Using the 12-Lead ECG to Localize the Origin of Atrial and Ventricular Tachycardias: Part 2—Ventricular Tachycardia

Monomorphic ventricular tachycardia (VT) can arise from multiple different ventricular locations in the context of several different underlying myocardial substrates. Despite this variability, the surface 12-lead electrocardiograph (ECG) has proven to be a robust and reproducible initial mapping tool that can provide useful information in localizing the origin of both focal and reentrant forms of VT. The second part of this review series will look at the use of the ECG in mapping the various forms of VT encountered in clinical practice.     

Electrophysiological Studies on Cardiac Catheter Ablation

Clinical and animal investigations have pointed out that high energy electrical shocks are associated with the development of cardiac arrhythmias and with variable success in permanent ablation. The effects of electrode configuration and location on the size of the recorded electrogram was investigated to help explain variable catheter ablation results. We analyzed the cellular effects of catheter ablation shocks and found depression of resting potential, action potential amplitude, dV/dt and action potential duration. The most severe effects were noted with high current densities in tissues located between the cathode and anode. Damage was worse nearest the cathode. Similar cellular studies were completed using argon laser photoablation. Again, there was a decrease in resting potential, action potential amplitude and dV/dt. Laser energy led to a more focal region of myocardium void of action potentials and the border zone of injury was smaller. We also investigated the effects of lower energy shocks)1 to 10 joule) on cardiac tissues. Using microelectrodes, we observed that the membrane potential can "hang up" at the depolarized levels for varying periods of time and that conduction is altered during this membrane "hang-up" period. The duration and membrane hang-up level correlated with shock intensity and shock duration. Sequential shocks resulted in additive membrane "hang-up". We believe that membrane hang-up may be associated with brief arrhythmias observed following catheter ablation since conduction, refractoriness and excitability are all altered.     

Cerebellar Stimulation for Spastic Cerebral Palsy; Preliminary Report; On-going Double Blind Study

To date, June 1, 1986, 33 spastic cerebral palsy (CP) patients have taken part in a double blind study testing the safety and efficacy of chronic cerebellar stimulation (CCS) for reduction of spasticity and improvement in function. Seven U.S. surgical centers involving ten neurosurgeons have implanted the Neurolith 601 cerebellar stimulator supplied by Pacesetter Systems Inc. (Sylmar, CA). A pilot study was run with three patients at Stanford University (Stanford, CA) using taped-on real (strong) and dummy (weak) magnets to control the ON-OFF status. Following the pilot study, a magnetically controllable switch was placed in line between the Neurolith stimulator and the cerebellar lead to allow more reliable switching sequences for the study. The test battery included joint angle measurements (passive and active), motor performance testing, reaction time, hand dynamometry, grooved peg board placement, hand/foot tapping, and rotary pursuit testing. Testing only was done at presurgery. Testing and ON-OFF switching was performed following recovery from surgery and at one, two, and four months. After four months, the switch was left turned ON. Of the 30 patients using the implanted switch, 11 were dropped from the study and seven are still in progress. Of the 11 dropped from the study, four were due to switch problems and three were due to double blind protocol violations, i.e., the participants discovered the stimulus status. The remaining four were removed because of a broken lead, infection, or unrelated medical problems, or refusal to participate after implant. A preliminary analysis indicated that three-quarters of the patients have a demonstrable quantitative improvement during the time the stimulation was "ON." Three patients showed no significant change.     

Outcomes in Patients Requiring Cardioversion Following Catheter Ablation of Atrial Fibrillation

Outcomes of Cardioversion Post AF Ablation.   Introduction: Early recurrence of atrial tachyarrhythmias is commonly noted after catheter ablation of atrial fibrillation (AF). The long-term outcomes of patients who require cardioversion for persistent AF after AF ablation is not known. This study reports the outcomes of patients who underwent cardioversion for persistent AF or atrial flutter following an AF ablation procedure.
Methods: The patient population comprised 55 patients (mean age 58 ± 10 years, 35% paroxysmal) who underwent catheter ablation of AF and subsequently required electrical cardioversion for persistent AF (45 patients) or atrial flutter (10 patients). Cardioversion was defined as early (within 90 days of the ablation procedure) or late (between 90 and 180 days following ablation).
Results: The mean follow-up duration was 15 ± 8 months. Forty-six of the 55 patients (84%) patients experienced recurrence during follow-up. The average time to recurrence after cardioversion was 37 days. Of the 55 patients, 8 (15%) patients had a complete success, 11 (20%) patients had a partial success and 36 patients (65%) had a failed outcome. Seven of the 43 patients (16%) who underwent early cardioversion had a complete success as opposed to one of 12 patients (8%) who underwent late cardioversion (P = 0.49).
Conclusions: This study shows that >80% of patients who undergo cardioversion for persistent AF or atrial flutter after AF ablation have recurrence. The timing of cardioversion did not affect the outcome. These findings allow clinicians to provide realistic expectations to patients regarding the long-term outcome and/or requirement for a second ablation procedure. (J Cardiovasc Electrophysiol, Vol. 21, pp. 27–32, January 2010)     

A Prospective Study Evaluating the Role of Obesity and Obstructive Sleep Apnea for Outcomes After Catheter Ablation of Atrial Fibrillation

Effect of Obesity and OSA on Outcomes Post AF Ablation . Background: Obesity and obstructive sleep apnea (OSA) have a strong association with atrial fibrillation (AF). The purpose of this study was to prospectively determine the effects of obesity, assessed by the body mass index (BMI) and OSA on the efficacy of catheter ablation of AF. Methods: The patient population consisted of 109 patients (mean age: 60 ± 10 years, 79% male, 67% paroxysmal, mean BMI 28 ± 5 kg/m²) who underwent catheter ablation of AF. Based on BMI, patients were classified as normal (<25 kg/m²), overweight (≥25 and <30 kg/m²), or obese (≥30 kg/m²). OSA was assessed by the Berlin questionnaire. Clinical success was defined as at least 90% reduction in AF burden after 3‐month blanking period. Mean duration of follow‐up was 11 ± 4 months. Results: Of the 75 patients with clinical success, 25 (33%) had normal BMI, 29 (39%) were overweight, and 21 (28%) were obese. Among the 34 patients with failed outcome, 5 (15%) had normal BMI, 14 (41%) were overweight, and 15 (44%) were obese (P = 0.04). Twenty‐eight of the 48 patients with OSA (58%) had clinical success as opposed to 47 of the 61 patients (77%) without OSA (P = 0.036). On multivariate analysis, only BMI emerged as an independent predictor of procedural failure ((OR 1.11, CI: 1.00–1.21, P = 0.03). Conclusions: The results of this prospective study show that obesity, a modifiable risk factor, is an independent predictor of procedural failure after catheter ablation of AF. Whether treating obesity may improve the results of catheter ablation of AF warrants further investigation. (J Cardiovasc Electrophysiol, Vol. 21, pp. 521‐525, May 2010)     

Vagal Paroxysmal Atrial Fibrillation: Prevalence and Ablation Outcome in Patients Without Structural Heart Disease

Prevalence of Vagal Paroxysmal Atrial Fibrillation . Introduction: The prevalence of vagal and adrenergic atrial fibrillation (AF) and the success rate of pulmonary vein isolation (PVI) are not well defined. We investigated the prevalence of vagal and adrenergic AF and the ablation success rate of antral pulmonary vein isolation (APVI) in patients with these triggers compared with patients with random AF. Methods and Results: Two hundred and nine consecutive patients underwent APVI due to symptomatic drug refractory paroxysmal AF. Patients were diagnosed as vagal or adrenergic AF if >90% of AF episodes were related to vagal or adrenergic triggers; otherwise, a diagnosis of random AF was made. Clinical, electrocardiogram (ECG), and Holter follow‐up was every 3 months in the first year and every 6 months afterward and for symptoms. Of 209 patients, 57 (27%) had vagal AF, 14 (7%) adrenergic AF, and 138 (66%) random AF. Vagal triggers were sleep (96.4%), postprandial (96.4%), late post‐exercise (51%), cold stimulus (20%), coughing (7%), and swallowing (2%). At APVI, 94.3% of patients had isolation of all veins. Twenty‐five (12%) patients had a second APVI. At a follow‐up of 21 ± 15 months, the percentage of patients free of AF was 75% in the vagal group, 86% in the adrenergic group, and 82% for random AF (P = 0.51). Conclusion: In patients with PAF and no structural heart disease referred for APVI, vagal AF is present in approximately one quarter. APVI is equally effective in patients with vagal AF as in adrenergic and random AF. (J Cardiovasc Electrophysiol, Vol. 21, pp. 489‐493, May 2010)     

Transcranial Doppler Quantification of Residual Shunt after Percutaneous Patent Foramen Ovale Closure. Comparison of Two Devices

Background: Recurrent paradoxical embolism after catheter‐based closure of right‐to‐left shunt (RLS) can be related to residual RLS. To improve closure success, we need a better understanding of the anatomic and device‐related factors associated with closure efficacy. Methods: Patients with cryptogenic neurologic events and severe RLS (Valsalva Spencer transcranial Doppler [TCD] grade 5/5+) who underwent patent foramen ovale (PFO) closure by either central pin (Amplatzer^® PFO [A‐PFO]) or central occluding (Amplatzer^® SO [A‐SO]) devices were evaluated for residual shunt by quantitative TCD evaluation at 3 months. The findings were correlated with atrial septal aneurysm (ASA), device type, and device size. Results: We closed 628 consecutive patients with either the A‐PFO (n = 327) or A‐SO (n = 301) device. The frequency of large defects, small defects, and ASA was 12%, 88%, and 44% of cases, respectively. Severe residual shunt was detected in 13% of A‐PFO and 7% of A‐SO recipients (P = 0.005). This difference was attributable to a much higher frequency of severe residual shunt among patients with large defects closed with the A‐PFO compared to the A‐SO device (12 out of 29 [41%] vs. 3 out of 42 [7%], respectively; P < 0.001). There was no significant difference in device failure frequency for small defects. The presence of ASA increased the frequency of severe residual shunt compared to those without this feature (36 out of 275 [13%] vs. 28 out of 353 [8%], respectively; P = 0.046) but did not influence device‐related differences. Conclusions: (1) Both noncentering and central occluding closure devices effectively reduce RLS after PFO closure. (2) Large PFO defects with or without ASA have lower residual shunt grades at 3 months when closed by central occluding devices. (J Interven Cardiol 2010;23:575–580)