David M. Fitzgerald

Radiofrequency catheter ablation for management of symptomatic ventricular ectopic activity

OBJECTIVES This study assessed the useful role of intracardiac mapping and radiofrequency catheter ablation in eliminating drug-refractory monomorphic ventricular ectopic beats in severely symptomatic patients. BACKGROUND Ventricular ectopic activity is commonly encountered in clinical practice. Usually, it is not associated with life-threatening consequences in the absence of significant structural heart disease. However, frequent ventricular ectopic beats can be extremely symptomatic and even incapacitating in some patients. Currently, reassurance and pharmacologic therapy are the mainstays of treatment. There has been little information on the use of catheter ablation in such patients. METHODS Ten patients with frequent and severely symptomatic monomorphic ventricular ectopic beats were selected from three tertiary care centers. The mean frequency +/- SD of ventricular ectopic activity was 1,065 +/- 631 beats/h (range 280 to 2,094) as documented by baseline 24-h ambulatory electrocardiographic (ECG) monitoring. No other spontaneous arrhythmias were documented. These patients had previously been unable to tolerate or had been unsuccessfully treated with a mean of 5 +/- 3 antiarrhythmic drugs. The site of origin of ventricular ectopic activity was accurately mapped by using earliest endocardial activation time during ectopic activity or pace mapping, or both. RESULTS During electrophysiologic study, no patient had inducible ventricular tachycardia. The ectopic focus was located in the right ventricular outflow tract in nine patients and in the left ventricular posteroseptal region in one patient. Frequent ventricular ectopic beats were successfully eliminated by catheter-delivered radiofrequency energy in all 10 patients. The mean number of radiofrequency applications was 2.6 +/- 1.3 (range 1 to 5). No complications were encountered. During a mean follow-up period of 10 +/- 4 months, no patient had a recurrence of symptomatic ectopic activity, and 24-h ambulatory ECG monitoring showed that the frequency of ventricular ectopic activity was 0 beat/h in seven patients, 1 beat/h in two patients and 2 beats/h in one patient. CONCLUSIONS Radiofrequency catheter ablation can be successfully used to eliminate monomorphic ventricular ectopic activity. It may therefore be a reasonable alternative for the treatment of severely symptomatic, drug-resistant monomorphic ventricular ectopic activity in patients without significant structural heart disease.

ICD Waveform Optimization: A Randomized, Prospective, Pair-Sampled Multicenter Study

The theoretical tissue model‐based estimates of phase 1 and phase 2 duration of biphasic waveforms are considerably shorter than the pulse widths currently used in ICDs with standard tilt. This study used a tissue resistance/capacitance (RC) model to identify optimal biphasic pulse widths. By paired step‐down defibrillation threshold (DFT) testing, the efficacy of standard versus “tuned” biphasic waveforms was evaluated in 91 patients. Standard waveforms consisted of a phase 1 set to 65% tilt and phase 2 = phase 1. The tuned waveform was based on an RC model of membrane characteristics with a time constant of 3.5 ms. The optimal phase 1 truncation point is at the peak of membrane response. The optimal phase 2 duration ends with a membrane response near or just below 0. In paired analysis, no significant differences were found in DFT or impedance between standard and tuned waveforms. In patients with DFTs > 400 V, the tuned waveform lowered the DFT by an average of 38 V (P < 0.05). Multivariate analyses showed a significant inverse relationship between DFT and impedance (P < 0.001). As impedance increased, the tuned waveform was associated with DFTs comparable to the standard waveform with shorter pulse duration and lower delivered energy. No single tilt value allowing an easy calculation of delivered energy was related to ICD waveform efficacy. The use of ICDs with tuned optimal pulse durations offer a greater flexibility of choice for patients with high DFTs.

ACC/AHA/ACR/ASE/ASNC/HRS/NASCI/RSNA/SAIP/SCAI/ SCCT/SCMR/SIR 2008 Key Data Elements and Definitions for Cardiac Imaging

The American College of Cardiology (ACC) and the American Heart Association (AHA) support their members’ goal to improve the prevention and care of cardiovascular diseases through professional education, research, development of guidelines and standards, and by fostering policy that supports optimal patient outcomes. The ACC and AHA recognize the importance of the use of clinical data standards for patient management, to assess outcomes, and conduct research, and the importance of defining the processes and outcomes of clinical care, whether in randomized trials, observational studies, registries, or quality improvement initiatives. Hence, clinical data standards strive to define and standardize data relevant to clinical topics in cardiology, with the primary goal of assisting data collection by providing a platform …

Defibrillator Twiddler's Syndrome Causing Device Failure in a Subpectoral Transvenous System

Twiddlers syndrome is well described as a complication of cardiac pacing. Defibrillator twiddlers syndrome has been recently reported with abdominal implantations of epicardial and transvenous defibrillator systems. We report a case of a patient with a transvenous defihrillator system implanted with the pulse generator placed in the Subpectoral plane. The patient developed twiddlers syndrome, which resulted in retraction of both leads. This caused inappropriate shocks due to sensing both the atriai and ventricular electrograms. While the Subpectoral position leaves the generator deeper and more difficult for the patient to access, it may not lessen the chance of twiddlers syndrome. It is possible that the Subpectoral position may actually predispose the patient to this malady.

P wave morphology during atrial pacing along the atrioventricular ring. ECG localization of the site of origin of retrograde atrial activation.

P wave morphology during atrial pacing along the atrioventricular (AV) ring was evaluated to develop electrocardiographic (ECG) criteria for identifying the site of origin of the atrial activation wave during reentrant supraventricular tachycardia. Because P wave morphology changes as the pattern of atrial activation changes, the P wave should show characteristic morphologies during reentrant supraventricular tachycardia with use of either accessory AV pathways or the AV node for retrograde atrial activation. In 14 patients, 12-lead ECGs were recorded during bipolar atrial pacing at sites in the coronary sinus vein (along the mitral annulus) and along the atrial endocardium of the tricuspid annulus. P wave morphology was graded for each lead at each site. Sensitivity, specificity, and predictive value of ECG criteria for left versus right and anterior versus posterior atrial pacing sites were evaluated. Data were obtained from 14 sites along the AV ring, including 71 recordings at 6 sites in the coronary sinus vein and 94 recordings at 8 sites along the tricuspid annulus. These recordings were further divided into 54 anterior sites and 80 posterior sites, as well as 62 recordings along the right free wall and 32 recordings along the right atrial septum. The predictive value of a positive P wave in lead I indicating right atrial site of origin was 98.9%, and that for a negative or isoelectric P wave in lead I indicating a left atrial site of origin was 94.6%. Negative P wave in leads II, III, and aVF indicated a posterior site of origin, with a predictive value of 91.2%. The predictive value of a negative or isoelectric P wave in lead V1 indicating a right atrial free wall site was 87.5%. Thus, P wave morphology can be used to localize the site of origin of the atrial depolarization wave to a region along the AV ring.

Effects of atrial fibrillation and atrial flutter on the signal-averaged electrocardiogram.

In conclusion, atrial flutter can create significant errors in the automated time-domain analysis of the SAECG that are only apparent when the study is repeated in sinus rhythm, thus lowering the predictive accuracy of the technique in patients with atrial flutter. Atrial fibrillation rarely creates problems with time-domain analysis of the SAECG. These findings suggest that, unless the performance of a specific signal-averaging device has been evaluated in patients with atrial flutter and found to have acceptable error rates, patients with atrial flutter should not have SAECGs performed for postinfarction risk assessment.

False‐Positive Behavior with the dP/dt Sensing Pacemaker: A Rare Complication of a Physiological Sensor

As with “nonphysiological” devices, sensors that directly measure physiological variables bave the potential to measure unexpected signals and for the physiological parameter being measured to respond in an unexpected manner. We present tbe case of a dP/dt sensing pacing system that functioned normally for 2 months and then developed upper rate behavior due to the sensing of a high frequency artifact on the pressure recording. Our case and others cited reinforce the need for future physiological rate responsive pacemakers to incorporate a second sensor to provide for backup rate response in cases of inappropriate rate response.

Radiofrequency Ablation Using a Porous Tip Electrode

Radiofrequency current was initially adapted for intracardiac catheter ablation using conventional diagnostic electrode catheters with a tip electrode 2 millimeters in length through which energy was delivered.1 However, power output was limited due to sudden increases in system impedance associated with the development of coagulated blood on the ablation electrode.2,3 In vitro studies of the thermodynamics of radiofrequency lesioning demonstrated that this sudden increase in impedance was related to local tissue overheating at the electrode-tissue interface and associated with surface tissue temperatures greater than 100 °C.4 This increase in surface tissue temperature to the boiling point of water could result in coagulation of blood. With increase in the size and surface area of the ablation electrode, sudden elevations of impedance were seen less frequently allowing higher power delivery to the tissue.5 Increasing the ablation electrode length from 2 to 4 millimeters markedly improved the efficacy and efficiency of the technique.6 However, sudden increases in impedance and coagulum formation were still a limiting factor with use of higher power outputs. Tip thermometry was developed to try and limit impedance rises and coagulum formation while maximizing energy delivery.7 By measuring tip temperature either inside the electrode or at its tip, power could be regulated to maintain temperature at a level that could result in tissue injury but not allow boiling of tissue water or blood.