Allan C. Shuros

Communicating Antitachycardia Pacing-Enabled Leadless Pacemaker and Subcutaneous Implantable Defibrillator

Transvenous lead-related complications occur throughout the spectrum of cardiac rhythm management device therapies [(1)][1]. These complications incur significant cost to the health care system and have tremendous impact on patient quality of life. The subcutaneous implantable-cardioverter

Ventricular Preexcitation Modulates Strain and Attenuates Cardiac Remodeling in a Swine Model of Myocardial Infarction

Background— Myocardial infarction modifies the distribution of stress within the heart, increasing wall stress in ischemic and surrounding tissue, which often leads to adverse left ventricular remodeling. Electrical preexcitation pacing with appropriate timing of high-stress regions can reduce local strain and may attenuate global remodeling. Methods and Results— Myocardial infarction was induced in 24 swine to study the short-term (n=12) and long-term (n=12) effects of therapy. Sonomicrometry and hemodynamic measurements were used to show the mechanistic effects of preexcitation and to determine the optimal stimulation site and atrioventricular delay. Lagrangian strain was used to assess regional loading characteristics. Long-term study animals were randomized to 8 weeks of preexcitation (therapy) or no pacing (control). Echocardiograms were performed 2 days after myocardial infarction and repeated at 60 days, when tissue weights and apoptosis were assessed. Preexcitation reduced regional strain in the short term, with the best results achieved when the border region was paced at an atrioventricular delay of 50% of the intrinsic PR interval. In the long term, the changes in left ventricular internal diameter and left atrial size were decreased in therapy animals versus control animals (0.9±0.3 versus 1.5±0.5 cm, P=0.03, and 1.06±0.78 versus 2.32±0.88 cm, P<0.04, respectively). Heart weight was significantly lower in the therapy animals than in the control animals (319.8±20.8 versus 359.6±29.3 g, P=0.02). Although not significant, cardiomyocyte apoptosis trended lower in the therapy group. Conclusions— Preexcitation of the left ventricle after myocardial infarction reduced strain and stroke work in the infarct and border regions in the short term and attenuated adverse ventricular remodeling in the long term.

Practical Considerations of Mapping Persistent Atrial Fibrillation With Whole-Chamber Basket Catheters

OBJECTIVESnThis study sought to evaluate basket catheter deployment, catheter-tissue contact, and time-space stability of unipolar atrial electrograms (aEGMs) recorded in persistent atrial fibrillation (AF) patients.nnnBACKGROUNDnPanoramic mapping of human AF using multiple-electrode basket catheters may identify AF sources. Although clinical results using this technique are provocative, questions remain about its effectiveness.nnnMETHODSnData were collected from patients (Nxa0= 25) undergoing catheter ablation for AF during the multicenter STARLIGHT (Signal Transfer of Atrial Fibrillation Data to Guide Human Treatment) trial (NCT01765075). Left and right aEGM signals were recorded using basket catheters during baseline AF, following ablation and during sinus rhythm. Data were analyzed for basket deployment, peak-to-peak voltage, and electrogram stability and organization. Electrogram stability and organization were evaluated via time-frequency analysis (TFA).nnnRESULTSnBasket catheters displayed equatorial bunching when deployed in atria. Interspline spacing ranged from 1.7 to 64.0 mm in the right atrial and from 1.5 to 85.08 mm in the left atrial basket. Approximately one-third of mapping electrodes failed to demonstrate a median peak-to-peak voltage >2× the low-voltage threshold. Time-space stability and organization was observed in 13 of 22 (59.09%) right atrial and 10 of 22 (45.45%) left atrial baskets.nnnCONCLUSIONSnDespite poor deployment and a large number of low-voltage electrodes, stability and organization was observed in about one-half of the mapped patients. Although this study suggests that basket catheters have limitations for patient-specific AF mapping, concordant activation occurs in some persistent AF patients, which may be amenable to high-density mapping techniques.

Acute and 3-Month Performance of a Communicating Leadless Antitachycardia Pacemaker and Subcutaneous Implantable Defibrillator

OBJECTIVESnThe primary objective was to assess the acute and 3-month performance of the modular antitachycardia pacing (ATP)-enabled leadless pacemaker (LP) and subcutaneous implantable cardioverter-defibrillator (S-ICD) system, particularly device-device communication and ATP delivery.nnnBACKGROUNDnTransvenous pacemakers and implantable cardioverter-defibrillators (ICDs) have considerable rates of lead complications. We examined the next step in multicomponent leadless cardiac rhythm management: feasibility ofxa0pacing (including ATP) by a LP, commanded by an implanted S-ICD through wireless, intrabody, device-device communication.nnnMETHODSnThe combined modular cardiac rhythm management therapy system of the LP and S-ICD prototypes was evaluated in 3 animal models (ovine, porcine, and canine) both in acute and chronic (90 days) experiments. LP performance, S-ICD to LP communication, S-ICD and LP rhythm discrimination, and ATP delivery triggered by the S-ICD were tested.nnnRESULTSnThe LP and S-ICD were successfully implanted in 98% of the animals (39 of 40). Of the 39 animals, 23 were followed up for 90 days post-implant. LP performance was adequate and exhibited appropriate VVI behavior during thexa090 days of follow-up in all tested animals. Unidirectional communication between the S-ICD and LP was successful in 99% (398 of 401) of attempts, resulting in 100% ATP delivery by the LP (10 beats at 81% of the coupling interval). Adequate S-ICD sensing was observed during normal sinus rhythm, LP pacing, and ventricular tachycardia/ventricular fibrillation.nnnCONCLUSIONSnThis study presents the preclinical acute and chronic performance of the combined function of an ATP-enabled LP and S-ICD. Appropriate VVI functionality, successful wireless device-device communication, and ATP delivery were demonstrated by the LP. Clinical studies on safety and performance are needed.

CHRONIC PERFORMANCE OF COMMUNICATING LEADLESS ANTI-TACHYCARDIA PACEMAKER AND SUBCUTANEOUS IMPLANTABLE CARDIOVERTER DEFIBRILLATOR

Background: Conventional pacemakers and implantable cardioverter defibrillators (ICD) have high rates of lead complications. We examine the next step in modular leadless cardiac rhythm management: chronic performance of an anti-tachycardia (ATP) leadless cardiac pacemaker (LCP), commanded by a

Novel Measure of Local Impedance Predicts Catheter–Tissue Contact and Lesion Formation

Background: Coupling between the ablation catheter and myocardium is critical to resistively heat tissue with radiofrequency ablation. The objective of this study was to evaluate whether a novel local impedance (LI) measurement on an ablation catheter identifies catheter–tissue coupling and is predictive of lesion formation. Methods and Results: LI was studied in explanted hearts (n=10 swine) and in vivo (n=10; 50–70 kg swine) using an investigational electroanatomic mapping system that measures impedance from an ablation catheter with mini-electrodes incorporated in the distal electrode (Rhythmia and IntellaNav MiFi OI, Boston Scientific). Explanted tissue was placed in a warmed (37 °C) saline bath mounted on a scale, and LI was measured 15 mm away from tissue to 5 mm of catheter–tissue compression at multiple catheter angles. Lesions were created with 31 and 50 W for 5 to 45 seconds (n=90). During in vivo evaluation of LI, measurements of myocardium (n=90) and blood pool (n=30) were guided by intracardiac ultrasound while operators were blinded to LI data. Lesions were created with 31 and 50 W for 45 seconds in the ventricles (n=72). LI of myocardium (119.7 Ω) was significantly greater than that of blood pool (67.6 Ω; P<0.01). Models that incorporate LI drop (&Dgr;LI) to predict lesion size had better performance than models that incorporate force-time integral (R2=0.75 versus R2=0.54) and generator impedance drop (R2=0.82 versus R2=0.58). Steam pops displayed a significantly higher starting LI and larger &Dgr;LI compared with successful radiofrequency applications (P<0.01). Conclusions: LI recorded from miniature electrodes provides a valuable measure of catheter–tissue coupling, and &Dgr;LI is predictive of lesion formation during radiofrequency ablation.