Mechanism of Double Ventricular Response to a Single Atrial Extrastimulus in Patients with Wolff-Parkinson-White Syndrome

The purpose of this study is to elucidate electrophysiological determinants of double ventricular response (DVR) to a single atrial extrastimulus in Wolff-Parkinson-White (WPW) syndrome. DVR was observed in 5 (3.4%) out of 146 consecutive patients with WPW syndrome. The site of accessory pathway was located in left lateral free wall in four patients and posterior septum in one. DVR was induced by extrastimulus from coronary sinus in four patients with left-sided accessory pathway, and from both coronary sinus and high right atrium in a patient with septal accessory pathway. However, it was not possible to induce DVR from high right atrium in patients with left-sided accessory pathway, because 50 to 80 ms are needed for intra-atrial conduction from high right atrium to coronary sinus. Critical prolongation of normal AV conduction allowing DVR was seen in the slow pathway of AV node in four patients. In the remaining patients requisite conduction delay occurred in both AV node and His-Purkinje system. Single right ventricular extrastimulus could easily elicit orthodromic AV reciprocating tachycardia or echo beat in four out of five patients and incremental ventricular stimulation induced it in the remaining patient, indicating the presence of retrograde block in the normal AV pathway. As requisites of DVR to a single atrial extrastimulus in WPW syndrome: (1) slow antegrade conduction and retrograde block in the normal AV pathway; and (2) stimulation site in the vicinity of accessory pathway, are needed.     

Resetting of Tachycardia Cycle by Single and Double Ventricular Extrastimuli in Recurrent Sustained Ventricular Tachycardia

In two cases with recurrent sustained ventricular tachycardia (VT) due to re-entry, the response pattern to extrastimuli during the tachycardia was studied. In each case, right ventricular extrastimuli with longer coupling intervals during VT were followed by fully compensatory pauses and with shorter coupling intervals reset the tachycardia cycle. In one case, a plateau was produced by a single extrastimulus, resembling that seen in the response curve of sinus node automaticity as well as ectopic atrial tachycardia. Two successive stimuli produced three definite zones, i.e., fully compensatory, reset producing a plateau, and progressive prolongation zones with shortening of the coupling intervals between the two stimuli, and terminated the tachycardia with further shortening of the coupling intervals. In conclusion, resetting phenomenon was confirmed on two cases with re-entrant VT. This phenomenon cannot be used as a criterion to determine the mechanism responsible for VT.     

Termination of Macro-Reentrant Tachycardia by a Single Extrastimulus Delivered During the ''Effective'' Refractory Period: A Computer Modeled ''Case Report''

A computer model of cardiac excitation sequences was used to reproduce atrioventricular (AV) reentrant tachycardia (AVRT) and its termination by a single 'on-circuit' extrastimulus. The model simulated activation waves revolving along a one-dimensional circular pathway, the portions of which represented the atrial, AV nodal, His-Purkinje, ventricular, and accessory pathway sections of the tachycardia circuit. The modeled pathway was composed of 289 elements. The model distinguished only the depolarised and resting states of constituent elements, but introduced differential refractoriness and conduction velocity for each element. These values approximated the natural situation established in a patient suffering from AVRT associated with the right bundle branch block. The results of the study suggest that: (A) the usual impression of a regular recovery wave and of a regular excitable window moving uniformly along the macro-reentrant circular path is incorrect; (B) during the tachycardia, islands of repolarized cells appear which are surrounded by tissue that is still refractory; (C) an extrastimulus which captures the island of early repolarized tissue may cause an excitation restricted to a small part of the myocardium but the local refractoriness following such an extrastimulus may be sufficient to terminate the tachycardia.     

Spontaneous Termination of Reentry Ventricular Tachycardia in the Late Myocardial Infarction Period: An Experimental Study in the Dog

Forty episodes of induced ventricular tachycardia in the late myocardial infarction period (4-6 days old) were analyzed in 12 dogs in an attempt to identify the possible mechanisms for the termination of reentry tachycardia. Multiple epicardial and endocardial composite electrograms were recorded in and around the central ischemic zone of the infarction. During tachycardia, the earliest site of activation was identified in the epicardial surface of the border or normal zone immediately adjacent to the ischemic zone in 36 of the 40 episodes, suggesting efferent epicardial spread from the site of the activity. In four instances, the efferent pathways were directed to the endocardial surface. Four distinct patterns of activation sequences were observed during spontaneous termination: (a) a shift of the efferent pathways from epicardial to endocardial site (19 instances); (b) a change of the efferent pathways within the endocardium (4 instances); (c) a shift of the earliest site of activation between the left and right ventricles (9 instances); and (d) no apparent change in the epicardial efferent pathways (4 instances). In four other instances, ventricular tachycardia deteriorated into ventricular fibrillation. In patterns (a) and (c), a shift of the efferent pathways resulted in a more rapid and homogeneous activation of the border and normal zone epicardium. These changes were associated with cessation of delayed or continuous activity in the ischemic zone epicardium, resulting in termination of tachycardia.     

Double Atrial Responses to a Single Ventricular Impulse in Long RP' Tachycardia

Double atrial responses (DARs) to a single ventricular impulse have been described in patients with long RP' tachycardia. To define the determinants for the occurrence of DARs. 8 cases with long RP' tachycardia were examined. The mechanism of long RP' tachycardia was the orthodromic atrioventricular reciprocating tachycardia (AVRT) involving a slow conducting concealed accessory pathway in 4 cases and uncommon (fast-slow) type of atrioventricular nodal reentrant tachycardia (AVNRT) in the other 4 cases. Programmed and rapid ventricular pacing was performed during sinus rhythm and also rapid ventricular pacing during tachycardia (i.e., entrainment). The retrograde effective refractory period (ERP) and the retrograde maximal 1:1 conduction rate of the fast and slow conducting pathways were examined. In 1 of the 4 cases with AVRT, DARs were observed during programmed and rapid ventricular pacing, performed during sinus rhythm and also during entrainment. In 1 of the 4 cases with AVNRT, DARs were observed only during entrainment. The determinants of DARs in cases with long RP' tachycardia were: (1) presence of two different retrogradely conducting pathways; (2) short ERP of the retrograde fast and slow conducting pathways and a short minimal pacing cycle length at which 1:1 ventriculoatrial conduction occurs via these pathways; (3) crucial conduction delay in the slow conducting pathway: and (4) preexisting antegrade unidirectional block in the slow conducting pathway or the antegrade block in the slow conducting pathway produced by collision with a previous retrograde impulse during entrainment.     

Double Response of the Ventricle During Transient Entrainment in a Common Atrioventricular Nodal Reentrant Tachycardia

We report a patient with slow-fast atrioventricuiar (AV)nodal reentrant tachycardia, in which double ventricuJar response was demonstrated during rapid pacing at cycle length of 300 msec or less from the high right atrium. The determinants of double ventricular response during transient entrainment in the present case were: (1)a crucial conduction delay in the slow pathway; (2)the collision between the activation via the antegrade fast pathway (antidromically)of the last paced beat and the activation via the antegrade slow pathway (orthodromically)of the previous paced beat, instead of the unidirectional block in the slow pathway; and (3)the enhanced AV nodal conduction over the antegrade fast pathway.     

Double Ventricular Responses to a Single Atrial Depolarization in a Patient with Dual AV Nodal Pathways

Electrophysiological study was performed in a patient with atrioventricular nodal reentrant tachycardia (AVNRT). Double ventricular responses through dual AV nodal pathways were observed by atrial extrastimulus technique followed by initiation of AVNRT. The difference in conduction time between the slow and fast AV nodal pathways was longer than 320 msec. A ventricular extrastimulus delivered during sinus rhythm, which was not followed by ventriculoatrial conduction, also induced AVNRT. These findings indicated the presence of an antegrade critical delay and retrograde block in the slow AV nodal pathway, criteria necessary for the occurrence of a double ventricular response.     

Septal Origin of Sustained Ventricular Tachycardia in a Patient with Right Ventricular Outflow Tract Obstruction After Correction of Tetralogy of Fallot

Right ventricular hypertension and ventricular arrhythmias are risk factors for sudden death after correction of tetralogy of Fallot, but sustained ventricular tachycardia has been reported only in patients without residual hemodynamic abnormalities. A patient with right ventricular hypertension and hypotensive ventricular tachycardia tolerated the arrhythmia better after relief of right ventricular outflow tract obstruction. This case provides insight into the relationship between hemodynamic abnormalities and the clinical consequences of arrhythmias. To our knowledge, it is the first report of ventricular tachycardia originating in scar adjacent to the ventricular septal defect patch after correction of tetralogy of Fallot.     

Prevalence, Therapeutic Response, and Outcome of Ventricular Tachycardia in the Out-of-hospital Setting: A Comparison of Monomorphic Ventricular Tachycardia, Polymorphic Ventricular Tachycardia, and Torsades de Pointes

OBJECTIVE: To investigate out-of-hospital ventricular tachycardia (VT) cardiac arrest patients, comparing the prevalences and outcomes of the following VT subtypes among this population: monomorphic VT (MVT), polymorphic VT (PVT), and torsades de pointes (TdP, PVT with a prolonged QT interval). METHODS: This was a retrospective review from a fire department-based paramedic system of nontraumatic VT cardiac arrest patients (January 1991 to December 1994) with a supraventricular perfusing rhythm (SVPR) at some time during out-of-hospital care, with a measurable QT interval. QT interval was measured from an SVPR, and corrected QT interval (QTc) was calculated and considered prolonged if > 0.45 sec. VT was classified as polymorphic or monomorphic. TdP was defined as PVT with a prolonged QT interval. RESULTS: 196 patients were identified; six were excluded due to incomplete medical records, leaving 190 who met inclusion criteria and were used for data analysis. 117 (62%) patients had MVT, while 73 (38%) patients had PVT; of the 73 patients with PVT, 37 (51%) had normal QTc (non-TdP PVT) and 36 (49%) had prolonged QTc (TdP PVT). 97 (51%) patients had prolonged QTc (PQTc). Regardless of VT type (i.e., MVT vs PVT), 97 (51%) patients had prolonged QTc, with a mean QTc of 0.476+/-0.15 seconds prearrest and 0.464+/-12 seconds postarrest. Patients with PQTc were not more likely to have PVT (70 [37%] vs 76 [40%]; p = 0.705). No significant difference with respect to paramedic-witnessed arrests in each VT morphology group and each QT group was found. The overall hospital discharge rate was 28.4%. Regardless of VT type, patients had similar rates of out-of-hospital return of spontaneous circulation (ROSC) and hospital discharge; patients with PQTc were less likely to be discharged from the hospital (19.6% vs 37.6%; p = 0.01). 27.8% of TdP and 26.8% of non-TdP patients were discharged (p = 0.912). CONCLUSIONS: In this population of out-of-hospital VT arrest patients, MVT is the most common form of VT encountered; PVT and the subtype TdP are also seen in this population with approximately equal frequencies. All three rhythm types demonstrate similar responses to standard Advanced Cardiac Life Support therapy with equal rates of out-of-hospital ROSC and hospital discharge. PQTc may be a marker of poor clinical outcome in patients with out-of-hospital VT arrest.     

Initiation of Ventricular Tachycardia by Interruption of Pacemaker-Mediated Tachycardia in a Patient with a Dual-Chamber Implantable Cardioverter Defibrillator

A 74-year-old man with a dual-chamber implantable cardioverter defibrillator implanted 3 years before experienced multiple ventricular tachycardias (VTs). All episodes were initiated by pacemaker-mediated tachycardia (PMT) that was either stopped by atrial undersensing or the tachycardia termination algorithm of the device. After the termination of PMT, two rapid ventricular paced beats, the first initiated by artificial triggering and the second due to retrograde conduction of the first one, initiated VT that was successfully terminated by antitachycardia pacing or a direct current shock of the device . All episodes revealed this pattern of initiation with a short-long-short ventricular sequence inducing VT.     

Radiofrequency Catheter Ablation of Ventricular Tachycardia Guided by Nonsurgical Epicardial Mapping in Chronic Chagasic Heart Disease

We report a case of a 63-year-old women with Chagas'disease and recurrent, syncopal VT treated by RF catheter ablation in whom endocardial application of RF energy was guided by nonsurgical epicardial mapping. The procedure was undertaken in the electrophysiology laboratory under deep anesthesia. VT was interrupted after 2.4 seconds of application and rendered noninducible afterwards. Two weeks after the procedure, a distinct morphology VT was induced by programmed ventricular stimulation, and the patient was started on amiodarone, remaining asymptomatic 12 months after the procedure.     

Frequency and Output-Dependent Change in Conduction Over Slow Pathways in a Patient with Sustained Ventricular Tachycardia Unrelated to Coronary Artery Disease

In a patient with sustained ventricular tachycardia, we obtained two different paced QRS morphologies from a single pacing site. In one QRS morphology the stimulus to the QRS complex was long, 150 msec, and in the other it was 100 msec. At the paced cycle length of 600 msec and the stimulus output of 4 V, one QRS morphology with the stimulus to the onset of QRS activation (St-QRS) interval of 150 msec was observed. At the paced cycle length of 400 msec, the other QRS morphology with a St-QRS interval of 100 msec was observed alternatively with the former. At the paced cycle length of 353 msec or 316 msec, the latter with a shorter St-QRS interval was exclusively observed. When the stimulus output was increased from 4 to 10 V, keeping with the paced cycle length at 400 msec, the St-QRS interval was shortened from 100 to 80 msec. For the two QRS morphologies with two St-QRS intervals, two slowly conducting pathways would be responsible. The site of the block in the faster pathway must be located at the proximity of the pacing site and the conduction at a shorter paced cycle length would be explained by "supernormal conduction."     

The Response of Digitalized Canine Ventricle to Programmed Stimulation: A Study on Triggered Activity Arrhythmias in the Whole Heart

Triggered activity (TA) has recently received increased attention as a mechanism responsible for cardiac arrhythmias. However, few studies have shown TA in the intact heart. In an ouabain-treated dog's heart we have shown: (a) overdrive acceleration, (b) a concordant relationship between the postpacing interval (PI) and pacing cycle length (CL), and (c) a discordant relationship between the PI and number of paced beats necessary to induce TA. These findings appear to agree with the distinctive characteristics of TA arrhythmias elucidated in previous in vitro studies and suggest TA rather than a reentrant tachycardia. In addition, it is possible that this heart preparation could be considered as a suitable model for the study of TA arrhythmias. These results were obtained using a programmed stimulation protocol in this dog model: (1) Following single programmed ventricular stimulation during sinus rhythm, a repetitive ventricular response (RVR) of more than 3 beats occurred in only 20% of hearts. The relationship between PI and the coupling interval (CI) of the extrastimulus was concordant in 80% (12/15) and discordant in 13% (2/15) of all experiments. The PI-CI relationship was influenced by the mutual relationship between the stimulating, recording, and originating sites of TA. (2) RVR of more than 3 beats was induced by consecutive overdrive ventricular stimulation during sinus rhythm (78%). In addition, the PI-pacing CL relationship was concordant (100%). (3) The transient termination of sustained VT that occurred spontaneously after administration of a large dose of ouabain was seen in only 15% of the cases after a single programmed premature ventricular stimulation. The return cycle-CI relationship was biphasic in 75% (15/20) experiments and discordant in 25% (5/20) of the experiments. (4) The termination of spontaneous sustained VT by overdrive ventricular stimulation occurred in only 8% of the cases. Transient overdrive acceleration of VT occurred after overdrive pacing (53%). In contrast, overdrive suppression occurred in only 13%. Thus, the characteristics of TA arrhythmias observed in the whole heart preparations differed, in some respects, from those obtained by in vitro studies. These quantitative observations could suggest a differentiation, based on probability, between TA and the reentrant mechanism that would respond to programmed stimulation in a similar manner. The differentiation between reentrant and triggered ventricular tachycardia can be made with reasonable assurance using these programmed stimulation techniques.     

三种超声心动图方法评价冠心病患者左室收缩功能的对比研究

采用三种评价左室收缩功能（LVSF）的方法，即二维超声心动图（ZDE）面积-长度法测算的左室射血分数（LVEF），源于多普勒的左室射血力（LVF）及校正的Q－V峰值间期（QVc），对39例冠心病患者（CHD）进行了研究，并以20例正常人（NS）作为对照。结果显示LVF、QVc、LVEF值，在NS组与CHD组间存在着显著差异（P均＜0．01）。在NS组及CHD组，LVF与LVEF相关性良好（r分别为0．8347，0．8126，P均＜0．01），QVc与LVEF相关世良好（r分别为一0．7735，－0．7941，P均＜0．01）。作者认为LVF、QVC是评价LVSF较好的指标。     

Polymorphous Ventricular Tachycardia Associated with a Marked Prolongation of the Q-T Interval Induced by Amiodarone

We report the case of a patient who developed a life-threatening polymorphous ventricular tachycardia (PVT) after six weeks of treatment with amiodarone. The Q-T interval was markedly prolonged at 0.86 second. The drug induction of PVT was strongly suggested by the fact that PVT resolved four days after withdrawal of amiodarone when the Q-T interval had shortened to 0.60 second; the arrhythmia has not recurred in the nine months of follow-up since then. Amiodarone, though a very effective antiarrhythmic agent, may induce serious PVT.     

Nontransmural Scar Detected by Magnetic Resonance Imaging and Origin of Ventricular Tachycardia in Structural Heart Disease

Background: Contrast-enhanced magnetic resonance imaging (CMR) identifies scar tissue as an area of delayed enhancement (DE). The scar region might be the substrate for ventricular tachycardia (VT). However, the relationship between the occurrence of VT and the characteristics of scar tissue has not been fully studied.
Methods: CMR was performed in 34 patients with monomorphic, sustained VT and dilated cardiomyopathy (DCM, n = 18), ischemic cardiomyopathy (ICM, n = 10), or idiopathic VT (IVT, n = 6). The VT exit site was assessed by a detailed analysis of the QRS morphology, including bundle branch block type, limb lead polarity, and precordial R-wave transition. On CMR imaging, the transmural score of each of the 17 segments was assigned, using a computer-assisted, semiautomatic technique, to measure the DE areas. Segmental scars were classified as nontransmural when DE was 1–75% and transmural when DE was 76–100% of the left ventricular mass in each segment.
Results: A scar was detected in all patients with DCM or ICM. Nontransmural scar tissue was often found at the VT exit site, in patients with DCM or ICM. In contrast, no scar was found in patients with IVT.
Conclusions: CMR clarified the characteristics and distribution of scar tissue in patients with structural heart disease, and the presence and location of scar tissue might predict the VT exit site in these patients.     

Suppression of Electrical Storm by Biventricular Pacing in a Patient with Idiopathic Dilated Cardiomyopathy and Ventricular Tachycardia

TANABE, Y., et al. : Suppression of Electrical Storm by Biventricular Pacing in a Patient with Idiopathic Dilated Cardiomyopathy and Ventricular Tachycardia. This study presents a patient with idiopathic dilated cardiomyopathy who had suffered from multiple ICD shocks. Amiodarone and a β-blocker failed to suppress ventricular tachycardia. His ECG showed a very wide QRS complex with an intraventricular conduction delay, so biventricular (BV) pacing was attempted. The BV pacing successfully prevented the multiple ICD shocks accompanied with an improvement in left ventricular systolic function and physical activity.(PACE 2003; 26[Pt. I]:101–102)     

Radiofrequency Catheter Ablation as a Primary Therapy for Treatment of Ventricular Tachycardia in a Patient After Repair of Tetralogy of Fallot

A 20-year-old man with previous surgical repair of tetralogy of Falht was admitted with hemodynamically significant ventricular tachycardia that was terminated witb cardioversion. He was found at electropbysiological study to bave easily inducible ventricular tacbycardia that was mapped to the rigbt ventricular outflow tract. Radiofrequency catheter ablation of tbe ventricular tacbycardia focus rendered tbe patient's arrbytbmia noninducible. Tbis case represents a successful radiofrequency catbeter ablation of a ventricular tacbycardia focus associated witb tetralogy of Fallot repair.     

Undersensing of the Tiny QRS Complexes That Emerged After the Isolation of the Right Ventricle in a Patient with Ventricular Tachycardia

This article describes a patient who underwent right ventricular disconnection for medically refractory ventricular tachycardia associated with arrhythmogenic right ventricular dysplasia. After the operation there was no ventricular tachycardia recurrence. Two years after the operation, he received a permanent VVI pacemaker for the symptomatic second-degree AV block. Sensing function of the pacemaker was normal for the normal QRS complexes, but the tiny QRS complexes that appeared after the arrhythmia surgery were not sensed by the pacemaker and therefore caused no problem.     

Successful Radiofrequency Catheter Ablation for Macroreentrant Ventricular Tachycardias in a Patient with Tetralogy of Fallot After Corrective Surgery

CHINUSHI, M., et al .: Successful Radiofrequency Catheter Ablation for Macroreentrant Ventricular Tachycardias in a Patient with Tetralogy of Fallot After Corrective Surgery . Radiofrequency (RF) catheter ablation was applied to two macroreentrant ventricular tachycardias (VTs) documented after corrective operation for tetralogy of Fallot. The activation wavefront of VT with a right bundle branch block pattern was found to revolve in a clockwise manner around a presumed myotomy scar in the right ventricle, and VT with a left bundle branch block pattern revolved around the same anatomical obstacle in a counterclockwise manner. In both VTs, the biggest conduction delay was confirmed at the right ventricular outflow tract. RF applications to the slow conduction area terminated each VT within a few seconds but were insufficient to cure the VTs. RF lesions were then applied to the, slow conduction area in a line to intersect the macroreentrant circuit, and both VTs became noninducible.