Isolated very low QRS voltage predicts response to tilt-table testing in patients with neurally mediated syncope.

BACKGROUND: A number of patients with neurally mediated syncope (NMS) have isolated QRS complexes of very low voltage (≤0.3 mV) in the frontal plane leads on the 12-lead electrocardiogram (ECG). HYPOTHESIS: The aim of this study was to assess the importance of QRS voltage in predicting response to tilt-table testing (TTT) in patients with suspected NMS. METHODS: We included 216 patients (age: 49 ± 20 years, 103 men) with suspected NMS who had either a positive or negative response to TTT (n = 91 TTT+, and n = 125 TTT-). The QRS voltage was measured in mV on 12-lead ECGs performed within 3 days of the TTT. The lowest QRS voltage (QRSmin), as well as the voltage in each of the 12 leads was also determined. RESULTS: Very low voltage (QRSmin  ≤ 0.3 mV) in the frontal leads was significantly more prevalent in the TTT+ group than in the TTT- group (74 vs 22%, respectively; P  < .001). Patients in the TTT+ group had significantly lower QRSmin when compared to patients in the TTT- group. QRSmin predicted a positive tilt-table test in a multivariate model that also included patient gender, height, history of presyncope, QRS duration, and left ventricular end-diastolic diameter indexed to height. ROC analysis showed that QRSmin of ≥0.3 mV discriminated between TTT+ and TTT- patients with a sensitivity of 78% and specificity of 68%. CONCLUSION: Isolated very low QRS voltage in the frontal leads predicts a positive response to TTT in patients with suspected NMS.

Isolated very low QRS voltage in the frontal leads predicts recurrence of neurally mediated syncope.

BACKGROUND: The study was prompted by our observation that some patients with neurally mediated syncope (NMS) have an isolated QRS complex, of very low voltage (≤0.3 mV cutoff), in 1 of the frontal leads on the 12-lead electrocardiogram. OBJECTIVE: To prospectively evaluate whether the presence of isolated very low voltage (VLV) predicts recurrence of NMS. METHODS: We included 205 patients (aged 50 ± 17 years) with a median of 3 syncopal episodes. Tilt testing was performed in all patients and was positive in 87 (42%). The patients were followed for a median of 14 months. RESULTS: VLV in frontal leads was present in 92 patients (45%). During the follow-up period 60 patients experienced recurrence of syncope. The actuarial total syncope recurrence rate at 1 year was 32% (95% confidence interval [CI 23%-44%) in patients with isolated VLV in frontal plane leads, and 14% (95% CI 8%-24%) in patients without VLV (log-rank test P < .0001). The significant relationship between the presence of isolated VLV in the frontal leads and syncope recurrence was retained in Cox multivariate analysis that included the history of presyncope and syncope as well as the left ventricular end-diastolic diameter. The presence of isolated VLV in frontal leads was associated with a 3-fold increase of the risk of recurrent syncope. CONCLUSIONS: Isolated very low QRS voltage in the frontal leads predicts recurrence of NMS independent of clinical factors that predict recurrence of syncope in such patients. This phenomenon may help generate new diagnostic tools and insights into the pathogenesis of NMS.

Ranolazine in High-Risk Patients With Implanted Cardioverter-Defibrillators: The RAID Trial.

BACKGROUND: Ventricular tachycardia (VT) and ventricular fibrillation (VF) remain a challenging problem in patients with implantable cardioverter-defibrillators (ICDs). OBJECTIVES: This study aimed to determine whether ranolazine administration decreases the likelihood of VT, VF, or death in patients with an ICD. METHODS: This was double-blind, placebo-controlled clinical trial in which high-risk ICD patients with ischemic or nonischemic cardiomyopathy were randomized to 1,000 mg ranolazine twice a day or placebo. The primary endpoint was VT or VF requiring appropriate ICD therapy or death, whichever occurred first. Pre-specified secondary endpoints included ICD shock for VT, VF, or death and recurrent VT or VF requiring ICD therapy. RESULTS: Among 1,012 ICD patients (510 randomized to ranolazine and 502 to placebo) the mean age was 64 ± 10 years and 18% were women. During 28 ± 16 months of follow-up there were 372 (37%) patients with primary endpoint, 270 (27%) patients with VT or VF, and 148 (15%) deaths. The blinded study drug was discontinued in 199 (39.6%) patients receiving placebo and in 253 (49.6%) patients receiving ranolazine (p = 0.001). The hazard ratio for ranolazine versus placebo was 0.84 (95% confidence interval: 0.67 to 1.05; p = 0.117) for VT, VF, or death. In a pre-specified secondary analysis, patients randomized to ranolazine had a marginally significant lower risk of ICD therapies for recurrent VT or VF (hazard ratio: 0.70; 95% confidence interval: 0.51 to 0.96; p = 0.028). There were no other significant treatment effects in other pre-specified secondary analyses, which included individual components of the primary endpoint, inappropriate shocks, cardiac hospitalizations, and quality of life. CONCLUSIONS: In high-risk ICD patients, treatment with ranolazine did not significantly reduce the incidence of the first VT or VF, or death. However, the study was underpowered to detect a difference in the primary endpoint. In prespecified secondary endpoint analyses, ranolazine administration was associated with a significant reduction in recurrent VT or VF requiring ICD therapy without evidence for increased mortality. (Ranolazine Implantable Cardioverter-Defibrillator Trial [RAID]; NCT01215253).

Epinephrine use results in 'stress' cardiomyopathy.

Epinephrine is a frequently used catecholamine, particularly in emergencies and during resuscitation attempts. It is not without side effects. We report a rare case of epinephrine-induced cardiomyopathy. Epinephrine was administered for bradycardia in our patient. He was treated conservatively and responded well to the treatment. Through our work we wish to highlight this adverse cardiac effect of epinephrine. We hope to increase awareness among residents and practicing physicians while using epinephrine. .

The ventriculophasic response: relationship to sinus arrhythmia and the duration of interposed QRS complexes.

BACKGROUND: The ventriculophasic response (VR) refers to shortening of sinus cycle length during heart block when a QRS complex is interposed between 2 P waves. Our purpose was to analyze its relationship to respiratory sinus arrhythmia (SA) and to compare VR in relation to paced versus intrinsic QRS complexes. METHODS: Patients with advanced heart block had their pacer devices temporarily programmed to ventricular inhibited mode at 30 ppm. In 35 subjects, we analyzed VR and SA before, during and after 3 cycles of deep breathing. In 16 other patients we compared VR in the presence of paced versus narrower intrinsic QRS complexes. RESULTS: The magnitude of P-P interval shortening surrounding QRS complexes during inspiration correlated with SA (r = 0.36, P = 0.03). The prevalence of VR increased from 37% at baseline to 77% of subjects during deep breathing (P = 0.02). The mean P-P interval shortening was greater surrounding intrinsic QRS complexes than paced QRS complexes (3.6 ± 3.6% vs. 1.4 ± 1.1%, P = 0.02). The prevalence of VR increased from 25% during paced rhythm to 56% when intrinsic complexes were present. CONCLUSION: VR, like SA, increases with deep breathing and likely reflects intact parasympathetic nervous system function. Its increase in the presence of narrower beats suggests it may reflect ventricular synchrony.

The ventriculophasic response revisited: analysis of clinical correlations using a new proposed definition derived in pacemaker patients.

BACKGROUND: The ventriculophasic response (VR) refers to shortening of atrial cycle length during heart block when a QRS complex is interposed between P waves. No formal quantitative definition has heretofore been proposed, nor have its potential clinical correlations been studied. HYPOTHESIS: We hypothesized that VR is present in selected patients who are distinguished by clinical features from those who lack VR. METHODS: Pacing devices were temporarily programmed to VVI mode at 30 ppm as electrocardiogram and intracardiac electrograms were recorded at 50 mm/sec paper speed. We measured the percentage decrease in a P-P interval (A-A interval on the atrial electrogram) containing a QRS, compared to the preceding P-P interval. Left ventricular ejection fraction (LVEF) was measured by echocardiogram. RESULTS: Shortening of P-P interval was observed chiefly when the interposed QRS occurred early in the anticipated P-P interval (as judged by the preceding P-P interval). P-P shortening of 0% to 3% occurred randomly. Defining VR as being a >3% P-P interval shortening when an interposed QRS occurred in the first 60% of the anticipated P-P interval, we found that VR was present in 28 (55%) of our patients. It was quite reproducible, was more common in women (81% vs 37% of men; P = 0.004), and positively correlated with LVEF (r = 0.41, P = 0.004). It did not correlate with age, diabetes, or ß-blocker use. CONCLUSIONS: Using our newly derived definition of VR, we found the phenomenon was present in 55% of our patients. It was reproducible and more commonly seen in women and patients with LVEF ≥40%.

Usefulness of high-speed rotational coronary venous angiography during cardiac resynchronization therapy.

Standard coronary venous angiography (SCVA) provides a static, fixed projection of the coronary venous (CV) tree. High-speed rotational coronary venous angiography (RCVA) is a novel method of mapping CV anatomy using dynamic, multiangle visualization. The purpose of this study was to assess the value of RCVA during cardiac resynchronization therapy. Digitally acquired rotational CV angiograms from 49 patients (mean age 69 +/- 11 years) who underwent left ventricular lead implantation were analyzed. RCVA, which uses rapid isocentric rotation over a 110 degrees arc, acquiring 120 frames/angiogram, was compared with SCVA, defined as 2 static orthogonal views: right anterior oblique 45 degrees and left anterior oblique 45 degrees . RCVA demonstrated that the posterior vein-to-coronary sinus (CS) angle and the left marginal vein-to-CS angle were misclassified in 5 and 11 patients, respectively, using SCVA. RCVA identified a greater number of second-order tributaries with diameters >1.5 mm than SCVA. The CV branch selected for lead placement was initially identified in 100% of patients using RCVA but in only 74% of patients using SCVA. RCVA showed that the best angiographic view for visualizing the CS and its tributaries differed significantly among different areas of the CV tree and among patients. The area of the CV tree that showed less variability was the CS ostium, which had a fairly constant relation with the spine in shallow right anterior oblique and left anterior oblique projections. In conclusion, RCVA provided a more precise map of CV anatomy and the spatial relation of venous branches. It allowed the identification of fluoroscopic views that could facilitate cannulation of the CS. The final x-ray view displaying the appropriate CV branch for left ventricular lead implantation was often different from the conventional left anterior oblique and right anterior oblique views. RCVA identified the target branch for lead implantation more often than SCVA.

Variability of coronary venous anatomy in patients undergoing cardiac resynchronization therapy: a high-speed rotational venography study.

BACKGROUND: Imaging the coronary venous (CV) tree to delineate the coronary sinus and its tributaries can facilitate electrophysiological procedures, such as cardiac resynchronization therapy (CRT) and catheter ablation. Venography also allows visualization of the left atrial (LA) veins, which may be a potential conduit for ablative or pacing strategies given their proximity to foci that can trigger atrial fibrillation. OBJECTIVE: The aim of this study was to provide a detailed description of CV anatomy using rotational venography in patients undergoing CRT. METHODS: Coronary sinus (CS) size and the presence, size, and angulation of its tributaries were determined from the analysis of rotational CV angiograms from 51 patients (age 68 +/- 11 years; n = 12 women) undergoing CRT. RESULTS: The CS, posterior veins, and lateral veins were identified in 100%, 76%, and 91% of patients. Lateral veins were less prevalent in patients with a history of lateral myocardial infarction than in patients without such a history (33% vs. 96%; P = .014). The diameters of the CS and its tributaries were fairly variable (7.3-18.9 mm for CS, 1.3-10.5 mm for CS tributaries). The CS was larger in men than in women and in cases of ischemic than in cases of nonischemic cardiomyopathy (all P <.05). The vein of Marshall, the most constant LA vein, was identified in 37 patients; its diameter is 1.7 +/- 0.5 mm, and its takeoff angle is 154 degrees +/- 15 degrees , making the vein potentially accessible for cannulation. CONCLUSIONS: Differences in CV anatomy that are related to either gender or coronary artery disease could have important practical implications during the left ventricular lead implantation. The anatomical features of the vein of Marshall make it a feasible potential conduit for epicardial LA pacing.

Implantable cardioverter-defibrillator shocks increase T-wave alternans.

INTRODUCTION: While implantable defibrillator shocks save lives, shock can lead to ventricular arrhythmias. However, the mechanism of shock-related proarrhythmia remains unclear. We evaluated the impact of ICD shock on repolarization instability, a factor associated with ventricular arrhythmogenesis. METHODS AND RESULTS: Sixty-five patients with ICDs underwent ambulatory ECG monitoring during defibrillation testing 3 months postimplant. TWA was analyzed continuously in the time domain during baseline, sedated, and post-shock states. RR, QRS, and QT intervals and catecholamines were also measured continuously. Adequate pre- and post-shock Holter data were recorded in 55 patients, 48 male, mean 64 +/- 12 years, 50 with coronary disease, 48 with prior spontaneous or induced arrhythmia. TWA significantly increased after shock, from 9.6 +/- 0.5 to 11.9 +/- 0.6 microV, as did QRS duration, epinephrine, and norepinephrine levels, compared with sedated and baseline states. RR intervals decreased minimally. TWA changes with shock were not associated with RR or QRS duration changes, but were associated with changes in epinephrine. CONCLUSIONS: ICD shock, even in the sedated state, increases repolarization instability as measured by TWA, an effect mediated in part by sympathetic stimulation. This association between shock and TWA may have important mechanistic and clinical implications for optimization of defibrillation therapy.

Electrophysiologic characteristics of anger-triggered arrhythmias.

BACKGROUND: Anger can precipitate ventricular arrhythmias in patients with implantable cardioverter-defibrillators (ICDs). Determining electrophysiologic characteristics of anger-triggered arrhythmias may help elucidate the mechanisms that link emotion and arrhythmia. OBJECTIVES: We sought to compare the morphology and initiation pattern between ventricular arrhythmias that are triggered by anger and those that are not. METHODS: At the time of shock, patients with ICDs recorded levels of defined mood states preceding the shock in a diary. Stored intracardiac electrograms (EGMs) were retrieved and analyzed in relation to corresponding mood states. The EGMs from 56 appropriate shocks in 24 patients (18 male, mean age 66 years, 74% with coronary artery disease) were reviewed and analyzed for morphology, mechanism of initiation (sudden onset vs. premature ventricular contraction [PVC]), pause dependence, and other characteristics. RESULTS: Polymorphic ventricular tachycardia was more common in anger-triggered events, occurring in three (37.5%) of eight anger-triggered events compared with five (10.4%) of 48 of non-anger-triggered events (P <.05). Anger-triggered events were more likely to have PVC initiation, occurring in eight (100%) of eight, compared with 30 (68%) of 44 of non-anger-triggered events (P <.05). More anger-triggered events were pause dependent: five (62.5%) of eight versus seven (15%) of 37 non-anger-related events (P <.01). No difference in response to initial therapy was observed in anger-triggered arrhythmias. CONCLUSION: Ventricular arrhythmias occurring in the setting of anger are more likely pause dependent and polymorphic. This suggests that in predisposed populations anger may create an arrhythmogenic substrate susceptible to more disorganized rhythms, a possible mechanism linking emotion and sudden death.

Ibutilide to expedite ED therapy for recent-onset atrial fibrillation flutter.

OBJECTIVE: Ibutilide is a type III antiarrhythmic agent approved for the pharmacologic conversion of atrial fibrillation (AF) and atrial flutter (AFl). Previous studies conducted outside the ED setting have demonstrated conversion rates of 60% to 80%. This response has been highest in patients with recent-onset AF-AFl. These observations and the 4-hour half-life of ibutilide suggest that it may be an excellent drug with which to treat AF-AFl in the ED. The purpose of the study was to examine the efficacy and safety of ibutilide in terminating AF-AFl in patients who present to the ED with symptoms of less than 3 days' duration, neither angina nor heart failure, and no comorbid conditions that require admission. METHODS: Among 36 enrolled patients, the admission electrocardiogram demonstrated AF in 26 and AFl in 10. Ibutilide 1 mg was administered intravenously for 10 minutes. If sinus rhythm was not present 10 minutes after the infusion concluded, a second infusion of 1 mg was given. Successful conversion was defined as restoration of sinus rhythm within 1 hour after the last dose of ibutilide. RESULTS: Sixteen (61.5%) of 26 patients with AF and 9 (90%) of 10 patients with AFl converted to sinus rhythm (overall conversion rate=69%). The mean time to arrhythmia termination was 19+/-9 minutes. The mean stay in the ED was 16.2 hours. No significant complications occurred. CONCLUSION: We conclude that ibutilide is an excellent therapy option for restoring sinus rhythm in the ED. Its use may obviate the need for admission, avoid the risks and inconveniences of general anesthesia to perform electrical cardioversion, and reduce the ED length of stay in selected patients with recent-onset atrial arrhythmias.

Benefits of cardiac rehabilitation in patients with implantable cardioverter-defibrillators: a patient survey.

OBJECTIVES: To determine whether participation in an outpatient cardiac rehabilitation (OCR) program increases exercise levels and decreases shocks in patients with implantable cardioverter-defibrillators (ICDs). DESIGN: Retrospective comparative survey. SETTING: University tertiary-care ICD clinic. PARTICIPANTS: Patients with ICDs and coronary artery disease. INTERVENTION: Participation in OCR (nonrandomized). MAIN OUTCOME MEASURES: Exercise levels and OCR participation were determined through a telephone survey of patients with ICDs. The incidence of shock-treated arrhythmia was determined by review of charts and ICD data storage disks. RESULTS: Of 82 patients (85% men; mean age, 61+/-8 y), 28 (34%) participated in OCR after receiving an ICD. There was no difference in age, sex, ejection fraction, or length of follow-up between OCR and non-OCR groups. Median intensity of regular exercise was 5.3 metabolic equivalents (METS) for OCR patients versus 3.5 METS for non-OCR patients (P<.02). In follow-up (mean, 48+/-3 mo), non-OCR patients were more likely to receive any shock, shocks during exercise, or shocks for ventricular arrhythmia during exercise than OCR patients (all P<.05). Non-OCR remained a predictor of shock after adjustment for exercise limitation (P<.05). CONCLUSIONS: OCR patients exercised more and had fewer shocks. Physicians and health plans should encourage ICD patients to participate in OCR.

Cost advantage of dual-chamber versus single-chamber cardioverter-defibrillator implantation.

OBJECTIVES: The purpose of this study was to determine the least expensive strategy for device selection in patients receiving implantable cardioverter-defibrillators (ICDs). BACKGROUND: Device cost for a single-chamber ICD is less than an atrioventricular (dual-chamber) ICD (AV-ICD); however, some patients without clinical need for AV-ICD at implantation might require a later upgrade, potentially offsetting the initial cost advantage of the single-chamber device. METHODS: Decision analysis was used to estimate expected resource utilization costs of three alternative implantation strategies: 1) single-chamber device in all, with later upgrade to AV-ICD if needed; 2) initial implantation of an AV-ICD in all; and 3) targeted device selection on the basis of results of electrophysiologic testing (presence or absence of induced bradyarrhythmias or atrial arrhythmias). Clinical base estimates were obtained from retrospective review of all patients receiving ICDs between June 1997 and July 2001 at a single university hospital. Economic inputs were collected from national and single-center sources. RESULTS: In patients without other indications for electrophysiologic study (EPS), the expected per-person cost was least with the strategy of universal initial AV-ICD implantation (36,232 dollars) compared with initial single-chamber ICD/upgrade as needed (39,230 dollars) or EPS-guided selection (41,130 dollars). Sensitivity analyses demonstrated that universal AV-ICD implantation remained least expensive with upgrade rates as low as 10%. At a 5% upgrade rate, AV-ICD remained cheapest if the device cost-differential narrowed to 1,568 dollars. For patients undergoing EPS for risk assessment, EP-guided selection was least expensive. CONCLUSIONS: The strategy of universal AV-ICD implantation, which provides the benefits of dual-chamber capability while obviating any potential need for future upgrade, is the least costly strategy for most patient populations receiving ICDs.

Coronary thrombosis related to use of Xenadrine RFA.

Recently, ephedra was removed from the U.S. marketplace due to a heightened concern that dietary supplements containing ephedra may present "an unreasonable risk of illness or injury." This is the 1st time the U.S. Food and Drug Administration has banned an herbal supplement, and the ban sheds light on the potential harm of nutritional supplements that are used for weight loss or as a boost to athletic performance. We report the case of a body builder who used Xenadrine RFA, an ephedra-containing supplement, at recommended doses for nearly a year; he then experienced an acute myocardial infarction, which was documented to be secondary to thrombosis in situ. We ruled out other possible causes of myocardial infarction, as well a hypercoagulable state. There was no evidence of illicit drug use. Our report serves as a poignant reminder of the potential dangers of herbal supplementation, especially when used to heighten athletic performance.

Effects of psychologic stress on repolarization and relationship to autonomic and hemodynamic factors.

INTRODUCTION: Psychological stress can precipitate ventricular arrhythmias in patients with ICDs, as well as sudden death. However, the physiologic pathways remain unknown. We sought to determine whether psychological stress induced in the laboratory setting alters indices of repolarization associated with arrhythmogenesis. METHODS AND RESULTS: Patients with ICDs and a history of ventricular arrhythmia underwent ambulatory ECG monitoring during a laboratory mental stress protocol (anger recall and mental arithmetic). Continuous changes in repolarization indices which have correlated with temporal and spatial myocardial heterogeneity of repolarization, including T-wave alternans (TWA), T-wave amplitude (Tamp), and T-wave area (Tarea) were analyzed in the time domain. In the 33 patients (85% male, 88% with coronary artery disease, mean ejection fraction 30%), norepinephrine, epinephrine, BP, and HR increased during mental stress. TWA increased from 22 (interquartile range 16-27) at baseline to 29 (21-38) uV during mental stress (P < 0.001). Changes in TWA correlated with changes in HR, systolic BP, and catecholamines. Tamp and Tarea also increased with mental stress (P < 0.01) but did not correlate with changes in other variables. CONCLUSION: Psychological stress increased TWA, Tamp, and Tarea. Autonomically mediated repolarization changes may be a pathophysiologic link between emotion and arrhythmia in susceptible patients.

Usefulness of procainamide challenge for electrophysiologic arrhythmia risk stratification.

Among 58 consecutive patients who underwent electrophysiologic testing for risk assessment and who subsequently received a third-generation implantable cardioverter-defibrillator, 39 had ventricular tachycardia induced in the baseline state and 19 had ventricular tachycardia induced only after administration of intravenous procainamide, increasing the yield of electrophysiologic risk assessment by 49%. At follow-up, ventricular arrhythmias requiring implantable cardioverter-defibrillator termination occurred in 14 of 39 patients inducible in the baseline state and in 7 of 19 patients inducible only with intravenous procainamide. The provocative use of intravenous procainamide during electrophysiologic risk assessment increases the detection rate for risk of sustained ventricular arrhythmias with no loss of positive predictive value.

Permanent pacemakers and implantable defibrillators: considerations for intensivists.

Pacemakers and cardioverter-defibrillators are implanted in patients with cardiovascular disease for an ever-increasing array of indications. Intensivists provide care frequently for patients who have these devices, and thus, they must be familiar with common problems and nuances that may contribute to critical illness. Close collaboration of the critical care physician and cardiologist/electrophysiologist assures that pacemakers and defibrillators are tuned to optimize the hemodynamic milieu of critically ill patients. Many recent advances in the sophistication of implanted devices are reviewed herein.

Gender differences in ventricular arrhythmia recurrence in patients with coronary artery disease and implantable cardioverter-defibrillators.

OBJECTIVES: We sought to determine whether men and women with coronary artery disease (CAD) and implantable cardioverter-defibrillators (ICDs) differ in frequency of arrhythmia recurrence and whether gender differences are independent of clinical, electrocardiographic, and electrophysiologic characteristics. BACKGROUND: Epidemiologic studies show that women have a lower rate of sudden cardiac death (SCD) than men, even among patients with CAD. Whether this is due to differing susceptibilities to ischemia or to arrhythmia is unknown. METHODS: The clinical records and ICD data disks of 340 men and 59 women with CAD who received an ICD between June 1990 and June 2000 were reviewed. Ventricular tachycardia (VT) or ventricular fibrillation (VF) recurrences were compared between genders and relationship with other factors was analyzed. RESULTS: Sustained VT/VF occurred in 52% of men and 34% of women (p < 0.01). Men experienced more total VT/VF events (p < 0.01), more shock-treated VT/VF events (p < 0.03), more electrical storms (p < 0.001), and had VT/VF on more days in follow-up (p < 0.01). Gender differences were independent of measured clinical, electrocardiographic, and electrophysiologic factors. In stratified analyses, the gender differences in VT/VF recurrence were greatest in patients presenting with sustained monomorphic VT and those with inducible VT at electrophysiology study. CONCLUSIONS: Women were less likely to experience VT/VF, and had fewer VT/VF episodes, than men. These findings were strongest in patients with evidence of a stable anatomic VT circuit: those with clinical or electrophysiologically induced VT. This study suggests that differing susceptibility to arrhythmia triggering may underlie the known differences in SCD rates between men and women.

Assessment and management of patients with pacemakers and implantable cardioverter defibrillators.

OBJECTIVE: To review the design and function of pacemakers and implantable cardioverter defibrillators with particular attention to those aspects that are of clinical relevance to perioperative and critical care physicians. MAIN POINTS: Pacemakers and implantable cardioverter defibrillators are complex devices that interact with cardiac function in ways that can significantly influence hemodynamics. A basic appreciation of device technology is essential to understanding both the normal patterns of pacemaker and implantable cardioverter defibrillator usage and the ways in which iatrogenic influences may result in adverse outcomes. The most important concern for pacemaker patients who enter the hospital is exposure to electromagnetic interference. Exposure is mainly from surgical cautery, but other sources are also present. With awareness of these concerns and an understanding of how to prevent adverse interactions, it is possible to safely care for these patients in the critical care setting. Despite recommended precautions, undesirable outcomes may occur and the clinician must be prepared to intervene in an appropriate manner to prevent patient injury.