Far-field Electrograms Research Articles

Intracardiac J-point elevation before the onset of polymorphic ventricular tachycardia and ventricular fibrillation in patients with an implantable cardioverter-defibrillator

The clinical importance of the J-point elevation on electrocardiogram is controversial. To study intracardiac J-point amplitude before ventricular arrhythmia. Baseline 12-lead electrocardiogram and far-field right ventricular intracardiac implantable cardioverter-defibrillator electrograms were recorded at rest in 494 patients (mean age 60.4 ± 13.1 years; 360 [72.9%] men) with structural heart disease (278 [56.3%] ischemic cardiomyopathy) who received primary (463 [93.9%] patients) or secondary prevention implantable cardioverter-defibrillator. Ten-second intracardiac far-field electrograms before the onset of arrhythmia were compared with the baseline. The J-point amplitude was measured on the baseline 12-lead surface electrocardiogram and the intracardiac far-field electrogram. The relative J-point amplitude was calculated as the ratio of J-point amplitude to peak-to-peak R-wave. The paired t test showed that the relative intracardiac J-point amplitude was significantly higher before polymorphic ventricular tachycardia/ventricular fibrillation (VF) onset (0.28 ± 0.08 vs -0.19 ± 0.39; P = .012) than at baseline. In a mixed-effects logistic regression model, adjusted for multiple episodes per patient, each 10% increase in relative J-point amplitude increased the odds of having ventricular tachycardia/VF by 13% (odds ratio 1.13 [95% confidence interval 1.07-1.19]; P < .0001) and increased the odds of having polymorphic ventricular tachycardia/VF by 27% (odds ratio 1.27 [95% confidence interval 1.11-1.46]; P = .001). The relative intracardiac J-point amplitude is augmented immediately before the onset of polymorphic ventricular tachycardia/VF in patients with structural heart disease.

A novel pulmonary vein potential mimic unique to cryoballoon ablation of atrial fibrillation

Figure 1A demonstrates a tracing during cryoballoon ablation of the right inferior pulmonary vein (RIPV). The 28 mm cryo-balloon catheter is positioned at the RIPV ostium (Figure 1B). A 20 mm Achieve circular mapping catheter (CMC) is positioned distallyin the RIPV to ensure catheter stability and optimize PV ostium–cryoballoon contact. During ablation the PN was continuously sti-mulated from a quadripolar catheter positioned in the superior vena cava (1000 ms; 10 mA; 1 ms) resulting in the recording of asurface diaphragmatic CMAP (PHREN2). A signal associated with, yet distinct from, the pacing artefact was recorded on the CMC(PV 1,2 to 8,1;*). This signal was dissociated from the far-field atrial (a) and ventricular electrograms (b) yet simultaneous to thesurface CMAP. Although PV potentials were recorded proximally at the PV ostium there were no pulmonary vein potential(PVPs) recorded in this very distal position (Figure 1C). While mimicking the appearance of a PVP this signal is the intrathoracic rep-resentation of the diaphragmatic CMAP as elicited by PN pacing. It is important to recognize that the possibility for recording diaphrag-matic potentials with very distal CMC positions exists. Differentiation of diaphragmatic CMAPs from PVPs is important in theavoidance of unnecessary right-sided cryoapplications and PN injury.Conflict of interest: none declared.

Implantable Defibrillator Electrograms and Origin of Left Ventricular Impulses: An Analysis of Regionalization Ability and Visual Spatial Resolution

The implantable cardioverter-defibrillator (ICD) electrogram (EG) is a documentation of ventricular tachycardia. We prospectively analyzed EGs from ICD electrodes located at the right ventricle apex to establish (1) ability to regionalize origin of left ventricle (LV) impulses, and (2) spatial resolution to distinguish between paced sites. LV electro-anatomic maps were generated in 15 patients. ICD-EGs were recorded during pacing from 22 ± 10 LV sites. Voltage of far-field EG deflections (initial, peak, final) and time intervals between far-field and bipolar EGs were measured. Blinded visual analysis was used for spatial resolution. Initial deflections were more negative and initial/peak ratios were larger for lateral versus septal and superior versus inferior sites. Time intervals were shorter for apical versus basal and septal versus lateral sites. Best predictive cutoff values were voltage of initial deflection <-1.24 mV, and initial/peak ratio >0.45 for a lateral site, voltage of final deflection <-0.30 for an inferior site, and time interval <80 milliseconds for an apical site. In a subsequent group of 9 patients, these values predicted correctly paced site location in 54-75% and tachycardia exit site in 60-100%. Recognition of paced sites as different by EG inspection was 91% accurate. Sensitivity increased with distance (0.96 if ≥ 2 cm vs 0.84 if < 2 cm, P < 0.001) and with presence of low-voltage tissue between sites (0.94 vs 0.88, P < 0.001). Standard ICD-EG analysis can help regionalize LV sites of impulse formation. It can accurately distinguish between 2 sites of impulse formation if they are ≥2 cm apart.

Abstract 9250: Endocardial Electrogram Characteristics Indicating an Epicardial Origin of Focal Ventricular Arrhythmias

Introduction: While most ventricular arrhythmias (VA) can be ablated successfully using an endocardial (ENDO) approach, epicardial (EPI) mapping and ablation is sometimes required. There may be clues on the surface electrocardiogram related to intrinsicoid deflection and QRS width; however, identification of an EPI origin of VA with certainty remains problematic, and there are no reported ENDO electrogram (EGM) characteristics that may direct ablation strategy. Methods: All patients referred for ablation of ventricular tachycardia or frequent ventricular ectopy from June 2006 through July 2010 were evaluated. Only patients with completed electroanatomical activation maps of a focal VA from ENDO and EPI were included. EGMs recorded by a bipolar mapping catheter in the area of earliest ENDO activation were analyzed and compared to the area of early EPI activation. Results: There were 17 patients with completed ENDO and EPI electroanatomical maps of a focal VA identified. We identified 3 characteristics from ENDO mapping that consistently indicated an EPI VA origin: 1) Diffusely early activation (&gt; 2cm2 region of sites with equally earliest activation within 10 msec; figure); 2) Sequence of a far-field EGM followed by a near-field EGM in the region of earliest ENDO activation; and 3) Inability to capture the far-field component of the earliest ENDO EGM (stimulus-QRS &lt; egm-QRS time) or reproduce the PVC or VT QRS complex morphology with pacing at the earliest ENDO activation site. Conclusions: The presence of a diffuse area of early activation and inability to capture a far-field electrogram from the endocardium indicates an epicardial origin of a focal ventricular arrhythmia.

Atrial Tachycardia Originating From the Junction of the Right Atrium and a Diverticulum of the Inferior Vena Cava

A 52-year-old woman without a history of cardiac surgery underwent electrophysiological study for an atrial tachycardia (AT). Echocardiography revealed no evidence of structural heart disease or anatomic abnormalities. At baseline, the AT was incessant and the P waves were upright in lead I and the inferior leads and biphasic (±) P waves in lead V1 (Figure 1). During mapping at the lower posterior right atrium (RA), an unexpected movement of the mapping catheter was observed. A right atriogram performed with a pigtail catheter revealed an aneurysmal structure between the RA and the diaphragm (Figure 2). This structure exhibited a passive expansion and shrinkage with each cardiac cycle. Far-field electrograms were recorded at the sites along the junction between the RA and this structure, and no electrograms were recorded at any other sites within this structure (Figure 3). Activation mapping revealed a centrifugal activation pattern from …

Intracardiac QT integral on far-field ICD electrogram predicts sustained ventricular tachyarrhythmias in ICD patients

Prediction of sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) could help to guide preventive interventions in at-risk patients. The QRST integral (∫QT) reflects intrinsic repolarization properties. The objective of this study was to determine whether intracardiac ∫QT predicts VT/VF in the next few months in patients with implantable cardioverter defibrillators (ICDs). Far-field (FF) and near-field (NF) right ventricular intracardiac electrograms (EGMs) were recorded via telemetry in 46 patients with structural heart disease and ICDs implanted for secondary prevention of sudden cardiac death. Epochs of 4.9 ± 0.4 minutes during sinus rhythm (mean heart rate 70.9 ± 15.2 beats/min) and ventricular pacing at 105 beats/min were analyzed. Mean ∫QT was calculated on FF and NF EGMs as the algebraic sum of areas under the QRST curve and adjusted by mean heart rate. Patients were followed up for at least 3 months. True VT/VF events treated by the ICD served as the end point. During a mean follow-up of 4.6 months, 22 patients (48%) were treated for VT/VF. Unadjusted and adjusted by heart rate, FF EGM ∫QT in sinus rhythm was a significant predictor of VT/VF (unadjusted ∫QT hazard ratio 1.007; 95% confidence interval 1.002 to 1.0013; P = .007; adjusted ∫QT hazard ratio 1.68; 95% confidence interval 1.19 to 2.36; P = .002). The highest quartile of intracardiac ∫QT predicted VT/VF (log-rank test P = .042) and identified patients at risk with a specificity of 86% and positive predictive value of 73%. Increased intracardiac FF EGM ∫QT predicts VT/VF in patients with structural heart disease and secondary prevention ICDs.

Teaching Points With 3-Dimensional Mapping of Cardiac Arrhythmias

Before creating a detailed 3-dimensional map of an arrhythmia, the electrophysiologist should already have a reasonable idea regarding which cardiac chamber contains either the focal site of origin of an automatic tachycardia or the relevant substrate for reentry. Typically, a combination of careful review of the ECG during tachycardia and knowledge of the location of abnormal substrate (such as myocardial infarction, atriotomy scar, etc) will allow focused mapping in the appropriate chamber. Prior teaching points have already discussed1,2 the fact that an isolated “early site of activation” is essentially meaningless for guiding ablation of macroreentry. However, in some circumstances, even for a focal “automatic” tachycardia, the apparently early site is not a suitable site to target for ablation. After constructing the activation map during tachycardia before ablation, especially if the earliest site of activation obtained does not appear to be particularly early compared with the surface ECG reference, the following should be considered. ### Overlapping Cardiac Structures Mapping a chamber other than the actual chamber where the tachycardia originates will clearly lead to a wrong conclusion. For example, when mapping premature ventricular tachycardias or monomorphic ventricular tachycardia in a structurally normal heart, a detailed map of the right ventricular outflow tract may show the “earliest site” of activation to be in the posterior wall of the right ventricular outflow tract. The true site of origin may, however, be in a coronary cusp or the subvalvar anterior left ventricular outflow tract. The posterior right ventricular outflow tract may appear to be early because a far-field signal is detected on the mapping electrode or because of breakthrough in the right ventricular outflow tract from the wave front originating on the other side of the region.3,4 After mapping the left ventricle and coronary cusps and combining the maps, the earliest activation …

Anti-tachycardia pacing degenerated fast ventricular tachycardia into undetectable life-threatening tachyarrhythmia in a patient with non-ischemic dilated cardiomyopathy

A 45-year-old man with dilated cardiomyopathy was admitted to our hospital due to congestive heart failure (CHF). Despite the optimal medical treatment, his condition had not improved because of severe left ventricular dysfunction. Because he experienced non-sustained ventricular tachycardia (VT), a biventricular implantable cardioverter-defibrillator (Bi-V ICD) was implanted for reduction of dyssynchrony and primary prevention of lethal tachyarrhythmia. After discharge, he developed CHF and was transported to our hospital by ambulance. In the ambulance, monomorphic sustained VT with 200bpm suddenly occurred. The ICD detected it as fast VT and anti-tachycardia pacing (ATP) was delivered. After the ATP therapy, RR intervals of VT became irregular and prolonged. Ventricular fibrillation-like electrical activity was recorded by a far-field electrogram from the defibrillator, but the tachycardia cycle length exceeded 400ms which is under the tachycardia detection rate. The device failed to deliver a shock and the patient had to be rescued with an external shock. This is a rare case of fast VT that degenerated into undetectable life-threatening tachyarrhythmia by ATP.

Focal ventricular arrhythmias originating from the left ventricle adjacent to the membranous septum

We report the features of focal ventricular arrhythmias (VAs) arising from the left ventricle (LV) adjacent to the membranous septum. We studied eight patients (five men, 65 ± 10 years) with (n = 2) or without structural heart disease (n = 6) who had ventricular tachycardia (n = 4) or premature ventricular contractions (n = 4) originating from the LV septum underneath the aorta. Ventricular arrhythmias exhibited a focal activation pattern, left (n = 4) or right bundle branch block (n = 4), respectively, left superior (n = 4) or inferior axis QRS morphology (n = 4), negative QRS polarity in lead III and early or no precordial transition in all. During all of these VAs, far-field electrograms in the His bundle (HB) region preceded the QRS onset. In all patients, ventricular pre-potentials were recorded during VAs while late potentials were recorded in sinus rhythm at the border of a localized low-voltage area underneath the aorta. Radiofrequency catheter ablation at the presumed sites of origin successfully eliminated VAs in five patients and was abandoned in the remaining three because the HB electrogram was recorded at that site. Focal VAs may arise from the LV adjacent to the membranous septum as a part of the LV ostium, and broadens the spectrum of LV ostium VAs.

Analyse intrakardialer Elektrogramme in Schrittmachern und ICDs der Firma Biotronik

Detailed analysis of stored electrograms is essential for the interpretation of arrhythmias, programming changes, and optimization of the medical therapy in patients with implanted pacemakers and defibrillators. The physician who cares for patients with implantable electrical devices has to be able to understand the detection and treatment algorithms of those devices. Biotronik pacemakers of newer generations are capable of storing intracardiac electrograms. Earlier devices store up to 12 electrograms of 10 s duration after certain trigger events, like atrial tachycardia or high ventricular rates. Cardiac resynchronization systems can store electrograms after patient activation with magnets in addition to the above mentioned trigger-activated electrograms. Defibrillators store intracardiac electrograms during tachycardia episodes with near-field and far-field electrograms of the right ventricular lead in addition to the markers in single and dual chamber defibrillators (in addition to an atrial electrogram) and near field electrograms of the atrial, the right, and the left ventricular electrode in addition to the markers in resynchronization systems. Each channel has a maximum storing capacity of 32 min. If there are more episodes than storing capacity, electrograms of older episodes will be overwritten, but if the newer episodes are all classified as supraventricular, the last two ventricular episodes (VT or VF) will remain in the episode memory. This article describes stored electrograms, detection, and treatment algorithms of implantable cardiac devices manufactured by Biotronik.

Analysis of Fractionated Atrial Fibrillation Electrograms by Wavelet Decomposition

This study introduces the use of wavelet decomposition of unipolar fibrillation electrograms for the automatic detection of local activation times during complex atrial fibrillation (AF). The purpose of this study was to evaluate this technique in patients with structural heart disease and longstanding persistent AF. In 46 patients undergoing cardiac surgery, unipolar fibrillation electrograms were recorded from the right atrium, using a mapping array of 244 electrodes. In 25 patients with normal sinus rhythm, AF was induced by rapid pacing, whereas 21 patients were in persistent AF. In patients with longstanding AF, the atrial electrograms showed a high degree of fractionation. In each patient, 12 s of AF were analyzed by wavelet transformation (15 scales). The finest scales (1-7) were used to reconstruct a "local" fibrillation electrogram, whereas with the coarse scales (9-15), a far-field signal was generated. With these local and far-field electrograms, the "primary" fibrillation potentials, due to wave propagation underneath the electrode, could be distinguished from double potentials and multiple components generated by remote wavefronts. Wavelet transformation resulted in AF histograms with a closely gaussian distribution and the automatically generated activation maps showed a good resemblance with fibrillation maps obtained by laborious manual editing. A special chaining algorithm was developed to detect multiple components in fractionated electrograms. The degree of fractionation showed a positive correlation with the complexity of fibrillation, thus providing an objective quantification of the degree of electrical dissociation of the atria. Wavelet transformation can be a useful technique to detect the primary potentials and quantify the degree of fractionation of fibrillation electrograms. This could enable real-time mapping of complex cases of human AF and classification of the underlying electropathological substrate.

Electromagnetic interference induced by magnetic resonance imaging

A 76-year-old man with a biventricular implantable cardioverter defibrillator (ICD) implanted for secondary prevention underwent a magnetic resonance imaging (MRI) scan of the head. The 1.5 T MRI was performed to guide ‘gamma-knife’ surgery for intractable Parkinsonian tremor. Device therapies were switched off during the procedure. On investigation of the device at follow-up, the device electrograms were noted to demonstrate a unique and intriguing pattern (Figure 1). Figure 1 Analysis of the local right ventricular apical electrogram (upper tracing) revealed the following two dissociated patterns: High-amplitude spikes at a regular interval of 1560 ms; and Clusters of high-frequency spikes (20 ms to 40 ms apart) that progressively increased in amplitude, then dissipated. Each cluster persisted for 960 ms and they were separated by isoelectric intervals of approximately 400 ms. This pattern was presumably generated by the oscillating magnetic pulse during scanning. The far-field electrogram (lower tracing) showed a rapid series of sinusoidal deflections concordant with the clusters described above. The ICD inappropriately diagnosed the interference as ventricular fibrillation (device annotations below tracings) based on rate. No residual effects on device function or lead integrity were noted following the procedure. Current barriers to performing MRI in patients with ICDs include under/oversensing, thermogenic damage, device malfunction and inappropriate recognition of electromagnetic interference that may lead to unnecessary ICD therapies. Recent research (1) has demonstrated the improved safety of a new pacemaker system designed to minimize complications from MRI. The present image illustrates a cause of ICD malfunction during MRI exposure and emphasizes the importance of further research into developing MRI-safe devices.

Electrophysiological evaluation of pulmonary vein isolation

Electrophysiologically demonstrated complete conduction block at the level of the veno-atrial junction is preferable as the endpoint of pulmonary vein (PV) ablation rather than circumferential periostial radiofrequency delivery. Knowledge of the individual anatomy of the PVs and the left atrium (LA), appropriate positioning of circular mapping catheters, and the electrophysiology of PV activation in addition to effective ablation tools is necessary to achieve this endpoint. Additional unnecessary ablation and possibly complications can be avoided by the recognition of non-PV myocardial contributions to PV electrograms. The posterior wall of the LA appendage contributes far-field electrograms to recordings from all left superior PVs (LSPV), the low lateral LA to 80% of left inferior PV (LIPV) recordings and the superior vena cava to 23% of right superior PV (RSPV) recordings. Each of these far-field components can be recognized in sinus rhythm as well as during ongoing atrial fibrillation. Finally, the creation of temporally stable and definitive PV isolation remains a currently unsolved problem.

Prediction of Ventricular Tachyarrhythmias by Intracardiac Repolarization Variability Analysis

Arrhythmic sudden cardiac death (SCD) is generally mediated by ventricular fibrillation (VF) or fast ventricular tachycardia (FVT). We studied the predictive value of temporal QT variability detected from various sources of cardiac electric signal: surface ECG, far-field (FF), and near-field (NF) intracardiac electrograms (EGMs) in patients with implantable cardioverter-defibrillators (ICDs). Surface ECG and FF and NF intracardiac EGMs were simultaneously recorded at rest (mean heart rate, 74+/-15 bpm) for 4.5+/-1.3 minutes in 298 patients (mean age, 59+/-14; 216 male [73%]) with structural heart disease and an implanted Medtronic ICD for primary (231 patients, 78%) or secondary (67 patients, 22%) prevention of SCD. During mean follow-up of 16+/-8 months, 52 (13.1% per person-year of follow-up) patients sustained VT/VF and received appropriate ICD therapies, but only 19 (4.8% per person-year of follow-up) patients sustained FVT/VF with cycle length <or=240 ms. The Kaplan-Meier survival analysis showed that the highest QT variability index (QTVI) quartile from all cardiac sources (surface ECG; NF and FF EGMs) is associated with event-free survival (P=0.038 for ECG; P=0.024 for FF EGM; P=0.012 for NF EGM). QTVI was a predictor of all VT/VF events and FVT/VF in the multivariate Cox model (including ischemic or nonischemic cardiomyopathy, history of revascularization procedures, LVEF, New York Heart Association class). Strong significant correlation among QTVI determined from all 3 sources was found. Repolarization lability is present throughout the ventricular myocardium. Increased intracardiac QT variability predicts VT/VF events in patients with structural heart disease.

Evaluating Pulmonary Vein Isolation

Pulmonary vein isolation is the electrophysiological endpoint of complete conduction block at the level of the veno-atrial junction and must be explicitly distinguished from encircling PV ablation which frequently does not result in isolation.The prerequisites for successful PV isolation include a knowledge of the individual anatomy of the PVs and the left atrium, appropriate positioning of circular mapping catheters, and a knowledge of the electrophysiology of PV activation, in addition to effective ablation tools. Excessive ablation, and possibly complications, can be avoided by the recognition of non-PV myocardial contributions to electrograms recorded from within the PVs. The posterior wall of the left atrial appendage contributes far-field electrograms to recordings from all or nearly all left superior PVs, the low anterior left atrium to 80% of left inferior PV recordings and the superior vena cava to 23% of right superior PV recordings. Recognition of these far-field components is feasible and accurate in sinus rhythm as well as during ongoing atrial fibrillation. Finally, the creation of temporally stable PV isolation remains a currently unsolved problem although prolonged post isolation surveillance, may be helpful.

Evaluating Pulmonary Vein Isolation

Pulmonary vein isolation is the electrophysiological endpoint of complete conduction block at the level of the veno-atrial junction and must be explicitly distinguished from encircling PV ablation which frequently does not result in isolation. The prerequisites for successful PV isolation include a knowledge of the individual anatomy of the PVs and the left atrium, appropriate positioning of circular mapping catheters, and a knowledge of the electrophysiology of PV activation, in addition to effective ablation tools. Excessive ablation, and possibly complications, can be avoided by the recognition of non-PV myocardial contributions to electrograms recorded from within the PVs. The posterior wall of the left atrial appendage contributes far-field electrograms to recordings from all or nearly all left superior PVs, the low anterior left atrium to 80% of left inferior PV recordings and the superior vena cava to 23% of right superior PV recordings. Recognition of these far-field components is feasible and accurate in sinus rhythm as well as during ongoing atrial fibrillation. Finally, the creation of temporally stable PV isolation remains a currently unsolved problem although prolonged post isolation surveillance, may be helpful.

Use of an Intracardiac Electrogram Eliminates the Need for a Surface ECG during Implantable Cardioverter‐Defibrillator Follow‐Up

A surface electrocardiogram (SECG) for pacing threshold measurements during routine implantable cardioverter-defibrillator (ICD) follow-up can be cumbersome. This study evaluated the use of an intrathoracic far-field electrogram (EGM) derived between the Can and superior vena cava (SVC) electrode -- the Leadless electrocardiogram (LLECG), in dual chamber ICDs in performing pacing threshold tests. The LLECG was evaluated prospectively during atrial and ventricular pacing threshold testing as a substudy of the Comparison of Empiric to Physician-Tailored Programming of Implantable Cardioverter-Defibrillators trial (EMPIRIC) in which dual chamber ICDs were implanted in 888 patients. Threshold tests were conducted at 1 volt by decrementing the pulse width. Follow-up at three months compared pacing thresholds measured using LLECG with those using Lead I of the surface ECG (SECG). The timesaving afforded by LLECG was assessed by a questionnaire. The median threshold difference between LLECG and SECG measurements for both atrial (0.00 ms, P = 0.90) and ventricular (0.00 ms, P = 0.34) threshold tests were not significant. Ninety percent of atrial and ventricular threshold differences were bounded by +/- 0.10 ms and -0.10 to +0.04 ms, respectively. We found that 99% of atrial and ventricular thresholds tests at six and 12 months attempted using LLECG were successfully completed. The questionnaire indicated that 65% of healthcare professionals found LLECG to afford at least some timesaving during device follow-ups. Routine follow-up can be performed reliably and expeditiously in dual chamber Medtronic (Minneapolis, MN, USA) ICDs using LLECG alone, resulting in overall timesaving.

Catheter ablation of ventricular arrhythmias originating in the vicinity of the His bundle: Significance of mapping the aortic sinus cusp

There is a close anatomical relationship between the right coronary cusp (RCC) and noncoronary aortic cusp (NCC) and sites recording His bundle (HB) activation in the right ventricle (RV). The purpose of this study was to examine the electrocardiographic and electrophysiological characteristics of ventricular arrhythmias (VAs) that originate near the HB and their potential as predictors of successful catheter ablation sites. We studied 147 consecutive patients undergoing successful catheter ablation of idiopathic VAs originating from the ventricular outflow tract of either ventricle or the HB region. In 13 (9%) patients with an origin in the RCC (n = 5), NCC (n = 1), or RV HB region (n = 7), the local RV activation in the HB region preceded the QRS onset. In two VAs originating from the RCC or NCC, failed radiofrequency applications near the HB region in the RV delayed the near-field ventricular electrogram and separated the far-field electrograms before the QRS onset in the HB region. The QRS transition in the precordial leads did not discriminate between an RV origin near the HB and an NCC or RCC origin. A QS pattern in lead aVL might be helpful for predicting an RCC origin. VAs originating near the HB have similar electrocardiographic and electrophysiological characteristics, regardless of whether the ablation site is in the RV or aortic sinuses because of the close anatomical relationship of these structures and rapid transseptal conduction. When RV mapping reveals an earliest ventricular activation in the HB region during VAs, mapping in the RCC and NCC should be added to accurately identify the site of origin.

Pacing maneuvers for nonpulmonary vein sources: Part II

Superior vena caval (SVC) potentials are similar to pulmonary vein (PV) potentials. The concepts of multiple far-field electrograms and the use of perivenous pacing and specific site and simultaneous pacing described above are equally applicable to understanding the complex electrograms found within the SVC (Figure 1). Specific sites that require pacing to determine the components of a complex electrogram found in the SVC include the right atrium (RA), azygos vein, anomalous PVs draining into the SVC, and right upper PV; in some cases, an anomalous superior branch of the right inferior PV may be required.

Development and testing of an algorithm to detect implantable cardioverter-defibrillator lead failure

Implantable cardioverter-defibrillator (ICD) lead failures often present as inappropriate shock therapy. An algorithm that can reliably discriminate between ventricular tachyarrhythmias and noise due to lead failure may prevent patient discomfort and anxiety and avoid device-induced proarrhythmia by preventing inappropriate ICD shocks. The goal of this analysis was to test an ICD tachycardia detection algorithm that differentiates noise due to lead failure from ventricular tachyarrhythmias. We tested an algorithm that uses a measure of the ventricular intracardiac electrogram baseline to discriminate the sinus rhythm isoelectric line from the right ventricular coil-can (i.e., far-field) electrogram during oversensing of noise caused by a lead failure. The baseline measure was defined as the product of the sum (mV) and standard deviation (mV) of the voltage samples for a 188-ms window centered on each sensed electrogram. If the minimum baseline measure of the last 12 beats was <0.35 mV-mV, then the detected rhythm was considered noise due to a lead failure. The first ICD-detected episode of lead failure and inappropriate detection from 24 ICD patients with a pace/sense lead failure and all ventricular arrhythmias from 56 ICD patients without a lead failure were selected. The stored data were analyzed to determine the sensitivity and specificity of the algorithm to detect lead failures. The minimum baseline measure for the 24 lead failure episodes (0.28 +/- 0.34 mV-mV) was smaller than the 135 ventricular tachycardia (40.8 +/- 43.0 mV-mV, P <.0001) and 55 ventricular fibrillation episodes (19.1 +/- 22.8 mV-mV, P <.05). A minimum baseline <0.35 mV-mV threshold had a sensitivity of 83% (20/24) with a 100% (190/190) specificity. A baseline measure of the far-field electrogram had a high sensitivity and specificity to detect lead failure noise compared with ventricular tachycardia or fibrillation.