MRI Mode Programming for Safe Magnetic Resonance Imaging in Patients With a Magnetic Resonance Conditional Cardiac Device.

Although diagnostically indispensable, magnetic resonance imaging (MRI) has been, until recently, contraindicated in patients with an implantable cardiac device. MR conditional cardiac devices are now widely used, but the mode programming needed for safe MRI has yet to be established. We reviewed the details of 41 MRI examinations of patients with a MR conditional device. There were no associated adverse events. However, in 3 cases, paced beats competed with the patient's own beats during the MRI examination. We describe 2 of the 3 specific cases because they illustrate these potentially risky situations: a case in which the intrinsic heart rate increased and another in which atrial fibrillation occurred. Safe MRI in patients with an MR conditional device necessitates detailed MRI mode programming. The MRI pacing mode should be carefully and individually selected.

Assessment of Efficacy and Necessity of Routine Defibrillation Threshold Testing in Patients Undergoing Implantable Cardioverter-Defibrillator (ICD) Implantation.

Defibrillation threshold (DFT) testing is performed routinely in patients undergoing implantable cardioverter-defibrillator (ICD) implantation to verify the ability of the ICD to terminate ventricular fibrillation (VF). However, neither the efficacy nor the safety of DFT testing has been proven; thus, the necessity of such testing is controversial. We conducted a retrospective study of the efficacy of DFT testing, particularly with respect to long-term outcomes of ICD implantation.The study included 150 patients (125 men, 25 women, aged 59.0 ± 17.6 years) who underwent ICD or cardiac resynchronization therapy defibrillator implantation, with (n = 73) or without (n = 77) intraoperative DFT testing, between June 1996 and September 2007. VF was induced by delivery of a T-wave shock, and a 20-25-J shock was then delivered. If the 20-25-J shock failed to terminate VF, 30 J was delivered. We assessed whether undersensed VF events occurred during DFT testing and/or during patient follow-up and checked for any association between undersensing and delayed shock delivery. During DFT testing, fine VF was sensed, and shocks were delivered in a timely manner. Nevertheless, 2 patients in the DFT testing group died from VF within 3 years after device implantation.DFT testing, in comparison to non-DFT testing, appeared to have no influence on the long-term outcomes of our patients, suggesting that DFT testing at the time of ICD implantation is limited.

Effects of quinidine on the action potential duration restitution property in the right ventricular outflow tract in patients with brugada syndrome.

BACKGROUND: On a cellular level, Brugada syndrome has been attributed to a deep phase 1 notch and subsequent shallow and prolonged repolarization in the right ventricular outflow tract (RVOT). A sodium channel mutation that leads to early inactivation of the late sodium current has been identified in some patients. Thus, drugs that inhibit the transient outward current (I(to)) responsible for the phase 1 notch and/or enhance the late sodium current might suppress arrhythmic events in patients with Brugada syndrome. The effects of quinidine gluconate, a potent inhibitor of I(to), on RVOT action potential duration (APD) restitution kinetics in patients with Brugada syndrome were evaluated. METHODS AND RESULTS: Programmed ventricular stimulation was performed in 9 Brugada syndrome patients by delivering up to 3 extrastimuli from the right ventricular apex and RVOT. RVOT monophasic action potentials (MAPs) were recorded before and after intravenous administration of quinidine (n=6) or ibutilide (n=3). All patients had inducible ventricular fibrillation (VF) before drug administration. Both quinidine and ibutilide increased steady-state and minimum RVOT MAP duration during programmed stimulation. Quinidine decreased the maximum slope of the RVOT APD restitution curve and VF could not be induced after administration of quinidine in 5 of the 6 patients. CONCLUSIONS: Quinidine appears to suppress the induction of VF by increasing RVOT MAP duration and decreasing the maximum slope of the restitution curve.

Ventricular fibrillation induced by radiofrequency ablation for slow ventricular tachycardia associated with left ventricular dysfunction.

A 59-year-old man with premature ventricular contractions (PVCs) and slow ventricular tachycardia (VT) underwent electrophysiologic testing. The left ventricular ejection fraction was 27%. Activation mapping showed the site of earliest activation to be the posterolateral site of the right ventricle inflow tract, and we considered this to be the focal mechanism underlying the PVCs/slow VT. Radiofrequency current delivered at this site induced a cluster of rapid ventricular beats (sustained VT) with the same QRS morphology as the PVCs, followed by ventricular fibrillation. The PVC/VT focus might have served as an abnormal automatic trigger and driver for the ventricular fibrillation.

Functional atrioventricular conduction block in an elderly patient with acquired long QT syndrome: elucidation of the mechanism of block.

The long QT syndrome (LQTS) is occasionally complicated by impaired atrioventricular (AV) conduction. This form of LQTS can manifest before birth or during neonatal life, and no previous report has demonstrated LQTS complicated by impaired AV conduction in elderly patient. This case report describes an elderly patient with an acquired form of LQTS who developed ventricular fibrillation that was successfully defibrillated during admission to the hospital. Electrophysiologic study demonstrated that HV interval was 38 milliseconds and QT interval was 635 milliseconds during sinus rhythm cycle length of 1167 milliseconds. 1:1 AV conduction was maintained to a pacing cycle length of 545 milliseconds with an AH interval of 144 milliseconds, HV interval of 44 milliseconds, and right ventricular monophasic action potential duration of 360 milliseconds. However, 2:1 HV block developed at a pacing cycle length of 500 milliseconds. Intravenous administration of mexiletine decreased the cycle length of developing HV block to 360 milliseconds.

A new criteria differentiating type 2 and 3 Brugada patterns from ordinary incomplete right bundle branch block.

The type 1 (coved) ECG pattern is diagnostic for Brugada syndrome; types 2 and 3 require antiarrhythmic drug challenge to confirm its presence. We evaluated a 12-lead ECG-based criterion to differentiate between ordinary incomplete right bundle branch block (iRBBB) and true type 2 and 3 patterns that evolve toward type 1 during drug challenge. The subjects were 22 patients (21 men, 1 woman; mean age, 46.8 ± 13.2 years) referred for drug challenge (1 mg/kg pilsicainide, iv). In magnified ECG lead V1 and/or V2 with an iRBBB pattern, the baseline angle defined as the cross section of the upslope of the r' wave with the downslope of the r' wave was measured and compared between patients responding negatively versus positively to drug challenge, and was found to be significantly smaller in patients responding negatively (20.9 ± 12.9°, n = 6, versus 38.7 ± 16.5°, n = 13; P = 0.009). This ECG-based method successfully discriminates between the ordinary iRBBB pattern and drug-induced evolution toward a type 1 Brugada ECG.

Temperature-controlled cooled-tip radiofrequency linear ablation of the atria guided by a realtime position management system.

Due to the difficulty in producing a transmural linear lesion and the possibility of complications such as thrombus formation leading to thromboembolism, the catheter-based maze procedure remains problematic. We tested, in pigs, the possibility of using a temperature-controlled cooled-tip radiofrequency (RF) ablation system together with a realtime position management (RPM) system to create a transmural linear lesion uncomplicated by thrombus formation.Nine pigs underwent insertion of two electrode catheters (each with two ultrasound electrodes), one into the coronary sinus (CS) and one into the right ventricular apex (references for ultrasound-based non-fluoroscopic three-dimensional mapping). A cooled-tip catheter (with two ultrasound electrodes) was introduced into the right atrium. Linear right atrial ablation was performed with a custom radiofrequency (RF) generator. The catheter was perfused with 0.66 mL/second of saline. RF was delivered for 60 seconds at a target temperature of 40°C. A linear ablation line was created between the superior vena cava and inferior vena cava. Three-dimensional isochronal maps were created during CS pacing before and after ablation. In 4 of the 9 pigs, a transmural linear ablation line was confirmed by three-dimensional mapping and postmortem macroscopic examination. No endocardial thrombus formation was noted. Temperature-controlled cooled-tip RF linear ablation guided by an RPM system appears to have potential for creating linear lesions in the atria. Further studies are needed to determine whether such an ablation technique and the parameters used will facilitate successful completion of the catheter-based maze procedure.

Clarifying the arrhythmogenic substrate for Brugada syndrome.

The right ventricular outflow tract (RVOT) is considered the arrhythmogenic region that gives rise to Brugada syndrome. To obtain a better understanding of this substrate, we performed electroanatomic mapping of the right ventricle (RV) in patients with Brugada syndrome. The RV was mapped electroanatomically with the CARTO system in 11 patients with asymptomatic Brugada syndrome but in whom ventricular fibrillation was induced by programmed ventricular stimulation, and in 5 control patients. The low voltage zone area (< 1.5 mV) was larger (16.1% versus 7.8%, P < 0.01) and the bipolar electrogram duration was greater (81.6 ± 7.8 ms versus 53.4 ± 5.6 ms, P < 0.01) in the patients with Brugada syndrome versus the control patients; the bipolar electrogram duration was greater in the septal portion and free wall of the RVOT. Our data suggest that regional endocardial conduction slowing based on structural abnormalities exists at the RVOT in Brugada syndrome.

Prolonged QRS duration in lead V2 and risk of life-threatening ventricular Arrhythmia in patients with Brugada syndrome.

Brugada syndrome is an inherited disorder that predisposes some patients to sudden cardiac death. It is not well established which Brugada syndrome patients are at risk of life-threatening arrhythmias. We investigated whether standard 12-lead electrocardiograms (ECG) can identify such patients. The subjects were 35 men with Brugada syndrome (mean age, 50.1 ± 12.4 years). Documented ventricular fibrillation or aborted sudden cardiac arrests were judged to be related to the Brugada syndrome. Ten patients (mean age, 49.6 ± 14.9 years) were symptomatic, and 25 (mean age, 50.3 ± 11.5 years) were asymptomatic. We determined the PR interval, QRS duration, and QT interval from baseline 12-lead ECG leads II and V2 as well as the J point elevation amplitude of lead V2. The QRS interval was measured from QRS onset to the J point in leads II and V2. The only significant difference between the symptomatic and asymptomatic patients was the QRS duration measured from lead V2. The mean QRS interval was 129.0 ± 23.9 ms in symptomatic patients versus 108.3 ± 15.9 ms in asymptomatic patients (P = 0.012). A QRS interval in lead V2 ≥ 120 ms was found to be a possible predictor of a life-threatening ventricular arrhythmia and/or syncope (P = 0.012). Prolonged QRS duration as measured on a standard 12-lead ECG is associated with ventricular arrhythmia and could serve as a simple noninvasive marker of vulnerability to life-threatening cardiac events in patients with Brugada syndrome.

Abnormal action potential duration restitution property in the right ventricular outflow tract in Brugada syndrome.

BACKGROUND: Although patients with Brugada syndrome (BS) are at risk of ventricular fibrillation (VF) and ensuing death, the action potential duration (APD) restitution properties of the right ventricular outflow tract (RVOT) in patients with BS remain undetermined. METHODS AND RESULTS: Endocardial monophasic action potentials (MAPs) were obtained from 16 patients with BS and 17 control patients. MAPs were recorded from the RVOT in all patients. The MAP duration at 90% repolarization (MAPD(90)), effective refractory period (ERP), and maximum slope of the APD restitution curve were obtained. VF was induced with up to 3 extrastimuli from the RV apex or RVOT. There was no difference in MAPD(90) between the 2 groups, but the ERP was significantly shorter in patients with BS than in control patients (210.7+/-10.5 vs 223.8+/-13.4 ms, P=0.008). MAPD at the shortest diastolic interval was significantly shorter in patients with BS than in control patients (149.9+/-19.9 vs 179.8+/-13.7 ms, P<0.001). The maximum slope of the APD restitution curve was steeper in patients with BS than in control patients (2.90+/-1.29 vs 1.38+/-0.41, P<0.001). CONCLUSIONS: The shorter ERP, shorter MAPD at the shortest diastolic interval and steeply sloped APD restitution curve in the RVOT appear to be related to the inducibility of VF in patients with BS.

Local conduction block of the atria by premature stimulus in a patient with Brugada syndrome.

A 46-year-old man with type II Brugada electrocardiogram pattern changed to a type I Brugada type electrocardiogram pattern by class I antiarrhythmic drug (pilsicainide) underwent electrophysiologic study. Ventricular fibrillation was induced by double extrastimuli from the right ventricular (RV) apex. Monophasic action potentials (MAPs) were then recorded from the high right atrium. Duration of MAP at a coupling interval of 220 milliseconds was 122 milliseconds, and local activation of S2 spread to the left atrium. However, MAP at a coupling interval of 210 milliseconds was 112 milliseconds, and local activation of S2 failed to spread to the rest of atrium.

Electrical remodeling in fibrillating canine atrium: action potential alternans during rapid atrial pacing and late phase 3 early afterdepolarization after cessation of rapid atrial pacing.

Sustained atrial fibrillation (AF) was induced by atrial burst pacing, and monophasic action potentials (MAPs) were recorded. MAP alternans was observed at a cycle length (CL) of 167.5 ± 28.2 msec before burst pacing and 201.3 ± 40.2 msec after burst pacing. AF > 5 minutes duration was induced in 1 dog in the control condition but in all 8 dogs after burst pacing. The difference in RA MAPD(80) of the first spontaneous beat and steady-state sinus rhythm was significantly larger after atrial burst pacing than before atrial burst pacing (31.5 ± 15.9 msec versus 8.2 ± 9.0 msec) In 4 dogs, late phase 3 early after depolarization was observed after rapid atrial pacing. Rapid atrial pacing-induced electrical remodeling includes APD alternans during rapid atrial pacing and also causes an increase in the MAPD of the initial several beats and the development of late phase 3 early afterdepolarizations after a sudden increase in CL.

Comparison of endocardial and epicardial lesion size following large-tip and extra-large-tip transcatheter cryoablation.

BACKGROUND: The efficacy of transcatheter cryoablation for ventricular tachycardia (VT) remains controversial because of the limited size of the lesion produced. An increased lesion size if the cryoablation catheter profile and catheter tip length were increased was hypothesized. METHODS AND RESULTS: Closed-chest transcatheter cryoablation was applied with 7F, 6-mm tip (n=11, 7F group) and 9F, 8-mm tip (n=8, 9F group) catheters to the left ventricular (LV) endocardium and epicardium. Catheter-tip temperature was set to -70 to -80 degrees C, and cryoablation duration was set to 240 s. In acute experiments in the 7F group, endocardial lesion volume was 144.1 +/-86.0 mm(3) and lesion depth was 5.1 +/-1.6 mm, and epicardial lesion volume was 205.6 +/-157.8 mm(3) and lesion depth was 4.7 +/-2.2 mm. In the 9F group, endocardial lesion volume was 301.5 +/-177.4 mm(3) (P<0.001 vs 7F group) and lesion depth was 8.4 +/-1.9 mm (P<0.001 vs 7F group), and epicardial lesion volume was 375.3 +/-167.6 mm(3) (P<0.01 vs 7F group) and lesion depth was 5.0 +/-2.3 mm. CONCLUSIONS: Transcatheter cryoablation of the LV endocardium and epicardium using a larger profile and longer tip electrode may be useful for treating VT originating from the midmyocardium or epicardium.

Anatomic and electrophysiologic differences between chronic and paroxysmal atrial flutter: intracardiac echocardiographic analysis.

BACKGROUND: It remains unknown why atrial flutter (AFL) occurs as either a chronic or paroxysmal arrhythmia. PURPOSE: The aim of the study was to compare intracardiac echocardiographic (ICE) images of the crista terminalis (CT) and transverse conduction properties of the CT between chronic and paroxysmal forms of common AFL. METHODS: Chronic AFL (n = 7) was defined as non-self-terminating AFL lasting >1 month, and paroxysmal AFL (n = 8) was defined as an intermittent arrhythmia with symptomatic episodes of 24 hours maximum duration. ICE images of the right atrium were recorded with a 9 F 9-MHz intracardiac ultrasound catheter during pullback at 0.5-mm intervals from the superior vena cava to the inferior vena cava triggered by electrocardiogram and respiration. The two-dimensional image of the right atrium was reconstructed into a three-dimensional (3-D) image. RESULTS: Three-dimensional images from patients with chronic AFL showed the CT to be thick and continuous, and conduction across the CT was blocked at a pacing rate just above sinus rhythm in all seven patients. In contrast, 3D images from paroxysmal AFL showed the CT to be thin and discontinuous, and conduction across the CT during midseptal pacing was observed in five of the eight patients. CONCLUSION: The nature of AFL is determined, at least in part, by anatomic and electrophysiologic characteristics of the CT.

Full-motion two- and three-dimensional pulmonary vein imaging by intracardiac echocardiography after pulmonary vein isolation.

BACKGROUND: The pulmonary veins (PVs) are topographically complex and motile, so angiographic visualization of the PVs anatomy is limited. An imaging technique that accurately portrays the pulmonary vein (PV) anatomy would be valuable during and after catheter ablation procedures. PURPOSE: We investigated whether three-dimensional (3D) intracardiac echocardiography (ICE) can visualize radiofrequency (RF)-induced tissue changes after PV isolation. METHODS: We performed 3D ICE studies with a 9F, 9-MHz ICE catheter after segmental or extended PV isolation. The ICE catheter was placed 3-4 cm inside the PV ostium and mounted onto a pullback device. Sequential two-dimensional (2D) images of the full length of the vein were obtained in 0.3 mm steps with cardiac and respiratory cycle gating. Each image was fed into a computer, and the aggregate data set was reconstructed into a 3D, full-motion image. RF lesion location and lesion size were studied on 67 pullback images from 29 patients. RESULTS: The 2D and 3D reconstruction was possible for 27 left superior PVs, 13 left inferior PVs, 26 right superior PVs, and one right inferior PV. The ablation site was identified 3-7 mm inside the PV ostium, and a 1/2 - 4/5 circumferential area was ablated with no clinically relevant stenosis. No significant differences were found on the ablated area or ablation site between segmental and extensive PV isolation. CONCLUSION: The 2D and 3D ICE of the PVs provides detailed anatomical information of the proximal PVs, and RF-induced tissue changes in the PV wall can be visualized by ICE.

Usefulness of the polarity in high-density wide range-filtered bipolar mapping to detect isthmus block during radiofrequency ablation of typical atrial flutter.

BACKGROUND: The atrial activation sequence around the tricuspid annulus (TA) cannot always be used to establish whether complete block has been achieved across the cavotricuspid isthmus (CTI) during radiofrequency ablation (RFCA) for typical counterclockwise atrial flutter (CCW-AFL). AIM: We examined whether a change in the polarity of the atrial high-density wide range-filtered bipolar electrograms recorded near the ablation line is an accurate indicator of complete CTI block. METHODS: Nineteen patients with CCW-AFL underwent RFCA. Electrograms were recorded around the TA with duodecapolar conventional (2mm x 8mm x 2mm spacing) and high-density (2-mm spacing) Halo catheters. The bipolar electrograms on the high-density Halo catheter recorded from a series of adjacent electrode pairs positioned just lateral to the ablation line were filtered at a bandpass setting of 0.05-500 Hz. The activation sequence on the conventional Halo catheter during coronary sinus pacing (CSp) and inferolateral TA pacing, and the bipolar electrograms on the high-density Halo catheter during CSp were determined before and after RFCA. The final complete CTI block was verified by the presence of widely split double electrograms > or =100 msec along the ablation line. RESULTS: The final complete CTI block was achieved in all the 19 patients. Before RFCA, the polarity of bipolar electrograms was predominantly negative during CCW-AFL and positive during CSp. In 18 of the 19 patients, the bipolar electrograms exhibited the CCW activation and a negative polarity during CSp only after complete CTI block. In one of those 18 patients, additional applications of RFCA changed the polarity of bipolar electrograms positive to negative although the conventional Halo electrogram activation sequence suggested complete CTI block during CSp. In seven patients, who had transverse conduction across the crista terminalis during CSp, the conventional Halo electrogram activation sequence suggested an incomplete CTI block. However, in six of those seven patients, the CCW activation had a predominantly negative polarity of the bipolar electrograms. In one of those seven patients, complete CTI block was unable to be detected even using the high-density Halo catheter. CONCLUSIONS: These data demonstrate that the high-density wide range-filtered mapping can identify the CTI block in undetectable cases of complete CTI block or incomplete CTI block by the conventional method. The polarity of the bipolar electrograms recorded just lateral to the ablation line during CSp after RFCA of AFL may be used as a simple and an accurate indicator of complete CTI block.

Anatomical characteristics of the cavotricuspid isthmus in patients with and without typical atrial flutter: Analysis with two- and three-dimensional intracardiac echocardiography.

INTRODUCTION: The cavotricuspid isthmus (CTI) is crucial in the ablation of typical atrial flutter (AFL), and consequently the CTI anatomy and/or its relation to resistant ablation cases have been widely described in human angiographic studies. Intracardiac echocardiography (ICE) has been shown to be a useful tool for determining detailed anatomical information. Thus, this technology may also allow the visualization of the anatomical characteristics of the CTI, providing an opportunity to further understand the anatomy. AIM: We conducted a study to compare the anatomy of the CTI between the patients with and without AFL and to characterize the anatomy of the CTI in the patients with AFL resistant to ablation. MATERIALS AND METHODS: Twelve patients with typical AFL and 20 without AFL were enrolled in the study. Two-dimensional (2D) intracardiac echocardiography (ICE) was performed. The recordings were obtained with a 9F, 9-MHz ICE catheter from the right ventricular outflow tract to the inferior vena cava by pulling the catheter back 0.3 mm at a time under guidance with echocardiographic imaging in a respiration-gated manner. Three-dimensional (3D) reconstruction of the images of the CTI were made with a 3D reconstruction system. After the acquisition of the ICE, the CTI ablation was performed in the patients with AFL. RESULTS: The 2D and 3D images provided clear visualization of the tricuspid valve, coronary sinus ostium, fossa ovalis and Eustachian valve/ridge (EVR). The CTI was significantly longer in the patients with AFL than in those without AFL (median length 24.6 mm (range 17.0-39.1 mm) versus median length 20.6 mm (range 12.5-28.0 mm), respectively, P < 0.05). However, a deep recess due to a prominent EVR was observed in 9 of 12 (75%) patients with AFL and in 12 of 20 (60%) patients without AFL (N.S.). A deep recess and the relatively long CTI were related to aging in all the study patients, and that relationship was similar in a limited number of patients without AFL. In five patients with AFL resistant to ablation, a deep recess and prominent EVR were observed. CONCLUSIONS: The 2D and 3D ICE were useful for visualizing the complex anatomy of the CTI and identifying the anatomical characteristics of the CTIs refractory to ablation therapy. The anatomical changes observed in the CTI region may simply be the result of aging and may partially be involved in the development of AFL.

Differential pacing for distinguishing slow conduction from complete conduction block of the tricuspid-inferior vena cava isthmus after radiofrequency ablation for atrial flutter--role of transverse conduction through the crista terminalis.

BACKGROUND: Partial conduction block has been suggested a predictor of recurrence of atrial flutter (AFL). AIM: The aim of this study was to assess transverse conduction by the crista terminalis (CT) as a problem in evaluating isthmus block and the usefulness of differential pacing for distinguishing slow conduction (SC) and complete conduction block (CB) across the ablation line. METHODS: We assessed 14 patients who underwent radiofrequency catheter ablation of the eustachian valve/ridge-tricuspid valve isthmus for typical AFL. Activation patterns along the tricuspid annulus (TA) suggested incomplete CB across the isthmus. In these patients, atrial pacing was performed from the low posteroseptal (PS) and anteroseptal (AS) right atrium (RA) while the ablation catheter was placed at the ablation line where double potentials (DPs) could be recorded. The pattern of activation of the RA free wall was assessed by a 20-pole catheter positioned along the CT during pacing from the coronary sinus (CS) ostium (CSos) and low lateral RA (LLRA). RESULTS: Faster transverse conduction across the CT resulted in simultaneous or earlier activation of the distal halo electrodes than of the more proximal electrodes, suggesting incomplete conduction block across the isthmus. CB (13) and SC (1) were detected as changes in the activation times of the first and second components of DPs (DP1, DP2) during PS RA pacing and AS RA. Similar changes in the activation times DP1 and DP2 during AS RA pacing as compared to PS RA reflected SC through the isthmus, whereas increased DP1 activation time and decreased of DP2 activation time reflected complete conduction block across the isthmus. CONCLUSIONS: Transverse conduction across the CT influences the sequence of activation along the TA after isthmus ablation. Differential pacing can distinguish SC from complete conduction block across the ablation line in the isthmus.