David Casavant

Lumbar Muscle Fatigue and Chronic Lower Back Pain

There currently is a clinical need for an objective technique to assess muscle dysfunction associated with chronic lower back pain. A Back Analysis System for objectively measuring local fatigue in the back extensor muscles is presented. The reliability and validity of this technique was evaluated by testing chronic low-back pain patients and control subjects without back pain. Concurrent surface electromyograms (EMG) were detected from multiple back muscles during sustained isometric contractions at different force levels of trunk extension. Median frequency parameters of the EMG power density spectrum were monitored to quantify localized muscle fatigue. Results indicated: 1) high reliability estimates for repeated trials; 2) significant differences (P<0.05) In median frequency parameters between lower back pain patients and control subjects for specific combinations of contractile force level and muscle site tested; 3) Median Frequency parameters correctly classified lower back pain and control subjects using a two-group discriminant analysis procedure. The applicability of this technique as a treatment outcome measure and diagnostic screening method for lower back pain patients is discussed.

Permanent, Direct His-Bundle Pacing A Novel Approach to Cardiac Pacing in Patients With Normal His-Purkinje Activation

BACKGROUND Direct His-bundle pacing (DHBP) produces synchronous ventricular depolarization and improved cardiac function relative to apical pacing. Although it has been performed transiently in the electrophysiology laboratory and persistently in open-chested canines, permanent DHBP in humans has not been achieved. METHODS AND RESULTS A total of 18 patients aged 69+/-10 years who had a history of chronic atrial fibrillation, dilated cardiomyopathy, and normal activation (ie, QRS< or =120 ms) were screened for permanent DHBP using an electrophysiology catheter. In 14 patients, the His bundle could be reliably stimulated. Of these 14, permanent DHBP using a fixed screw-in lead was successful in 12 patients. Radiofrequency atrioventricular node ablation was performed in patients exhibiting a fast ventricular response. All patients received single-chamber rate-responsive pacemakers. Acute pacing thresholds were 2.4+/-1.0 V at a pulse duration of 0.5 ms. Lead complications included exit block requiring reoperative adjustment and gross lead dislodgment. Echocardiographic improvement in heart function was shown by reductions in the left ventricular end-diastolic dimension from 59+/-8 to 52+/-6 mm (P</=0.01) and in the end-systolic dimension from 51+/-10 to 43+/-8 mm (P<0.01), with an accompanying increase in fractional shortening from 14+/-7% to 20+/-10% (P=0.05). The left ventricular ejection fraction improved from 20+/-9% to 31+/-11% (P<0. 01), and the cardiothoracic ratio decreased from 0.61+/-0.06 to 0. 57+/-0.07 (P<0.01). Despite DHBP, 2 patients died at 8 and 36 months. Conclusions-Permanent DHBP is feasible in select patients who have chronic atrial fibrillation and dilated cardiomyopathy. Long-term, DHBP results in a reduction of left ventricular dimensions and improved cardiac function.

Multicenter, Prospective, Randomized Safety and Efficacy Study of a New Atrial‐Based Managed Ventricular Pacing Mode (MVP) in Dual Chamber ICDs

Background: Ventricular desynchronization caused by right ventricular pacing may impair ventricular function and increase risk of heart failure (CHF), atrial fibrillation (AF), and death. Conventional DDD/R mode often results in high cumulative percentage ventricular pacing (Cum%VP). We hypothesized that a new managed ventricular pacing mode (MVP) would safely provide AAI/R pacing with ventricular monitoring and DDD/R during AV block (AVB) and reduce Cum%VP compared to DDD/R.

Efficacy of atrial antitachycardia pacing using the Medtronic AT500 pacemaker in patients with congenital heart disease.

Patients with congenital heart disease are vulnerable to atrial tachyarrhythmias, especially after atrial surgeries. We evaluated the efficacy of atrial arrhythmia detection and antitachycardia pacing (ATP) using the Medtronic AT500 pacemaker in 28 patients with congenital heart disease (age 30 +/- 18 years). Of 15 patients with atrial arrhythmias, 14 had atrial tachycardia events that were appropriately detected. ATP was enabled for 167 treatable episodes, successfully converting 90 (54%). Rhythms classified as ventricular tachycardia were detected 127 times, yet most were actually atrial or sinus tachycardia with 1:1 atrioventricular conduction. Atrial tachycardias in congenital heart disease are amenable to ATP algorithms in the AT500 pacemaker.

Findings From aCGH in Patients With Congenital Diaphragmatic Hernia (CDH): A Possible Locus for Fryns Syndrome

Congenital diaphragmatic hernia (CDH) is a common and often devastating birth defect that can occur in isolation or as part of a malformation complex. Considerable progress is being made in the identification of genetic causes of CDH. We applied array‐based comparative genomic hybridization (aCGH) of ∼1Mb resolution to 29 CDH patients with prior normal karyotypes who had been recruited into our multi‐site study. One patient, clinically diagnosed with Fryns syndrome, demonstrated a de novo 5Mb deletion at chromosome region 1q41–q42.12 that was confirmed by FISH. Given prior reports of CDH in association with cytogenetic abnormalities in this region, we propose that this represents a locus for Fryns syndrome, a Fryns syndrome phenocopy, or CDH.

Aborted Implantable Cardioverter-Defibrillator Shock During Facial Electrosurgery

A patient with a fourth‐generation transvenous implantable cardioverter‐defibrillator system nearly received an inappropriate defibrillation discharge while undergoing electrofulguration of keratotic facial skin lesions. The incident was confirmed by analyses of the implantable cardioverter‐defibrillators time/date stamped event log and stored electrogram record. Therapy was withheld by the noncommitted implantable cardioverter‐defibrillator as the pulsed electrocautery was not continued beyond the charging period.

Combined Use of a True‐Bipolar Sensing Implantable Cardioverter Defibrillator in a Patient Having a Prior Implantable Spinal Cord Stimulator for Intractable Pain

Reported is a case involving a patient with a previously implanted spinal cord stimulator (SCS) who presented for an implantable. Cardioverter defibrillator (ICD). The SCS device was located in the left lower abdominal quadrant with a stimulation electrode array placed on the dorsal aspect of the spinal cord at the T‐11 thoracic level. Interaction testing demonstrated that the bipolar sensing transvenous ICD system (Medtronic 7221Cx PCD) did not detect the stimulators output at burst rates ranging from 20–130 pulses/s, even with the ICD set to its maximum sensitivity of 0.15 mV and the stimulator programmed to the highest patient tolerated output combinations of 5 V, 0.45 ms in the bipolar configuration and 3 V, 0.45 ms in the unipolar (i.e., case‐electrode) configuration.

Initial Experience with 1.5-mm2 High Impedance, Steroid-luting Pacing Electrodes

In this human study, 21 atrial and 62 ventricular 1.5‐mm2 unipolar steroid‐eluting pacing electrodes were implanted in 64 patients. Pacing thresholds, lead impedance, and sensing measurements were measured via pacemaker telemetry within 24 hours postimplont, and at 1, 2, 3, 4, 6, 12. 24. and 52 weeks. Acute pacing impedances measured via a pacing systems analyzer were 1,039 ± 292 (atrial) and 1,268 ± 313 ohms (ventricular). A10%‐15% decline in the mean telemetered atrial and ventricular pacing impedances was observed at 1 week, but thereafter remained stable. Acute pacing thresholds at 0.5 ms were 0.5 ± 0.3 V (atrial) and 0.4 ± 0.1 V (ventricular). Filtered P and B wave amplitudes were 3.7 ± 2.3 mV and 14.9 ± 5.9 mV, respectively. In 21 patients, no complications related to the atrial electrode were observed. Of 62 patients with ventricular electrodes, 4 patients (6%) experienced complications and required surgical intervention. On these, causative factors included micro‐dislodgment (l patient), and perforation (l patient). Sudden unexplained exit block occurred late (> 6 weeks) in two patients. In the remainder of patients, pacing thresholds and sensed electrogram amplitudes remained stable throughout the 52‐week follow‐up period. Conclusions: The‐ present study validates that smaller surface (i.e., 1.5 mm2) steroid‐ eluting electrode designs offer excellent pacing and sensing performance with significantly higher pacing impedances. Although questions remain as to the cause of late exit block in two patients in this series, this relatively small surface electrode design offers promise toward achieving greater pacing efficiency and a theoretical 13%‐16% (minimum) enhancement in permanent pacemaker longevity.

Combined third-generation implantable cardioverter defibrillator with permanent unipolar pacemakers: preliminary observations.

As implantable Cardioverter defibrillators (ICDs) are strictly contraindicated in the presence of unipolar pacemakers, currently available options in patients having such chronic pacing systems include: abandoning the implanted pacemaker and selecting an ICD with ventricular demand (VVI) pacing; or replacing the chronic (dual chamber) unipolar pacing system with a dedicated bipolar version prior to ICD implantation. In three patients with previously implanted unipolar pacemakers, we challenged the premise that all ICD systems are incompatible by combining with a third‐generation transvenous ICD system (Medtronic 7217B PCD® incorporating true bipolar sensing, a self‐limiting auto‐adjusting sensitivity, and a tolerant VF detection algorithm. The potential for pace‐maker‐ICD interaction was minimized by separating the tip of the ICDs transvenous right ventricular pace/sense‐defihrillation coil lead from that of the chronic pacemaker lead by > 2–3 cm, and by performing “worst case” intraoperative testing. Although ICD double‐counting of the dual chamber pacemakers atrial and ventricular pacing spikes could be provoked at extreme high output settings, it did not occur at clinically appropriate settings. More importantly, continuous high output asynchronous pacing during ventricular fibrillation (VF) did not interfere with ICD detection. During a mean follow‐up period of 18 months, one patient has had VF appropriately terminated bv the ICD. In the remaining two patients, proper VF detection and ICD function was reassessed at 3 months and/or at 1 year during noninvasive testing. Conclusion: These preliminary findings demonstrate that this transvenous ICD systems VF sensing and detection features combined with careful implant technique, rigorous “worst case” testing for possible pacemaker‐ICD interaction with regular follow‐up, may permit implantation of this ICD system in patients with chronic unipolar pacing systems. Further studies are needed to validate the long‐term clinical safety of this promising revised approach to a currently contraindicated device combination.

Analysis of pacing/defibrillator lead failure using device diagnostics and pacing maneuvers.

Patients with Medtronic Sprint Fidelis (Medtronic Inc., Minneapolis, MN, USA) lead failures present with oversensing, resulting in pacing inhibition and inappropriate shocks. We present a case of lead noise from the right ventricular (RV) ring conductor, resulting in multiple inappropriate shocks with subsequent pacing inhibition and syncope. RV pacing lead impedance at no point exceeded 1,000 ohms. We found that increased noise and oversensing was more likely to be induced when pacing at higher pulse widths. RV pacing outputs at lower pulse widths may decrease susceptibility to noise generation and prove an effective temporizing measure in pacing‐dependent patients.