Coronary Sinus Ostium Research Articles

Anatomical Reconstructions of the Human Cardiac Venous System using Contrast-computed Tomography of Perfusion-fixed Specimens

A detailed understanding of the complexity and relative variability within the human cardiac venous system is crucial for the development of cardiac devices that require access to these vessels. For example, cardiac venous anatomy is known to be one of the key limitations for the proper delivery of cardiac resynchronization therapy (CRT)(1) Therefore, the development of a database of anatomical parameters for human cardiac venous systems can aid in the design of CRT delivery devices to overcome such a limitation. In this research project, the anatomical parameters were obtained from 3D reconstructions of the venous system using contrast-computed tomography (CT) imaging and modeling software (Materialise, Leuven, Belgium). The following parameters were assessed for each vein: arc length, tortuousity, branching angle, distance to the coronary sinus ostium, and vessel diameter. CRT is a potential treatment for patients with electromechanical dyssynchrony. Approximately 10-20% of heart failure patients may benefit from CRT(2). Electromechanical dyssynchrony implies that parts of the myocardium activate and contract earlier or later than the normal conduction pathway of the heart. In CRT, dyssynchronous areas of the myocardium are treated with electrical stimulation. CRT pacing typically involves pacing leads that stimulate the right atrium (RA), right ventricle (RV), and left ventricle (LV) to produce more resynchronized rhythms. The LV lead is typically implanted within a cardiac vein, with the aim to overlay it within the site of latest myocardial activation. We believe that the models obtained and the analyses thereof will promote the anatomical education for patients, students, clinicians, and medical device designers. The methodologies employed here can also be utilized to study other anatomical features of our human heart specimens, such as the coronary arteries. To further encourage the educational value of this research, we have shared the venous models on our free access website: www.vhlab.umn.edu/atlas.

Supraventricular tachycardia and atrial flutter associated with a coronary sinus diverticulum: A case report

The case of a patient with narrow QRS-complex supraventricular tachycardia and atrial flutter is described. The 12-lead surface electrocardiogram (ECG) revealed sinus rhythm with ventricular pre-excitation and negative δ waves in leads II, III and aVF, indicating Wolff-Parkinson-White syndrome with a posteroseptal accessory pathway (AP). Coronary sinus angiography revealed the presence of a diverticulum near the coronary sinus ostium. The AP was successfully ablated using radiofrequency energy applied in the neck of the diverticulum, following several failed attempts at catheter ablation from the endocardial surface of the posteroseptal space.

Anatomical and electrophysiological variations of Koch’s triangle and the impact on the slow pathway ablation in patients with atrioventricular nodal reentrant tachycardia: a study using 3D mapping

This study aimed to reveal individual variations in Koch's triangle using NavX and to evaluate the efficacy of the NavX-guided slow pathway ablation. A regional geometry around Koch's triangle was constructed in 42 consecutive patients with atrioventricular nodal reentrant tachycardia (AVNRT), and a bipolar electrogram map was created with 72 ± 30 sampling points during sinus rhythm to identify sites with Haissaguerre's slow potentials (SPs) and His bundle electrograms (HBEs) to examine the anatomical and electrical variations. Radiofrequency ablation was performed at the most prominent SP recording site. The acute results and long-term outcome were examined in comparison to another 42 consecutive patients who underwent a conventional fluoroscopy-guided slow pathway ablation in the previous months. The size of Koch's triangle and the coronary sinus ostium varied over a wide range of 132 to 490 and 69 to 346mm(2), respectively. HBEs were recorded linearly along the antero-septal right atrium (n = 29) or deviated downward toward the midseptum (n = 13, 31%). The SPs were always distributed below the lowest HBE recording site. The NavX-guided ablation eliminated AVNRT with a median of 1 radiofrequency pulse, 9.1 ± 4.6min of fluoroscopy, and 49 ± 14min of procedure time, all of which were significantly smaller than those in fluoroscopy-guided ablation. No procedure-related complications or long-term recurrence was noted in either group. Koch's triangle varies in terms of the size and electrogram distribution, and the NavX-guided slow pathway ablation overcomes the diversity and seems more effective than fluoroscopy-guided ablation.

Nodoventricular pathways

We appreciate the interest and insightful comments by Dr Katritsis in this unusual case,1 and we offer a few remarks. Indeed, nodoventricular (or fascicular) pathways are rare but perhaps are also underrecognized. Two additional cases of nodofascicular pathways have been reported recently by our group.2,3 While the insertion site of the pathway into the atrioventricular node is inferred by the tachycardia response to pacing maneuvers, the earliest site of atrial activation during atypical atrioventricular nodal reentrant tachycardia (AVNRT) is dependent not so much on the insertion site but rather on the location of the retrograde atrionodal slow pathway near the coronary sinus ostium.

A case of atrial tachycardia which presents saw-tooth P-wave morphology suggestive of typical atrial flutter, and whose mechanism was considered to be a microreentry around the coronary sinus ostium

A case of atrial tachycardia which presents saw-tooth P-wave morphology suggestive of typical atrial flutter, and whose mechanism was considered to be a microreentry around the coronary sinus ostium

Incidental Visualization of the Septal Vein of the Left Atrium

A 58-year-old man with paroxysmal supraventricular tachycardia was admitted to our hospital for catheter ablation. Cannulation of the patient's coronary sinus using a long sheath multipolar catheter was difficult and the catheter was positioned in the interatrial septum. The tip of the catheter was directed to the left atrium (Fig. 1A). Angiography using the long sheath catheter showed a vein (Fig. 1B, arrows) draining to the left atrial appendage (Fig. 1B, arrowheads). The septal vein of the left atrium could be visualized in the right anterior oblique (Fig. 1C) and left anterior oblique views (Fig. 1D) after placement of a multipolar catheter in the coronary sinus. Atrioventricular nodal reentrant tachycardia was induced by programmed electrical stimulation and slow pathway modification was performed successfully. Fig. 1 Difficult cannulation of the coronary sinus may be due to Thebesian valve, valve of Vieussens or congenital anomaly such as atresia of the coronary sinus ostium.1) Little attention has been paid to the atrial veins, except vein of Marshall as an arrhythmogenic focus.2) There are 3 groups of veins draining the left atrium: septal veins, lateral veins and proper veins of the left atrium.3) The veins from the left atrial appendage are drained usually via the lateral atrial vein into the coronary sinus. In this case, the vein from the left atrial appendage was connected to the septal vein. In conclusion, we report incidental angiographic visualization of an interatrial septal vein during a cardiac electrophysiology study.

Intraisthmus Reentry

A 70-year-old man presented with repeat atrial flutter 2 years after apparently successful cavotricuspid isthmus (CTI) ablation for typical atrial flutter. An electrophysiology study was then performed, and CARTO electroanatomic 3-dimensional mapping of the tachycardia was consistent with typical flutter. However, entrainment mapping from the lateral and mid CTI revealed postpacing intervals greater than 30 milliseconds more than the tachycardia cycle length. Entrainment mapping from the septal CTI and coronary sinus ostium was in the circuit. A diagnosis of intraisthmus reentry was made and successful ablation was achieved with termination, with radiofrequency ablation directly outside the coronary sinus ostium.

Abstract 18477: Outcome of Anatomical Approach of Radiofrequency Catheter Ablation for Atrioventricular Nodal Reentrant Tachycardia: 15 years experience

BACKGROUND: Even though the anatomical approach as the radiofrequency (RF) ablation for atrioventricular nodal reentrant tachycardia (AVNRT) has been introduced long ago, large population based outcome of this approach remains unclear. Moreover, electrophysiologic characteristics between different successful target sites have not been identified as well. The purpose of this study was to investigate outcome and electrophysiologic characteristics according to successful target site. METHODS: A total of 1391consecutive patients (mean age 45±16 years, female 63%) who underwent RF catheter ablation based on anatomical approach for AVNRT between 1996 and 2010 were enrolled in this study. The tricuspid annulus between the coronary sinus ostium and the His bundle recording site was divided into posterior (P), medial (M), and anterior (A) regions. Serial RF energy applications were delivered from P site to superior side until junctional rhythm was inducible. RESULTS: Dual AV nodal physiology was documented in 91.9 %, typical AVNRT was 92.4 %. The mean procedure time, fluoroscopic time, and the ablation time was 63±28 min, 12±7 min, and 226±176 sec, respectively. Successful target site was P in 46.7% (n=684), M in 47.9% (n=701), and A in 0.7% (n=5). Long-term recurrence rate was 1.8% (n=25). AV nodal block requiring pacemaker occurred in 0.2 % (n=3). When divided into two groups, A (successful ablation at P site) and B (successful ablation at M and A sites), there was no difference between two groups in age, gender, tachycardia cycle length, atrial effective refractory period (ERP), AV block cycle length (BCL), ERP of fast and slow pathway, ventricular ERP, temperature, RF power, and long-term recurrence (all p values > 0.05). However, group A had more atypical form (9.4% vs. 6.0%, p=0.019), longer shortest VA interval (30.0±1.35 vs. 24.5±1.13 msec, p=0.002), longer VA BCL (376±102 vs. 361±88 msec, p=0.007), and shorter RF time (180±121 vs. 317±226 sec, p<0.001) than group B. CONCLUSION: Anatomical approach of RF ablation for AVNRT showed excellent long-term outcome. The electrophysiologic characteristics were different according to successful ablation site.

Variance in Coronary Venous Anatomy: A Critical Determinant in Optimal Candidate Selection for Cardiac Resynchronization Therapy

Knowledge of coronary sinus (CS) anatomy and its variations is one of the important factors determining the final position of left ventricle pacing lead during cardiac resynchronization therapy. Coronary venous system anatomy, including number, diameter, and opening angles of tributaries, was studied in 50 normal formalin-fixed adult cadaveric hearts. Thebesian valve (TV) and Vieussens valve were present in 64% and 60% cases, respectively. CS ostium coverage of ≥75% by TV was seen in 25% (8/32) cases. Number of prominent tributaries lying between anterior interventricular vein and middle cardiac vein varied from 1-4. In 28% of hearts, only one prominent tributary was present. Midlateral vein (average diameter 1.75 ± 0.66 mm) with an average distance of 43.5 ± 12.2 mm from coronary ostium was present in 58% (29/50) hearts, of which it formed an acute angle with CS axis in four (13.39%) cases. Posterolateral vein (average diameter 1.62 ± 0.45 mm) with an average distance of 33.4 ± 11.7 mm from coronary ostium was found in 72% (36/50) cases and formed an acute angle with CS in three (8.33%) cases. Restrictive TV covering ≥75% CS ostium (25% cases), presence of single prominent tributary (28% cases), and formation of acute angle of tributary with CS axis (1/4 cases with anterolateral vein, 4/29 cases with midlateral vein, 3/36 cases with posterolateral vein, and 3/28 cases with posterior veins of the left ventricle) can impede successful cannulation of CS.

Impact of respiration on electroanatomical mapping of the right atrium: implication for cavotricuspid isthmus ablation

Cavotricuspid isthmus (CTI) ablation for typical atrial flutter (AFL) has become the preferred treatment for this arrhythmia. The aims of this study were to assess the impact of respiratory gating (RG) on electroanatomical mapping of CTI and to assess the efficiency of CTI ablation guided by the Carto3® system equipped with the new respiration gating software. Forty-four consecutive patients (mean age, 60 ± 13 years; 25 male) undergoing cavotricuspid ablation for symptomatic common AFL were randomly assigned to CARTO™ mapping with or without enabling RG module (Group A, RG OFF, Group B, RG ON). A significant reduction in mean RA volume, CTI central length and CS ostium maximum diameter has been observed in the RG maps. The mean total procedural, fluoroscopy and radiofrequency (RF) time were 102.9 ± 35.3, 10.6 ± 3.3, 22.9 ± 14.2 min in group A and 75.3 ± 21.7, 3.6 ± 4.5, 10.4 ± 5.7 min in group B, respectively (p < 0.05). Electroanatomical mapping systems' accuracy may be strongly influenced by respiration movements. The current study showed that automatic respiratory gated acquisition resulted in a better visualization of CTI, and this determines a relevant reduction in fluoroscopy and RF times.

Endless loop tachycardia below the upper tracking rate of a pacemaker: A case report

An 82-year-old female with a history of hypertrophic cardiomyopathy (HCM), sick sinus syndrome (SSS), and an implanted DDD pacemaker was admitted to our hospital for congestive heart failure caused by rapid atrial fibrillation. After administration of amiodarone, atrial fibrillation (AF) became atrial flutter (AFL). Electrophysiological investigation revealed counterclockwise AFL. Catheter ablation of the cavotricuspid isthmus was performed. Burst pacing from the coronary sinus ostium to confirm the block line of the isthmus induced rapid, regular, ventricular pacing at a rate of 110bpm. The differential diagnosis of this tachycardia included ectopic atrial tachycardia and pacemaker-mediated, endless loop tachycardia (ELT). We diagnosed this arrhythmia as ELT, because temporary reprogramming of the pacemaker mode from DDD to VVI terminated the tachycardia. In this patient, pacing parameters favored ELT (long atrioventricular delay [AVD] and short postventricular atrial refractory period [PVARP]), and atrioventricular and ventriculoatrial conduction time was prolonged as a result of amiodarone administration.The ELT continued because the rate was lower than the programmed upper tracking rate. Reprogramming the parameter (decreasing AVD and increasing PVARP) resulted in termination of ELT.

Anatomy of the Coronary Sinus and Epicardial Coronary Venous System in 620 Hearts: An Electrophysiology Perspective

Cannulation of the coronary sinus (CS) is a prerequisite for left ventricular (LV) pacing and certain ablation procedures. The detailed regional anatomy for the coronary veins and potential anatomic causes for difficulty with these procedures has not been established. Therefore, we performed macroscopic measurements in 620 autopsied hearts (mean age 60 ± 23 years, 44% female). The CS was preserved for analysis in 96%. Sixty-three percent had a Thebesian valve that covered the posterior aspect of the CS ostium with extension to the superior (50%) and inferior aspects (18%) and was obstructive with fenestrations in 3 specimens. Partial or near occlusive valves were present occasionally at the ostium of the great cardiac vein (Vieussens; 8%) and middle cardiac vein (5%). Ninety-three percent had left atrial branches, and 41% had at least one branch with lumen > 3 French. For CRT lead placement, the mid-lateral LV was accessible from the middle cardiac vein (20%), the left posterior vein (92%) or the anterior interventricular vein (86%). Among specimens where the left phrenic nerve was preserved it crossed the LV mid-lateral wall in 45%. Epicardial coronary vein anatomy is variable, and the mid-lateral LV wall can potentially be accessed through various tributaries of the epicardial veins. The orientation of the Thebesian valve favors cannulation of the CS from an anterior (ventricular) and inferior approach. Anterobasal, mid-lateral, and inferior apical LV coronary veins lie in proximity to the course of the phrenic nerve.

Imaging findings of coronary sinus with left atrium muscle connections on dual-source CT coronary angiography

Objective To investigate the morphologic features of coronary sinus (CS)-left atrium muscle connections,and evaluate the function and anatomical features of coronary sinus on dual-source CT coronary angiography (DSCTCA).Methods Images of DSCTCA of 144 patients [ control group consisted of 96 patients,and atrial fibrillation (AF) group consisted of 48 patients] were reviewed.The existence of coronary sinus-right atrium muscle connections was indirectly evaluated by measuring the cross-sectional area changes of the CS during atrial systole and atrial diastolic.The number,location,length of the CS-left atrium muscle connections and the relationship between CS-left atrium muscle connections and CS morphological characteristics were studied.The t test for continuous variables and Chi-square test for categorical variables were used in statistical analysis.Results ( 1 )The anatomic course of the CS in relation to the mitral ring was straight,mild curvature and high riding of 62,16 and 18 cases in control group and 10,8 and 30 cases in AF group,respectively.There was not statistical significance between the 2 group (x2 =0.093,P=0.954). (2)The CS length was (34.1 ±9.1),(33.8 ±8.9)mm in Control group and AF group,respectively.There was no statistical significance between the 2 group ( t =- 0.486,P =0.628 ).(3) Coronary sinus-left atrium muscle connections were seen in 131 of the 144 patients (91.0％).A single connection was seen in 103 of the 144 patients,with a mean length of (22.6 ± 12.7)mm within (6.3 ± 5.8 ) mm of the coronary sinus ostium.28 patients had two connections; distal connections measured ( 13.2 ± 6.2)mm in length within (16.7 ± 6.8 ) mm of the coronary sinus ostium,and proximal connections measured ( 11.1 ± 3.6 ) mm in length within (2.1 ± 1.9) mm of the coronary sinus ostium.And there was no statistical difference the number and length of CS-left atrium connections in between Control group and AF group (P ＞ 0.05 ).(4)The CS narrowed 22.4％ (44.5/198.8 )in cross-sectional area from atrial diastolic to atrial systole in control group( t =- 21.076,P ＜ 0.01 ),while the CS had no obvious contraction in AF group(t =0.374,P ＞ 0.05).The cross-sectional area of the coronary sinus during diastole was obviously larger in the AF group than in the control group[( 230.4 ±77.0) mm2 vs (198.8 ±65.4) mm2,respectively,t =- 2.579,P =0.01 ].In control group ( n =9 ),the coronary sinus-left atrium connection was not seen,however,all showed a CS constriction during atrial systole,indicating that coronary sinus-left atrium muscle continuity is not likely the primary cause for coronary sinus contractions. Conclusions DSCTCA can clearly show the anatomical characteristics of CS,it can help to understand the length,number and location of the CS-left atrium muscle connection. Key words: Coronary sinus ; Tomography, x-ray computed ; Anatomy

Diagnosis of atrial tachycardias originating from the lower right atrium: importance of P-wave morphology in the precordial leads V3–V6

This study aimed to characterize P-wave morphology (PWM) in leads V3-V6 during focal atrial tachycardia (AT) originating from the lower right atrium (RA), and to investigate the role of interatrial conduction (IAC) pathways in the formation of PWM. Twenty-eight consecutive patients with tachycardia foci in the lower RA underwent detailed atrial endocardial activation mapping and radiofrequency catheter ablation. P-wave configuration was analysed using standard 12-lead electrocardiogram. Atrial tachycardia originated from lower non-septal tricuspid annulus (LTA) (n = 11), coronary sinus ostium (CSo) (n = 11), lower crista terminalis (LCT) (n = 4), or lower free wall (n = 2). In leads V3-V6, PWM showed a negative pattern in at least two consecutive leads during AT originating from CSo (11/11) and LTA (9/11), with an associated sensitivity of 91%, specificity of 100%, positive predictive value (PPV) of 100%, and negative predictive value (NPV) of 75%. A positive PWM was observed in three of four ATs originating from LCT, with an associated sensitivity of 75%, specificity of 100%, PPV of 60%, and NPV of 96%. A negative PWM in V3-V6 was consistent with a preferential IAC through musculature in the vicinity of the CS and an activation of both atria in an antero-posterior direction. In contrast, a positive PWM was associated with the engagement of a posterior (non-CS-related) interatrial connection. Characteristic PWMs in V3-V6 may accurately differentiate the anatomic sites of AT from the low RA with high PPVs and NPVs. P-wave morphology in V3-V6 is likely to be influenced by the engagement of the preferential IAC.

Comparison of the Location of Slow Conduction Velocity in Cavotricuspid‐Dependent Atrial Flutter in Patients With and Without Prior Atriotomy: Different Arrhythmogenic Basis and Clinical Implications for Placement of Atriotomy

Slow Zone in CTI-Dependent Flutter After Atriotomy. Earlier studies have shown that the slow conduction zone in patients with cavotriscuspid (CTI)-dependent atrial flutter without prior surgery (NS-AFL) is the CTI. However, the location of this slow zone in patients with CTI-dependent flutter and a prior atriotomy has not been formally studied. Identification of the slow zone in patients with prior atriotomy and CTI-dependent atrial flutter (PA-AFL) and comparison with NS-AFL may have important clinical implications. Seventeen consecutive patients with PA-AFL and 17 consecutive patients with NS-AFL were included. Conduction velocity (CV) was measured using 3-dimensional mapping in 3 areas around the TVA. These regions were defined as the CTI area from lateral inferior vena cava orifice to coronary sinus ostium (region I), mid- to upper-septum (S), and free wall (F). In region F, the CV was much slower in PA-AFL than in NS-AFL patients (0.43 ± 0.13 vs 0.76 ± 0.26 m/s, P < 0.01). However, region I was slower in NS-AFL than PA-AFL (0.57 ± 0.18 m/s vs 0.84 ± 0.24 m/s, P < 0.01). In all PA-AFL patients, the slow zone was in region F. But in most (11/17) NS-AFL patients the slow zone was in region I. There was no significant difference in CV in region S between the 2 groups. Unlike NS-AFL, CTI in PA-AFL displays relatively normal conduction but the slow zone is on the free wall. This arrhythmogenecity of atriotomy may perhaps be avoided if the incisional line were altered to extend to the TV. (J Cardiovasc Electrophysiol, Vol. 23, pp. 988-995, September 2012).

Active fixation mechanism complicates coronary sinus lead extraction and limits subsequent reimplantation targets

Implantation of cardiac resynchronization therapy (CRT) devices is technically challenging and can be limited by lead dislodgement. The Attain Starfix active fixation coronary sinus (CS) lead (model 4195, Medtronic, Minneapolis, MN, USA) was introduced to reduce the rate of lead dislodgement, but the active fixation mechanism presents additional difficulties should these leads require extraction. CS lead extraction procedures at our institution from 2003 to 2011 were reviewed. Procedural variables were compared between extraction of the Starfix lead and passive fixation CS leads. Attempts at reimplantation post Starfix lead extraction were examined. Four Starfix CS leads were extracted in four patients during this time period. The mean implant duration was 784 days (range, 392-1,029 days). The indication for extraction was infection in all four cases. Mean total procedure time was 141.5 min (range, 92-205 min). None of the fixation lobes could be retracted in one lead and only the most proximal lobes could be retracted in the remaining three leads. All four leads were removed in their entirety. The excimer laser sheath (Spectranetics Laser Sheath II, Spectranetics Corp., Colorado Springs, CO,USA) was required to remove the lead in all 4 cases (100 %) compared to 25 of 131 (19.1 %) of passive fixation CS lead extractions (mean implant duration, 659 ± 697 days) performed at our institution over the same time period (P < 0.001). In three cases, the laser sheath had to be advanced past the CS ostium to remove the Starfix lead. After extraction, fibrous material which had grown between the lobes of the fixation mechanism was noted in all four cases. No complications occurred. Transvenous CS lead reimplantation was attempted at a median of 7.5 days post extraction in all four patients. The original target branch was occluded in three patients and the main CS in one patient. Reimplantation was successful in another branch of the CS in three of four patients; one underwent minimally invasive epicardial lead placement. The Starfix active fixation CS lead presents additional procedural complexity and uniform use of excimer laser sheath compared to other CS leads. Reimplantation was not possible in the same venous branch in our experience.

Novel tips for engaging the coronary sinus guided by right ventricular lead

This study investigated the relationship between the ostia of the coronary sinus (CS) and the tricuspid annulus (TA) for CS cannulation using a right ventricular (RV) lead, which could map out the TA by forming a curve when placed at the apex or low septum. Seventy patients (45 males, 67 ± 12 years) who were admitted for CRT device implant were included in the evaluation of the relationship between the CS ostia and TA. An electrophysiological (EP) mapping catheter was used to probe the CS. The ostium was shown by the CS venography at the left anterior oblique (LAO) 20° and caudal 20°. Local electrograms were collected with CS catheters in the CS or RV. Transthoracic echocardiography was evaluated before each procedure. All CS ostia were located within 3.75 cm around the tip of TA. Sixty-two subjects (Group I, 89%) had CS ostia located under the TA. Eight patients (Group II) with CS ostia over the TA revealed larger left ventricular (LV) size and a smaller ratio of left atrium (LA)/LV size. LV enlargement predicted the presence of CS ostia over the TA. Typical CS electrograms were used to further confirm if the EP catheter was in the CS in all the subjects. Use of the RV lead revealed that the CS ostia had a close relationship with the TA.

Role of the coronary sinus ostium musculature in reentrant formation

Radiofrequency ablation of focal atrial tachycardias (AT) is a validated technique with high success rates. However, electrophysiological (EP) characteristics and ablation strategy of localized reentrant AT originating from the coronary sinus ostium (CSo) have not been reported in detail so far. From January 2009 to July 2010, 1,453 patients underwent clinically motivated EP studies. Four patients were diagnosed with localized reentrant AT originating from the CSo. P wave morphology and consistency of tachycardia cycle length were studied. Subsequently, if reentry was suggested as an underlying mechanism for AT, color-coded 3-dimensional (3D) entrainment mapping was performed to localize the reentrant circuit or differentiate a localized reentrant AT from macroreentant AT, and also confirm reentry as an underlying mechanism of AT by evaluating consistency of return cycles after entrainment at multiple sites in both atria. Finally, activation mapping was performed to localize the earliest activation site. The P wave morphologies and isoelectric line between the P waves suggested most likely an AT originating from the CSo with a centrifugal activation pattern, which was confirmed by activation mapping. Consistency of return cycles and continuously fragmented local electrograms at successful ablation sites suggested reentry as an underlying AT mechanism. Color-coded 3D entrainment mapping in all 4patients located the reentrant circuit in the CSo. There were also two specific features observed. One was fragmented and/or double potentials recorded in the CSo with prominent prolonged electrogram duration compared to those during sinus rhythm. The other is a significant conduction delay within the CS. The myocardium of the CSo was suggested as a part of the critical isthmus within the reentrant circuit, while the rest of atria distal to the CSo and myocardial coat of the distal CS were not involved in the tachycardia circuit, which was confirmed by entrainment mapping. Although CSo myocardium has been implicated to be a part of atrioventricular nodal reentrant tachycardia, to the best of our knowledge, this is the first report showing the localized reentrant AT confined to the CSo. Three of our patients (75%) had concomitant atrial fibrillation (AF). Further studies should be warranted to clarify the role of AT from the CS in triggering AF.

Thrombus at Ostium of Coronary Sinus Discovered during Evaluation for Cardiac Resynchronization Therapy

A 50-year-old male patient with dilated cardiomyopathy was evaluated for cardiac resynchronization therapy. A transthoracic echocardiogram revealed a mass in close proximity to the coronary sinus ostium.The mass was considered to be a thrombus and found to have disappeared at the repeat echocardiogram performed following a month of anticoagulation therapy with warfarin. In this case report, we aim to emphasize the importance of coronary sinus imaging, especially during echocardiographic evaluation for cardiac asynchrony.

Rate-Dependent and Site-Specific Conduction Block at the Posterior Right Atrium and Drug Effects Evaluated Using a Noncontact Mapping System in Patients with Typical Atrial Flutter

Conduction block in the posterior right atrium (RA) plays an important role in perpetuating atrial flutter (AFL). Although conduction blocks have functional properties, it is not clear how the block line changes with the pacing rate, pacing site, and administration of antiarrhythmic drugs. Forty patients with typical AFL were enrolled. Pacing (110, 170, 230 ppm) from the coronary sinus ostium (CSo) and low lateral RA was performed. After 1 mg/kg pilsicainide (pure sodium channel blockade) administration, the pacing protocol was repeated. Conduction block was assessed based on a color-coded isopotential map and 20 points of virtual unipolar electrograms in the posterior RA using noncontact mapping. Block line proportion was defined as the percentage of length of the block line between the superior and inferior vena cava. The pacing rate-dependent extension of the block proportion was significant during pacing from both sides (pacing from the CSo: 59 ± 17% at 110 ppm, 69 ± 16% at 230 ppm, P < 0.05; pacing from the low lateral RA: 43 ± 19% at 110 ppm, 55 ± 22% at 230 ppm, P < 0.05). The block line was significantly longer during CSo pacing than during low lateral RA pacing at each rate (all P < 0.05). After pilsicainide administration, the block line extended further. In addition to pacing rate-dependent and site-dependent changes in the block line, pilsicainide further extended the block line length. This phenomenon explains the clinical observation that counterclockwise AFL occurs more frequently than clockwise AFL, and the mechanism of class IC AFL.