Naoya Tsuboi

Idiopathic ventricular arrhythmias originating from the aortic root prevalence, electrocardiographic and electrophysiologic characteristics, and results of radiofrequency catheter ablation.

OBJECTIVES This study investigated the prevalence and electrocardiographic and electrophysiologic characteristics of aortic root ventricular arrhythmias (VAs). BACKGROUND Idiopathic VAs originating from the ostium of the left ventricle may be ablated at the base of the aortic cusps. METHODS We studied 265 patients with idiopathic VAs with an inferior QRS-axis morphology. RESULTS The successful ablation site was within (or below) the aortic cusps in 44 patients (16.6%). The site of the origin was the left coronary cusp (LCC) in 24 (54.5%), the right coronary cusp (RCC) in 14 (31.8%), the noncoronary cusp (NCC) in 1 (2.3%), and at the junction between the LCC and RCC (L-RCC) in 5 (11.4%) cases. The maximum amplitude of the R-wave in the inferior leads was significantly greater with an LCC than with an RCC origin (p < 0.05). The ratio of the R-wave amplitude in leads II and III was significantly greater with an LCC than with an RCC origin (p < 0.01) and was significantly smaller in the NCC than in the other sites (p < 0.0001). The ventricular deflection in the His bundle electrogram was significantly later relative to the surface QRS with an LCC or L-RCC origin than with an RCC or NCC origin (p < 0.0001). The ratio of the atrial-to-ventricular deflection amplitude was significantly greater in the NCC than in the other sites (p < 0.0001). No other factors predicted the site of origin. CONCLUSIONS Idiopathic VAs are more common in the LCC than in the RCC and rarely arise from the NCC. The electrocardiogram is useful for differentiating the site of origin.

Effects of activation sequence and anisotropic cellular geometry on the repolarization phase of action potential of dog ventricular muscles.

The influence of activation sequences on action potential configuration, especially in the repolarization phase, was examined in isolated canine ventricular muscles. Action potentials were recorded from the epicardial surface in the center of a preparation having nearly uniform fiber orientation (25 X 25 mm). Stimuli applied just adjacent to the recording site produced nearly centrifugal propagation. An activation sequence either parallel (longitudinal) or perpendicular (transverse) to the long axis of the muscle fibers was produced by peripheral stimulation. Action potential duration at -60 mV (APD-60 mV) during centrifugal propagation was significantly longer than that during longitudinal propagation. Further shortening of APD-60 mV was observed during transverse propagation. When a collision of longitudinal or transverse wavefronts (longitudinal or transverse collision) was produced at the action potential recording site, the shortest APD was recorded. During centrifugal propagation, action potential mapping around the stimulating electrodes revealed that APD-60 mV shortened gradually as the recording site was moved further from the stimulation site. The spatial gradient of APD was steeper in the transverse than in the longitudinal direction, causing a distortion in the repolarization sequence and the recovery of excitability near the center of the tissue. Premature stimuli applied to an area near the central stimulation site induced one-way block and circus movement of the wavefront, indicating reentry of excitation. We concluded that the activation sequence and anisotropic cellular geometry substantially affect APD, and that such a change contributes to the spatial inhomogeneity of refractoriness leading to reentrant arrhythmias.

ATP directly affects junctional conductance between paired ventricular myocytes isolated from guinea pig heart.

Effects of ATP on junctional conductance (gj) were investigated in paired ventricular myocytes isolated from guinea pig hearts. One cell of the pair was voltage-clamped with a single-patch pipette, and gj was measured after the perforation of the nonjunctional membrane of the partner cell. The current-voltage relation of gj was linear between -30 and +30 mV. The control gj at 5.0 mM ATP in 88 pairs of cells ranged from 100 to 1,055 nS (average, 268 nS). ATP within the range from 0.1 to 5.0 mM increased gj in a dose-dependent manner. The Hill coefficient was 2.6, and the half-maximum effective concentration of ATP was 0.68 mM. Adenylylimidodiphosphate (2 mM) caused a transient increase in gj in the presence of 0.5 mM ATP, but forskolin (30 microM), cyclic AMP (50 microM), catalytic subunit of cyclic AMP-dependent protein kinase (1 microM), and ADP (10 mM) had no significant effect on gj. The temperature coefficient of gj in the presence of 5.0 mM ATP was 1.29. These findings suggest that gj in paired ventricular myocytes is directly regulated by ATP probably through a specific ligand-receptor interaction between ATP and gap junctional channel protein.

Difference in percentage of ventricular pacing between two algorithms for minimizing ventricular pacing: results of the IDEAL RVP (Identify the Best Algorithm for Reducing Unnecessary Right Ventricular Pacing) study

Aims Managed ventricular pacing (MVP) and Search AV+ are representative dual-chamber pacing algorithms for minimizing ventricular pacing (VP). This randomized, crossover study aimed to examine the difference in ability to reduce percentage of VP (%VP) between these two algorithms. Methods and results Symptomatic bradyarrhythmia patients implanted with a pacemaker equipped with both algorithms (Adapta DR, Medtronic) were enrolled. The %VPs of the patients during two periods were compared: 1 month operation of either one of the two algorithms for each period. All patients were categorized into subgroups according to the atrioventricular block (AVB) status at baseline: no AVB (nAVB), first-degree AVB (1AVB), second-degree AVB (2AVB), episodic third-degree AVB (e3AVB), and persistent third-degree AVB (p3AVB). Data were available from 127 patients for the analysis. For all patient subgroups, except for p3AVB category, the median %VPs were lower during the MVP operation than those during the Search AV+ (nAVB: 0.2 vs. 0.8%, P < 0.0001; 1AVB: 2.3 vs. 27.4%, P = 0.001; 2AVB: 16.4% vs. 91.9%, P = 0.0052; e3AVB: 37.7% vs. 92.7%, P = 0.0003). Conclusion Managed ventricular pacing algorithm, when compared with Search AV+, offers further %VP reduction in patients implanted with a dual-chamber pacemaker, except for patients diagnosed with persistent loss of atrioventricular conduction.

Antiarrhythmic Efficacy of Dipyridamole in Treatment of Reperfusion Arrhythmias Evidence for cAMP-Mediated Triggered Activity as a Mechanism Responsible for Reperfusion Arrhythmias

BACKGROUND Intracellular calcium overload is believed to play an important role in development of reperfusion arrhythmias. Dipyridamole, an inhibitor of cellular uptake of adenosine, may prevent or terminate reperfusion arrhythmias by reducing intracellular calcium overload. METHODS AND RESULTS First, we tested for a preventive effect of dipyridamole. Sixty-one patients who underwent primary PTCA for treatment of acute anterior wall myocardial infarction were enrolled in this prospective study. Patients were divided into dipyridamole (DP) and nondipyridamole (non-DP) groups. The 2 groups had similar baseline characteristics. In the DP group, dipyridamole 0.5 mg/kg was infused intravenously for 3 minutes immediately before reperfusion during primary PTCA. Arrhythmias after reperfusion were analyzed from continuous ECG recordings. None of the patients in the DP group (n=23) had accelerated idioventricular rhythms (AIVR) or ventricular tachycardia (VT). In contrast, 7 (18.4%) had AIVR and 3 (7.9%) had VT in the non-DP group (n=38; P<0.01). Second, we tested for a termination effect of dipyridamole. Dipyridamole 0.5 mg/kg was infused intravenously while continuous ECG recordings were obtained in 9 patients who had either sustained AIVR (n=7) or sustained VT (n=2) after reperfusion of occluded coronary artery. Arrhythmias were terminated in all patients. CONCLUSIONS These results indicate that administration of dipyridamole can prevent and terminate reperfusion arrhythmias such as AIVR and VT. cAMP-mediated triggered activity may, at least in part, be responsible for reperfusion-induced AIVR and VT.

Efficacy of electroanatomic mapping in the catheter ablation of premature ventricular contractions originating from the right ventricular outflow tract

BackgroundMapping of premature ventricular contractions (PVCs) originating from the right ventricular outflow tract (RVOT) sometimes is not easy because of an unstable incidence and multiple foci of the PVCs. The aim of this study was to evaluate the effectiveness of electroanatomic mapping in catheter ablation of those PVCs.Methods and resultsOne hundred patients with 134 RVOT origin PVCs were randomly allotted to undergo either conventional (group I; 50 patients with 65 PVCs) or electroanatomic mapping (group II; 50 patients with 69 PVCs). In group II, electroanatomic mapping of the RVOT was performed using auto-freeze maps in patients with frequent PVCs, and pace mapping was performed marking the pacing sites on the remap which was made by extracting the anatomic frame out of the baseline map during sinus rhythm in patients with infrequent PVCs. Successful ablation was achieved in 44 (88%) group I patients and 48 (96%) group II patients (p = 0.14). The fluoroscopy and procedure times and those per PVC morphology were all significantly shorter in group II than group I overall (p < 0.0001 for all comparisons), and in each patient group with infrequent PVCs, frequent PVCs or unstable PVCs (p < 0.05–0.0001). The number of RF applications and that per PVC was significantly smaller in group II than group I (5.3 ± 1.8 vs 6.2 ± 2.4, and 4.4 ± 1.2 vs 5.2 ± 2.1; p < 0.05).ConclusionsThe use of electroanatomic mapping may reduce the fluoroscopy and procedure times in the ablation of RVOT PVCs, but there is no evidence that it improves the overall efficacy of the procedure.

Body surface distribution of abnormally low QRST areas in patients with Wolff-Parkinson-White syndrome. Evidence for continuation of repolarization abnormalities before and after catheter ablation.

BackgroundWhether the Wolff-Parkinson-White syndrome (WPW) is associated with repolarization abnormalities is controversial. The QRST isointegral map (I-map) is theoretically independent of the activation sequence and dependent on repolarization properties. There have been no reports concerning the effects of radiofrquency (RF) catheter ablation of accessory pathway (AP) on repolarization properties analyzed by I-mapping. Methods andResults. I-maps were constructed from data recorded in 38 patients with WPW to investigate repolarization properties and their body surface distribution in a physiological state, without pharmacological influences, and in 13 ablated patients to elucidate the effects of RF ablation on repolarization properties. Patients were divided into three groups: group A, 15 patients with type AWPW (left-sided AP); group B, 10 patients with type B (right-sided AP); and group C, 13 patients who were successfuly ablated. Group C consisted of three subgroups: subgroup CA, 7 patients with type A WPW; subgroup CB, 3 patients with type B WPW; and subgroup Cc, 3 patients with concealed WPW. Controls consisted of 608 normals. Although I-maps ofWPWwere highly (r=.87) correlated with the mean normal I-map, the location of the minimum in groups A and B differed significantly from that in normals. The minimum was located over the upper right anterior chest in normal subjects, over the back in 82% of 22 patients with type A WP1W including ablated patients (groups A±CA), and over the mid to lower right anterior chest in 62% of 13 patients with type B WPW including ablated patients (groups B±CJ). Groups A±CA and B±CB had an abnormally low QRST area (“-2SD area”) over the back and right anterior chest, respectively. The abnormally located minimum and the “-2SD area” were present in 7 of 10 ablated patients with manifest WPW (groups CA±CB). After RF ablation, the distribution of the minimum, initially abnormal, became normal over a period of days or weeks, and the “-2SD area” disappeared over 1 week in all 7 patients. Correlation coefficients between I-maps and the mean normal I-map increased after RF ablation. Conclusions(1) WPW is often associated with abnormalities in repolarization properties. (2) Repolarization abnormalities were located over the back in type A WPW and over the right mid to lower chest in type B WPW. (3) The abnormalities remain immediately after RF ablation and gradually normalize. These findings support the concept that ST-T abnormalities in 12-lead ECGs following RF ablation are attributable to “cardiac memory.”

Maximum Derivative of Left Ventricular Pressure Predicts Cardiac Mortality After Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) has been reported to improve cardiac performance. However, CRT in patients with advanced heart failure is not always accompanied by an improvement in survival rates. We investigated the association between hemodynamic studies and long‐term prognosis after CRT.

Computerized Three-Dimensional Potential Mapping with a Multielectrode Basket Catheter Can be Useful for Pulmonary Vein Electrical Disconnection ∗

Introduction: Pulmonary vein (PV) isolation (PVI) has been recently proposed as an effective technique to cure atrial fibrillation (AF).Aims of the Study: The aim of this study was to investigate the efficacy of a novel technique utilizing a computerized three-dimensional mapping system (QMS2TM) with a multielectrode basket catheter (MBC) for PVI and to reveal the relation between the style of breakthrough and the network of the PV musculature.Methods: Sixty-five consecutive patients with frequent AF attacks underwent PV mapping with a 31-mm MBC, and a three-dimensional color animation of the potential map was constructed by the QMS2TM. The animation color schema was arranged to minimize the low-amplitude left atrial (LA) potentials and emphasize the high-amplitude PV potentials (PVPs). The longitudinal PVP map enabled us to recognize the true breakthroughs and reveal the network of the PV musculature.Results: A total of 205 PVs (65 left superior PVs, 65 right superior PVs, 57 left inferior PVs and 18 right inferior PVs) were mapped and successful PVI was achieved in all PVs, except one that had no PVPs, with a mean radiofrequency duration of 7 ± 5 minutes per PV. In about 90% of the PVs, a final radiofrequency application eliminated all the distal PVPs simultaneously because the PVI was performed at the appropriate LA-PV junction. A single segmental breakthrough was detected in 17 PVs, single broad breakthrough in 83 PVs, multiple separate breakthroughs with a distal connection between the PV musculatures extending from each separate breakthrough in 88 PVs and multiple separate breakthroughs without that connection in 16 PVs. During the follow-up period, fifty-one (78%) patients were free of symptomatic AF without any antiarrhythmic drugs after multiple procedures (thirty-three (51%) of those patients after the first procedure) and no PV stenosis was found.Conclusions: Computerized three-dimensional potential mapping can be useful for PVI because it can not only identify the true breakthrough, but can also confirm the elimination of the breakthroughs by the change in the activation sequence through the network of the PV musculature.

Impact of coronary stent designs on acute stent recoil

BACKGROUND Acute stent recoil has been often observed following stent delivery balloon deflation in coronary arteries and the recoil rate varies by stent design. Accordingly, the purpose of the present study was to evaluate the impact of stent designs on acute stent recoil after new generation drug-eluting stent implantation. METHODS AND RESULTS A total of 154 lesions [56 treated with biolimus-eluting stent (BES), 46 with cobalt chromium everolimus-eluting stent (CoCr-EES), and 52 with platinum chromium everolimus-eluting stent (PtCr-EES)] were evaluated. Quantitative coronary angiography was used to measure the minimal lumen diameter (MLD). MLD1 was defined as a MLD of complete expansion of the last stent delivery balloon at the highest pressure. MLD2 was defined as a MLD immediately after the last stent delivery balloon deflation. Acute stent recoil was determined by the calculation as (MLD1-MLD2)/MLD1. Acute stent recoil was significantly higher in the CoCr-EES group versus the BES group and PtCr-EES group (10.1 ± 6.9%, 6.7 ± 5.5%, and 6.5 ± 4.8%, respectively, p = 0.01). Multivariate linear regression analysis demonstrated that the use of CoCr-EES and the number of stent delivery balloon inflations were independent predictors of acute stent recoil (r = 0.26, β = 0.21, p = 0.01 and r = -0.51, β = -0.58, p < 0.01, respectively). CONCLUSION Acute stent recoil occurred more frequently with the CoCr-EES compared with both BES and PtCr-EES. Strategies with multiple balloon inflation might be needed to overcome this recoil phenomenon.