John A. Yeung-Lai-Wah

High success rate of atrioventricular node ablation with radiofrequency energy.

Radiofrequency current was introduced as an alternative energy source for transcatheter ablation of cardiac arrhythmias to avoid the complications associated with direct current shocks. Initial use of radiofrequency current for complete ablation of the atrioventricular (AV) node yielded only moderate success rates, presumably because of the small size of electrodes and difficulty in localizing the AV node. The use of a larger 4-mm tip electrode for delivery of radiofrequency current and a method to better localize the AV node were prospectively studied in 32 patients undergoing catheter ablation of the AV node. There were 21 men and 11 women with a mean age of 62 +/- 12 years. Complete AV block was achieved immediately in 31 patients (97%) and it persisted in 28 patients (88%) during a mean follow-up period of 12 +/- 6 months. Three patients who had return of AV condition required no drug therapy for control of ventricular rate during atrial fibrillation. The number of radiofrequency pulses used to achieve complete AV block ranged from 1 to 5 (mean 1.9 +/- 1.1). In greater than 50% of the cases, only one radiofrequency pulse was required. The mean power and duration of radiofrequency pulses were 21.2 +/- 4.5 W and 33 +/- 15 s, respectively. All patients developed a stable junctional escape rhythm within 45 min of successful ablation. The QRS configuration was unchanged in 30 patients. One patient had a new right bundle branch block after ablation. There were no complications related to the ablation procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial flutter in patients treated for atrial fibrillation with propafenone

Abstract The class IC antiarrhythmic drug, propafenone, has been used successfully for the prevention of atrial fibrillation (AF), with few reported adverse cardiovascular effects. 1–3 Propafenone depresses the rate of rise and amplitude of phase 0 of the action potential, slowing conduction in the atrium. 4 Although it has mild β-adrenergic antagonist effects, it has relatively less effect on atrioventricular refractoriness, although in AF the ventricular response may slow. 5 With slower atrial arrhythmias such as atrial flutter, where less concealment of conduction occurs, it is possible that the same effect on ventricular rate may not be seen. This study defines the incidence of atrial flutter developing in a heterogeneous population of patients with recurrent AF and observes the ventricular response during this arrhythmia.

Nonsustained ventricular tachycardia arising from the right ventricular outflow tract

Characteristics of left bundle branch block morphology, inferiorly directed frontal plane QRS axis and repetitive nonsustained salvos were used to define a discrete subgroup of patients with ventricular tachycardia (VT). The origin of this tachycardia was thought to be the right ventricular outflow tract. Twenty-six patients with this definition (group 1) were compared with 29 consecutive patients with all other forms of VT (group 2). When compared with patients in group 2, group 1 patients were younger (average age 37 vs 51 years, p less than 0.005), had less structural heart disease (2 of 26 vs 25 of 29 patients, p less than 0.005) and had a better prognosis (no deaths) after an average follow-up time of 28 months in comparison with 5 deaths after an average follow-up of 35 months (p less than 0.05). Induction of VT was possible using isoproterenol infusion in 14 of 20 group 1 patients, but no VT could be induced in 9 group 2 patients (p less than 0.05). Exercise stress testing induced VT in 11 of 21 group 1 patients and 2 of 9 group 2 patients (p greater than 0.05). Programmed electrical stimulation failed to induce VT in 9 group 1 patients, but did induce it in 15 of 20 group 2 patients (p less than 0.005). Successful therapy in group 1 patients was achieved by beta blockers alone (7 patients), beta blockers plus type 1A antiarrhythmic drugs (9 patients), procainamide alone (2 patients), sotalol (3 patients) and amiodarone (2 patients). Three patients were not treated.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of Junctional Rhythm After Atrioventricular Node Ablation

BACKGROUND Catheter ablation of the atrioventricular (AV) node with radiofrequency current (RFC) is associated with the short-term onset of a junctional escape rhythm (JER) in nearly all patients. However, the origin of the JER and short-term thermal effects of RFC on this junctional pacemaker activity are ill defined. METHODS AND RESULTS Short-term and noninvasive long-term follow-up studies were performed to examine the electrophysiological characteristics of the underlying JER in 45 patients who had undergone AV nodal ablation with RFC. Baseline characteristics and responses to overdrive ventricular pacing and intravenous atropine followed by an incremental isoproterenol infusion were determined. Short- and long-term responses were compared. HV intervals before and after ablation were 49 +/- 9 and 48 +/- 9 milliseconds, respectively (P = NS). Follow-up was 11 +/- 8.3 months. JER cycle length was 1526 +/- 298 milliseconds in the short-term setting and was present in 44 patients (98%) in the long-term setting, measuring 1426 +/- 223 milliseconds (P < .005). Junctional recovery times increased exponentially as overdrive pacing rates increased-there was no difference between short-term and long-term responses. Drug responses within each study were all significant when compared with baseline. However, there was no significant difference between short- and long-term responses, except at the highest dose of isoproterenol. Intravenous atropine (1 mg) caused an 8.6 +/- 9.3% decrease in JER cycle length in the short-term setting compared with a 7.6 +/- 7.3% decrease in the long-term setting. The decreases in JER cycle length with isoproterenol infusion (short-term versus long-term) were 10.1 +/- 9.6% versus 9.6 +/- 7.4% with 1 microgram/min, 15.8 +/- 11.7% versus 17.4 +/- 8.5% with 2 micrograms/min, 17.9 +/- 11.2% versus 21.4 +/- 9.1% with 3 micrograms/min (all P = NS), and 20.6 +/- 12.1% versus 24.8 +/- 9.1% with 4 micrograms/min (P < .01). CONCLUSIONS Radiofrequency ablation of the AV node is associated with development of a JER that is stable in the long-term setting. The lack of change in HV interval after ablation locates the junctional pacemaker proximal to the central fibrous body. The pattern of drug responses suggests an origin within the proximal His bundle at its junction with the AV node rather than the AV node itself. The overall similarity between short- and long-term characteristics of junctional pacemaker activity mitigates against any reversible thermal effects of RFC on this pacemaker focus.

Prognostic impact of inappropriate defibrillator shocks in a population cohort

Background There is a relative paucity of data linking inappropriate implantable cardioverter-defibrillator (ICD) shocks to adverse clinical outcomes. Objective To examine the association between inappropriate ICD shocks and mortality or heart transplantation in a large population cohort. Design, setting, patients A cohort study which included all subjects who underwent ICD implantation between 1998 and 2008 and were followed up at our institution. Main outcome measures Multivariable Cox regression analyses were conducted to investigate the effect of inappropriate shocks on the risk of death and heart transplantation. Appropriate and inappropriate ICD therapies were modelled as time-dependent covariates. Results A total of 1698 patients were included. During a median follow-up of 30 months, there were 246 (14.5%) deaths and 42 (2.5%) heart transplants. The incidence of inappropriate shocks was 10% at 1 year and 14% at 2 years. In the adjusted model, inappropriate shocks were not associated with death or transplantation (HR=0.97, 95% CI 0.70 to 1.36, p value=0.873). In contrast, appropriate shocks were associated with adverse outcomes (HR=3.11, 95% CI 2.41 to 4.02, p value<0.001). The lack of association between inappropriate shocks and outcomes persisted for those with severely impaired left ventricular function (ejection fraction <30%) and for those receiving multiple inappropriate treatments. Conclusions In this study, we observed no association between inappropriate ICD shocks and increased mortality or heart transplantation, even among those with severely impaired cardiac function. These findings question whether inappropriate ICD shocks lead to adverse outcomes.

Initial experience with a co-radial bipolar pacing lead.

A new type of endocardial bipolar pacing lead has been designed to overcome the potential drawbacks of the conventional coaxial bipolar pacing had. We prospectively evaluated the new co‐radial bipolar pacing leads (Intermedics Thin Line), which are thinner (5 Fr vs 6—8 Fr) than standard coaxial bipolar leads. X‐ray visibility and lead handling were subjectively assessed (excellent, good, adequate, or poor) at implant; lead impedance, sensitivity threshold, and pacing threshold were measured at implant, then at 1, 3. 6, 12, and 18 months. The results were as follows: 103 patients (51 M; age 63.8 ± 17.4 years) received 71 atrial (A) and 89 ventricular (V) leads. X‐ray visibility was excellent in 59/103; good in 23/103; adequate in 11/103; and poor in 10/103. Overall handling was excellent in 56/71 A and 69/89 V; good in 11/71 A and 18/89 V; adequate in 3/71 A and 1/89 V; poor in 1/71 A and 1/89 V. There were two perioperative complications. At implant: impedance in A and V were 370.1 ± 74.7 and 501.5 ± 124.4 Ω, sensing thresholds in A and V were 3.0 ± 1.5 and 9.9 ± 5.0 mV, pacing thresholds at 0.45 ms in A and V were 0.59 ± 0.21 and 0.41 ± 0.15 volt, respectively. At 1, 3, 6. 12, and 18 months of follow‐up: no pacing lead related complications were reported; pacing lead characteristics remained outstanding and stable. This new lead appears to have significant clinical advantages over the conventional coaxial bipolar pacing lead. Long‐term follow‐up is required to confirm its reliability and chronic performance characteristics.

Long-Term Survival Following Radiofrequency Catheter Ablation of Atrioventricular Junction for Atrial Fibrillation: Clinical and Ablation Determinants of Mortality

AbstractBackground: For patients with drug-refractory atrial fibrillation, radiofrequency catheter ablation of the atrioventricular junction and pacemaker implantation is a nonpharmacologic option routinely used nowadays. Few data are available on the long-term survival following the procedure or on evaluation of the risk factors for death in a large study cohort. Methods: The patient population included 359 subjects undergoing atrioventricular junction ablation and pacemaker insertion. Fourteen clinical and 9 ablation variables were collected at baseline. During a mean following-up of 40.8±25.6 months, 46 patients died. Survival probability was estimated by the Kaplan-Meier methods. Multivariate Cox proportional hazards regression analysis was applied to define predictors of death. Results: Mean age was 64.6±10.6 years with 203 male (57.7%). Actuarial survival probability for the total patients was 0.953 and 0.827 at 1 and 5 year. Four clinical variables, but no ablation variables, were found to be independent predictors of death: age ≥65 year (hazard ratio [HR], 1.92; 95% confidence interval [CI], 1.00–3.69), the presence of heart failure (HR, 3.83; 95% CI, 1.87–7.86), coexisting diabetes (HR, 2.91; 95% CI, 1.47–5.77), and the value of fractional shortening ≤20% (HR, 5.79, 95% CI, 3.00–11.18). There were 20 deaths in 28 patients with ≥3 risk factors and 4 deaths in 115 patients with no risk factor. Conclusion: The risk of death in patients undergoing ablation and pacing can be identified by readily available clinical variables. Patients with multiple risk factors are associated with an increasing mortality.

Propafenone-mexiletine combination for the treatment of sustained ventricular tachycardia

OBJECTIVES The purpose of this study was to explore the efficacy of combined therapy with propafenone and mexiletine for control of sustained ventricular tachycardia. BACKGROUND Combination antiarrhythmic drug therapy may enhance efficacy and lead to control of ventricular arrhythmias in some patients. Few reports have studied the combination of class IB and class IC drugs. Thus, this study was designed to investigate a combination of mexiletine and propafenone in patients with refractory ventricular tachycardia. METHODS Sixteen patients with sustained ventricular tachycardia had their clinical arrhythmia induced by programmed stimulation. Procainamide and propafenone alone failed to prevent reinduction of tachycardia in all. Mexiletine was subsequently added to propafenone and programmed stimulation was repeated. RESULTS With combination therapy ventricular tachycardia was noninducible in three patients (19%). A fourth who had presented with polymorphic ventricular tachycardia had slow bundle branch reentry (cycle length 500 ms) induced. In the other 12, tachycardia cycle length increased from 262 +/- 60 ms at baseline to 350 +/- 82 ms with propafenone and to 390 +/- 80 ms with propafenone plus mexiletine (p less than 0.0001 compared with baseline). Hemodynamic deterioration requiring defibrillation occurred in six patients at baseline study, in five taking propafenone and in two taking both drugs. CONCLUSIONS The combination of propafenone and mexiletine is effective in suppressing the induction of ventricular tachycardia in some patients refractory to procainamide and propafenone alone. In those in whom ventricular tachycardia could still be induced, the rate was slower and hemodynamically tolerated.

Cerebral oxygenation during defibrillator threshold testing of implantable cardioverter defibrillators.

Background: The induction of ventricular fibrillation (VF) during defibrillator threshold testing of implantable cardioverter defibrillators (ICD) provokes global cerebral hypoperfusion and impaired oxygen delivery. Limited data are available on the neurophysiological effects of defibrillator threshold testing. Near infrared spectroscopy (NIRS) can noninvasively measure changes in specific chromophores, which reflect cerebral oxygenation at the intravascular and mitochondrial levels. We performed a prospective trial using NIRS to analyze cerebral cortical oxygenation during defibrillator threshold testing.

Pacing in right ventricular dysplasia after disconnection surgery.

Pacing in Right Ventricular Dysplasia. This report describes a 33‐year‐old patient with arrhythmogenic right ventricular (RV) dysplasia who had a dual chamber pacemaker implanted at age 23 years for drug‐induced bradycardia. Pacing was continued after right ventricular free‐wall disconnection (RVFVVD) at age 24 years. Her pacemaker was not replaced after battery depletion 7 years later. She presented the following year in severe right‐sided heart failure. Her old pacemaker generator was replaced. This was followed by rapid resolution of her clinical failure and return to a full, active, physical lifestyle. This observation suggests the potential benefit of dual chamber pacing in patients with RV dysplasia after RVFWD.