Effect of ventricular pacing lead position on tricuspid regurgitation: A randomized prospective trial.

BACKGROUND: Pacing lead-related tricuspid regurgitation (TR), a recognized complication of ventricular pacing lead implantation, may be affected by lead position or diameter. OBJECTIVE: This study sought to determine the effect of ventricular pacing lead position and diameter on pacing lead-related TR. METHODS: A randomized prospective trial compared pacing leads in the right ventricular apex (RVA), right ventricular septum (RVS), or left ventricle via the coronary sinus (LV-CS) in a 1:1:1 fashion. Patients undergoing implantable cardioverter-defibrillator lead implantation in the RVA (RVA-ICD) were enrolled in a comparison group. Patients with preexisting moderate or greater TR were excluded. Prospective clinical evaluation, transthoracic echocardiograms, and device interrogation occurred 24 hours and 12 months after device implantation. RESULTS: Sixty-three patients undergoing pacemaker implantation were randomized to RVA, RVS, or LV-CS pacing, and 48 RVA-ICD patients were enrolled as a comparison group. At 12 months, 6 patients (6.4%) developed moderate or greater TR. Moderate or greater TR was not significantly different between groups if analyzed by intention to treat (RVA 5.9%, RVS 10.0%, LV-CS 6.7%, and RVA-ICD 4.8%) or if analyzed by final lead location (RVA 4.8%, RVS 10.5%, LV-CS 8.3%, and RVA-ICD 5.1%). Ventricular lead-related complications occurred in 3 patients with right ventricular leads (3.2%) and 2 patients with LV-CS leads (11.1%) (P = .184). CONCLUSION: Neither pacing lead position nor diameter appears to affect TR development significantly. LV-CS leads failed to achieve a statistically significant reduction in TR as compared with right ventricular leads.

Ankle MRI and Arthroscopy Correlation With Cartilaginous Defects and Symptomatic Os Trigonum.

Arthroscopic intervention of the foot and ankle is used for a growing number of procedures. Magnetic resonance imaging (MRI) can be a helpful technique while detecting pathology before surgical intervention. A common use of MRI is detecting osteochondral lesion of the talus; however, other pathology can be detected including but not limited to symptomatic Os trigonum and subtalar osteochondral defects. An MRI sensitivity and specificity for detecting these pathologies vary. Correlating findings on MRI with arthroscopy is helpful in determining its accuracy and will be discussed in the following case examples.

Implantable Cardioverter Defibrillator Programming Characteristics, Shocked Rhythms, and Survival Among Patients Under Thirty Years of Age.

INTRODUCTION: Indications for implantable cardioverter defibrillators (ICDs) in young patients have expanded and differ from those in older adults. We sought to provide descriptive characteristics and data regarding ICD therapy and outcomes among younger and older ICD recipients. METHODS AND RESULTS: Demographics, device type and programming, remotely transmitted data, shock events, and survival were compared among younger (≤30 years) and older (>30 years) cohorts with ICDs from a single manufacturer followed on a remote network. The younger cohort included 904 patients (1.6% of all implants). This group had more females (46% vs. 25%; P < 0.01), single-coil leads (21% vs. 4%; P < 0.01), and single-chamber devices (46% vs. 34%; P < 0.01). Shock incidence was higher (40% younger vs. 32% older at 4 years; P < 0.01) and survival was better over comparable follow-up (88% vs. 72%; P < 0.01). Remote monitoring was associated with improved survival in both groups (93% vs. 86% ≤ 30 years, P < 0.01; 73% vs. 66% > 30 years, P < 0.01). Shock for polymorphic ventricular tachycardia/fibrillation (VT/VF) was more frequent in younger patients (12% vs. 5%; P < 0.01); 39% of all shocks were inappropriate. A 10-fold increased risk of mortality was seen among young patients with shocks for atrial fibrillation/flutter (AF/AFL). CONCLUSIONS: Differences in survival, shock incidence, and prognostic significance of VT/VF and AF/AFL exist between younger and older ICD recipients. These suggest distinct differences in myocardial substrates and diseases that ultimately impact ICD management.

Entrapment of a Pacing Lead within a Chiari Network: Utility of Intracardiac Echo and a Laser Sheath.

Although rare, Chiari networks are elaborate embryological remnants that can pose distinct challenges for catheter and pacing lead manipulation within the right atrium. Device entrapment may require open thoracotomy for removal, with significant morbidity. We report an unusual case of pacing lead entanglement within this structure, followed by prompt intracardiac echocardiographic identification and laser sheath removal.

Recent Advances in the Pharmacological Management of Atrial Fibrillation.

Atrial fibrillation (AF) is a highly prevalent cardiac arrhythmia that leads to hospitalizations for complications and adverse events each year. Despite significant improvement in our therapeutic approaches in the past decade, management of AF remains a difficult task. Novel therapies have failed to terminate AF and prevent its recurrence, and patients with AF continue to have thromboembolic complications. With the increasingly aging population and associated conditions, the prevalence of AF is expected to progressively increase, becoming a public health problem. Most patients with AF have multiple comorbidities and are of advanced age, making long-term anticoagulation challenging. This article provides an overview of the current pharmacological therapies for the management of AF, with particular emphasis on the emerging agents.

Left Atrial Appendage Patency at Cardioversion After Surgical Left Atrial Appendage Intervention.

BACKGROUND: Surgical left atrial appendage (LAA) closure is often incomplete, with patients frequently requiring direct current cardioversion (DCCV) for atrial arrhythmias. Transesophageal echocardiography (TEE) is often performed before DCCV to exclude LAA thrombus. The impact of incomplete surgical LAA closure on patients referred for postoperative DCCV is unknown. METHODS: We retrospectively reviewed patients undergoing TEE-guided DCCV within 30 days of cardiac surgery and surgical LAA closure. All pre-DCCV TEEs were reviewed to assess LAA patency and the presence of thrombus. RESULTS: Ninety-three patients (mean age 68 years; 61 men [66%]) had a median time from surgery to DCCV of 6 days. Duration of atrial fibrillation was 48 hours or more in 85% (n = 79). On pre-DCCV TEE, a residual communication from the LAA was noted in 37% (n = 34). The rate of LAA patency was higher after suture closure than after surgical excision or staple closure. Thrombus was present in 26 of the 93 patients (28%), including 16 of 34 patients (47%) with incomplete closure of LAA. The strongest risk factor for thrombus was a patent, partially closed LAA (odds ratio 4.36, p = 0.003). Systemically accessible thrombus was present in 19 of the 93 patients (20%), and cardioversion was cancelled owing to thrombus in 15 (16%). CONCLUSIONS: Surgical closure of the LAA is often incomplete. Interrogation of the residual LAA after surgical LAA intervention with TEE before DCCV frequently detects thrombus and alters clinical management. Patients undergoing DCCV after surgical LAA intervention require evaluation with TEE for LAA patency and thrombus.

Atrioventricular and ventricular-to-ventricular programming in patients with cardiac resynchronization therapy: results from ALTITUDE.

PURPOSE: Cardiac resynchronization therapy (CRT) improves outcomes in patients with heart failure, yet response rates are variable. We sought to determine whether physician-specified CRT programming was associated with improved outcomes. METHODS: Using data from the ALTITUDE remote follow-up cohort, we examined sensed atrioventricular (AV) and ventricular-to-ventricular (VV) programming and their associated outcomes in patients with de novo CRT from 2009-2010. Outcomes included arrhythmia burden, left ventricular (LV) pacing, and all-cause mortality at 4 years. RESULTS: We identified 5709 patients with de novo CRT devices; at the time of implant, 34% (n = 1959) had entirely nominal settings programmed, 40% (n = 2294) had only AV timing adjusted, 11% (n = 604) had only VV timing adjusted, and 15% (n = 852) had both AV and VV adjusted from nominal programming. Suboptimal LV pacing (<95%) during follow-up was similar across groups; however, the proportion with atrial fibrillation (AF) burden >5% was lowest in the AV-only adjusted group (17.9%) and highest in the nominal (27.7%) and VV-only adjusted (28.3%) groups. Adjusted all-cause mortality was significantly higher among patients with non-nominal AV delay >120 vs. <120 ms (adjusted heart rate (HR) 1.28, p = 0.008) but similar when using the 180-ms cutoff (adjusted HR 1.13 for >180 vs. ≤180 ms, p = 0.4). CONCLUSIONS: Nominal settings for de novo CRT implants are frequently altered, most commonly the AV delay. There is wide variability in reprogramming. Patients with nominal or AV-only adjustments appear to have favorable pacing and arrhythmia outcomes. Sensed AV delays less than 120 ms are associated with improved survival.

Total ankle arthroplasty with severe preoperative varus deformity.

Advancements in total ankle arthroplasty (TAA) over the past several decades have led to improved patient outcomes and implant survivorship. Despite these innovations, many implant manufacturers still consider a preoperative coronal plane deformity greater than 10° a relative contraindication to TAA. Without proper intraoperative alignment, these implants may experience abnormal wear and hardware failure. Correcting these deformities, often through the use of soft tissue procedures and/or osteotomies, not only increases the difficulty of a case, but also the intraoperative time and radiation exposure. The authors report a case in which a 54-year-old man with a severe right ankle varus deformity of 29° underwent successful TAA using the INBONE II Prophecy total ankle system (Wright Medical Technology, Inc, Memphis, Tennessee) and additional soft tissue reconstruction. Intraoperatively, the patient's coronal deformity was corrected to 1.8°. At 8 months postoperatively, the patient ambulated without restriction and had substantial improvement in validated patient outcome scores, specifically the Academy of Orthopaedic Surgeons Foot and Ankle Module and the Short Form Health Survey-12 This unique report documents the first time that this particular implant, with an exclusive preoperative computed tomography-derived patient-specific guide, has been used effectively for a severe preoperative varus deformity greater than 20° without the need for an osteotomy. Future studies should be directed toward the prospective evaluation of different total ankle implant systems and their outcomes with severe coronal plane deformity, specifically computed tomography-derived patient-specific guided implants.

Correlation of geomagnetic activity with implantable cardioverter defibrillator shocks and antitachycardia pacing.

OBJECTIVE: To investigate a potential relationship between implantable cardioverter defibrillator (ICD) therapies and daily geomagnetic activity (GMA) recorded in a large database. PATIENTS AND METHODS: The ALTITUDE database, derived from the Boston Scientific LATITUDE remote monitoring system, was retrospectively analyzed for the frequency of ICD therapies. Daily GMA was expressed as the planetary K-index and the integrated A-index and was graded as levels I (quiet), II (unsettled), III (active), and IV (storm). RESULTS: A daily mean ± SD of 59,468±11,397 patients were monitored between January 1, 2009, and May 15, 2012. The distribution of days according to GMA was as follows: level I, 924/1231 (75%); level II, 226/1231 (18%); level III, 60/1231 (5%); and level IV, 21/1231 (2%). The daily mean ± SD numbers of ICD shocks received per 1000 active patients in the database were 1.29±0.47, 1.17±0.46, 1.03±0.37, and 0.94±0.29 on level I, II, III, and IV days, respectively; the daily mean ± SD sums of shocks and antitachycardia pacing therapies were 9.29±2.86, 8.46±2.45, 7.92±1.80, and 7.83±2.28 on quiet, unsettled, active, and storm days, respectively. A significant inverse relationship between GMA and frequency of ICD therapies was identified, with the most pronounced difference between level I and level IV days (P<.001 for shocks; P=.008 for shocks + antitachycardia pacing). CONCLUSION: In a large-scale cohort analysis, ICD therapies were delivered less frequently on days of higher GMA, confirming the previous pilot data and suggesting that higher GMA does not pose an increased risk of arrhythmias using ICD therapies as a surrogate marker. Further studies are needed to gain an in-depth understanding of the underlying mechanisms.

Transesophageal echocardiography-guided cardioversion after cardiac operations.

BACKGROUND: Transesophageal echocardiography (TEE) is often performed during cardiac operations. The need to repeat TEE to exclude left atrial or left atrial appendage thrombus before direct current cardioversion (DCCV) in patients with a recent intraoperative TEE showing no thrombus is unclear. We sought to determine the incidence of and risk factors for new thrombus in patients undergoing TEE-guided DCCV after cardiac operations. METHODS: We reviewed 817 patients referred for TEE-guided DCCV within 30 days of a cardiac operation and an intraoperative TEE. Patients were excluded if the intraoperative TEE showed thrombus or a surgical left atrial appendage intervention was performed. Univariate logistic regression identified risk factors for thrombus. RESULTS: The study included 362 patients (71% male) with a mean age of 69 years. Median time from the operation to DCCV was 6 days. Thrombus was present in 13 patients (3.6%) on TEE before cardioversion; DCCV was cancelled in these patients. Heart failure was associated with a significantly higher risk of new thrombus formation (7% vs 2%; odds ratio, 3.26; 95% confidence interval, 1.07 to 9.95). Preoperative atrial arrhythmias, duration of perioperative arrhythmias, level of anticoagulation, and time from operation to DCCV were not significantly associated with thrombus. Thrombus was not associated with 30-day mortality. CONCLUSIONS: Development of new thrombus in patients with atrial arrhythmias early after cardiac operations is not uncommon, especially in patients with heart failure. Patients at high risk for thromboembolic events should undergo TEE before DCCV, even if a recent intraoperative TEE showed no thrombus.

Predictors and outcomes of "super-response" to cardiac resynchronization therapy.

BACKGROUND: Cardiac resynchronization therapy (CRT) has been shown to improve heart failure (HF) symptoms and survival. We hypothesized that a greater improvement in left-ventricular ejection fraction (LVEF) after CRT is associated with greater survival benefit. METHODS AND RESULTS: In 693 patients across 2 international centers, the improvement in LVEF after CRT was determined. Patients were grouped as non-/modest-, moderate-, or super-responders to CRT, defined as an absolute change in LVEF of ≤5%, 6-15%, and >15%, respectively. Changes in New York Heart Association (NYHA) functional class and left ventricular end-diastolic dimension (LVEDD) were assessed for each group. There were 395 non-/modest-, 186 moderate-, and 112 super-responders. Super-responders were more likely to be female and to have nonischemic cardiomyopathy, lower creatinine, and lower pulmonary artery systolic pressure than non-/modest- and moderate-responders. Super-responders were also more likely to have lower LVEF than non-/modest-responders. There was no difference in NYHA functional class, mitral regurgitation grade, or tricuspid regurgitation grade between groups. Improvement in NYHA functional class (-0.9 ± 0.9 vs -0.4 ± 0.8 [P < .001] and -0.6 ± 0.8 [P = .02]) and LVEDD (-8.7 ± 9.9 mm vs -0.5 ± 5.0 and -2.4 ± 5.8 mm [P < .001 for both]) was greatest in super-responders. Kaplan-Meier survival analysis revealed that super-responders achieved better survival compared with non-/modest- (P < .001) and moderate-responders (P = .049). CONCLUSIONS: Improvement in HF symptoms and survival after CRT is proportionate to the degree of improvement in LV systolic function. Super-response is more likely in women, those with nonischemic substrate, and those with lower pulmonary artery systolic pressure.

Increase in pulmonary arterial pressure after atrial fibrillation ablation: incidence and associated findings.

PURPOSE: The stiff left atrial (LA) syndrome is defined as pulmonary hypertension (PH) secondary to reduced LA compliance and has recently been shown to be one cause of PH after atrial fibrillation (AF) ablation. We aimed to determine the incidence of an increase in pulmonary arterial (PA) pressure post-ablation and examine the clinical and echocardiographic associations. METHODS: Patients who underwent AF ablation between 1999 and 2011 were included if they had both an echocardiogram pre-ablation and 3 months post-ablation. Patients were then separated into two groups with the increased PA pressure group defined as patients with >10 mmHg increase in right ventricular systolic pressure (RVSP) post-ablation and a post-ablation RVSP >35 mmHg. RESULTS: Of the 499 patients meeting the study criteria, 41 (8.2%) had an increase in RVSP >10 mmHg and RVSP >35 mmHg post-ablation. On echocardiogram, the two groups had similar E/A and E/e' ratios pre-ablation. However, post-ablation, the increased PA pressure group had higher E/A (2.12 vs. 1.49, p < 0.01) and E/e' (14.7 vs. 11.2, p < 0.01) ratios. LA expansion index values were lower in the increased PA pressure group pre-ablation (51 vs. 92%, p < 0.01), but not significantly different post-ablation (82 vs. 88%, p = 0.44). CONCLUSIONS: Around 8% of patients develop an increase in estimated PA pressure after AF ablation. Echocardiographic parameters suggest that patients who develop increased PA pressure are developing (or unmasking) left ventricular diastolic dysfunction.

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.

Symptomatic pulmonary hypertension with giant left atrial v waves after surgical maze procedures: evaluation by comprehensive hemodynamic catheterization.

BACKGROUND: The surgical maze procedure is highly effective in treating symptomatic atrial fibrillation but may have detrimental effects on left atrial (LA) contractile function and compliance. OBJECTIVE: To describe a series of patients presenting with symptomatic pulmonary hypertension due in part to LA dysfunction after surgical maze procedures. METHODS: This report includes 9 patients who (1) presented to Mayo Clinic (Rochester, MN) between 2008 and 2012 with unexplained dyspnea and pulmonary hypertension after the surgical maze procedure, (2) underwent comprehensive hemodynamic catheterization with transseptal measurement of LA pressure, (3) had large v waves on LA pressure waveforms, and (4) did not have significant mitral valve regurgitation or stenosis or pulmonary vein stenosis. RESULTS: Invasive hemodynamic assessment revealed (1) severe pulmonary hypertension (mean pulmonary pressure 47 ± 6 mm Hg), (2) severe LA hypertension (27 ± 4 mm Hg), (3) giant LA v waves (to 50 ± 8 mm Hg), (4) absence of LA or left ventricular a waves, and (5) blunted x descents (2 ± 1 mm Hg). Left ventricular end-diastolic pressure was also elevated (20 ± 5 mm Hg). CONCLUSIONS: Abnormalities in LA compliance and contractility may lead to giant LA v waves and symptomatic pulmonary hypertension after surgical maze procedures. This syndrome should be considered in the differential diagnosis for pulmonary hypertension and underscores the importance of comprehensive hemodynamic catheterization.

Phase 4 paroxysmal AV block in a patient with scleroderma.

A 72-year-old man with limited cutaneous systemic scleroderma was hospitalized for two episodes of witnessed syncope. The baseline 12-lead electrocardiogram was normal but on telemetry there were numerous episodes of paroxysmal AV block with asystolic periods of up to 7.5 s duration. Analysis of the rhythm strips revealed phase 4 intra-His bundle block characterized by critical P-P intervals that triggered the AV block, and a narrow range of junctional escape to subsequent P wave intervals that were required to release the AV block. A dual chamber pacemaker was implanted.

Survival after shock therapy in implantable cardioverter-defibrillator and cardiac resynchronization therapy-defibrillator recipients according to rhythm shocked. The ALTITUDE survival by rhythm study.

OBJECTIVES: This study sought to determine if the risk of mortality associated with inappropriate implantable cardioverter-defibrillator (ICD) shocks is due to the underlying arrhythmia or the shock itself. BACKGROUND: Shocks delivered from ICDs are associated with an increased risk of mortality. It is unknown if all patients who experience inappropriate ICD shocks have an increased risk of death. METHODS: We evaluated survival outcomes in patients with an ICD and a cardiac resynchronization therapy defibrillator enrolled in the LATITUDE remote monitoring system (Boston Scientific Corp., Natick, Massachusetts) through January 1, 2010. First shock episode rhythms from 3,809 patients who acutely survived the initial shock were adjudicated by 7 electrophysiologists. Patients with a shock were matched to patients without a shock (n = 3,630) by age at implant, implant year, sex, and device type. RESULTS: The mean age of the study group was 64 ± 13 years, and 78% were male. Compared with no shock, there was an increased rate of mortality in those who received their first shock for monomorphic ventricular tachycardia (hazard ratio [HR]: 1.65, p < 0.0001), ventricular fibrillation/polymorphic ventricular tachycardia (HR: 2.10, p < 0.0001), and atrial fibrillation/flutter (HR: 1.61, p = 0.003). In contrast, mortality after first shocks due to sinus tachycardia and supraventricular tachycardia (HR: 0.97, p = 0.86) and noise/artifact/oversensing (HR: 0.91, p = 0.76) was comparable to that in patients without a shock. CONCLUSIONS: Compared with no shock, those who received their first shock for ventricular rhythms and atrial fibrillation had an increased risk of death. There was no significant difference in survival after inappropriate shocks for sinus tachycardia or noise/artifact/oversensing. In this study, the adverse prognosis after first shock appears to be more related to the underlying arrhythmia than to an adverse effect from the shock itself.

Delayed intrinsicoid deflection onset in surface ECG lateral leads predicts left ventricular reverse remodeling after cardiac resynchronization therapy.

BACKGROUND: Up to one-third of the patients who undergo cardiac resynchronization therapy (CRT) are not responders. OBJECTIVE: To demonstrate that delayed lateral left ventricular activation time determined through time to intrinsicoid deflection onset (ID) predicts response after CRT. METHODS: The ID in leads I, aVL, V1 and V2, and V5 and V6 were measured in 135 patients who underwent CRT. A CRT response was defined as a decrease in left ventricular end-systolic volume (LVESV) exceeding 15% at 6 months. RESULTS: In patients with left bundle branch block or nonspecific intraventricular conduction delay, response was predicted by longer ID in lead I (odds ratio [OR] 3.23; 95% confidence interval (CI) 1.4-7.4; per 20-ms increase), in lead aVL (OR 3.0; 95% CI 1.2-7.3; per 20-ms increase), and in lead I minus lead V1 (OR 2.4; 95% CI 1.2-4.7) adjusting for baseline QRS duration and LVESV. Results were similar after adjusting for postimplant or change in QRS duration. The ID parameters were better predictors of response than QRS duration parameters. ID in lead I/QRS duration ratio (OR 3.1; 95% CI 1.6-5.9) also increased the odds of response after adjusting for baseline LVESV. Cutoff values for ID in leads--I, 110 ms; aVL, 130 ms; I minus V1, 90 ms--and ID in lead I/QRS duration ratio of 0.69 yielded a sensitivity and a specificity as high as 83% and 81%. CONCLUSIONS: Measurement of ID on surface electrocardiography permits a preimplant, noninvasive means of determining left ventricle activation delay; is a good predictor of CRT response; and represents a promising alternative to QRS duration parameters.

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.