Idiopathic premature ventricular contractions arising from the intraventricular septum adjacent to the his bundle.

A 57-year-old woman with idiopathic premature ventricular contractions (PVCs) exhibiting a left bundle branch block and left inferior axis QRS morphology underwent electrophysiological testing. Mapping revealed that the earliest ventricular activation times during the PVCs recorded on either side of the interventricular septum were the same and no excellent pace maps were reproduced at these sites. Successful radiofrequency catheter ablation was achieved in the right ventricular septum adjacent to the recording site of the His bundle electrogram. These findings suggested that the origin of this PVC was located in the intraventricular septum rather than the endocardial surface.

Comparison of the temperature profile and pathological effect at unipolar, bipolar and phased radiofrequency current configurations.

With a multi-electrode catheter, phased radiofrequency (RF) delivers current between each electrode and a backplate as well as between adjacent electrodes. This study compared the tissue heating and lesion dimensions created by phased and standard RF. Ablation was performed on the in vivo thigh muscles in 5 pigs. Six lesions were created on each thigh muscle using phase angle 0 degrees RF, 127 degrees RF, 180 degrees RF with and without a backplate, and standard RF in bipolar and sequential unipolar configurations. Two plunge needles, each with 6 thermocouples 1 mm apart, were inserted into the tissue with one needle beside an electrode and the other midway between electrodes for tissue temperature measurement. The 0 degrees RF created lower tissue temperatures and smaller lesions between electrodes than those beside electrode. With 127 degrees and 180 degrees RF, tissue temperature and lesion dimensions between electrodes were similar to beside electrode, while the 127 degrees RF created higher tissue temperature and deeper lesions than 180 degrees RF (both with and without a backplate) at both sites. Standard RF bipolar ablation created similar tissue temperatures and lesion depths at both sites, but required greater power than the 127 degrees RF. Standard RF sequential unipolar ablation created only a slight temperature increase and no lesions between electrodes 3 and 4. As judged by tissue temperature, lesion depth and uniformity, and RF power requirement, 127 degrees RF may be a better energy configuration for linear ablation than the other RF modalities tested.

Clinical validation of new pacing-sensing configurations for atrial automatic capture verification in pacemakers.

INTRODUCTION: This study evaluated an atrial automatic capture verification scheme based on atrial evoked response (AER). Atrial pacing was between Atip and Can (Atip-Can) using different coupling capacitances (CCs). Independent pairs of sensing electrodes between Aring and Vtip (Aring-Vtip) or between Aring and a separate indifferent electrode (Aring-Indiff) were used to reduce pacing-induced afterpotentials. METHODS AND RESULTS: A custom-made external pacing system was used to perform automatic step-up and step-down pacing (0.1 to 7.1 V at 0.5 msec, step size of 0.1 V) using different CCs (2 or 15 microF). Intracardiac signals from Aring-Indiff and Aring-Vtip were independently recorded and analyzed both in real time and off-line to detect AER. Every paced beat also was visually inspected and compared with surface ECG to verify the captures. With the intracardiac signals properly filtered, AER detection was based on the signal within a window of 12 to 65 msec after the stimulus. Data from 27 patients (4 chronic and 23 acute implantations; age 65.6+/-13.9 years) were analyzed. Bipolar atrial lead measurements using a standard pacing system analyzer were as follows (mean +/- SD): impedance 695+/-227 ohms, P wave amplitude 4.2+/-2.3 mV, slew rate 1.1+/-0.9 V/sec, and pacing threshold at 0.5 msec 1.0+/-0.5 V. The results with CC = 2 microF showed that of 9,500 atrial paced beats, correct capture verification rates were 99.8% (Aring-Indiff) and 99.4% (Aring-Vtip). Similar results were achieved with CC = 15 microF (99.7% and 99.5%, respectively). CONCLUSION: AER can be reliably detected using independent pacing (Atip-Can) and sensing (Aring-Vtip or Aring-Indiff) electrodes. Therefore, atrial automatic capture verification by AER detection is feasible.

Reduction of pacing output coupling capacitance for sensing the evoked response.

Sensing of the intracardiac evoked response (ER) after a pacing stimulus has been used in implantable pacemakers for automatic verification of capture. Reliable detection of ER is hampered by large residual afterpotentials associated with pacing stimuli. This led to the development of various technological solutions, like the use of triphasic pacing pulses and low polarizing electrode systems. This study investigated the effect of reducing the coupling capacitance (CC) in the pacemaker output circuitry on the magnitude of afterpotential, and the ability to automate detection of ventricular evoked response. A CC of 2.2 microF and four different blanking and recharge time settings were clinically tested to evaluate its impact on sensing of the ventricular ER and pacing threshold. Using an automatic step-down threshold algorithm, 54 consecutive patients, aged 70 +/- 10 years with acutely (n = 27) or chronically (n = 27) implanted ventricular pacing leads were enrolled for measurement testing. Routine measurements, using a standard pacing system analyzer (PSA), were (mean +/- SD) impedance 569 +/- 155 omega, R wave amplitude baseline to peak 9.8 +/- 3.7 mV and threshold 0.9 +/- 0.7 V at 0.4-ms pulse width. This new capture verification scheme, based on a CC of 2.2 microF and recharge/blanking timing setting of 10/12 ms, was successful in 52 patients which is equivalent to a success rate of 96%. In a subgroup of 26 patients implanted with bipolar ventricular leads (10 chronic, 16 acute), data were collected in unipolar (UP) and bipolar (BP) pace/sense configurations. Also, ER signals were recorded with two different band-pass filters: a wider band (WB) of 6-250 Hz and a conventional narrow band (NB) of 20-100 Hz. WB sensing from UP lead configuration yielded statistically significant larger signal to artifact ratios (SAR) than the other settings (P < 0.01). A dedicated unipolar ER sensing configuration using a small output capacitor and a wider band-pass filter enables adequate automatic capture verification, without any restrictions on pacing lead models or pacing/sensing configurations.

Catheter ablation of atrial fibrillation: challenges and promise.

Although atrial fibrillation is the most common sustained arrhythmia that requires medical attention, it remains a challenge to treat. Nevertheless, considerable progress has been made toward developing curative, catheter-based treatments for selected patients with atrial fibrillation. The most significant clinical observation during electrophysiologic testing in patients with atrial fibrillation has been a recognition of the importance of the pulmonary veins for the initiation of this arrhythmia. In addition to being the most common site of arrhythmogenic foci that trigger the onset of atrial fibrillation, the unique electrophysiologic characteristics of the pulmonary veins may serve to perpetuate established atrial fibrillation. Because of the very short-duration refractory periods that are measured within the pulmonary veins, these structures may serve as a site of high frequency activation due to reentrant activation with small wavelengths. Catheter ablation strategies that are designed to ablate the site of triggering foci with the pulmonary veins have been very successful in selected patients with paroxysmal atrial fibrillation, although the risk of recurrent arrhythmias remains relatively high. In addition, ablation strategies that are designed to electrically isolate the pulmonary veins from the bulk of the left atrium are likely to lead to improvements in the long-term outcome of ablation. For patients with permanent atrial fibrillation, considerable progress has been made in the restoration of sinus rhythm by linear ablation strategies in the left atrium. It is likely that a comprehensive nonpharmacologic treatment for atrial fibrillation will incorporate the lessons learned from each of these approaches and lead to a genuine cure of this vexing arrhythmia.

Tachycardia-related cardiomyopathy: a common cause of ventricular dysfunction in patients with atrial fibrillation referred for atrioventricular ablation.

OBJECTIVE: To determine the frequency of tachycardia-related cardiomyopathy in patients with atrial fibrillation and systolic dysfunction referred for atrioventricular node ablation. PATIENTS AND METHODS: This prospective multicenter cohort study was conducted at 16 tertiary care centers. The ejection fraction was measured before and 3 and 12 months after atrioventricular node ablation. Patients with reduced systolic function (ejection fraction < or = 45%) before atrioventricular ablation were included in this study. Patients whose ejection fraction increased by at least 15 percentage points and to higher than 45% were considered to have tachycardia-related cardiomyopathy. RESULTS: Of 63 patients with systolic dysfunction, 48 had at least 1 adequate follow-up echocardiographic study. Sixteen (25%) of the 63 had marked improvement in the ejection fraction (mean +/- SD change, 27 +/- 8 percentage points) to a value higher than 45% after ablation. CONCLUSIONS: Tachycardia-related cardiomyopathy is common in patients with atrial fibrillation and systolic dysfunction referred for atrioventricular node ablation. This diagnosis should be considered in all patients in whom systolic dysfunction occurs subsequent to or concomitant with onset of atrial fibrillation.

Pathological effects of extensive radiofrequency energy applications in the pulmonary veins in dogs.

INTRODUCTION: The long-term complications of catheter ablation within the pulmonary veins are unknown. The development of pulmonary vein stenosis has recently been described after catheter ablation to treat either chronic or paroxysmal atrial fibrillation. The purpose of this study was to examine the pathological and hemodynamic effects of radiofrequency (RF) energy application within the pulmonary veins. METHODS AND RESULTS: Right heart and transseptal catheterization were performed in 9 anesthetized mongrel dogs. The pulmonary vein ostia were cannulated and pulmonary venous pressure was measured before RF energy application in up to 4 separate pulmonary veins. Animals were euthanized at intervals of 2 to 4 weeks (n=3), 6 to 8 weeks (n=3), or 10 to 14 weeks (n=3) after ablation. Repeat catheterization before euthanasia demonstrated statistically significant differences in pulmonary capillary wedge pressure, cardiac output, pulmonary vascular resistance, and systemic vascular resistance (P<0.05) compared with the baseline. Luminal narrowing was observed in 22 of 33 pulmonary veins to which RF energy was applied. Of these, 7 were totally occluded, 7 had severe stenosis, and 8 were only minimally narrowed. Histological examination revealed intimal proliferation with organizing thrombus, necrotic myocardium in various stages of collagen replacement, endovascular contraction, and a proliferation of elastic lamina. CONCLUSIONS: Applications of RF current within the pulmonary veins may result in pulmonary vein narrowing or complete occlusion. These observations should be considered in treatment of arrhythmias originating within the pulmonary veins.

Clinical outcomes after ablation and pacing therapy for atrial fibrillation : a meta-analysis.

BACKGROUND: Radiofrequency ablation of the atrioventricular node and permanent pacing are used for symptomatic relief in patients with medically refractory atrial fibrillation. In this study, meta-analysis was used to clarify clinical outcomes and survival after ablation and pacing therapy using data from the published literature. METHODS AND RESULTS: We used 21 studies with a total of 1181 patients in the meta-analysis. All patients had medically refractory atrial tachyarrhythmias, primarily atrial fibrillation (97%). Nineteen measures of clinical outcome, encompassing quality of life, ventricular function, exercise duration, and healthcare use, were derived from the studies. The meta-analysis demonstrated significant improvement after ablation and pacing therapy in all outcome measures except fractional shortening, which demonstrated a trend toward improvement (P=0.08). Ejection fraction did show significant improvement (P<0.001). The calculated 1-year total and sudden death mortality rates after ablation and pacing therapy were 6.3% and 2.0%, respectively. CONCLUSIONS: Ablation and pacing therapy improves a broad range of clinical outcomes for patients with medically refractory atrial fibrillation. The calculated 1-year mortality rates after this therapy are low and comparable with medical therapy.

Programming of sensor driven pacemakers.

The chronotropic response is the most important means by which cardiac output is increased and oxygen delivery is maintained in response to increased oxygen consumption during exercise or stress. When the chronotropic response is suboptimal or absent, exercise intolerance results. This condition, called chronotropic incompetence can be treated effectively with a sensor-driven rate-responsive pacemaker. The effectiveness of this therapy assumes that the pacemaker is programmed appropriately. This article focuses on the programming of sensor-driven pacemakers and provides additional suggestions for follow-up testing to ensure maximal benefit from these devices.

Electrode impedance: an indicator of electrode-tissue contact and lesion dimensions during linear ablation.

Pre-ablation impedance was evaluated for its ability to detect electrode-tissue contact and allow creation of long uniform linear lesions with a multi-electrode ablation catheter. The study consisted of 2 parts, both of which used the in vivopig thigh muscle model. In part 1, a 7 Fr. multi-electrode catheter was held in 3 electrode-tissue contact conditions: (1) non-contact; (2) light contact with a 30g downward force; and (3) tight contact with a 90g downward force. Impedances were measured in unipolar, modified unipolar and bipolar configurations using a source with frequencies from 100Hz to 500kHz. Compared with non-contact, the impedance increased 35 +/- 22 % with 30g contact pressure and 68 +/- 40% when the contact pressure was increased to 90g across the range of frequencies studied. In part 2, the same catheter was held against the tissue with different forces. Pre-ablation impedance was measured using a 10kHz current. Phased radiofrequency energy was applied to the 5 electrodes simultaneously using 10W power at each electrode for 120s. A total of 32 linear lesions were created. The lesion dimensions correlated with pre-ablation impedance. A unipolar impedance > or = 190 Omega indicates 95% possibility to create a uniform linear lesion of at least 3mm depth with our ablation system. We conclude that pre-ablation impedance may be a useful indicator for predicting electrode-tissue contact and the ability to create a continuous and transmural linear lesion with a multi-electrode catheter.

Risks of spontaneous injury and extraction of an active fixation pacemaker lead: report of the Accufix Multicenter Clinical Study and Worldwide Registry.

BACKGROUND: The Telectronics Accufix pacing leads were recalled in November 1994 after 2 deaths and 2 nonfatal injuries were reported. This multicenter clinical study (MCS) of patients with Accufix leads was designed to determine the rate of spontaneous injury related to the J retention wire and results of lead extraction. METHODS AND RESULTS: The MCS included 2589 patients with Accufix atrial pacing leads that were implanted at or who were followed up at 12 medical centers. Patients underwent cinefluoroscopic imaging of their lead every 6 months. The risk of J retention wire fracture was approximately 5.6%/y at 5 years and 4.7%/y at 10 years after implantation. The annual risk of protrusion was 1.5%. A total of 40 spontaneous injuries were reported to a worldwide registry (WWR) that included data from 34 672 patients (34 892 Accufix leads), including pericardial tamponade (n=19), pericardial effusion (n=5), atrial perforation (n=3), J retention wire embolization (n=4), and death (n=6). The risk of injury was 0.02%/y (95% CI, 0.0025 to 0. 072) in the MCS and 0.048%/y (95% CI, 0.035 to 0.067) in the WWR. A total of 5299 leads (13%) have been extracted worldwide. After recall in the WWR, fatal extraction complications occurred in 0.4% of intravascular procedures (16 of 4023), with life-threatening complications in 0.5% (n=21). Extraction complications increased with implant duration, female sex, and J retention wire protrusion. CONCLUSIONS: Accufix pacing leads pose a low, ongoing risk of injury. Extraction is associated with substantially higher risks, and a conservative management approach is indicated for most patients.

High-resolution mapping and histologic examination of long radiofrequency lesions in canine atria.

INTRODUCTION: Catheter ablation may prevent conduction of multiple atrial wavefronts and/or reduce the critical mass of atrial myocardium required to sustain fibrillation. The purpose of this study was to examine the effect of radiofrequency (RF) energy application on conduction in canine atria by performing high-density epicardial mapping and careful histologic examination of the ablation zone. METHODS AND RESULTS: RF energy was applied to the right atrial endocardium in nine anesthetized mongrel dogs in an attempt to create a line of conduction block spanning the vertical length of a 504-channel epicardial mapping plaque. The mean length and width of the histologically determined ablation zone was 34 +/- 4 and 7.3 +/- 2.6 mm, respectively. No thrombus was present. Conduction block that spanned the mapping plaque in 6 of 9 animals was matched histologically by continuous transmural necrosis in five. In one, only a portion of the ablation zone was transmural; the remainder was wide but nontransmural. In 2 of 3 animals with conduction, a narrow region was present where continuous transmural necrosis was absent. In the other animal, conduction was present despite continuous transmural necrosis. CONCLUSION: Conduction block usually occurred when continuous transmural necrosis was present, and conduction usually persisted when continuous transmural necrosis was absent. However, important exceptions were observed, including block when the ablation zone was wide but nontransmural, and conduction despite a thin line of continuous transmural necrosis.

Nonpharmacologic validation of the intrinsic heart rate in cardiac transplant recipients.

BACKGROUND: The maximum sinus rate during exertion in humans is inversely related to age. However, the sinus rate at rest is quite variable. The intrinsic heart (IHR) following pharmacologic blockade of autonomic tone with propranolol and atropine has been proposed as a test of sinus node function and is related to age by the linear regression equation: IHR = 118.1 - (0.57 x age). Whether this relationship exists for transplanted hearts for which the donor sinus node is denervated has not been determined. METHODS: The relationship between the resting heart rate and the age of the donor heart was examined in 103 patients 1 year following orthotopic cardiac transplantation in the absence of rejection or intercurrent illness. Patients receiving beta-blockers, calcium blockers, antiarrhythmic drugs, digitalis, theophylline, or with biopsy evidence of rejection or abnormal coronary arteriograms were excluded from analysis. RESULTS: The recipient age, left ventricular ejection fraction, pulmonary capillary pressure, cardiac index, donor heart ischemic time and cardiopulmonary bypass time did not correlate with the rate of the resting donor sinus node. The resting heart rate was inversely related to age of the donor heart by the linear regression equation: HR = 112.0 - (046 x age). CONCLUSION: The resting rate of the denervated sinus node is related to donor age with a regression equation that is similar, though slightly slower, than that predicted after pharmacologic autonomic blockade.

Inducibility of sustained ventricular tachycardia in a closed-chest ovine model of myocardial infarction.

The two goals of this study were (1) to develop a closed-chest animal model of monomorphic ventricular tachycardia; and (2) to investigate the effect of dual site pacing on inducibility of ventricular tachycardia. In the first part of the study, 10 of 14 sheep underwent successful induction of myocardial infarction by temporary balloon occlusion of the left anterior descending coronary artery. After a follow-up period of 21-43 days, sustained monomorphic ventricular tachycardia could be induced during programmed electrical stimulation using a "clinical" stimulation protocol in 8 of the 10 sheep. The number of ventricular tachycardia episodes per animal varied between 5 and 70. Ventricular fibrillation was never induced during programmed electrical stimulation. Ventricular tachycardia episodes lasted from 30 seconds up to 15 minutes and were terminated by antitachycardia pacing or DC cardioversion. In the second part of the study, the effect of dual site stimulation on ventricular tachycardia inducibility was investigated. High current stimuli from an area within the infarcted zone were given with the S1 programmed stimulation protocol. This dual site stimulation showed no effect on ventricular tachycardia induction during programmed electrical stimulation. This animal model shows a high induction rate of sustained monomorphic ventricular tachycardia in the chronic phase of myocardial infarction. The high incidence of ventricular tachycardia inducibility provides a reliable tool to study new techniques for the prevention of ventricular tachyarrhythmias.

A new system for catheter ablation of atrial fibrillation.

Increased attention is now being focused on developing new technologies to cure atrial fibrillation using catheter ablation techniques. The performance of a MAZE-type procedure using standard catheter ablation technologies is arduous and is associated with an unacceptable risk of complications. The Guidant Heart Rhythm Technologies Linear Ablation System was developed to create long transmural linear lesions. Unique features of this system include the availability of different preshaped multi-electrode steerable ablation catheters, the use of phased radiofrequency (RF) energy, and the control of RF output by varying the duty cycle. A prospective multicenter clinical trial to evaluate the safety and efficacy of a right atrial ablation procedure using this technology to treat atrial fibrillation is currently underway. To date, 15 patients have been enrolled and the procedure was acutely effective in 14 of 15 patients with no complications. Atrial fibrillation has recurred during short-term follow-up in 12 of 15 patients, a not surprising result, because this initial phase of testing involved only right-sided ablation. The early results of the phase I clinical trial confirm the findings of others that successful ablation of chronic atrial fibrillation is likely to require a left atrial approach. This clinical trial, as well as others that are currently underway, will be invaluable in the continuing development of catheter ablation of atrial fibrillation and, ultimately, in determining if the routine use of this therapeutic tool can become a reality.

The influence of ventricular fibrillation duration on defibrillation efficacy using biphasic waveforms in humans.

OBJECTIVES: The purpose of this study was to prospectively investigate the influence of ventricular fibrillation (VF) durations of 5, 10 and 20 s on the defibrillation threshold (DFT) during implantable cardioverter-defibrillator (ICD) implantation. BACKGROUND: Although the DFT using monophasic waveforms has been shown to increase with VF duration in humans, the effect of VF duration on defibrillation efficacy using biphasic waveforms in humans is not known. METHODS: Thirty patients undergoing primary ICD implantation or pulse generator replacement were randomly assigned to have the DFT determined using biphasic shocks at two durations of VF each (5 and 10 s, 10 and 20 s or 5 and 20 s). RESULTS: There was no statistically significant difference in the mean DFT comparing VF durations of 5 s (9.5+/-6.0 J) and 10 s (10.8+/-7.0 J) (p=0.4). The mean DFT significantly increased from 10.9+/-6.1 J at 10 s of VF to 12.6+/-5.6 J (p=0.03) at 20 s of VF, and from 7.0+/-3.5 J at 5 s of VF to 10.5+/-6.3 J (p=0.04) at 20 s of VF. An increase in the DFT was observed in 14 patients as VF duration increased. There were no clinical characteristics that differentiated patients with and without an increase in the DFT. CONCLUSIONS: Defibrillation efficacy decreases with increasing VF duration using biphasic waveforms in humans. Ventricular fibrillation durations greater than 10 s may negatively affect the effectiveness of ICD therapy.