Assessing the Risks Associated with MRI in Patients with a Pacemaker or Defibrillator.

BACKGROUND: The presence of a cardiovascular implantable electronic device has long been a contraindication for the performance of magnetic resonance imaging (MRI). We established a prospective registry to determine the risks associated with MRI at a magnetic field strength of 1.5 tesla for patients who had a pacemaker or implantable cardioverter-defibrillator (ICD) that was "non-MRI-conditional" (i.e., not approved by the Food and Drug Administration for MRI scanning). METHODS: Patients in the registry were referred for clinically indicated nonthoracic MRI at a field strength of 1.5 tesla. Devices were interrogated before and after MRI with the use of a standardized protocol and were appropriately reprogrammed before the scanning. The primary end points were death, generator or lead failure, induced arrhythmia, loss of capture, or electrical reset during the scanning. The secondary end points were changes in device settings. RESULTS: MRI was performed in 1000 cases in which patients had a pacemaker and in 500 cases in which patients had an ICD. No deaths, lead failures, losses of capture, or ventricular arrhythmias occurred during MRI. One ICD generator could not be interrogated after MRI and required immediate replacement; the device had not been appropriately programmed per protocol before the MRI. We observed six cases of self-terminating atrial fibrillation or flutter and six cases of partial electrical reset. Changes in lead impedance, pacing threshold, battery voltage, and P-wave and R-wave amplitude exceeded prespecified thresholds in a small number of cases. Repeat MRI was not associated with an increase in adverse events. CONCLUSIONS: In this study, device or lead failure did not occur in any patient with a non-MRI-conditional pacemaker or ICD who underwent clinically indicated nonthoracic MRI at 1.5 tesla, was appropriately screened, and had the device reprogrammed in accordance with the prespecified protocol. (Funded by St. Jude Medical and others; MagnaSafe ClinicalTrials.gov number, NCT00907361 .).

Biventricular ICD Placement Percutaneously Via the Iliac Vein: Case Reports and a Review.

Cardiac resynchronization therapy (CRT) has been demonstrated to improve symptoms of heart failure. As a result, it has become the standard of care in selected patients, and is commonly completed with three leads placed via an upper-extremity vein. However, in rare situations, such as in the case of superior vena cava occlusion, venous access is not possible via the upper extremity. It is in such instances that alternative means must be sought. Here, two patients who received a CRT defibrillator via an iliac vein approach with a mid-abdominal generator are introduced, and a review of the techniques used is presented. Technical aspects to this approach are discussed, including iliac venous access, defibrillation electrode positioning, coronary sinus access, and lead tunneling to an abdominal generator for patient comfort. This approach should be considered when vascular access is compromised, at least until combined leadless CRT pacing and subcutaneous implantable cardioverter-defibrillator devices become available and feasible for use.

A novel patch for heart rhythm monitoring: is the Holter monitor obsolete?

A number of substantial improvements to the 60-year-old concept of the Holter monitor have recently been developed. One promising advance is the Zio(®) Patch (iRhythm Technologies, Inc., CA, USA), a small 2 × 5-inch patch, which can continuously record up to 14 days of a single ECG channel of cardiac rhythm without the need for removal during exercise, sleeping or bathing. Its ease-of-use, which enables optimal long-term monitoring, has been established in the ambulatory setting, although some insurance carriers have been reluctant to reimburse appropriately for this advance, an issue characteristic of other heart monitors, treated as 'loss-leaders.' In this article, in addition to discussing possible reasons for this reluctance, a novel model for direct-to-consumer marketing of heart monitoring, outside of the traditional health insurance reimbursement model, is also presented. Additional current and future advances in heart rhythm recording are also discussed. Such potentially revolutionary opportunities have only recently become possible as a result of technologic advances.

Cardiac-resynchronization therapy for the prevention of heart-failure events.

BACKGROUND: This trial was designed to determine whether cardiac-resynchronization therapy (CRT) with biventricular pacing would reduce the risk of death or heart-failure events in patients with mild cardiac symptoms, a reduced ejection fraction, and a wide QRS complex. METHODS: During a 4.5-year period, we enrolled and followed 1820 patients with ischemic or nonischemic cardiomyopathy, an ejection fraction of 30% or less, a QRS duration of 130 msec or more, and New York Heart Association class I or II symptoms. Patients were randomly assigned in a 3:2 ratio to receive CRT plus an implantable cardioverter-defibrillator (ICD) (1089 patients) or an ICD alone (731 patients). The primary end point was death from any cause or a nonfatal heart-failure event (whichever came first). Heart-failure events were diagnosed by physicians who were aware of the treatment assignments, but they were adjudicated by a committee that was unaware of assignments. RESULTS: During an average follow-up of 2.4 years, the primary end point occurred in 187 of 1089 patients in the CRT-ICD group (17.2%) and 185 of 731 patients in the ICD-only group (25.3%) (hazard ratio in the CRT-ICD group, 0.66; 95% confidence interval [CI], 0.52 to 0.84; P=0.001). The benefit did not differ significantly between patients with ischemic cardiomyopathy and those with nonischemic cardiomyopathy. The superiority of CRT was driven by a 41% reduction in the risk of heart-failure events, a finding that was evident primarily in a prespecified subgroup of patients with a QRS duration of 150 msec or more. CRT was associated with a significant reduction in left ventricular volumes and improvement in the ejection fraction. There was no significant difference between the two groups in the overall risk of death, with a 3% annual mortality rate in each treatment group. Serious adverse events were infrequent in the two groups. CONCLUSIONS: CRT combined with ICD decreased the risk of heart-failure events in relatively asymptomatic patients with a low ejection fraction and wide QRS complex. (ClinicalTrials.gov number, NCT00180271.)

Adjudication of mortality events in a heart failure-arrhythmia trial by a multiparameter descriptive method: comparison with methods used in heart failure trials and methods used in arrhythmia trials.

INTRODUCTION: Mortality events in studies of cardiovascular disease are currently adjudicated using different methodologies depending on the investigators' preferences. Traditionally, deaths have been categorized by a single term, such as sudden, ischemic, or pump failure, a method that can be referred to as "categorical". In contrast, deaths may be categorized using several specific pieces of information about the event, a method that can be referred to as "multiparameter descriptive." Herein, we describe an adaptation of this descriptive method in a trial of patients with heart failure and arrhythmias. METHODS AND RESULTS: Case examples were selected from two clinical trials of an investigational implantable cardioverter-defibrillator (ICD)-biventricular pacing system in patients with symptomatic heart failure and a class I indication for ICD implantation, and the complete results for one of the trials are given. Deaths were classified according to the new descriptive method, and also according to published categorical methods for heart failure and arrhythmia trials. The descriptive method preserved traditional arrhythmia and heart failure trial single category classifications of death. Furthermore, there was agreement between the arrhythmia and heart failure category classifications in 126 of the 148 of the mortality events adjudicated (85%). CONCLUSION: A descriptive method for the classification of death retains more data and allows for comparison among trials using different classification schemes. This may allow greater mechanistic insight into study populations that have diverse and frequently multiple etiologies of death.

Inappropriate implantable cardioverter-defibrillator shocks in MADIT II: frequency, mechanisms, predictors, and survival impact.

OBJECTIVES: This study sought to identify the incidence and outcome related to inappropriate implantable cardioverter-defibrillator (ICD) shocks, that is, those for nonventricular arrhythmias. BACKGROUND: The MADIT (Multicenter Automatic Defibrillator Implantation Trial) II showed that prophylactic ICD implantation improves survival in post-myocardial infarction patients with reduced ejection fraction. Inappropriate ICD shocks are common adverse consequences that may impair quality of life. METHODS: Stored ICD electrograms from all shock episodes were adjudicated centrally. An inappropriate shock episode was defined as an episode during which 1 or more inappropriate shocks occurred; another inappropriate ICD episode occurring within 5 min was not counted. Programmed parameters for patients with and without inappropriate shocks were compared. RESULTS: One or more inappropriate shocks occurred in 83 (11.5%) of the 719 MADIT II ICD patients. Inappropriate shock episodes constituted 184 of the 590 total shock episodes (31.2%). Smoking, prior atrial fibrillation, diastolic hypertension, and antecedent appropriate shock predicted inappropriate shock occurrence. Atrial fibrillation was the most common trigger for inappropriate shock (44%), followed by supraventricular tachycardia (36%), and then abnormal sensing (20%). The stability detection algorithm was programmed less frequently in patients receiving inappropriate shocks (17% vs. 36%, p = 0.030), whereas other programming parameters did not differ significantly from those without inappropriate shocks. Importantly, patients with inappropriate shocks had a greater likelihood of all-cause mortality in follow-up (hazard ratio 2.29, p = 0.025). CONCLUSIONS: Inappropriate ICD shocks occurred commonly in the MADIT II study, and were associated with increased risk of all-cause mortality.

Multicenter automatic defibrillator implantation trial-cardiac resynchronization therapy (MADIT-CRT): design and clinical protocol.

The planned MADIT-CRT trial is designed to determine if CRT-D will reduce the risk of mortality and HF events by approximately 25% in subjects with ischemic (NYHA class I-II) and non-ischemic (NYHA class II) cardiomyopathy, left ventricular dysfunction (EFor=130 ms).

Efficacy of lower-energy biphasic shocks for transthoracic defibrillation: a follow-up clinical study.

OBJECTIVE: This clinical study prospectively evaluated the first-shock defibrillation efficacy of 150-joule impedance-compensated, 200-microF biphasic truncated exponential (BTE) shocks in patients with electrically-induced ventricular fibrillation (VF), and compared it with a historical control group treated with 200-J monophasic damped sine (MDS) shocks. METHODS: Ventricular tachyarrhythmias were induced in patients undergoing electrophysiologic (EP) testing for ventricular arrhythmias or testing of an implantable cardioverter-defibrillator (ICD). A 150-J shock was delivered as the primary therapy to terminate induced arrhythmias in the EP group, and as a "rescue" shock when a single ICD shock failed to terminate the arrhythmias in the ICD group. RESULTS: Ninety-six patients received study shocks. The preshock rhythm was classified as VF in 77 patients and as ventricular tachycardia (VT) in 19 patients. First-shock success rates for VF and VT were 75 out of 77 (97.4%) and 19 out of 19 (100%) for the 150-J BTE compared with the historical control rates of 61 out of 68 (89.7%) and 29 out of 31 (94%) for 200-J MDS. The first-shock success rate for VF treated with 150-J BTE was technically equivalent to that of 200-J MDS (p=0.001). The transthoracic impedance did not vary between groups, yet the peak current delivered by the 150-J BTE shock was about 50% lower. CONCLUSIONS: This study demonstrated that 150-J shocks of this impedance-compensated, 200-microF BTE waveform provided very high efficacy for defibrillation of short duration, electrically-induced VF. These lower-energy biphasic shocks had a success rate equivalent to that of 200-J MDS shocks, and they provided this efficacy while exposing patients to much less current than the monophasic shocks.

Cardiac resynchronization therapy for the treatment of heart failure in patients with intraventricular conduction delay and malignant ventricular tachyarrhythmias.

OBJECTIVES: This study was conducted to assess the safety and effectiveness of cardiac resynchronization therapy (CRT) when combined with an implantable cardioverter defibrillator (ICD). BACKGROUND: Long-term outcome of CRT was measured in patients with symptomatic heart failure (HF), intraventricular conduction delay, and malignant ventricular tachyarrhythmias (ventricular tachycardia/ventricular fibrillation [VT/VF]) requiring therapy from an ICD. METHODS: Patients (n = 490) were implanted with a device capable of providing both CRT and ICD therapy and randomized to CRT (n = 245) or control (no CRT, n = 245) for up to six months. The primary end point was progression of HF, defined as all-cause mortality, hospitalization for HF, and VT/VF requiring device intervention. Secondary end points included peak oxygen consumption (VO(2)), 6-min walk (6 MW), New York Heart Association (NYHA) class, quality of life (QOL), and echocardiographic analysis. RESULTS: A 15% reduction in HF progression was observed, but this was statistically insignificant (p = 0.35). The CRT, however, significantly improved peak VO(2) (0.8 ml/kg/min vs. 0.0 ml/kg/min, p = 0.030) and 6 MW (35 m vs. 15 m, p = 0.043). Changes in NYHA class (p = 0.10) and QOL (p = 0.40) were not statistically significant. The CRT demonstrated significant reductions in ventricular dimensions (left ventricular internal diameter in diastole = -3.4 mm vs. -0.3 mm, p < 0.001 and left ventricular internal diameter in systole = -4.0 mm vs. -0.7 mm, p < 0.001) and improvement in left ventricular ejection fraction (5.1% vs. 2.8%, p = 0.020). A subgroup of patients with advanced HF (NYHA class III/IV) consistently demonstrated improvement across all functional status end points. CONCLUSIONS: The CRT improved functional status in patients indicated for an ICD who also have symptomatic HF and intraventricular conduction delay.

Automatic Implantable Cardiac Defibrillators.

Since its first human application in 1980, the automatic implantable cardioverter defibrillator (ICD) has undergone remarkable advances leading to expanded acceptance. Originally indicated only for patients who had survived two cardiac arrests, the devices have recently been shown to improve survival in all patients with prior myocardial infarction and an ejection fraction of 30% or less. The devices have been miniaturized and are now implanted transvenously, often with hospital discharge within 24 hours of surgery. The ICD is now considered standard therapy for the prevention of life-threatening arrhythmias. Current versions not only treat ventricular arrhythmias with pacing and shock therapy, but some versions also have the capability to treat and suppress atrial arrhythmias, resynchronize the ventricles to manage heart failure symptoms, or pace the heart with all the features of a dual chamber pacemaker. Technologic advances have dramatically expanded the indications for ICD implantation.

Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction.

BACKGROUND: Patients with reduced left ventricular function after myocardial infarction are at risk for life-threatening ventricular arrhythmias. This randomized trial was designed to evaluate the effect of an implantable defibrillator on survival in such patients. METHODS: Over the course of four years, we enrolled 1232 patients with a prior myocardial infarction and a left ventricular ejection fraction of 0.30 or less. Patients were randomly assigned in a 3:2 ratio to receive an implantable defibrillator (742 patients) or conventional medical therapy (490 patients). Invasive electrophysiological testing for risk stratification was not required. Death from any cause was the end point. RESULTS: The clinical characteristics at base line and the prevalence of medication use at the time of the last follow-up visit were similar in the two treatment groups. During an average follow-up of 20 months, the mortality rates were 19.8 percent in the conventional-therapy group and 14.2 percent in the defibrillator group. The hazard ratio for the risk of death from any cause in the defibrillator group as compared with the conventional-therapy group was 0.69 (95 percent confidence interval, 0.51 to 0.93; P=0.016). The effect of defibrillator therapy on survival was similar in subgroup analyses stratified according to age, sex, ejection fraction, New York Heart Association class, and the QRS interval. CONCLUSIONS: In patients with a prior myocardial infarction and advanced left ventricular dysfunction, prophylactic implantation of a defibrillator improves survival and should be considered as a recommended therapy.

The Low Energy Safety Study (LESS): rationale, design, patient characteristics, and device utilization.

BACKGROUND: A 10-J energy safety margin has traditionally been used in programming implantable cardioverter defibrillators (ICDs). The Low Energy Safety Study (LESS) tests the hypothesis that programming shocks to lower energy margins is safe and effective. METHODS: Patients with standard ICD indications undergo defibrillation threshold testing (DFT) at the time of ICD implant, with reconfirmation of lowest successful energy twice (DFT++). Patients are randomized to 2 groups: the first has the initial 2 shocks for ventricular fibrillation conversion programmed at 2 energy steps above DFT++ (typically 4-6 J, maximum 10 J) with subsequent shocks at maximum energy, and the second has all shocks programmed at maximum energy. Patients are followed up every 3 months for 2 years to assess shock conversion efficacy of spontaneous arrhythmias. In a subgroup of patients, there is a second randomization to energy levels of 0, 1, 2, 3, or 4 steps above implant DFT++ for conversion testing of 3 induced ventricular fibrillation episodes at prehospital discharge, 3 months, and 12 months after implant. RESULTS: Enrollment is complete (702 patients), but follow-up results are pending. There were no significant variations in implant indications and baseline antiarrhythmic drug use over the 3-year enrollment period, although an increase in the percentage of dual-chamber ICDs implanted occurred, with the majority (65%) of implanted ICDs being dual-chamber devices by the end of the enrollment period. CONCLUSION: The results of LESS should facilitate the development of algorithms for programming ICD energy safety margins.