monitor RFAs as it is capable of visualizing variations in local stiffnesses within the myocardium. We demonstrate ARFI imaging with an intracardiac probe that creates higher quality images of the developing lesion. We evaluated the performance of an ICE probe with ARFI imaging in monitoring RFAs. The intracardiac probe was used to create high contrast, high resolution ARFI images of a tissue-mimicking phantom containing stiffer spherical inclusions. The probe also was used to examine an excised segment of an ovine right ventricle with a RFA-created surface lesion. Although the lesion was not visible in conventional B-mode images, the ARFI images were able to show the boundaries between the lesion and the surrounding tissue. ARFI imaging with an intracardiac probe then was used to monitor cardiac ablations in vivo. RFAs were performed within the right atrium of an ovine heart, and B-mode and ARFI imaging with the intracardiac probe was used to monitor the developing lesions. Although there was little indication of a developing lesion within the B-mode images, the corresponding ARFI images displayed regions around the ablation site that displaced less.

Experimental model of inappropriate sinus tachycardia: initiation and ablation

OBJECTIVE

The purpose of the present study was to develop an experimental model of inappropriate sinus tachycardia (IST) by injecting a catecholamine into a fat pad containing autonomic ganglia (AG) innervating the sinus node (SN).

METHODS

Initial protocols in 3 groups of pentobarbital anesthetized dogs consisted of (1) slowing the heart rate (HR) by electrical stimulation of AG in the fat pad; (2) the effect of intravenous injection of epinephrine (0.1-0.3 mg) on the HR and systolic blood pressure (BP); (3) the response of SN rate to intravenously injected isoproterenol (1 microgm/kg). These studies established a reference for the response to epinephrine injection (mean dose 0.2 +/- 0.9 mg, n = 14) into the fat pad at the base of the right superior pulmonary vein (RSPV). ECG leads, right atrial and His bundle electrograms, BP and core body temperature were continuously monitored.

RESULTS

Epinephrine, injected into the fat pad, caused a significant increase in heart rate (HR, average: 211 +/- 11/min, p < 0.05 compared to control) but little change in systolic BP, 149 +/- 10 mmHg, p = NS (Group I, N = 8). The tachycardia lasted >30 minutes. Ice mapping and P wave morphology showed the tachycardia origin in the SN in 6/8 and in the crista terminalis (CT) in 2. Injection of 0.4 cc of formaldehyde into the FP restored HR (159 +/- 16) toward baseline (154 +/- 18). In Group II (N = 6), the same regimen induced a significant increase in both HR and systolic BP (194 +/- 17/min and 230 +/- 24 mmHg, respectively) compared to control values (143 +/- 23/min, 162 +/- 24 mmHg) which lasted for > 30 minutes. Ice mapping and P wave morphology showed that the pacemaker was in the SN (1), overlying the CT (2), or atrioventricular junction (2). Formaldehyde (0.4 cc) injected into the FP restored both HR and systolic BP toward baseline values (148 +/- 29/min and 152 +/- 24 mmHg, p = NS) and prevented, slowing of the HR by electrical stimulation of the AG; moreover, the same dose of epinephrine injected intravenously increased HR and SBP but only for 2-5 minutes; Isoproterenol (1 microg/kg) injected intravenously induced essentially the same increase in sinus rate after AG ablation as in the control state (194 +/- 15/min vs 193 +/- 23/min, p = NS).

CONCLUSION

Experimental IST is mainly localized in the SN or CT. Ablation of the AG terminates IST without impairing the SN response to an adrenergic challenge.

Sinus Node Injury as a Complication of Superior Vena Cava Isolation

We report a case with SVC ectopy initiating AF; the origin and breakout point of the sinus node was inside the SVC, and the SVC ectopy was conducted through the same path as the sinus node activation to depolarize the right atrium. Injury to the sinus node happened after successful isolation of SVC.

Protected circumferential conduction in the posterior atrioventricular vestibule of the left atrium: electrophysiologic and anatomic correlates

BACKGROUND

The anatomic substrate for protected isthmus conduction in the right atrium has been well defined. Little is known of similar substrates in the left atrium (LA).

METHODS

Patients (pts) with reentrant tachycardia (AVRT) supported by a single left-sided accessory pathway were studied retrospectively (n = 64) and prospectively (n = 31). Intracardiac electrograms were recorded from the His bundle position and coronary sinus (CS). The LA was mapped with a steerable catheter using the transseptal approach. LA anatomy was examined grossly and histologically in six cadaver hearts after removal of endocardium.

RESULTS

A distal-to-proximal CS activation sequence during AVRT was seen in all patients with a left lateral accessory pathway before ablation. After one to three radiofrequency (RF) energy deliveries that did not interrupt accessory pathway conduction, the CS activation sequence was reversed in three patients in the retrospective group and bidirectional conduction block in the posterior atrioventricular vestibule of the LA (PAVV) was demonstrated in nine patients in the prospective group. Four of the six cadaver hearts showed a distinct circumferential inferoposterior myocardial bundle that coursed parallel to the CS in the PAVV.

CONCLUSIONS

We described evidence of bidirectional intraatrial block in the PAVV after application of RF energy during accessory pathway ablation. Such conduction block may mimic the presence of a second accessory pathway. Our data suggest that circumferential conduction in the PAVV may be poorly coupled to the rest of the LA and may be involved in the macro-reentrant circuit around the mitral annulus. The circumferential inferoposterior myocardial bundle may serve as the underlying anatomic substrate.

Superior Vena Cava Rhythm Masquerading as Normal Sinus Rhythm

We report the case of a patient with persistent cardiac rhythm originating from the superior vena cava (3 cm above the vena cava-atrial junction). It was detected by noncontact balloon mapping before induction of tachycardia and confirmed by conventional contact mapping with image studies. Thus, a 12-lead ECG showing normal morphologies of P waves may not indicate that the P waves are of sinus node origin.

Visualization of elusive structures using intracardiac echocardiography: insights from electrophysiology

Electrophysiological mapping and ablation techniques are increasingly used to diagnose and treat many types of supraventricular and ventricular tachycardias. These procedures require an intimate knowledge of intracardiac anatomy and their use has led to a renewed interest in visualization of specific structures. This has required collaborative efforts from imaging as well as electrophysiology experts. Classical imaging techniques may be unable to visualize structures involved in arrhythmia mechanisms and therapy. Novel methods, such as intracardiac echocardiography and three-dimensional echocardiography, have been refined and these technological improvements have opened new perspectives for more effective and accurate imaging during electrophysiology procedures. Concurrently, visualization of these structures noticeably improved our ability to identify intracardiac structures. The aim of this review is to provide electrophysiologists with an overview of recent insights into the structure of the heart obtained with intracardiac echocardiography and to indicate to the echo-specialist which structures are potentially important for the electrophysiologist.

Combined Epicardial-Endocardial Approach to Ablation of Inappropriate Sinus Tachycardia

A combined epicardial-endocardial approach to ablation of inappropriate sinus tachycardia in a highly symptomatic patient who failed to respond to medical therapy and endocardial ablation is described. The anatomy and physiology of the sinus node is discussed, providing a basis for performing this procedure. This case provides an additional therapeutic option for a condition that often is difficult to manage.

Role of intracardiac ultrasound in interventional electrophysiology

PURPOSE OF REVIEW

Interventional procedures in the electrophysiology and catheterization laboratory are rapidly advancing. Critical to the advancement of these procedures is accurate identification of critical anatomic landmarks and catheter position. Fluoroscopy remains the mainstay for general identification of anatomic landmarks but is inadequate for the precise imaging needed for complex procedures. Precise imaging of anatomic landmarks and catheter position is now possible during the procedure with the use of intracardiac echocardiography (ICE). This paper reviews the rapid development and utilization of ICE in interventional electrophysiology.

RECENT FINDINGS

Several recent studies show ICE as a major contribution to providing a safer, more reliable, and more cost-effective means of accomplishing the tasks performed by existing techniques. In the electrophysiology laboratory, the dependence on this new technology has been due to the rapid development of catheter-based radiofrequency ablation of the pulmonary veins for treatment of atrial fibrillation. Since the initial use of ICE in facilitating ablation of atrial fibrillation, other uses for ICE are continuously being identified.

SUMMARY

A comprehensive look is provided at the history and development of this new technology along with the most recent applications of ICE in interventional electrophysiology.

Determination of lesion size by ultrasound during radiofrequency catheter ablation

The catheter tip temperature that is used to control the radiofrequency generator output poorly correlates to lesion size. We, therefore, evaluated lesions created in vitro using a B-mode ultrasound imaging device as a potential means to assess lesion generation during RF applications non-invasively. Porcine ventricular tissue was immersed in saline solution at 37 degrees C. The catheter was fixed in a holder and positioned in a parallel orientation to the tissue with an array transducer (7.5 MHz) app. 3 cm above the tissue. Lesions were produced either in a temperature controlled mode with a 4-mm tip catheter with different target temperatures (50, 60, 70 and 80 degrees C, 80 W maximum output) or in a power controlled mode (25, 50 and 75 W, 20 ml/min irrigation flow) using an irrigated tip catheter. Different contact forces (0.5 N, 1.0 N) were tested, and RF was delivered for 60 s. A total of 138 lesions was produced. Out of these, 128 could be identified on the ultrasound image. The lesion depth and volume was on average 4.1 +/- 1.6 mm and 52 +/- 53 mm3 as determined by ultrasound and 3.9 +/- 1.7 mm and 52 +/- 55 mm3 as measured thereafter, respectively. A linear correlation between the lesion size determined by ultrasound and that measured thereafter was demonstrated with a correlation coefficient of r = 0.87 for lesion depth and r = 0.93 for lesion volume. We conclude that lesions can be assessed by B-mode ultrasound imaging.

Phased-array intracardiac echocardiography for defining cavotricuspid isthmus anatomy during radiofrequency ablation of typical atrial flutter

INTRODUCTION

Cavotricuspid isthmus (CTI) topography includes ridges, pouches, recesses, and trabeculations. These features may limit the success of radiofrequency ablation (RFA) of typical atrial flutter (AFL). The aim of this study was to assess the utility of phased-array intracardiac echocardiography (ICE) for imaging the CTI and monitoring RFA of AFL.

METHODS AND RESULTS

Fifteen patients (mean age 64 +/- 9 years) underwent ICE assessment (imaging frequency 7.5-10 MHz) before and after RFA of AFL. The ICE catheter was positioned at the inferior vena cava-right atrial junction and the following parameters were measured: (1) CTI length from the tricuspid valve to the eustachian ridge; (2) extent of CTI pouching; and (3) thickness pre/post RFA of the anterior, mid, and posterior CTI. CTI length was 35 +/- 6 mm at end-ventricular systole but shorter (30 +/- 6 mm) and more pouched at end-ventricular diastole (P = 0.02). A pouch or recess was seen in 11 of 15 patients (mean depth 6 +/- 2 mm). The septal CTI was more pouched than the lateral CTI, but the latter had more prominent trabeculations. Trabeculations were seen in 10 of 15 patients, and at these locations the CTI was 4.6 +/- 1 mm thick. Anterior, mid, and posterior CTI thickness pre-RFA was 4.1 +/- 0.8, 3.3 +/- 0.5, and 2.7 +/- 0.9 mm, respectively (P < 0.001 by analysis of variance). ICE guided RFA away from unfavorable CTI features (recesses/thick trabeculations). RFA applications created discrete CTI lesions that coalesced, forming diffuse CTI swelling. Post-RFA thickness was as follows: anterior 4.8 +/- 0.8 mm (P = NS vs pre); mid 3.8 +/- 0.8 mm (P = 0.05 vs pre); and posterior 3.8 +/- 0.8 mm (P = 0.02 vs pre).

CONCLUSION

Phased-array ICE permits novel real-time CTI imaging with excellent endocardial resolution and may facilitate RFA of AFL.

IVUS guidance of thoracic and complex abdominal aortic aneurysm stent-graft repairs using an intracardiac echocardiography probe: preliminary report

PURPOSE

To report our learning experience using an intracardiac echocardiography (ICE) probe to guide endovascular aortic procedures.

METHODS

Between November 1999 and July 2001, 17 patients (12 men; mean age 73.1+/-2.3 years) underwent endovascular repair of 9 thoracic, 6 complex abdominal, and 2 thoracoabdominal aortic aneurysms. The most suitable dimensions and configuration of the stent-graft were based on preoperative computed tomographic (CTA) or magnetic resonance (MRA) angiography. Intraoperative intravascular ultrasound (IVUS) imaging was obtained using a 9-F, 9-MHz ICE probe, 110 cm in length, inserted through a 10-F, 55 degrees precurved long polyethylene sheath.

RESULTS

The endografts were deployed as planned by CTA or MRA. Before stent-graft deployment, interrogation with the ICE probe visualized the aortic arch and descending thoracoabdominal aorta without position-related artefacts and identified the sites of stent-graft fixation. After stent-graft deployment, visualization with the ICE probe detected the need for additional procedures in 8 patients, including 2 incompletely expanded thoracic grafts, which were treated with adjunctive balloon angioplasty. In 1 patient, ICE probe interrogation determined that the lesion was inappropriate for endovascular exclusion.

CONCLUSIONS

ICE probe interrogation provides accurate information on the anatomy of thoracic and abdominal aortic aneurysms and allows rapid identification of attachment sites and stent-graft characteristics. It might be considered as a valid imaging modality for monitoring all phases of endovascular procedures.

High density endocardial mapping of shifts in the site of earliest depolarization during sinus rhythm and sinus tachycardia

Previous mapping studies of sinus rhythm suggest faster rates arise from more cranial sites within the lateral right atrium. In the intact, beating heart, mapping has been limited to epicardial plaques or single endocardial catheters. The present study was designed to examine shifts in the site of the earliest endocardial depolarization during sinus rhythm and sinus tachycardia using high density activation mapping. Noncontact mapping of the right atrium during sinus rhythm was performed on ten anesthetized swine. Recordings were made during sinus rhythm, phenylephrine infusion, and isoproterenol infusion. The hearts were then excised and the histological sinus node identified. The mean minimum and maximum cycle lengths recorded were 355 +/- 43 and 717 +/- 108 ms. A median of three (range two to five) sites of earliest endocardial depolarization were documented in each animal. With increasing heart rate the site of earliest endocardial depolarization remained stationary until a sudden shift in a cranial or caudal direction, often to sites beyond the histological sinoatrial node. The endocardial shift was unpredictable with considerable variation between animals; however, faster rates arose from more cranial sites (r = 0.46, P = 0.023). There was no difference in the mean cycle length of sinus rhythm originating from specific positions on the terminal crest (r = 0.44, P = 0.17). Cranial sites displayed a more diffuse pattern of early depolarization than caudal sites. In the porcine heart the relationship between heart rate and site of earliest endocardial depolarization shows considerable variation between individual animals. These findings may have implications for clinical mapping and ablation procedures.

IVUS guidance of thoracic and complex abdominal aortic aneurysm stent-graft repairs using an intracardiac echocardiography probe: preliminary report

PURPOSE

To report our learning experience using an intracardiac echocardiography (ICE) probe to guide endovascular aortic procedures.

METHODS

Between November 1999 and July 2001, 17 patients (12 men; mean age 73.1+/-2.3 years) underwent endovascular repair of 9 thoracic, 6 complex abdominal, and 2 thoracoabdominal aortic aneurysms. The most suitable dimensions and configuration of the stent-graft were based on preoperative computed tomographic (CTA) or magnetic resonance (MRA) angiography. Intraoperative intravascular ultrasound (IVUS) imaging was obtained using a 9-F, 9-MHz ICE probe, 110 cm in length, inserted through a 10-F, 55 degrees precurved long polyethylene sheath.

RESULTS

The endografts were deployed as planned by CTA or MRA. Before stent-graft deployment, interrogation with the ICE probe visualized the aortic arch and descending thoracoabdominal aorta without position-related artefacts and identified the sites of stent-graft fixation. After stent-graft deployment, visualization with the ICE probe detected the need for additional procedures in 8 patients, including 2 incompletely expanded thoracic grafts, which were treated with adjunctive balloon angioplasty. In 1 patient, ICE probe interrogation determined that the lesion was inappropriate for endovascular exclusion.

CONCLUSIONS

ICE probe interrogation provides accurate information on the anatomy of thoracic and abdominal aortic aneurysms and allows rapid identification of attachment sites and stent-graft characteristics. It might be considered as a valid imaging modality for monitoring all phases of endovascular procedures.

Shifting of Puncture Site in the Fossa Ovalis During Radiofrequency Catheter Ablation: Intracardiac Echocardiography-guided Transseptal Left Heart Catheterization

Intracardiac echocardiography (ICE) serves as an adjunct to fluoroscopy for electrophysiological procedures by identifying critical anatomic landmarks and confirming catheter-endocardial contact. In the present study, we investigated the usefulness of ICE for radiofrequency catheter ablation. ICE was utilized to guide transseptal puncture in 19 patients undergoing radiofrequency catheter ablation. The fossa ovalis, which was one critical anatomic landmark, had an average vertical diameter of 18.5 +/- 6.9 mm and an average horizontal diameter of 10.0 +/- 2.4 mm, as measured by ICE and fluoroscopy. Although there was only a small shift of the puncture site in the horizontal direction, the puncture site shifted towards the upper edge of the fossa ovalis for 17 patients (89%). Furthermore, we could verify that the distance between the apex of the tent-shape formed by the pressure of the puncture needle in the fossa ovalis and the left atrial wall opposing it was sufficient to carry out the procedure safely. Confirming the puncture site using ICE is useful in carrying out transseptal left heart catheterization safely.

Intracardiac phased-array imaging: methods and initial clinical experience with high resolution, under blood visualization: initial experience with intracardiac phased-array ultrasound

OBJECTIVES

This study was designed to test the feasibility of high-resolution phased-array intracardiac imaging.

BACKGROUND

Intracardiac echocardiographic imaging of the heart during interventional electrophysiologic (EP) procedures has been limited by inadequate ultrasound penetration and absence of Doppler hemodynamic and flow information produced by rotating mechanical ultrasound elements.

METHODS

A 10F (3.2 mm) phased-array, variable 5.5 to 10 MHz frequency imaging catheter with a four-way deflectable tip was applied in 24 patients undergoing EP studies. Sixteen prespecified cardiac targets were imaged from a right heart venue.

RESULTS

Fifteen patients had no underlying organic heart disease; nine had ischemic, cardiomyopathic, valvular or congenital heart disorders. Longitudinal and short-axis imaging readily disclosed each cardiac valve, support structures and chamber, as well as the pericardium, right and left atrial appendages, the junction of the right atrium and superior vena cava, crista terminalis, tricuspid valve isthmus, coronary sinus orifice, membranous fossa ovalis and pulmonary veins. The average target depth was 8.8+/-1.5 cm (range 0.5 to 15 cm), with adequate penetration at a 7.5 MHz imaging frequency. Color flow and Doppler utilities clearly characterized transaortic and pulmonic valve and pulmonary vein blood flow, including during low output states.

CONCLUSIONS

These first human studies with this technology demonstrate the methods, feasibility and utility of intracardiac phased-array vector and Doppler imaging for long-axis, apex-to-base global cardiac imaging. High resolution of endocardial structures and catheters suggests additional utility for visualizing interventional procedures from the right heart.

Transseptal left heart catheterisation guided by intracardiac echocardiography

OBJECTIVE

To develop a novel approach of transseptal puncture guided by intracardiac echocardiography and to assess its efficacy.

METHODS

Transcatheter intracardiac echocardiography with a 9 MHz rotating transducer was performed to guide transseptal puncture in 12 patients (mean age 43.1 years, range 31-68) who underwent radiofrequency catheter ablation of left sided accessory pathways. Initially, the echocardiography and transseptal catheters were placed adjacent to each other in the superior vena cava and were withdrawn to the level of the fossa ovalis.

RESULTS

The successful puncture site was associated with visualisation of the fossa ovalis (12 patients, 100%) and the aorta (12 patients, 100%), tenting of the fossa (six patients, 50%), penetration of the needle visualised by the ultrasound catheter (12 patients, 100 %), and echocardiographic contrast material applied in the left atrium (12 patients, 100%). The characteristic jump of the needle onto the fossa ovalis was observed simultaneously with fluoroscopy and intracardiac ultrasound (12 patients, 100%). All procedures were successful. There were no complications associated with the transseptal procedure.

CONCLUSIONS

Intracardiac echocardiography is feasible to guide transseptal puncture. The optimal puncture site can be assessed by simultaneous detection of the characteristic downward jump of the transseptal needle onto the fossa ovalis by intracardiac ultrasound and fluoroscopy.

Advances in cardiac electrophysiology and pacing

Significant advances have been made in the management of cardiac arrhythmias. New technology has enhanced the ability to understand and treat a variety of tachycardias. Excitement and caution surround ablative approaches for atrial fibrillation. The role of ICDs and class III antiarrhythmic drugs in the management of patients at risk for sudden cardiac death has been clarified. A new indication for cardiac pacing is evolving as a supplemental treatment for patients with refractory congestive heart failure. These and other advances provide numerous exciting options for management of cardiac patients.

Intracardiac echocardiography: newest technology

Intracardiac echocardiography, defined as ultra-sonographic navigation and visualization within large blood-filled cavities or vessels of the cardio-vascular system, has recently undergone refinement as a clinical tool through technologic advances in transducer miniaturization. Intra-cardiac ultra-sound catheters image at lower frequencies than current conventional intravascular ultrasound catheters used for intracoronary imaging. The lower imaging frequency enables greater tissue penetration, permitting whole-heart evaluation from a right-sided catheter position. Newer devices are steerable, have variable imaging frequency (5.5 to 10 MHz), and full Doppler capability (pulsed, continuous wave, and tissue Doppler). These advances have made intracardiac high-resolution imaging as well as hemodynamic assessment possible. A historical perspective, current capabilities and limitations, and potential clinical and research applications of this new imaging technique are discussed.

The utility of intracardiac echocardiography in interventional electrophysiology

With the mounting of an ultrasound transducer on the end of a percutaneously placed catheter, intracardiac echocardiography is now possible. It has become clear that endocardial anatomy plays a critical role in a variety of cardiac arrhythmias. The ability to visualize this anatomy, and it's relationship to mapping and ablation catheters, may greatly enhance the safety and efficacy of catheter ablation procedures.

Accuracy of fluoroscopic localization of the Crista terminalis documented by intracardiac echocardiography

The crista terminalis is an important anatomic target for ablation of atrial arrhythmias. We determined the accuracy of catheter placement guided by fluoroscopy alone when directed to 24 sites along the crista terminalis in 6 patients. The sites selected included the most medial superior, most lateral superior, mid lateral, and most inferolateral sites along the crista terminalis in each patient. These sites were selected because of their recognized importance in sinus node and/or atrial tachycardia ablation and the importance of avoiding caval structures when targeting the most superior and/or inferior right atrium. The position of the catheter tip was documented using a catheter based ultrasound transducer in the right atrium or vena cava. The operator was blinded to the intracardiac echocardiographic (ICE) results until reviewing the images after the procedure in each patient. The catheter tip, guided by fluoroscopy alone, was identified by ICE to be within the right atrium and within 1cm of the crista terminalis at only 10 of the 24 sites (42%). Importantly, when targeting the most superior and inferior sites along the crista terminalis, the catheter tip, guided by fluoroscopy, was noted to be adjacent to the venous junction with the right atrium but actually located in the superior or inferior vena cava at 5 of the 18 such sites. The catheter was positioned appropriately (within 1 cm of the crista and within the right atrium) guided by fluoroscopy alone when targeting 1 of the 12 sites in the first 3 patients versus 9 of 12 sites in the last 3 patients, p<0.05. In conclusion, it appears that using fluoroscopic guidance alone: 1) localization of the crista terminalis is frequently inaccurate and 2) catheter positioning in the superior/inferior vena cava is commonly noted when targeting very superior and inferior sites along the crista terminalis. A learning curve, assisted by review of ICE recordings after each procedure, appears to improve the accuracy of catheter placement by fluoroscopy alone but still does not result in uniform success. ICE appears to facilitate and ensure accurate targeting of specific anatomic sites along the crista terminalis and thus may serve as an important adjunctive imaging technique in electrophysiology.

Catheter ablation in the year 2000

After its introduction in 1987, radiofrequency catheter ablation became established as a safe and effective therapy for the cure of many cardiac arrhythmias in people. The possibility of assessing the relationship between the anatomical target and the electrophysiologic changes produced by radiofrequency pulse delivery has also provided significant improvement in the physician's knowledge of the pathophysiology of the underlying rhythm disturbance. Nowadays, using this therapy, success rates well above 90% with recurrence rates lower than 5% are expected after treatment of most regular supraventricular arrhythmias. As catheter ablation techniques develop, success rates in the range of those obtained for regular supraventricular arrhythmias are expected in the future in the treatment of regular ventricular and irregular supraventricular arrhythmias.

Low-power radiofrequency application and intracardiac echocardiography for creation of continuous left atrial linear lesions

INTRODUCTION

Continuity of radiofrequency (RF) lesions for a catheter-based cure of atrial fibrillation is essential in order to avoid reentrant tachycardias. In the present study, we assessed the value of intracardiac echocardiography and preablation electrode-tissue interface parameters for creation of left atrial linear lesions.

METHODS AND RESULTS

In six healthy dogs, two left atrial linear lesions (lesion 1, along the inferior posterior left atrium; lesion 2, from the appendage to the left atrial roof) were attempted via a transseptal approach using a deflectable catheter with six 7-mm coil electrodes. In a randomized fashion, one lesion was performed under echocardiographic guidance and one with blinded echocardiographic monitoring. The following preablation parameters were assessed for every coil electrode: (1) mean atrial electrogram amplitude of six consecutive sinus beats; (2) diastolic pacing threshold; and (3) temperature response to application of 5 W for 10 seconds. After ablation (target temperature 70 degrees C, maximum power 50 W, duration 60 sec), the excised left atrium was examined macroscopically and histologically for lesion length, continuity, and presence or absence of lesions associated with each coil. Out of 12 attempted RF lesions, 7 were continuous (length, 47+/-5 mm, lesion 2, n = 6) and 5 were discontinuous (lesion 1, n = 5). Fifty-two of 70 coil electrodes (74%) had pathologic evidence of lesion creation. Intracardiac echocardiography was superior to fluoroscopy with respect to the actual number of coil electrodes creating lesions, and lesion continuity was correctly predicted in 9 of 12 lesions. Intracardiac echocardiography was 85% sensitive and 54% specific in predicting lesions created by individual coils. The correlation between the mean 60-second ablation temperature and the preablation parameters was 0.45 for the electrogram amplitude, -0.67 for the pacing threshold, and 0.81 for the temperature response to low-power application. Sensitivity and specificity for prediction of lesions created by individual coils, respectively, were 84% and 48% for the electrogram amplitude, 90% and 68% for the pacing threshold, and 96% and 76% for the low-power RF application.

CONCLUSION

Long linear lesions can be safely and effectively performed in the canine left atrium, using a tip-deflectable multielectrode catheter. Intracardiac echocardiography may be helpful for positioning the ablation catheter in some parts of the left atrium, and preablation parameters, especially a nontraumatic low-power RF application, are able to predict ultimate lesion creation with high accuracy.

Intracardiac echocardiography to guide transseptal left heart catheterization for radiofrequency catheter ablation

INTRODUCTION

The purpose of this study was to assess the feasibility and safety of intracardiac echocardiography to guide transseptal puncture for radiofrequency catheter ablation.

METHODS AND RESULTS

Transcatheter intracardiac echocardiography (9 MHz) was utilized to guide transseptal puncture in 53 patients undergoing radiofrequency catheter ablation. The anatomy and relationship of intra- and extracardiac structures were visualized with the ultrasound transducer positioned at the fossa ovalis. The tip of the transseptal dilator and tenting of the fossa ovalis and the left atrial wall were simultaneously visualized in a single ultrasound image in all patients. With maximum tenting of the fossa ovalis, the mean distance from the fossa to the left atrial wall was 11.9 +/- 5.8 mm (range: 1.8 to 25.6 mm). In four patients (8%), the tented fossa ovalis abutted the left atrial wall and the transseptal dilator was redirected with ultrasound guidance. Puncture of the interatrial septum was achieved through the fossa ovalis in each patient and required a single attempt in 51 patients (96%). The mean number of punctures per patient was 1.1 +/- 0.4. The mean time to perform transseptal catheterization was 18.2 +/- 6.8 minutes. There were no complications.

CONCLUSION

Intracardiac echocardiography delineated the anatomy of intra- and extracardiac structures not identified with fluoroscopy and simplified correct positioning of the transseptal dilator, puncture of the fossa ovalis, and cannulation of the left atrium in a timely and uncomplicated fashion.

Ablation of right and left ectopic atrial tachycardias using a three-dimensional nonfluoroscopic mapping system

We report our experience with mapping and ablation of right and left atrial tachycardia using a 3-dimensional nonfluoroscopic mapping system. Twenty-nine ectopic atrial tachycardias were successfully ablated. This novel mapping system has the potential to increase a successful cure of this arrhythmia by catheter ablation.

Supraventricular tachyarrhythmias involving the sinus node: clinical and electrophysiologic characteristics

Supraventricular tachyarrhythmias occur quite commonly and are now evaluated more often because of technological advances in the field of electrophysiology. Arrhythmias that involve the sinus node, namely, the syndrome of inappropriate sinus tachycardia and sinus node reentry, are rare. Because of their origin in the sinus node, the surface electrocardiogram (ECG) in these patients can present a diagnostic challenge to the clinician and in fact may elude recognition as an abnormal heart rhythm. Presented in this review are the clinical characteristics of these arrhythmias, as well as the mechanisms of action. Pharmacotherapy may be therapeutic in certain patients in preventing recurrences; however, radiofrequency catheter ablation offers a lifelong curative effect for these patients.

"Cristal tachycardias": origin of right atrial tachycardias from the crista terminalis identified by intracardiac echocardiography

OBJECTIVES

We sought to use intracardiac echocardiography (ICE) to identify the anatomic origin of focal right atrial tachycardias and to define their relation with the crista terminalis (CT).

BACKGROUND

Previous studies using ICE during mapping of atrial flutter and inappropriate sinus tachycardia have demonstrated an important relation between endocardial anatomy and electrophysiologic events. Recent studies have suggested that right atrial tachycardias may also have a characteristic anatomic distribution.

METHODS

Twenty-three consecutive patients with 27 right atrial tachycardias were included in the study. ICE was used to facilitate activation mapping in relation to endocardial structures. A 20-pole catheter was positioned along the CT under ICE guidance. ICE was also used to assist in guiding detailed mapping with the ablation catheter in the right atrium.

RESULTS

Of 27 focal right atrial tachycardias, 18 (67%, 95% confidence interval [CI] 46% to 83%) were on the CT (2 high medial, 8 high lateral, 6 mid and 2 low). ICE identified the location of the tip of the ablation catheter in immediate relation to the CT in all 18 cases. The 20-pole mapping catheter together with echocardiographic visualization of the CT provided a guide to the site of tachycardia origin along this structure. Radiofrequency ablation was successful in 26 (96%) of 27 (95% CI 81% to 100%) right atrial tachycardias.

CONCLUSIONS

This study demonstrates that approximately two thirds of focal right atrial tachycardias occurring in the absence of structural heart disease will arise along the CT. Recognition of this common distribution may potentially facilitate mapping and ablation of these tachycardias.

Catheter ablation for atrial flutter and fibrillation. An effective alternative to medical therapy

Atrial flutter and atrial fibrillation are common arrhythmias that can be difficult to manage clinically. In many patients, these conditions are refractory to pharmacologic therapy because of drug failure or intolerance. Radiofrequency catheter ablation may be a reasonable alternative in patients with typical atrial flutter. The procedure has a high initial success rate and a low complication rate. However, recurrence after ablation is common, and a second treatment session may be needed. In selected patients with atrial fibrillation, radiofrequency ablation can be useful for rate control. However, its use in curing chronic fibrillation is still experimental. The procedure involves insertion of a pacemaker, anticoagulation therapy is still needed in most patients, and the need for antiarrhythmic medication may not be obviated.