Selection of ablation site with automatic atrial tachycardia.
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Adult↗
Biomedical subjects
G J Klein
Publications and source records attributed to G J Klein.
High voltage shock induced cellular electrophysiological effects: transient refractoriness and bimodal changes in action potential duration.
The cellular electrophysiological effects of defibrillation shocks on the myocardium during ventricular fibrillation are not clear. The present study investigated the effects of high voltage shocks on membrane potentials of isolated guinea pig and pig papillary muscles during rapid activations simulating ventricular fibrillation. High voltage shocks induced an action potential with a prolonged duration, followed by a transient refractory state. Subsequent action potentials following this refractory state had shortened durations. The duration of the transient refractory state varied in proportion to shock intensity and stimulation rate, whether the shock was biphasic or monophasic. Shock induced prolonged depolarization was not a consistent finding and mainly observed with slow stimulation rates. In conclusion, high voltage shocks induce bimodal changes of the action potential duration associated with a transient refractory state during rapid activation. The rate dependency of this refractory state suggests that the duration of the shock induced refractory state may be longer in the fibrillating than the normal beating heart, and may contribute to successful defibrillation.
Action Potentials↗
Catheter ablation of idiopathic left ventricular tachycardia.
Idiopathic left ventricular tachycardia (ILVT) characterized by right bundle branch block, left axis morphology, response to verapamil and inducibility from the atrium in patients without structural heart disease may represent a distinct clinical entity. We report our experience with catheter ablation of this uncommon arrhythmia using radiofrequency energy (RF) and/or direct current (DC) shocks. Six men and 2 women, aged 16-50 years (mean +/- SD, 32 +/- 13), had recurrent VT for 16 +/- 16 years with a mean frequency of 4 +/- 3 episodes/year. Three patients had syncope during VT. None had identifiable structural heart disease. Catheter ablation was guided by earliest endocardial activation, presence of a high frequency presystolic potential and/or pacemapping of the left ventricle. The left ventricle was accessed via a retrograde aortic approach in 6 patients, a transeptal approach in 1 patient, and a combined approach in the remaining patient. All patients had inducible right bundle branch block morphology, left axis VT with a mean cycle length (CL) of 361 +/- 61 ms. A presystolic potential preceding ventricular activation and the His potential during VT was identified in 4 patients. All ablation sites were identified in a relatively uniform location, in the inferoapical left ventricle. Noninducibility of VT was obtained with RF in 3 patients and with DC in 5 patients. In 1 patient, DC delivery after unsuccessful RF prevented further inducibility. Similarly, RF was successful in 1 patient in whom an initial DC attempt was ineffective. Mean total procedure time was 282 +/- 51 minutes and mean total fluoroscopy time was 40 +/- 15 minutes. There were no complications. One patient treated with DC shock had recurrence of VT during treadmill test the day after ablation and refused repeat ablation. During a mean follow-up of 17 +/- 13 months, no VT recurrences or other cardiovascular events occurred. In conclusion, catheter ablation in the inferoapical left ventricle is an effective treatment for this type of ILVT. RF energy can be safely complemented by low energy DC shocks when the former is ineffective.
Adult↗
Inappropriate sinus tachycardia: evaluation and therapy.
Inappropriate sinus tachycardia is an ill-defined clinical syndrome characterized by an increased resting heart rate accompanied by an exaggerated response to exercise or stress. It is not associated with underlying structural heart disease. The mechanism may involve a primary abnormality of the sinus node demonstrating enhanced automaticity or, alternatively, a primary autonomic disturbance with increase sympathetic activity and enhanced sinus node beta-adrenergic sensitivity. The diagnosis of inappropriate sinus tachycardia is one of exclusion. It is most common in young females, with a disproportionate number employed in the health care field. Autonomic and electrophysiologic testing may be required in selected individuals to clarify the mechanism and rule out sinus node reentry or right atrial tachycardia. Therapy of inappropriate sinus tachycardia is empiric. Pharmacologic approaches include beta blockers or verapamil. Radiofrequency catheter ablation of the superior portion of the sinus node shows promise as a useful alternative in patients with refractory symptoms.
Adult↗
Effect of isoproterenol on accessory pathways without overt retrograde conduction.
INTRODUCTION: Absence of overt retrograde accessory pathway conduction may be related to low resting sympathetic tone in patients with apparent unidirectional anterogradely conducting accessory pathways (UACAP). METHODS AND RESULTS: To test this hypothesis, we studied the effect of isoproterenol on accessory pathway function and tachycardia induction in 18 patients (12 men and 6 women, ages 34 +/- 16 years [mean +/- SD]) with UACAP. After baseline study in the drug-free state, electrphysiologic testing was repeated during infusion of isoproterenol (0.5 to 1.5 micrograms/min, titrated to increase heart rate by 20%). Isoproterenol shortened the anterograde effective refractory period (398 +/- 117 vs 305 +/- 63 msec; P < 0.01; basic drive cycle length 600 msec) of the accessory pathway. However, retrograde accessory pathway conduction and atrioventricular reentrant tachycardia were exposed in only 3 (17%) patients by isoproterenol infusion. All 3 patients with retrograde accessory pathway revealed after isoproterenol had clinically documented tachycardia (supraventricular tachycardia in 2, atrial fibrillation in 1) during exercise, while none of the patients with persistent absence of retrograde accessory pathway conduction had this symptom. CONCLUSIONS: We conclude that absence of overt retrograde conduction over accessory pathways may be related to low resting sympathetic tone in some individuals. Restoration of retrograde conduction with isoproterenol is unusual and most likely to be observed in patients with clinically documented paroxysmal supraventricular tachycardia related to exercise.
Accessory Nerve↗
Head-up tilt testing: the balance of evidence.
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Adrenergic beta-Antagonists↗
Atypical retrograde atrial activation in 'typical' atrioventricular nodal reentrant tachycardia.
Atrioventricular nodal reentrant tachycardia (AVNRT) can be cured by radiofrequency catheter ablation by selective ablation of the slow or the fast pathway. Retrograde fast pathway ablation is performed anterosuperiorly at the apex of Koch's triangle, whereas slow pathway ablation is performed at the base of Koch's triangle near the coronary sinus ostium. A patient with otherwise typical slow-fast AVNRT who demonstrated earliest retrograde atrial activation at the proximal coronary sinus rather than the usual His bundle recording position is described. Loss of retrograde fast pathway conduction occurred after radiofrequency ablation at the base of Koch's triangle, suggesting an atypical location of the fast pathway. This supports recent evidence that the retrograde fast pathway may be located near the coronary sinus ostium in some patients with otherwise typical AVNRT.
Adult↗
Time and frequency domain analyses of heart rate variability during orthostatic stress in patients with neurally mediated syncope.
The role of autonomic balance during upright tilt in patients with neurally mediated syncope is unclear. To assess the characteristics of autonomic tone during orthostatic stress, 15 patients (mean age 32 years) with recurrent episodes of syncope (> or = 2) and a positive response to a 30-minute 60 degrees upright tilt were compared with the following control groups: (1) 15 patients (mean age 33.5 years) with > or = 2 episodes of recurrent syncope and a negative tilt response, and (2) 15 age- and sex-matched healthy volunteers (mean age 34 years) with no previous history of presyncope or syncope. Time domain measurements assessed were mean RR interval, standard deviation of normal RR intervals, and percentage of normal consecutive RR intervals differing by > 50 ms. Frequency domain measurements of the low-frequency (LF) and high-frequency (HF) bands were obtained, and the LF/HF ratio was also calculated. All variables were calculated in the supine position and during the first 5 minutes of upright tilt. No significant difference was observed in the time and frequency domain variables in the supine position between control groups with a negative head-up tilt response and the group with a positive response. The percentage of normal consecutive RR intervals differing by > 50 ms during the first 5 minutes of head-up tilt was significantly higher in the group with positive tilt tests than in the controls (25 +/- 12% vs 7 +/- 4%, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Radiofrequency ablation of decremental accessory pathways mimicking "nodoventricular" conduction.
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Adult↗
Radiofrequency catheter ablation in patients with Wolff-Parkinson-White syndrome.
OBJECTIVE: To report on the experience with radiofrequency catheter ablation of accessory atrioventricular pathways in patients with Wolff-Parkinson-White syndrome in terms of the duration of fluoroscopy exposure to the patient and the operator and the effect of accessory-pathway location and operator experience on the success rate. DESIGN: Retrospective review. SETTING: Tertiary care university hospital. PATIENTS: Two hundred consecutive patients with Wolff-Parkinson-White syndrome who underwent radiofrequency catheter ablation between September 1990 and June 1992. INTERVENTIONS: Electrophysiologic study and radiofrequency catheter ablation. MAIN OUTCOME MEASURES: Success rate, duration of fluoroscopy, complications and long-term follow-up. RESULTS: Of the 224 accessory pathways in the 200 patients 135 were left free wall, 47 posteroseptal, 32 right free wall and 10 anteroseptal. The overall success rate increased from 53% in the first 3 months of the study period to 96% in the last 3 months. The success rate depended on the location of the accessory pathway. The duration of fluoroscopic exposure decreased from 50 (standard deviation [SD] 21) minutes in the first 3 months to 40 (SD 15) minutes in the last 3 months (p < 0.05). Complications occurred in 3.5% of the patients; they included hemopericardium, cerebral embolism, perforation of the right atrial wall, air embolism in a coronary artery and hematoma at the arterial perforation site. None of the complications resulted in death. CONCLUSIONS: With experience, radiofrequency catheter ablation of accessory pathways can have an overall success rate of more than 95% and a complication rate of less than 4%. Such rates make this procedure suitable for first-line therapy for patients with Wolff-Parkinson-White syndrome.
Adolescent↗
Embolic complications after radiofrequency catheter ablation.
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Adolescent↗
Clinical predictors of successful implantable cardioverter defibrillator implantation.
Successful implantation of an implantable cardioverter defibrillation system is critically dependent on demonstration that the lead system to be implanted can defibrillate reliably. Defibrillation efficacy in turn is dependent on several sets of factors that include: (1) defibrillation technique and the lead system being tested; (2) defibrillation testing protocol and criteria for implantation; and (3) clinical variables that may be intrinsic to the patient or extrinsic factors to which the patient is being exposed. Existing clinical data are limited but suggest that poor left ventricular function is the clinical variable most consistently associated with poor defibrillation efficacy and a failure to meet implant criteria of the epicardial lead systems. Antiarrhythmic drugs may elevate the defibrillation threshold, but evidence that this has important clinical ramifications on implantation success rates is very limited and incomplete.
Anti-Arrhythmia Agents↗
Pronounced increase in defibrillation threshold associated with pacing-induced cardiomyopathy in the dog.
Progressive changes in myopathology after implantation of an automatic defibrillator could compromise device efficacy. The influence of heart failure development on the defibrillation threshold was evaluated by means of a rapid ventricular pacing model of heart failure in dogs. After transvenous pacemaker lead implantation, adult mongrel dogs were randomly assigned to either the control (n = 7) or rapidly paced group (240 beats/min, n = 6). Seventeen days after implantation, triplicate determinations of the defibrillation threshold were made with three epicardial electrodes. The average defibrillation threshold was four times higher in the rapidly paced group, 13.3 +/- 2.0 joules (mean +/- SEM), than in the control group, 3.3 +/- 0.7 joules (p < 0.01), and was significantly correlated with ventricular weight (r = 0.70, p < 0.01). Both defibrillation threshold energy per gram of ventricle and ventricular weight corrected for body weight were significantly higher in rapidly paced dogs compared with control dogs. It was concluded that myocardial hypertrophy and heart failure may profoundly increase defibrillation energy requirements.
Animals↗
Encircling endocardial cryoablation for ventricular tachycardia after myocardial infarction: experience with 33 patients.
Encircling endocardial cryoablation, consisting of circumferential cryoablation of the infarct scar, can be curative in selected patients with ventricular tachycardia (VT). We describe our experience with and long-term outcome in 33 patients undergoing this procedure. The interval between myocardial infarction and the onset of tachycardia varied from 2 weeks to 22 years (mean 38 +/- 63 months and median 3 months). All patients had a left ventricular aneurysm (anterior in 20, posterior in 12, and lateral in 1) and significant coronary artery disease. Fourteen patients had clinical evidence of heart failure preoperatively. Twenty-eight patients had sustained monomorphic VT (incessant in 3); 3 had polymorphic or nonsustained tachycardia; 2 had primary ventricular fibrillation; and 1 had associated Wolff-Parkinson-White syndrome. Surgery was undertaken after failed drug therapy and consideration of left ventricular anatomy and function. At surgery, 32 patients had encircling endocardial cryoablation, and 1 patient had partial right ventricular free-wall disconnection (right ventricular infarct). Thirteen patients underwent concomitant coronary artery bypass grafting. An implantable cardioverter defibrillator (ICD) was implanted in 2 patients and prophylactic ICD patches in 1. One patient died postoperatively; 3 had recurrent VT perioperatively; 1 was treated with amiodarone; and 2 had ICD implantation. During long-term follow-up (mean 5 years), all patients who were free of tachycardia at discharge remained alive and free of arrhythmias or syncope. The patient receiving amiodarone sustained a cardiac arrest subsequently and received an ICD implant. One patient with an ICD continued to receive appropriate shocks frequently and died 2 years after surgery. Nine patients had congestive heart failure postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)
Actuarial Analysis↗
Operation for the Wolff-Parkinson-White syndrome in the catheter ablation era.
Catheter ablation has greatly altered surgical referral patterns for the Wolff-Parkinson-White syndrome. We describe 51 patients (aged 9 to 63 years; 35 male, 16 female) referred for operation from our institution and elsewhere between August 1990 and August 1993, coincident with the inception of our ablation program. During the same period, 375 patients with problematic Wolff-Parkinson-White syndrome had ablation procedures. Operation was the initial therapy in 26 patients, due to physician preference in 23 and the need for a concomitant cardiac operation in 3. Operation was related to ablation failure in 22 patients and was urgent in 3 patients. Previous ablation was not associated with added surgical difficulties, and all pathways were ablated intraoperatively on the first attempt using the epicardial approach. Visible epicardial lesions were observed in 8 patients at the site of the accessory pathway. In 2 patients, the lesions were remote to the atrioventricular ring. There was a striking significant increase in proportion of right free wall pathways after attempted ablation (27% versus 8%) as compared with the preablation era. We conclude that previous attempted ablation does not impair efficacy and safety of operative therapy. Operation remains a useful alternative for ablation failure and as a back-up for acute complications.
Adolescent↗
Effect of shock timing on efficacy and safety of internal cardioversion for ventricular tachycardia.
OBJECTIVES: We examined the effect of shock timing within the QRS complex on cardioversion efficacy in a randomized crossover test of shocks delivered at two timing intervals relative to QRS onset. BACKGROUND: The local ventricular electrogram is used in implantable cardioverter-defibrillators to synchronize cardioversion shocks to terminate ventricular tachycardia. However, the timing of the local electrogram relative to global ventricular depolarization is variable, depending on the site of ventricular tachycardia origin. METHODS: Transvenous defibrillation leads were positioned in the right ventricular apex (cathode), coronary sinus and superior vena cava (anodes) of patients with sustained monomorphic ventricular tachycardia. After repeat ventricular tachycardia induction, sequential shocks with energy settings of 0.5 to 22 J were delivered simultaneously with QRS onset (QRS + 0 shock) or 100 ms after QRS onset (QRS + 100 shock). QRS onset was determined from the surface electrocardiogram. Cardioversion threshold, defined as the lowest shock energy for successful ventricular tachycardia termination, was measured for these two timings. RESULTS: Fifteen patients (13 men, 2 women; mean [+/- SD] age 60.5 +/- 7.7 years) completed testing. Cardioversion threshold was significantly lower with QRS + 100 shocks than QRS + 0 shocks (3.1 +/- 3.5 vs. 10.5 +/- 7.4 J, p < 0.01). Thirteen patients (87%) experienced ventricular tachycardia acceleration with QRS + 0 shocks, but only three patients (20%) had ventricular tachycardia acceleration using QRS + 100 shocks (p < 0.01). Of the 32 failed QRS + 0 shocks, 25 (78%) caused ventricular tachycardia acceleration, whereas only 5 (36%) of the 14 failed QRS + 100 shocks caused ventricular tachycardia acceleration (p < 0.05). Cardioversion threshold was not correlated with ventricular tachycardia cycle length, QRS duration, left ventricular ejection fraction or left ventricular diastolic volume (p = NS). CONCLUSIONS: Internal cardioversion shocks delivered late in the QRS complex during ventricular tachycardia are more effective and have a lower risk of ventricular tachycardia acceleration than those delivered near QRS onset.
Aged↗
Effect of adenosine or adenosine triphosphate on antidromic tachycardia.
OBJECTIVES: This study was designed to determine the effect of adenosine or adenosine triphosphate (ATP) on antidromic tachycardia. BACKGROUND: Adenosine and adenosine triphosphate are useful for differential diagnosis of wide QRS tachycardia. It has been believed that tachycardia termination caused by these agents is due to the preferential depressive effect on the atrioventricular (AV) node, whereas their effect on accessory pathways is minimal. METHODS: We studied the effect of adenosine or ATP on the termination pattern of antidromic tachycardia in 17 patients (10 men, 7 women; mean age [+/- SD] 32 +/- 11 years) with one or more accessory pathways. Adenosine (6 to 12 mg [n = 10]) or ATP (8 to 20 mg [n = 7]) was injected rapidly through a central venous line and followed by 10 ml of saline flush after induction of sustained antidromic tachycardia. RESULTS: Tachycardia was terminated in < 2 min in 14 patients (82%) after the injection and remained unchanged in 3 (18%). Tachycardia termination was due to conduction block in the accessory pathway (anterograde limb) in seven patients (50%) and in the AV node (retrograde limb) in another seven. Adenosine or ATP caused accessory pathway block in seven (88%) of the eight patients lacking retrograde accessory pathway conduction and in none of the nine patients having retrograde accessory pathway conduction (p < 0.01). All five patients with an atriofascicular accessory pathway and unidirectional anterograde conduction had tachycardia termination due to anterograde accessory pathway block after injection of adenosine or ATP. CONCLUSIONS: 1) Adenosine or ATP effectively terminates antidromic tachycardia; 2) the termination is related to block in either the accessory pathway or the AV node; 3) accessory pathway block occurs in patients with a unidirectional, anterogradely conducting accessory pathway, especially an atriofascicular accessory pathway.
Adenosine↗
Combination biphasic waveform plus sequential pulse defibrillation improves defibrillation efficacy of a nonthoracotomy lead system.
OBJECTIVES: We hypothesized that combining biphasic waveform and sequential pulse defibrillation techniques would lower the defibrillation threshold of a nonthoracotomy lead system in humans below that obtained with biphasic or sequential pulse defibrillation alone. BACKGROUND: Previous studies have shown that sequential pulse monophasic shocks and biphasic waveform shocks are more effective than single monophasic shocks for ventricular defibrillation. METHODS: Thirteen patients aged 48 to 71 years undergoing nonthoracotomy defibrillation lead testing participated in the study. Transvenous electrodes were positioned in the right ventricular apex, superior vena cava and coronary sinus. A cutaneous patch electrode was placed on the left chest wall. All electrodes were connected to an external defibrillator. In random order, defibrillation threshold measurements were made for biphasic defibrillation alone, sequential defibrillation alone and combined biphasic plus sequential defibrillation. RESULTS: The mean defibrillation threshold-delivered energy was 18.0 +/- 11.9 J for biphasic defibrillation and 16.3 +/- 9.0 J for sequential defibrillation. Biphasic plus sequential defibrillation significantly reduced the threshold energy to 10.2 +/- 5.3 J (p < 0.001). Threshold peak voltage and current values showed corresponding reductions. The combined waveform resulted in a greater reduction in defibrillation threshold in patients with threshold energies > 18 J versus those with threshold values < or = 18 J for sequential (p = 0.001) or biphasic (p < 0.01) waveform alone. The nonthoracotomy lead implantation rate was improved from 62% with each of the single techniques (biphasic waveform or sequential pulse defibrillation) to 85% with the combined waveform. CONCLUSIONS: Adding biphasic waveform to sequential pulse defibrillation significantly reduced the defibrillation threshold compared with either technique alone, and nonthoracotomy lead system implantation can be enhanced by this combined technique.
Aged↗