Performance of an automatic arrhythmia classification algorithm: comparison to the ALTITUDE electrophysiologist panel adjudications.

INTRODUCTION: Adjudication of thousands of implantable cardioverter defibrillator (ICD)-treated arrhythmia episodes is labor intensive and, as a result, is most often left undone. The objective of this study was to evaluate an automatic classification algorithm for adjudication of ICD-treated arrhythmia episodes. METHODS: The algorithm uses a machine learning algorithm and was developed using 776 arrhythmia episodes. The algorithm was validated on 131 dual-chamber ICD shock episodes from 127 patients adjudicated by seven electrophysiologists (EPs). Episodes were classified by panel consensus as ventricular tachycardia/ventricular fibrillation (VT/VF) or non-VT/VF, with the resulting classifications used as the reference. Subsequently, each episode electrogram (EGM) data was randomly assigned to three EPs without the atrial lead information, and to three EPs with the atrial lead information. Those episodes were also classified by the automatic algorithm with and without atrial information. Agreement with the reference was compared between the three EPs consensus group and the algorithm. RESULTS: The overall agreement with the reference was similar between three-EP consensus and the algorithm for both with atrial EGM (94% vs 95%, P = 0.87) and without atrial EGM (90% vs 91%, P = 0.91). The odds of accurate adjudication, after adjusting for covariates, did not significantly differ between the algorithm and EP consensus (odds ratio 1.02, 95% confidence interval: 0.97-1.06). CONCLUSIONS: This algorithm performs at a level comparable to an EP panel in the adjudication of arrhythmia episodes treated by both dual- and single-chamber ICDs. This type of algorithm has the potential for automated analysis of clinical ICD episodes, and adjudication of EGMs for research studies and quality analyses.

Noise, artifact, and oversensing related inappropriate ICD shock evaluation: ALTITUDE noise study.

BACKGROUND: Approximately 12-21% of implantable cardioverter defibrillator (ICD) patients receive inappropriate shocks. We sought to determine the incidence and causes of noise/artifact and oversensing (NAO) resulting in ICD shocks. METHODS: A random sample of 2,000 patients who received ICD and cardiac resynchronization therapy defibrillator shocks and were followed by a remote monitoring system was included. Seven electrophysiologists analyzed stored electrograms from the 5,279 shock episodes. Episodes were adjudicated as appropriate or inappropriate shocks. RESULTS: Of the 5,248 shock episodes with complete adjudication, 1,570 (30%) were judged to be inappropriate shocks. Of these 1,570, 134 (8.5%) were a result of NAO. The 134 NAO episodes were determined to be due to external noise in 76 (57%), lead connector-related in 37 (28%), muscle noise in 11 (8%), oversensing of atrium in seven (5%), T-wave oversensing in two (2%), and other noise in one (1%). The ICD shock itself resulted in a marked decrease in the level of noise in 60 of 134 (45%) NAO episodes, and the magnitude of this effect varied with the type of NAO (58% for external noise, 35% for muscle, 27% for lead/connector, and 0% for oversensing; P = 0.03). There was no significant difference in NAO likelihood based on type of lead (integrated bipolar 89/1,802 vs dedicated bipolar 9/140, P = 0.67). CONCLUSIONS: External noise and lead/connector noise were the primary causes, while T-wave oversensing was the least common cause of NAO resulting in ICD shock. Noise/artifact decreased immediately after a shock in nearly half of episodes. The specific ICD lead type did not impact the likelihood of NAO.

Ventricular tachycardia in the era of ventricular assist devices.

Sustained ventricular tachycardia (VT) in patients with advanced cardiomyopathy is a potentially life-threatening arrhythmia. Newer treatment strategies have evolved that combine the use of catheter ablation to target the substrate for VT and ventricular assist devices (VADs) to hemodynamically support the failing ventricle. This editorial is targeted to the practicing clinician caring for these difficult patients. The current article reviews the use of percutaneous VADs to support catheter ablation of VT, the use of durable VADs to support the failing heart in patients with recurrent VT, ventricular arrhythmias in patients with durable VADs, and the use of catheter ablation to treat VT in patients with durable VADs.

Impact of relaxation training on patient-perceived measures of anxiety, pain, and outcomes after interventional electrophysiology procedures.

BACKGROUND: Electrophysiology procedures vary in invasiveness, duration, and anesthesia utilized. While complications are low and efficacy high, cases are elective and patient experiences related to anxiety, pain, and perceived outcomes are not well studied. We sought to determine if a 30-minute audio compact disc (CD) that teaches relaxation techniques and wellness perception prior to an elective procedure impacts validated measures of anxiety, pain, and procedural outcomes. METHODS: Sixty-one patients were randomly assigned to a control group (CG) (N(CG) = 31) or interventional group (IG) (N(IG) = 30). Both groups answered a baseline Hospital Anxiety and Depression Scale (HADS-A) survey consisting only of anxiety assessment questions. The IG listened to the CD the night prior to their procedure. Heart rate and blood pressure were monitored on admission and prior to the procedure. Postprocedure, both groups completed two HADS-A surveys as well as two Patient Experience Surveys (PES). There was no statistical difference in the demographics and the rate of procedural complications between the groups. The statistical significance of our data was determined using a Student's t-test and χ(2) test. RESULTS: At baseline, both groups had equal amounts of anxiety prior to their procedures (P = 0.2). The patients in the IG had lower systolic blood pressures during admission and prior the administration of analgesics in comparison to the CG. Postprocedure, results from administering the HADS-A demonstrated that the IG had 33% lower anxiety (P = 0.02) than CG patients. CONCLUSION: The implementation of basic relaxation teaching techniques prior to planned electrophysiology procedures lowers systolic blood pressure and postprocedural anxiety.

Implantable cardioverter defibrillator electrogram adjudication for device registries: methodology and observations from ALTITUDE.

BACKGROUND: The increasing use of remote monitoring with the associated large retrievable databases provides a unique opportunity to analyze observations on implantable cardioverter-defibrillator (ICD) therapies. Adjudication of a large number of stored ICD electrograms (EGMs) presents a unique challenge. The ALTITUDE study group was designed to use the LATITUDE remote monitoring system to evaluate ICD patient outcomes across the United States. METHODS AND RESULTS: Of 81,081 patients on remote monitoring, a random sample of 2,000 patients having 5,279 shock episodes was selected. The ALTITUDE EGM review committee was comprised of seven electrophysiologists from four institutions. An online EGM adjudication system was designed. Episodes were classified as appropriate (70% of shock episodes) or inappropriate ICD therapies (30%). Light's Kappa was used to assess agreement. Interobserver and intraobserver Kappa scores for dual-chamber ICDs were 0.84 (0.71-0.91) and 0.89 (0.82-0.95), consistent with substantial agreement. Interobserver and intraobserver Kappa scores for single-chamber ICDs were 0.61 (0.54-0.67) and 0.69 (0.59-0.79). The rhythm categories of "nonsustained arrhythmia" and "polymorphic and monomorphic ventricular tachycardia" resulted in the greatest degree of discordant adjudication between reviewers. CONCLUSIONS: This method of adjudication of a large volume of stored EGM data prior to device therapies will allow new observations in regards to device performance and has the potential to improve device programming and design. There was substantial interreviewer agreement for rhythm classification. Agreement was greater for dual-chamber compared to single-chamber devices, indicating the atrial lead adds diagnostic value in rhythm interpretation.

Novel use of a vascular plug to anchor an azygous vein ICD lead.

We describe the case of a young patient with severe hypertrophic cardiomyopathy and marginal defibrillation thresholds (DFTs) at implant of a standard transvenous implantable cardioverter-defibrillator (ICD) system. The patient subsequently experienced multiple failed ICD shocks during a prolonged episode of spontaneous ventricular tachycardia/fibrillation. Placement of a second single-coil shocking lead in the azygous vein resulted in acceptable DFTs, but the new lead migrated superiorly within hours of the procedure. To stabilize the lead position, a vascular plug was placed in the distal azygous vein, and the shocking lead screw was actively fixated to the meshwork of the device. Subsequent testing confirmed both adequate defibrillation and stable lead position.

Usefulness of preimplantation B-type natriuretic peptide level for predicting response to cardiac resynchronization therapy.

Nearly 1/3 of patients with heart failure (HF) fail to respond to cardiac resynchronization therapy (CRT). The purpose of this study was to evaluate the value of preimplantation brain natriuretic peptide (BNP) in predicting the clinical response to CRT. We retrospectively analyzed 164 patients who underwent CRT. Patients with New York Heart Association functional class III or IV HF symptoms despite maximal medical therapy, who were not on inotropic medications, had left ventricular ejection fraction < or =35%, and QRS duration >130 ms were included in the study. CRT response in patients who survived at 6-month follow-up was defined as no HF hospitalization and improvement of > or =1 grades in the New York Heart Association classification. BNP assays were performed before implantation and at 6-month follow-up. Patients had ischemic (47%) or nonischemic (53%) cardiopathy. Responders (n = 107) and nonresponders (n = 57) had similar baseline characteristics. Cardiac death and hospitalization for HF occurred in 5 (4.7%) and 18 (31.6%) patients, respectively. CRT responders compared with nonresponders exhibited higher preimplantation BNP levels (800 +/- 823 vs 335 +/- 348 pg/ml, p = 0.0002) and a significant reduction in the QRS duration after implantation (-6 +/- 34 vs +7 +/- 32 ms, p = 0.048). The preimplantation BNP was the only independent predictor of the CRT response (p = 0.001). A BNP value > or =447 pg/ml demonstrated a sensitivity of 62% and specificity of 79% in identifying CRT response. In a subgroup of 41 patients who underwent Doppler tissue imaging analysis, the preimplantation BNP was higher in patients presenting with intraventricular dyssynchrony (845 +/- 779 vs 248 +/- 290 pg/ml, p = 0.04). In conclusion, the preimplantation BNP value independently predicts CRT response and was superior to QRS duration reduction in identifying CRT responders.

Changes and predictive value of dispersion of repolarization parameters for appropriate therapy in patients with biventricular implantable cardioverter-defibrillators.

BACKGROUND: The impact of cardiac resynchronization therapy (CRT) on dispersion of repolarization is controversial. The benefit of CRT on sudden cardiac death has been demonstrated only after 3 years follow-up. OBJECTIVE: The purpose of this study was to explore the immediate effect of CRT on dispersion of repolarization and to define the value of dispersion of repolarization parameters as predictors of appropriate implantable cardioverter-defibrillator (ICD) therapy. METHODS: Data from 100 patients who underwent CRT-ICD placement were analyzed retrospectively. Patients had symptoms of New York Heart Association functional class III or IV heart failure, left ventricular ejection fraction < or =35%, and QRS duration >130 ms or QRS < or =130 ms with left intraventricular dyssynchrony. ECG indices of dispersion of repolarization before and immediately after CRT implantation (QT dispersion, Tpeak-Tend [Tp-e], and Tp-e dispersion) were measured. RESULTS: In patients who were upgraded to a biventricular system, Tp-e did not increase significantly after CRT. However, Tp-e increased significantly after CRT in patients with left bundle branch block or narrow QRS at baseline. After 12-month follow-up, 22 patients had received appropriate ICD therapy. ICD therapy and no ICD therapy groups had similar baseline characteristics, such as secondary prevention and ischemic cardiomyopathy. Postimplantation Tp-e was the only independent predictor of future ICD therapy (P = .02). CONCLUSION: Immediately after CRT, Tp-e did not increase in patients who received a biventricular upgrade; however, Tp-e did increase in patients with preimplantation left bundle branch block or narrow QRS. Postimplantation Tp-e was the only independent predictor of appropriate ICD therapy.

Left ventricular apical wall motion abnormality is associated with lack of response to cardiac resynchronization therapy in patients with ischemic cardiomyopathy.

BACKGROUND: Many patients with appropriate indications fail to respond to cardiac resynchronization therapy (CRT). OBJECTIVE: The purpose of our study was to determine the relationship between CRT response and preimplantation apical wall motion abnormality. METHODS: We analyzed data from 83 patients with ischemic cardiomyopathy who underwent CRT. All patients had New York Heart Association class III or IV symptoms despite maximal medical therapy, left ventricular ejection fraction (LVEF) < or =35%, and QRS duration > or =130 ms or <130 ms with left ventricular dyssynchrony. CRT responders at 6 months were defined as surviving patients with: (1) no hospitalization for heart failure, and (2) improvement of New York Heart Association classification. Patients underwent echocardiography before and 6 months after implantation to assess changes in regional wall motion and LVEF. RESULTS: At baseline, CRT responders (n = 39) and nonresponders (n = 44) had similar LVEF (22.9% +/- 6.9% vs 23.1% +/- 8.3%), QRS duration (159 +/- 43 ms vs 159 +/- 36 ms), and medical treatment. CRT nonresponders had a higher prevalence of preimplantation apical wall motion abnormality (68% vs 33%, P = .003). Patients with baseline apical wall motion abnormalities (n = 43) were less likely than others (n = 40) to show improvement in wall motion at 6 months (30% vs 81%, P < .001) or clinical response to CRT (31% vs 64%, P = .003). CONCLUSION: The presence of a preimplantation apical wall motion abnormality was associated with a lower rate of CRT response in patients with ischemic cardiomyopathy.

Biventricular pacing and defibrillator use in chronic heart failure.

Since the 1970s when the implantable cardioverter defibrillator (ICD) was developed, multiple clinical trials have documented survival benefits in certain high-risk subsets of heart failure patients. Over the past decade, cardiac resynchronization therapy (CRT) emerged as an important therapy in carefully selected patients with ongoing symptoms despite optimized pharmacological therapy. ICDs should be considered first-line therapy for survivors of life-threatening ventricular arrhythmic events. Subsets of patients with both ischemic and nonischemic dilated cardiomyopathy appear to have a survival benefit from primary ICD therapy. CRT has resulted in substantial symptomatic improvement and survival benefits in a subgroup of chronic heart failure patients. CRT should be considered in heart failure patients undergoing ICD implantation who have evidence of ventricular dyssynchrony.

Alterations in ion channel physiology in diabetic cardiomyopathy.

Diabetes mellitus is one of the most common chronic illnesses worldwide. This article focuses on a subgroup of diabetic patients with a specific cardiac complication of this disease--diabetic cardiomyopathy. This article initially gives some general background on diabetic cardiomyopathy and ion channels. Next the focus is on how diabetic cardiomyopathy alters calcium homeostasis in cardiac myocytes and highlights the specific alterations in ion channel function that are characteristic of this type of cardiomyopathy. Finally, the importance of the renin-angiotensin system in diabetic cardiomyopathy is reviewed.

Value of high-density endocardial and epicardial mapping for catheter ablation of hemodynamically unstable ventricular tachycardia.

BACKGROUND: Percutaneous epicardial mapping has been used for ablation of recurrent ventricular tachycardia (VT). OBJECTIVES: The purpose of this study was to use a combined epicardial and endocardial mapping strategy to delineate the myocardial substrate for recurrent VT in both ischemic (n = 12) and nonischemic cardiomyopathy (n = 8), and to define the role of epicardial ablation. METHODS: Electroanatomic mapping was performed in 20 patients. High-density voltage maps were obtained by acquiring both endocardial and epicardial electrograms. Electrograms derived from six patients with structurally normal hearts were used as controls. A total of 26 VTs were targeted in the 20 patients. RESULTS: Most VTs (23/26 [88.5%]) were hemodynamically unstable. In patients with ischemic cardiomyopathy, the extent of endocardial scar was greater than epicardial scar. A definable pattern of scar could not be demonstrated in nonischemic cardiomyopathy. Pathologic examination of explanted hearts in two patients with nonischemic cardiomyopathy demonstrated that low-voltage areas were not always predictive of scarred myocardium. A substrate-based approach was used for catheter ablation. Catheter ablation was performed on the endocardium in all patients; additional epicardial delivery of radiofrequency energy was required in 8 (40%) of 20 patients for successful ablation. During follow-up (12 +/- 4 months), 15 (75%) of 20 patients have been arrhythmia-free. CONCLUSION: Patients with ischemic cardiomyopathy tend to have a larger endocardial than epicardial scar. Use of epicardial and endocardial electroanatomic mapping to define the full extent of myocardial scars allows successful catheter ablation in patients with hemodynamically unstable VTs.

Percutaneous intrapericardial echocardiography during catheter ablation: a feasibility study.

BACKGROUND: Percutaneous pericardial access, epicardial mapping, and ablation have been used successfully for catheter ablation procedures. OBJECTIVES: The purpose of this study was to evaluate the safety and feasibility of closed-chest direct epicardial ultrasound imaging for aiding cardiac catheter ablation procedures. METHODS: An intracardiac ultrasound catheter was used for closed-chest epicardial imaging of the heart in 10 patients undergoing percutaneous epicardial access for catheter ablation. All patients underwent concomitant intracardiac echocardiography and preprocedural transesophageal echocardiography. Using a double-wire technique, two sheaths were placed in the pericardium, and a phased-array ultrasound catheter was manipulated within the pericardial sinuses for imaging. RESULTS: Multiple images from varying angles were obtained for catheter navigation. Notably, image stability was excellent, and structures such as the left atrial appendage were seen in great detail. No complications resulting from use of the ultrasound catheter in the pericardium occurred, and no restriction of movement due to the presence of the additional catheter in the pericardial space was observed. Wall motion was correlated to voltage maps in five patients and showed that areas of scars correlated with wall-motion abnormalities. Normal wall-motion score correlated to sensed signals of 4.2 +/- 0.3 mV (normal myocardium >1.5 mV), and scores >1 correlated to areas with signals <0.5 mV in that territory). CONCLUSION: Intrapericardial imaging using an ultrasound catheter is feasible and safe and has the potential to provide additional valuable information for complex ablation procedures.

Impedance monitoring during catheter ablation of atrial fibrillation.

BACKGROUND: Delivery of radiofrequency energy in proximity of a pulmonary vein can cause vein stenosis. A sudden decrease in impedance as the catheter is moved from the vein into the left atrium (LA) has been used to define the pulmonary vein-LA transition during ablation procedures. OBJECTIVES: The purpose of this study was to define the variables affecting impedance measurement. METHODS: In vitro analysis of impedance was performed in a saline bath using sheaths and a plastic stereolithographic model of the LA. Impedance was continuously monitored during a calibrated pullback from the pulmonary vein into the LA in 37 veins of 10 patients referred for catheter ablation. Location of the catheter was confirmed by the following imaging modalities: intracardiac echocardiography, contrast venography, electroanatomic mapping, and computed tomography/magnetic resonance imaging (offline) in all patients. RESULTS: Larger cross-sectional areas containing the catheter correlated with lower impedance in an exponential manner both with respect to sheath size (R(2) = 0.99) and in the stereolithographic model (R(2) = 0.91). In vivo, the impedance in the pulmonary veins decreased in an exponential manner as the catheter was pulled back into the LA. However, impedance at the vein orifice was not significantly higher than the LA. A defined cutoff value for defining the pulmonary vein-LA transition could not be identified. CONCLUSION: The primary determinant of impedance is the cross-sectional area of the space containing the catheter. Impedance monitoring alone does not guarantee a catheter tip position outside the pulmonary vein. Intraprocedural imaging confirmation should be considered to avoid radiofrequency application within pulmonary veins.

Percutaneous epicardial mapping during ablation of difficult accessory pathways as an alternative to cardiac surgery.

OBJECTIVES: The aim of this study was to define the role of percutaneous epicardial mapping for the ablation of previous failed ablation of accessory pathways. BACKGROUND: Cardiac surgery is the only curative option for failed radiofrequency (RF) catheter ablation of accessory pathway (AP)-mediated tachycardias. We investigated a combined percutaneous epicardial and endocardial approach for failed AP ablations. METHODS: We present our experience in a series of 6 cases (7 APs) with previous failed attempts at catheter ablation (median 2 attempts, range 1-4) and persistent symptomatic tachycardias. Endocardial mapping of the APs was performed using conventional techniques. Sites with local electrograms suggestive of AP location were selected. When initial endocardial mapping was not successful for ablation of the pathway, percutaneous transthoracic pericardial puncture was performed via a subxiphoid approach, and an ablation catheter was positioned at the epicardial aspect of the putative AP location for epicardial-endocardial electrogram comparison. Endocardial RF energy was applied to locations considered appropriate. Epicardial RF applications were delivered when endocardial applications failed. Coronary arteriography was performed to assess the proximity of coronary arteries to the ablation catheter. RESULTS: APs were located in the right free wall (4 patients, 5 APs) and the right (1 patient) and left (1 patient) posteroseptal regions. In all patients, epicardial mapping assisted in identifying successful ablation sites. In 3 patients, the earliest atrial activation during orthodromic tachycardia was present in an epicardial electrogram. Successful AP ablation was achieved with an epicardial RF application in 2 patients, either alone or with simultaneous endocardial-epicardial delivery. In the remaining 4 patients, APs were successfully ablated endocardially after epicardial mapping. These patients represent 18% of all cases referred to our institution for ablation of previously failed accessory pathways (6/32 patients). CONCLUSIONS: A combined endocardial-epicardial approach to mapping and RF ablation can facilitate successful endocardial ablation in most cases. In selected cases, APs can be ablated by epicardial delivery of RF. Epicardial mapping is an effective alternative to cardiac surgery for patients in whom prior attempts at AP ablation have failed.

Beta-blocker therapy for heart failure: the standard of care.

Sympathetic nervous system activation plays an important role in the genesis of symptoms, functional impairment, progressive ventricular dysfunction, and mortality in patients with heart failure. Prospective, randomized clinical trials of beta-blockers in patients with heart failure have demonstrated mortality reductions in patients across the spectrum of clinical presentations and etiologies. Additionally, these trials have provided important information regarding the indications, dosing, and extent of therapeutic benefits of the different beta-blockers studied in patients with heart failure. The recognition that beta-blockers relieve symptoms, reduce hospitalizations, and prolong survival in patients with heart failure represents one of the most important therapeutic advances in the treatment of this complex disorder. Beta-blockers, along with angiotensin-converting enzyme inhibitors and aldosterone antagonists, now represent the standard of care for patients with heart failure.

Cardiac mass in the setting of acute myocardial infarction.

When a middle-aged woman with a complex cardiac history presented with a cardiac mass in the setting of an evolving myocardial infarction, it created a diagnostic dilemma. This case report describes the diagnostic evaluation of such a patient and discusses the rare finding of an intramyocardial hematoma.

Physical and psychological attributes of fatigue in female heart transplant recipients.

BACKGROUND: The attributes of fatigue after orthotopic heart transplantation (OHT) are poorly understood. We conducted this study to assess the prevalence, severity and correlates of fatigue among female OHT survivors. METHODS: Fifty women (age 54.7 +/- 13.0 years) from a single heart transplant center, who underwent OHT 5.1 +/- 4.4 (mean +/- SD) years earlier, completed a battery of questionnaires including the Profile of Mood States-fatigue sub-scale to assess levels of fatigue, the Beck Depression Inventory to measure depression, and the Short Form-36 to measure functional status and mental health. Demographic and clinical data were obtained from self-reports and medical chart reviews. RESULTS: Women reported mean scores of 15.7 +/- 6.8 (range 3 to 27), 13.2 +/- 8.2 (range 0 to 38), 37.2 +/- 10.8 (range 22 to 62) and 41.5 +/- 11.2 (range 17 to 60) for fatigue, depression, functional status and mental health, respectively. Univariate analyses revealed that sociodemographic and clinical variables (e.g., age, employment status, anemia, renal insufficiency) were significantly related to fatigue (p < 0.001). Likewise, depression, functional status and mental health were also significantly related to fatigue (p < 0.001). In a multivariate model, age (adjusted R(2) = 0.23, p < 0.001), anemia (adjusted R(2) = 0.39, p < 0.001), functional status (adjusted R(2) = 0.60, p < 0.001) and depression (adjusted R(2) = 0.69, p < 0.001) were significant predictors of fatigue. The model explained 69% of the variance in fatigue (p < 0.001). CONCLUSIONS: Fatigue is common in women after OHT and is associated with both physiologic and psychologic factors. Clinicians should evaluate all female recipients for symptoms of fatigue, especially those with anemia, renal insufficiency, poor functional status and depression. Other potential mediators of fatigue, such as the denervated donor heart and type of immunosuppressive regimen, may also play a role and require further study.

Electrophysiological characterization of cardiac veins in humans.

BACKGROUND: The coronary sinus is a complex structure with a surrounding myocardial coat and muscle bundles that course within it. The purpose of this study was to evaluate the electrical activity of the coronary sinus (CS), great cardiac vein (GCV) and related structures, such as the Vein of Marshall (VOM). METHODS AND RESULTS: Data obtained from adult ( n = 114) and pediatric patients ( n = 16) were analyzed. The width of atrial electrograms (EGMs) within the CS at a basic pacing cycle length of 600 ms was 46 +/- 7.4 ms (mean +/- SD) vs. 29.7 +/- 6.3 ms in the GCV ( p < 0.01). With decremental pacing the width of the EGM within the CS at 300 ms increased to 66.6 +/- 8.5 ms ( p < 0.1 compared to CS EGM at pacing cycle length of 600 ms). The width of the EGM within the GCV increased from 29.7 +/- 6.3 ms at a pacing cycle length of 600 ms to 34.6 +/- 6.0 at 300 ms ( p = NS). There were no significant differences in the atrial EGM width between CS and GCV in the pediatric patients. CONCLUSIONS: We conclude that atrial electrograms are wider in the CS but not in the GCV. This finding can be explained by the presence of a myocardial coat around the CS. The rate response characteristics of the atrial electrograms within the CS are consistent with a lack of tight coupling between muscle bundles and the CS musculature. Further, the absence of such differences in pediatric patients could partly explain relative differences in types of supraventricular arrhythmias seen in different age groups.

Impact of shock energy and ventricular rhythm on the success of first shock therapy: the ALTITUDE first shock study.

BACKGROUND: The efficacy of shock in converting different ventricular tachyarrhythmias has not been well characterized in a large natural-practice setting. OBJECTIVE: To determine shock success rate by energy and ventricular rhythm in a large cohort of patients with implantable cardioverter-defibrillators. METHODS: Two thousand patients with 5279 shock episodes were randomly sampled for analysis from the LATITUDE remote monitoring system. Within an episode, the rhythm preceding therapy (shock or antitachycardia pacing [ATP]) was adjudicated. Patients who died after unsuccessful implantable cardioverter-defibrillator shocks did not transmit final remote monitoring data and were not included in the study. RESULTS: Of 3677 shock episodes for ventricular tachyarrhythmia, 2679 were treated with shock initially and were classified as monomorphic ventricular tachycardia ( n = 1544), polymorphic/monomorphic ventricular tachycardia (n = 371), or ventricular fibrillation (n = 764). The success rate after the first, second, and final shock averaged 90.3%, 96.4%, and 99.8%, respectively. After unsuccessful initial ATP (n = 998), the first, second, and final shock was successful in 84.8%, 92.9%, and 100% of the episodes. The success rate after the first or second shock was significantly lower after failed ATP compared to shock as first therapy (both P<.001). Among episodes treated initially with shock, the success rate for monomorphic ventricular tachycardia (89.2%) when treated with energy level ≤ 20 J was significantly higher than that for ventricular fibrillation (80.8%) (P = .04). The level of shock energy was a significant predictor of the success of the first shock (odds ratio 1.16; 95% confidence interval 1.03-1.30; P = .013). CONCLUSIONS: The success rate of first shock as first therapy is approximately 90%, but was lower after failed ATP. Programming a higher level of energy after ATP is suggested.