Physical activity is reduced prior to ventricular arrhythmias in patients with a wearable cardioverter defibrillator.

INTRODUCTION: The utility of accelerometer-based activity data to identify patients at risk of sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) has not previously been investigated. The aim of the current study was to determine whether physical activity is associated with manifesting spontaneous sustained VT/VF requiring emergent defibrillation in patients with an ejection fraction of ≤35%. METHODS: Patients consecutively prescribed a wearable cardioverter defibrillator (WCD) from April 2015 to May 2018 were included. Shock data and 4 weeks of physical activity data, beginning with the first week of WCD wear, were analyzed. RESULTS: Based on the ROC curve outcome generated from 4057 patients, average daily step count during the first week accurately predicted those patients with sustained VT/VF compared to those without (shocked (n = 81) vs nonshocked (n = 3976) area under the curve, c-index = 0.71, 95% CI = 0.65-0.77, P < .001). An average cutoff of 3637 daily steps during week 1 separated the groups. Patients who averaged fewer than 3637 steps per day during the first week of WCD use were 4.3 times more likely to experience a shock than those who walked more than 3637 steps per day (OR = 4.29, 95% CI = 2.58-7.15, P < .001). DISCUSSION: Average daily step counts are lower in WCD patients who manifest spontaneous VT/VF. Whether these findings represent a causal or correlational relationship, future studies to encourage a minimum daily step count in high-risk patients may impact the incidence of sustained VT/VF.

Characterization of cardiac acoustic biomarkers in patients with heart failure.

BACKGROUND: The wearable cardioverter defibrillator (WCD) records electrocardiograms and cardiohemic vibrations that can be algorithmically combined to provide cardiac acoustic biomarkers (CABs). We characterized CAB variability, diurnal variations, and changes over time among heart failure patients. METHODS: Wearable cardioverter defibrillator heart failure patients who had CAB recordings from March 2015 to July 2017 were included. CAB parameters included: electromechanical activation time (EMAT), EMATc (EMAT/RR interval), left ventricular systolic time (LVST), LVSTc (LVST/RR interval), S3 and S4 strengths, and systolic dysfunction index (SDI). Descriptive statistics, correlation analysis, and analysis of variance were used to report temporal and clinical associations. RESULTS: One thousand and sixty-six WCD patients met the study criteria. Diastolic CAB parameters showed significantly greater intra-subject variability than systolic CAB parameters (>29% vs. <15%, p < .01). CAB parameters varied very little with age, gender, and ejection fraction (R2  = 0.004 to 0.06) in this heart failure population. Similarly, all CABs except SDI (R2  = 0.58) were independent of QRS duration, (R2  = -0.01 to 0.58). Heart rate had a more of significant influence on the systolic CABs than the diastolic CABs (p < .05). CABs were significantly different when measured at daytime versus nighttime (p < .01) and were significantly lower at the end of WCD wear compared with the beginning of wear (p < .05). CONCLUSIONS: Noninvasive CABs offer the possibility to assess parameters associated with LV function, clinical status, and other aspects of cardiovascular physiology that differ between normal and heart failure states. The present study provides critical information about typical values in heart failure patients, intra-subject variability, circadian rhythms, and changes over time of these parameters.

Identification and electrophysiological characterization of early left atrial structural remodeling as a predictor for atrial fibrillation recurrence after pulmonary vein isolation.

BACKGROUND: Voltage-guided substrate ablation following pulmonary vein isolation (PVI) improves atrial fibrillation (AF) ablation outcomes. However, by setting an upper voltage cutoff of 0.5 mV during sinus rhythm (SR) to guided substrate ablation using electroanatomic voltage mapping (EAVM), mildly affected low-voltage area (maLVA) may be undetected. We sought to determine the optimal bipolar voltage cutoff to identify maLVA, its electrogram complexity, and the implication on ablation outcome. METHODS AND RESULTS: Left atrial (LA) EAVMs were obtained in patients without AF and structural heart disease (control) to devise a voltage cutoff to identify maLVA. Subsequently, we investigated 100 patients without low-voltage area (LVA) of < 0.5 mV who underwent PVI alone. In our 6 control cohorts, 95% of LA regional bipolar voltage was > 1.17 mV. maLVA, defined as <1.1 mV, was present in 43% of AF patients, associated with higher prevalence of abnormal electrograms (44.1% vs. 4.4%, P < 0.001). During a median of 2.4 years, patients with maLVA had higher recurrence rate (Log-rank P < 0.001), and maLVA was an independent predictor for recurrence in a multivariate analysis (hazard ratio [HR] 3.944; 95% confidence interval [CI] 1.292-12.042; P = 0.016). CONCLUSIONS: A control-derived LA voltage cutoff of <1.1 mV for EAVM in SR reveals maLVA, harboring abnormal electrograms, as an independent predictor for recurrences after PVI alone in patients without LVA (< 0.5 mV). Adjunctive maLVA-guided substrate ablation targeting mildly remodeled and potentially arrhythmogenic LA substrate may further improve the long-term outcome of AF ablation.

Long-Term Outcome of Left Atrial Voltage-Guided Substrate Ablation During Atrial Fibrillation: A Novel Adjunctive Ablation Strategy.

INTRODUCTION: Left atrium (LA) low voltage area (LVA) on 3-D electroanatomic bipolar voltage mapping (EAVM), as a surrogate for scar, is associated with poor AF ablation outcome. We evaluated the long-term outcome of an LVA-guided atrial fibrillation (AF) substrate modification strategy as an adjunct to pulmonary vein isolation (PVI). METHODS AND RESULTS: Two hundred and one consecutive patients with AF (82% persistent/Non-PAF, age 65 years), who underwent EAVM during AF prior to PVI, were divided into 2 groups according to the presence or absence of LVA outside the PV antra, defined as bipolar voltage of <0.5 mV. LVA-guided substrate modification was performed after PVI in patients with LVA. LVA was found in 159 patients (79%). Non-PAF (OR 3.851, P = 0.002) and CHA2 DS2 -VASc score (OR 1.815, P < 0.001) were independent predictors for the LVA. After the index procedure, 144 patients (72%) were free from AF at 12 months. With multiple procedures, 148 patients (74%) during a median follow-up of 3.1 years were free from the recurrence. There was no difference in the recurrence (log-rank P = 0.746), and complications (0% vs. 7%, P = 0.125) between the groups. Neither LVA nor Non-PAF was an independent predictor for the recurrence in a multivariate analysis. CONCLUSIONS: Patients with LVA had an equally favorable long-term ablation outcome compared to those without. As an adjunct to PVI, voltage-guided substrate modification may be an important ablation strategy in patients with LA structural remodeling.

Correlation of Left Atrial Voltage Distribution Between Sinus Rhythm and Atrial Fibrillation: Identifying Structural Remodeling by 3-D Electroanatomic Mapping Irrespective of the Rhythm.

INTRODUCTION: Left atrial (LA) electroanatomical voltage mapping (EAVM) correlates with scar on LGE-MRI and has been used to guide ablation of low voltage area (LVA) in sinus rhythm (SR). We compared EAVM in SR and AF in a cohort of AF patients, and in SR between patients with AF and without AF or structural heart disease (control). METHODS AND RESULTS: Twenty-seven AF patients, 9 with paroxysmal AF (PAF), underwent point-by-point EAVM during SR and AF using same Carto3 geometry. Only adjacent SR-AF points (≤ 5 mm apart) were compared. In addition, 6 control patients were evaluated. There was a linear bipolar voltage correlation between SR and AF (r = 0.707, P < 0.001, Y = 1.515X + 0.786). LA bipolar voltage in patients with PAF was higher than those with Non-PAF in SR (2.24 ± 1.51 vs. 1.56 ± 1.53 mV) and AF (0.81 ± 0.60 vs. 0.58 ± 0.62 mV, both for P < 0.001). The pulmonary vein antra voltage was significantly lower than other LA regions in PAF (1.28 ± 0.79 vs. 2.54 ± 1.50 mV, P < 0.001) and Non-PAF patients (1.13 ± 1.04 vs. 1.86 ± 1.72 mV, P < 0.001), while no voltage differences was found in the control group (P = 0.998). CONCLUSION: There was a linear voltage correlation between SR and AF, suggesting a similar extent of LA fibrotic substrate can be identified on EAVM by adjusting the voltage cutoff. Structural remodeling starts in the PV antra and may progress to other LA regions.

A Shocking End to the Defibrillator as We Know It: Unmet Needs and the Case for a Stand-Alone Device that Uses Pacing Only to Treat the Risk of Life-Threatening Arrhythmias.

The defining feature of an ICD is its capacity to deliver a shock. However, the past decade has seen a marked de-emphasis on the perceived value, necessity and safety of shocks. As a consumer product, it is time to reimagine the ICD, decoupling the shock feature from pacing and antitachycardia pacing.

Standardized MR terminology and reporting of implants and devices as recommended by the American College of Radiology Subcommittee on MR Safety.

Considerable confusion exists among the magnetic resonance (MR) imaging user community as to how to determine whether a patient with a metal implanted device can be safely imaged in an MR imaging unit. Although there has been progress by the device manufacturers in specifying device behavior in a magnetic field, and some MR imaging manufacturers provide maps of the "spatial gradients," there remains significant confusion because of the lack of standardized terminology and reporting guidelines. The American College of Radiology, through its Subcommittee on MR Safety, has proposed standardized terminology that will contribute to greater safety and understanding for screening metal implants and/or devices prior to MR imaging.

ACR guidance document on MR safe practices: 2013.

Because there are many potential risks in the MR environment and reports of adverse incidents involving patients, equipment and personnel, the need for a guidance document on MR safe practices emerged. Initially published in 2002, the ACR MR Safe Practices Guidelines established de facto industry standards for safe and responsible practices in clinical and research MR environments. As the MR industry changes the document is reviewed, modified and updated. The most recent version will reflect these changes.

Randomized trial of pacemaker and lead system for safe scanning at 1.5 Tesla.

BACKGROUND: Magnetic resonance imaging (MRI) of pacemakers is a relative contraindication because of the risks to the patient from potentially hazardous interactions between the MRI and the pacemaker system. Chest scans (ie, cardiac magnetic resonance scans) are of particular importance and higher risk. The previously Food and Drug Administration-approved magnetic resonance conditional system includes positioning restrictions, limiting the powerful utility of MRI. OBJECTIVE: To confirm the safety and effectiveness of a pacemaker system designed for safe whole body MRI without MRI scan positioning restrictions. METHODS: Primary eligibility criteria included standard dual-chamber pacing indications. Patients (n = 263) were randomized in a 2:1 ratio to undergo 16 chest and head scans at 1.5 T between 9 and 12 weeks postimplant (n = 177) or to not undergo MRI (n = 86) post-implant. Evaluation of the pacemaker system occurred immediately before, during (monitoring), and after MRI, 1-week post-MRI, and 1-month post-MRI, and similarly for controls. Primary end points measured the MRI-related complication-free rate for safety and compared pacing capture threshold between MRI and control subjects for effectiveness. RESULTS: There were no MRI-related complications during or after MRI in subjects undergoing MRI (n = 148). Differences in pacing capture threshold values from pre-MRI to 1-month post-MRI were minimal and similar between the MRI and control groups. CONCLUSIONS: This randomized trial demonstrates that the Advisa MRI pulse generator and CapSureFix MRI 5086MRI lead system is safe and effective in the 1.5 T MRI environment without positioning restrictions for MRI scans or limitations of body parts scanned.