Presence of obesity is associated with lower mortality in elderly patients with implantable cardioverter defibrillator.

BACKGROUND: Higher body mass index (BMI) is associated with greater prevalence of cardiovascular risk factors, yet an inverse relationship between obesity and survival after cardiovascular events has been described. It is unclear whether a similar relationship exists for patients with implantable cardioverter defibrillators (ICDs) at high risk for mortality. We aimed to assess the impact of BMI on mortality and cardiovascular hospitalization in patients with ICD. METHODS: Patients who underwent ICD implantation in 2010-2011 were divided into normal (<25 kg m-2), overweight (25-29.9 kg m-2) and obese (⩾30 kg m-2) groups based on BMI. Clinical parameters were compared and long-term outcomes were determined using χ2 test, Wilcoxon's rank-sum test, logistic regression models and Kaplan-Meier curves. RESULTS: Of 904 patients (mean age 67±13 years), 26% had normal BMI, 32% were overweight and 42% were obese. No significant baseline differences in ventricular ejection fraction, ICD for primary or secondary prevention, history of heart failure, syncope or cardiac arrest existed. Despite a greater prevalence of diabetes, hypertension and prior myocardial infarction, the obese and overweight groups had lower mortality (10.1% and 7.9%, respectively) than the normal group (22.9%, P<0.001). On multivariate logistic regression, BMI in the obese and overweight range (odds ratio (OR): 0.35; 95% confidence interval (CI): 0.21-0.58 and OR: 0.25; 95% CI: 0.13-0.40, respectively) was protective against mortality, whereas history of diabetes (OR: 2.01; 95% CI: 1.30-3.09), myocardial infarction (OR: 1.76; 95% CI: 1.11-2.80), heart failure (OR: 3.88; 95% CI: 1.56-9.66), stroke (OR: 3.19; 95% CI: 1.63-6.23) and history of cardiac arrest (OR: 2.65; 95% CI: 1.37-5.15) were independent risk factors for higher mortality. CONCLUSIONS: A paradoxical relationship between BMI and mortality risk is present in elderly patients with ICD at high risk of sudden death with a lower mortality in obese or overweight patients than in those with normal BMI.

Usefulness of midodrine in patients with severely symptomatic neurocardiogenic syncope: a randomized control study.

INTRODUCTION: The efficacy of midodrine for the management of patients with neurocardiogenic syncope was assessed prospectively in a randomized control study. METHODS AND RESULTS: Patients who had at least monthly occurrences of syncope and a positive tilt-table test were included in the study. A total of 61 patients were randomly allocated to treatment either with midodrine or with fluid, salt tablets, and counseling. Midodrine was given at a starting dose of 5 mg three times a day and increased up to a dose of 15 mg three times a day when required. Midodrine was given during the daytime every 6 hours. Thirty-one patients were assigned to treatment with midodrine; the other 30 patients were advised to increase their fluid intake and were instructed to recognize their prodromes and abort the progression to syncope. Patients were followed-up for at least 6 months. A quality-of-life questionnaire was administered at the time of randomization and 6 months after. At the 6-month follow-up, 25 (81%) of 31 midodrine-treated patients and 4 (13%) of the 30 fluid-therapy patients had remained asymptomatic (P < 0.001). One patient had to discontinue taking midodrine due to severe side effects and another six patients experienced minor side effects that did not require drug discontinuation. CONCLUSION: Midodrine appeared to provide a significant benefit in patients with neurocardiogenic syncope. To prevent recurrence of symptoms, dose adjustments were required in about one third of patients.

Noncontact mapping for radiofrequency ablation of complex cardiac arrhythmias.

Radiofrequency (RF) catheter ablation is the current treatment of choice for several cardiac arrhythmias. The conventional approach utilizing intracardiac electrograms during sinus rhythm and during tachycardia has inherent limitations, including limited two-dimensional fluoroscopic imaging and limited ability to evaluate several potential sites for ablation then go precisely to the most suitable site. Recently, a noncontact mapping system has been developed that can be used to perform single beat high resolution mapping of cardiac arrhythmias. In this report, we describe the advantage of utilizing the system in facilitating a successful outcome in 5 patients with different complex arrhythmias.

Ventricular fibrillation sensing and detection by implantable defibrillators: is one better than the others? A prospective, comparative study.

INTRODUCTION: We prospectively compared the performance of the sensing and detection systems of three leading defibrillator manufacturers: Medtronic, Guidant, and Ventritex. METHODS AND RESULTS: Ventricular fibrillation signal was digitally recorded during defibrillator implantation and subsequently played back sequentially to a Medtronic Micro Jewel II 7223Cx, a Guidant MINI II 1762, and a Ventritex Cadet V-115C. The devices were programmed for single-zone detection, at nominal settings. Rate cutoff was set at 320 msec (185/min for the MINI). We analyzed 253 episodes from 47 patients. Median undersensing was 0%, 2.1%, and 5.3% for the Jewel, MINI, and Cadet, respectively (P < 0.001 for each paired comparison). Detection time was 4.1 +/- 1.6 seconds, 3.4 +/- 1.6 seconds, and 4.3 +/- 2.2 seconds for the Jewel, MINI, and Cadet, respectively (P < 0.001 between MINI-Jewel and MINI-Cadet; P < 0.01 between Jewel-Cadet). Delayed detection (detection time longer than the mean of all observations + 2 SD) occurred in 3 (1.2%), 7 (2.8%), and 18 (7.1%) episodes for the Jewel, MINI, and Cadet, respectively. Performance for all devices was worse when the short-separation integrated bipolar lead was used and when the episode followed a failed high-energy shock. CONCLUSION: Statistically significant differences were seen in sensing and detection performance among the devices and device/lead combinations during ventricular fibrillation. These differences are related to specific features of the respective devices and should be taken into account during clinical practice, as well as in future device development.

Correlation of spontaneous and induced premature atrial complexes initiating atrial fibrillation in humans: electrophysiologic parameters for guiding therapy.

INTRODUCTION: The low frequency of spontaneous premature atrial contractions (PACs) may be an impediment to mapping and ablation of atrial fibrillation (AF). It has been shown that PACs following external or internal cardioversion of AF can initiate AF. If this method could reproducibly induce PACs from the same location as spontaneous PACs, it would be clinically significant. High-resolution noncontact mapping can map a single beat, should help identify the sites of spontaneously occurring PACs and PACs induced following cardioversion of spontaneous or induced AF, and could help correlate the trigger sites for AF induction. METHODS AND RESULTS: Twelve patients (8 men and 4 women; mean age 49+/-10 years) with spontaneous PACs were included in the study. In all patients, AF was induced and subsequently cardioverted to assess and map isolated PACs or PACs that induced AF. Using the EnSite 3000 noncontact mapping system, mapping was performed of spontaneously occurring isolated PACs and PACs that induced AF and PACs (both with and without AF) that occurred on at least two different occasions following cardioversion. The locations of the spontaneous and the induced PACs were similar; 97% of induced PACs came from the same locations as those of spontaneous PACs (P = 0.5). Radiofrequency lesions guided by this mapping technique were delivered at 14 pulmonary vein sites. Following a single ablation attempt during a mean follow-up of 19+/-4 weeks, 42% of the patients were in sinus rhythm and drug-free, whereas an additional 24% of patients could be maintained in sinus rhythm on drugs that had failed before. CONCLUSION: There is a high degree of correlation between spontaneous and induced PACs as the trigger sites for AF initiation. Cardioversion of spontaneous or induced AF could be used as an electrophysiologic parameter for guiding therapy.

Electroanatomically guided catheter ablation of ventricular tachycardias causing multiple defibrillator shocks.

With conventional techniques, RF catheter ablation is difficult in patients with unstable VT or with multiple VTs. The feasibility of RF catheter ablation guided by three-dimensional electroanatomic mapping technique in patients whose implanted ICD continued to deliver multiple shocks due to VT despite use of antiarrhythmic medications was assessed in 19 patients (15 men, 4 women; mean age [+/- SD] 70+/-7 years). All had a prior history of MI and subsequently had received an ICD due to VT. During the 12-week preablation period, these patients received 31+/-15 shocks (range 4-62 shocks) due to refractory monomorphic VTs. An electroanatomic mapping technique using the CARTO system was performed to delineate scar tissue. RF catheter ablation was then performed at appropriate sites identified by pace mapping and by substrate mapping. Seventeen patients were on amiodarone at the time of ablation. Twenty-seven VTs were documented clinically, and 45 were induced during electrophysiological evaluation. Of the 45 tachycardias induced, 38 VTs were targeted for ablation. Catheter ablation was performed during sinus rhythm in 31 episodes and during VT in 7 episodes. During a mean follow-up of 26+/-8 weeks (range 18-48 weeks), 13 (66%) patients had no recurrence of VT (P < 0.0001) and antiarrhythmic drugs were discontinued or the number of medications reduced in 17 patients (P < 0.0001). Electroanatomic mapping is helpful in identifying sites for catheter ablation in highly symptomatic patients with refractory VT associated with myocardial scarring.

Electroanatomic mapping to identify breakthrough sites in recurrent typical human flutter.

The accuracy of conventional techniques in localizing previous radiofrequency (RF) ablation sites and thus breakthrough sites of recurrent atrial flutter is somewhat limited. We investigated the role of electroanatomic mapping for identifying breakthrough sites or "gaps" at the tricuspid annulus and inferior vena cava (IVC)/eustachian ridge isthmus to help RF ablation in patients with recurrent typical flutter. Twelve patients (8 men, 4 women, age 63 +/- 10 years) with recurrent typical atrial flutter were included in the study. An electroanatomic mapping system (CARTO) was used to create a voltage map and activation and propagation patterns in the right atrium. Detailed voltage, activation, and propagation mapping of the tricuspid annulus and IVC/eustachian ridge isthmus allowed precise identification of gaps in all 12 patients at the tricuspid annulus (eight sites), IVC ridges (two sites), mid-isthmus region (one site), and tricuspid annulus and IVC ridges (one site). Radiofrequency energy directed at these sites eliminated atrial flutter in all 12 patients, confirmed by noninducibility of atrial flutter and demonstration of conduction block during atrial pacing on either side of the lesion lines. During a mean follow-up of 14.8 +/- 3.5 months (range 8-19 months), paroxysmal atrial flutter recurred in only one patient and was subsequently treated with amiodarone, although this had been ineffective prior to ablation. Electroanatomic mapping can precisely identify gaps in the lesion line responsible for breakthrough of recurrent typical atrial flutter at the tricuspid annulus and at the IVC/eustachian ridge isthmus. These sites can be targeted with RF ablation with a high degree of success.

Atrial fibrillation: epidemiology, mechanisms and management.

The incidence of AF, the most common sustained arrhythmia in clinical practice, increases with age and coronary artery disease, hypertension and valvular heart disease are common underlying substrates; however, occasionally, AF may occur without any underlying heart disease. The most widely accepted theory of its mechanism is Moe's multiple wavelet hypothesis, although recent studies are helping to shed light on other mechanisms, including the focal origin of AF in some patients. Most patients experience palpitations, but fatigue, dyspnoea, and dizziness may also occur. Therapy includes prevention of thromboembolism, control of rate, and restoration and maintenance of sinus rhythm. The risks and benefits of each treatment modality need to be assessed according to each patient's circumstances. Unlike other arrhythmias, there is still no highly successful therapy for treating AF. However, significant advances are being made using non-pharmacological approaches to either prevent or cure this troublesome arrhythmia.

Inappropriate shock delivery by implantable defibrillators with dual chamber pacing during nonsustained ventricular tachycardia in patients with heart block.

Transvenous implantable cardioverter defibrillators (ICDs) have improved the management of patients with ventricular tachycardia/ventricular fibrillation (VT/VF). Many patients with sustained VT/VF have bradyarrhythmias and nonsustained VT. Shock delivery due to nonsustained VT would be an undesirable feature. Abortive shock capability (noncommitted shocks) is a feature available in devices to prevent delivery of shocks for nonsustained VT. Recently, the availability of dual chamber pacing capability has improved the efficacy of ICDs by obviating the need of separate pacemaker implantation in patients with VT/VF and concomitant bradyarrhythmias. However, interaction between bradyarrhythmias and VT/VF has not been described and has important clinical implications. We report a case in which a patient with complete atrioventricular (AV) block and ventricular arrhythmias received an inappropriate shock following spontaneous termination of nonsustained VT, showing an important shortcoming of devices with these features.

Implantable atrial defibrillator and detection of atrial flutter.

The implantable atrial defibrillator (IAD) is designed to detect and treat atrial fibrillation (AF) with low energy synchronized shocks. A patient with a history of persistent AF was implanted with an IAD after ineffective treatment with procainamide and sotalol. Through four months of follow-up, the IAD performed appropriate detection and treatment of AF. During the fifth month, the patient was put on flecainide in an attempt to minimize the AF recurrence rate. On flecainide the patient experienced typical atrial flutter which required IAD reprogramming for appropriate detection and therapy delivery. This case report examines the optimization of the IAD to detect atrial flutter. Six months of follow-up after optimization the IAD has shown appropriate detection of both atrial flutter and AF. During the entire follow-up period the IAD had appropriate detection of sinus rhythm (no false positive detection, i.e. sinus rhythm as AF).

Endocardial noncontact activation mapping of idiopathic left ventricular tachycardia.

Idiopathic left ventricular tachycardia with a right bundle, left-axis deviation is thought to originate from posterior fascicles. Recently, there has been considerable interest in the anatomic and mechanistic basis of this arrhythmia. We report our experience with a 26-year-old man in whom new noncontact mapping technology was used to acquire detailed data from the left ventricle, identify the mid-diastolic potential and part of the ventricular tachycardia circuit, and perform successful ablation. This information helped define the physiologic aspects of this unique tachycardia.

Sudden cardiac death.

SCD continues to be an important cause of death and morbidity. Despite expanding insight into the mechanisms causing SCD, the population at high risk is not being effectively identified. Although there is still much to do in the management phase of SCD (predicting the efficacy of various therapies), recent clinical trials have helped define the relative risks and benefits of therapies in preventing SCD. Trials are underway to determine whether treating other patient populations, including asymptomatic patients after MI, will improve survival rate. The approach to reducing mortality rate will always be multifaceted; primary prevention of coronary artery disease and prompt salvage of jeopardized myocardium are 2 important aspects of this approach. In addition to interventions for MI, such as myocardial revascularization when indicated, simple and easily administered therapies that are likely to remain the most effective prophylactic interventions are aspirin, ACE inhibitors, beta-blockers, and cholesterol-lowering agents. However, the MADIT and AVID data clearly demonstrate a role for ICD therapy in a subgroup of patients who have VT/VF and are at risk of cardiac arrest. Even though the absolute magnitude of benefit associated with ICDs is still to be determined, the AVID study and other recent reports provide convincing evidence that patients who have VT/VF fare better with ICDs than with antiarrhythmic drug therapy. For the high-risk population described in this article, in addition to aggressive anti-ischemic and heart failure therapy, ICDs are now a mainstay of life-saving treatment. Still to be surmounted is the challenge of identifying patients who have nonischemic substrates and of providing them with the appropriate therapy. Guided by genetic studies and new insight into the mechanisms of such problems as congenital long QT syndrome, life-saving and life-enhancing therapies may soon be available for the management of SCD.

Electroanatomic mapping for radiofrequency ablation of cardiac arrhythmias.

Radiofrequency catheter ablation is the current treatment of choice for several cardiac arrhythmias. The conventional approach utilizing intracardiac electrograms during sinus rhythm and during tachycardia has inherent limitations including limited two-dimensional fluoroscopic imaging and the ability to evaluate several potential sites for ablation and to go precisely to the most suitable site. Recently, a nonfluoroscopic three-dimensional electroanatomic system has been developed for mapping arrhythmias. We describe in this report the advantage of utilizing the system in facilitating a successful outcome in three patients with different arrhythmias.

Ventricular arrhythmias, electrophysiologic studies, and devices.

Because of the high incidence of heart disease in the elderly, ventricular tachyarrhythmias are not infrequent. Determining the nature and extent of the underlying heart disease and identifying precipitating causes is required prior to instituting long-term therapy. Recent studies suggest that for hemodynamically unstable ventricular tachyarrhythmias, mortality is lower with the implantable cardioverter-defibrillator compared with pharmacologic therapy. This benefit is likely to be more modest in the elderly because of competing cardiac and noncardiac causes of death. For similar reasons, the favorable results reported with the prophylactic use of the implantable cardioverter-defibrillator are likely to be attenuated in the elderly.

Atrial fibrillation detection and R-wave synchronization by Metrix implantable atrial defibrillator: implications for long-term efficacy and safety. The Metrix Investigators.

BACKGROUND: The long-term efficacy of atrial fibrillation (AF) detection and R-wave synchronization are critical safety requirements for the development of an implantable atrial defibrillator (IAD) for treatment of AF. METHODS AND RESULTS: The long-term efficacy of the Metrix IAD for AF detection and R-wave synchronization was tested in 51 patients. The mean duration of follow-up was 259+/-138 days (72 to 613 days). AF detection tests were performed 2240 times during observed operation with 100% specificity and 92.3% sensitivity for differentiation between sinus rhythm and AF; 2219 episodes and their electrograms stored in the device during AF detection were analyzed. The positive predictive value of the AF detection algorithm was 97.4% (lower 95% confidence limit [CL], 94.5%) in the out-of-hospital setting. A total of 242 435 R waves were analyzed for R-wave synchronization. Of these, 49% were marked for synchronized shock delivery, 82% of sinus rhythm and 36% of AF R waves, respectively. All shock markers were properly synchronized and within the R wave (overall synchronization accuracy, 100%; lower 95% CL, 99.999%). Overall, 3719 shocks have been delivered via the IAD with no instance of unsynchronized shock delivery or any episode of proarrhythmia. The observed proarrhythmic risk was 0%, with an estimated maximum proarrhythmic risk of 0.084% per shock (95% upper CL). CONCLUSIONS: The Metrix IAD can appropriately detect AF with a high specificity and sensitivity and reliably synchronize within a suitable R wave for shock delivery to minimize the risk of ventricular proarrhythmia.