Unipolar Sensing Abnormalities: Incidence and Clinical Significance of Skeletal Muscle Interference and Under sensing in 228 Patients

Compared to bipolar lead configurations, unipolar pacing systems presumably enhance sensing of cardiac electrical events but are ore susceptible to electrical interference, including skeletal myopotentials. The incidence and clinical significance of oversensing and of undersensing by unipolar R-wave inhibited pacemakers in 228 patients were assessed by 24-hour Holter monitoring and/or by pectoral muscle exercises. Overall, 38% of patients exhibited oversensing and false inhibition due to skeletal myopotentials. Symptoms due to oversensing occurred in 14% of patients and 58% of these required corrective intervention. The presence of silastic coating on the pulse generator had no effect on the sensing of myopotentials. In addition, the incidence of undersensing as assessed by Holter monitoring was 17% despite adequate implantation R wave amplitudes. Thus, oversensing remains a major clinical problem when using unipolar pacemaker systems and their use has not eliminated undersensing.     

Ventricular Oversensing:

WERETKA, S., et al. : Ventricular Oversensing: A Study of 101 Patients Implanted with Dual Chamber Defibrillators and Two Different Lead Systems . Modern dual chamber ICD systems are able to overcome various sensing problems. However, improvement of their performance is still required. The aim of this study was to assess the sensing function in 101 consecutive patients (84 men, 17 women; mean age 63 ± 12 years; mean follow-up 24 ± 4 months) implanted with dual chamber defibrillators and integrated (IB) or dedicated bipolar (DB) lead systems. Follow-up data were analyzed for the presence of ventricular oversensing. Oversensing occurred in 25 (25%) patients, significantly more frequent in patients implanted with IB compared to DB lead systems (21/52 vs 4/49, P = 0.0002). Patients with cardiomyopathies (CMs) were more prone to sensing malfunctions than patients with no CM (12/30 vs 13/71, P = 0.04). T wave oversensing (n = 14), respirophasic ventricular oversensing (n = 4), and P wave oversensing (n = 6) were the most common pitfalls of ventricular sensing. P wave oversensing was unique to the IB lead system. CT scans performed in these patients disclosed the position of the RV coil to be proximal to the tricuspid area. Four patients received inappropriate ICD shocks due to oversensing. In all but two patients who received lead revision, oversensing was resolved by noninvasive means. In conclusion: (1) ventricular oversensing is a common problem occurring in up to 25% of patients with dual chamber ICDs; (2) P wave oversensing is a ventricular sensing problem affecting function of 11% of dual chamber devices with IB lead systems; (3) IB leads are significantly more susceptible to T wave and P wave oversensing than DB leads; and (4) patients with cardiomyopathies are more prone to oversensing than patients with other heart diseases. (PACE 2003; 26[Pt. I]:65–70)     

After-Potential Oversensing by a Programmable Puise Generator

Oversensing and recycling due to a pacemaker stimulus after-potentials are recognized complications of non-competitive pacing. Often masquerading as T-wave sensing, after-potential oversensing may result in slowing or acceleration of pacing rate. We report two cases of after-potential oversensing in patients with R-wave inhibited (VVI) programmable pulse generators. In both cases, recycling of the pulse generators by the sensed after-potentials resulted in slowing of the pacing rates. This phenomenon was abolished non-invasively by decreasing the duration or width of the stimulus pulse which diminished the magnitude of the after-potential signal.     

Characteristics and Clinical Effects of Myopotential Signals in a Unipolar DDD Pacemaker Population

Myopotential signals were recorded from atrial and ventricular leads during isometric exercise in 25 patients who had chronically implanted dual chamber pacemakers using the electrogram telemetry capability of the pacemakers. Average electrogram amplitude on the atrial channel was 0.92 mV (range 0.3 to 1.9) and on the ventricular channel was 0.98 mV (range 0.3 to 2.2); the difference was not significant. There was a strong correlation (R = 0.82) between the amplitude of myopotentials on the atrial and ventricular leads for individual patients. Myopotential sensing caused ventricular output inhibition in two patients (8%) and ventricular tracking in sixteen patients (64%). Pacemaker reprogramming abolished ventricular myopotential inhibition in all patients and stopped ventricular myopotential tracking in seven patients. We conclude that myopotentials can be analyzed and their effects ameliorated by a multiprogrammable pacemaker with electrogram telemetry capability.     

Strategy to Eliminate Inappropriate Shocks Secondary to T-Wave Oversensing in a Biventricular ICD

T-wave oversensing represents a common cause of inappropriate shocks in patients with implanted cardiac defibrillators. This case report demonstrates a strategy of device programming using V-V pace delay (sequential rather than simultaneous biventricular pacing) to eliminate T-wave oversensing without decreasing sensitivity to detect true tachyarrhythmia.     

Advances in Catheter Ablation use of Unipolar Electrograms

Ventricular tachycardia in man can be eliminated by relatively small lesions in the reentrant circuit. This report includes a review of available energy sources, and methods for localizing arrhythmias. Methods to assure contact and prevent perforation using low frequency electrograms are presented including the new finding of reverse ST deflection with contact. Experience with laser energy in dogs showed discrete homogenous lesions. When compared with DC shock the animals showed far less arrhythmia and the lack of far field effect greatly reduced echo abnomalities in the post shock period. Studies with radiofrequency show ability to produce localized lesions similar to the laser but with a more flexible catheter. Localization requires a correlation of techniques including pacemapping, activation maps and pacing during tachycardia. Early activation (< −60 ms) at times 180–320 ms, with comparable pace to QRS during tachycardia with no change in morphology best localized the slow zone of the reentrant circuit. The low frequency unipolar electrogram from the tip and immediately proximal electrode revealed contact with ST deviation. The distal deviation was always greater than the proximal RV free wall and posterior basal produced depression rather than elevation of the electrogram. While the mechanism of ST reversal with contact is not understood and may relate to the type of indifferent reference used (Wilson central terminal), the ST depression reveals the same information about contact that elevation does in most other areas of the heart studied in our patients.     

The Effect of Electrode Configuration on the Unipolar His-Bundle Electrogram

Although "unipolar electrograms" recorded from the His-bundle position have been used to help position catheters for His-bundle ablation, the techniques used to record such electrograms have not been standardized. The effects of five anode locations (right chest wall, anterior chest wall, left chest wall, posterior chest wall, and inferior vena cava) on unipolar atrial, His bundle and ventricular electrograms recorded from the His-bundle position were examined in ten patients undergoing clinical electrophysiology studies. Electrograms were recorded at filter settings of 50-500 as well as 0.05-1000 Hz. The location of the anode had no consistent effect on the amplitude, duration or morphology of any of the electrograms at either filter setting, but signals recorded with the inferior vena cava anode had the highest signal-to-noise ratio. A filter setting of 50-500 Hz decreased the amplitude of atrial (0.72 to 0.33 mV-P less than 0.01), His bundle (0.38 vs 0.32 mV-P less than 0.01) and ventricular electrograms (3.71 vs 2.01 mV-P less than 0.001) compared to a filter setting of 0.05-1,000 Hz. The filter setting did not affect electrogram duration. We concluded that the use of an electrode catheter in the inferior vena cava as the anode when recording "unipolar electrograms" from the His-bundle position yields a better signal-to-noise ratio than a skin patch on the chest and appears to be the optimal method for recording unipolar electrograms.     

Myopotential Inhibition of Unipolar QRS-inhibited (VVI) Pacemakers, Assessed by Ambulatory Holter Monitoring of the Electrocardiogram

Seventy-four patients with unipolar QRS-inhibited pacemakers (VVI) were Holter monitored to assess the occurrence of pacemaker inhibition caused by skeletal muscle potentials during daily activities. Fifty patients had high-grade atrioventricular block and 24 had sinoatrial disease. Chest wall stimulation prior to monitoring revealed asystole of > 4 seconds duration in 22 patients, and ventricular rates between 25 and 56 beats per minute in 52 patients. Fifty-one patients (69%) had one or more episodes of pacemaker inhibition from myopotentials. Inhibition occurred in all types of pacemakers studies, but was most frequent and of longest duration in patients with Siemens-Elema 207/70 (13/14 patients), Cordis Omni-Stanicor (6/7 patients), CPI Microlith (5/6 patients), and Medtronic 5945 (8/10 patients). This was not unexpected considering the filter characteristics of the pacemakers. Nine patients (12%) presented symptoms which might be ascribed to pacemaker inhibition. The longest asystole observed was 3.2 s. Seven patients had pacemakers spikes falling on or near T-waves of spontaneous heart beats because their pacemakers had been rendered refractory by myopotentials. No serious arrhythmias were seen during episodes of pacemaker inhibition or interference. More emphasis should be put on the improvement of filter characteristics of unipolar VVI-pacemakers. Pacemaker patients with symptoms of myopotential inhibition should be equipped with either a bipolar or ventricular triggered (VVT) pacemaker or with a sensitivity and/or pacing mode programmable pacemaker.     

Diaphragmatic Myopotential Oversensing Caused by Change in Implantable Cardioverter Defibrillator Sensing Bandpass Filter

Diaphragmatic myopotential oversensing (DMO) causes inhibition of pacing and inappropriate detection of ventricular fibrillation in implantable cardioverter defibrillators (ICDs). It occurs almost exclusively with integrated bipolar leads and is extremely rare with dedicated bipolar leads. If DMO cannot be corrected by reducing programmed sensitivity, ventricular lead revision is often required. The new Low Frequency Attenuation (LFA) filter in St. Jude Medical ICDs (St. Jude Medical, Sylmar, CA, USA) alters the sensing bandpass to reduce T‐wave oversensing. This paper aims to present the LFA filter as a reversible cause of DMO. Unnecessary lead revision can be avoided by the simple programming solution of deactivating this LFA filter.     

Inappropriate ICD Discharges Due to Noise Oversensing as the First Sign of Repetitive Perforations of the Right Ventricular Lead

Acute lead perforation is one of the major complications associated with implantable cardioverter defibrillator (ICD) implantation. We describe a case with repetitive inappropriate ICD discharges due to noise oversensing as the first sign of lead perforation.     

Bipolar versus Unipolar Issues in DDD Pacing

Les mérites relatifs de la stimulation unipolaire et bipulaire sont discutés dans le contexte des stimulateurs DDD. Pour assurer le recueil du potentiel auricuiaire en présence de potentiel musculaire, l'utilisation d'un systéme bipolaire est préferable. Le recueil bipolaire ventriculaire réduira l'incidence d'inhibition par des myopotentiels et pourrait aussi réduire la possibilité de l'écoute croisée. Cependant, la stimulation est mieux obtenue par un systéme unipolaire. C'est pourquoi nous développons un nouveau stimulates qui fournira la slimulation en unipolaire et le recueil du potentiel en bipolaire. Ce stimulateur est conçu et basé sur un schéma unipolaire, avec la simplicité et la fiabilité inhéreutes à ce mode.     

The Effect of Left Ventricular Intracavitary Volume on the Unipolar Electrogram

In order to examine the effects of ventricular distention on the unipolar electrogram (UEG), an isolated rabbit heart modified Langendorff preparation was utilized. Left ventricular (LV) volume was adjusted using ionically permeable (PB = 9 hearts) or ionically impermeable balloons (IB = 4 hearts). LV UEGs, LV end-diastolic pressure (EDP), and LV minor axis dimension (MAD), as measured by ultrasonic transducers, were recorded. Three hundred twenty-five eiectrograms were digitized and analyzed with customdesigned software, In the PB group, a significant inverse linear relationship was found between UEG amplitude and changes in MAD (P < 0.0001). For each animal, this relationship had an R value > 0.8 and a P value < 0.0001. There was also a significant inverse linear relationship between UEG slope and changes in MAD (P < 0.01). UEG amplitude and slope also exhibited a significant inverse relationship to changes in LV EDP, which were best described by a third order polynomial function. In the IB group, no significont relationship was found between either UEG amplitude or slope and MAD or EDP. In this study, intracavitary volume exerted a profound and significant influence on UEG amplitude and slope. This effect was due to increases in conductive intraventricular volume and not to myocardial stretch     

Unipolar Electrode System for an Implantable Defibrillator: New Experimental Approaches

Chez le chien normal nous avons étudié le seuil de défibrillation après induction de fibrillation ventriculaire par un courant alternatif. Après une période de fibrillation soutenue de 10 secondes, des chocs d'énérgie progressivement croissante sont delivrés. Le systèeme d'éléctrode endocavitaire est capable d'une configuration unipolaire ou bipolaire; l'électrode distale se situe è l'apex du ventricule droit. Les résultats suggèrent que pour une capacité optimale de 9-20 uF, les chocs unipolaires (3-10j) sont plus éfficaces que les chocs bipolaires (10-30j). En plus, des arrythmies diverses telles que la tachycardie ventriculaire rapide, le rythme idioventriculaire accéleré et le bloc AV transitoire sont frequemment observées. Nous concluons que: (1) un défibrillateur endocardique unipolaire et implantable semble faisable; (2) il devrait incorporer des circuits appropriés pour le traitement des arrythmies observées après choc.     

Intermittent Oversensing due to Internal Insulation Damage of Temperature Sensing Rate Responsive Pacemaker Lead in Subclavian Venipuncture Method

A 49-year-old male patient developed sensing failure (oversensing) 6 months after the implantation of a temperature sensing rate responsive pacemaker by the subclavian venipuncture method. Intermittent oversensing appeared in the sitting position, but did not appear in the supine position. Temperature telemetry showed an excessive fluctuation of the temperature data points while sitting and while doing a treadmill exercise test. Internal insulation damage was found approximately 31 cm from the distal tip of the explanted lead. The electrical resistance between one thermistor coil and the pacing coil changed from 9 kiloohms to 40 ohms when moderate pressure was applied to the outside lead in the fault area. This electrical shunt resulted from internal insulation damage that resulted from compression of the pacemaker lead between the first rib and the clavicle.     

A Rare type of Ventricular Oversensing in ICD Therapy—Inappropriate ICD Shock Delivery Due to Triple Counting

Irregular sensing by triple counting of wide QRS complexes resulted in inappropriate shocks in a patient with a biventricular implantable cardioverter defibrillator (ICD): A 66‐year‐old male patient with ischemic cardiomyopathy, left bundle branch block, and impaired left ventricular function received a biventricular ICD for optimal therapy of heart failure (CHF). Two years after implantation, the patient experienced recurrent unexpected ICD shocks without clinical symptoms of malignant tachyarrhythmia, or worsened CHF. The patient's condition rapidly worsened, with progressive cardiogenic shock and electrical–mechanical dissociation. After unsuccessful resuscitation of the patient the interrogation of the ICD showed an initial triple counting of extremely wide and fragmented QRS complexes with inappropriate shocks. (PACE 2010; 33:e17–e19)     

Myopotential Inhibition of Unipolar Pacing in Children

Myopotential inhibition of unipolar demand pacing systems has been shown to be a frequent occurrence in adults with transvenous pacing systems in which the pulse generators are implanted adjacent to the pectoralis muscle. To evaluate this problem in children, most of whom have epimyocardial systems and abdominal wall generator implants, 50 patients underwent electrocardiographically monitored exercise and 24-hour ambulatory electrocardiograph monitoring. Patients' ages at the time of study ranged from less than one year to 18 years, and weights ranged from less than 5 kg to 63 kg. Sixteen different models of pulse generators from five manufacturers were involved. Pacing modes were VVI, DVI, AAI, VDD, and DDD. Forty-seven patients had epimyocardial systems. None of the patients was symptomatic as a result of myopotential inhibition. Only three patients (6%) had any evidence of myopotential inhibition and all three demonstrated this inhibition on both monitored exercise and ambulatory electrocardiograph. The inhibition was eliminated by reprogramming the sensitivity levels of the three generators without compromising R-wave sensing. Thirteen of the remaining 35 patients with multiprogrammable generators had induction of myopotential inhibition when exercised after temporary programming to maximal sensitivity settings. Myopotential inhibition of unipolar demand pacing appears to be less frequent and less problematic in the pediatric population, even though they are physically quite active. It is not clear whether this is a function of patient size or the abdominal wall position of the pulse generator.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Clinical Incidence and Significance of Myopotential Sensing with Unipolar Pacemakers

Myopotential oversensing by unipolar pulse generators can cause patient symptoms ranging from dizziness and syncope to ventricular tachycardia. Seventy-seven patients with implanted unipolar pacemakers from three manufacturers participated in isometric and reach exercises to evaluate their pacemakers susceptibility to myopotentials. Myopotential inhibition occurred in 47% of the patients performing the reach maneuver. Testing revealed a wide difference in level of susceptibility to myopotentials between pacemakers of different manufacture (a low of 33% inhibition for the least susceptible to a high of 78% inhibition for the most susceptible during the reach maneuver). The normal pacing interval was extended by myopotential oversensing for each manufacturer's model within a range of 0.3–3.9 seconds. Pulse generators incorporating additional automatically-adjusting threshold and reversion circuits in the sense amplifier along with standard bandpass filtering exhibited: a) two-to-three times less susceptibility to myopotentials; and b) a 75% reduction in the maximum pacing interval extension as compared with pacemakers with bandpass filtering alone. The effectiveness of insulative coating in reducing myopotential inhibition was substantiated as coated pulse generators had a 22% lower incidence of muscle sensing than those than were uncoated. Six out of seven patients tested had symptoms during Holter monitoring which correlated with pacemaker myopotential inhibition. Selecting pulse generators with improved sensing amplifiers, clinical testing of patients with unipolar pacemakers using the reach method, and reprogramming of sensitivity will significantly reduce the incidence of myopotential inhibition.     

Inappropriate ICD Discharge Due to T-Wave Oversensing in a Patient with Short QT Syndrome

A 45-year-old man with diagnosis of short QT syndrome underwent successful implantation of dual-chamber implantable cardioverter-defibrillator (ICD) to prevent sudden cardiac death. Ten days after implantation, the patient was treated by inappropriate ICD discharges for frequent T-wave oversensing. After careful reprogramming of the ICD, the T-wave oversensing was eliminated and no T-wave oversensing or inappropriate discharge was documented during 6-month follow-up period. (PACE 2010; 113–116)     

A Comparison of Unipolar and Bipolar Electrodes During Cardiac Mapping Studies

Controversy exists as to whether the unipolar or bipolar electrode configuration is superior in detecting local activations during cardiac mapping studies. However, the strengths and weaknesses of each mode suggest that they may provide complementary information. To examine therelative merits of unipolar and bipolar electrode configurations, recordings by each were simultaneously acquired during episodes of ventricular tachycardia in eight consecutive patients undergoing map guided arrhythmia surgery. Unipolar electrograms were classified as either unambiguous or ambiguous according to whether or not they were polyphasic in nature. The activation times from the unambiguous electrograms were compared with activation times from the corresponding bipolar signals where local activation was measured both at the signal's peak amplitude (BI-PK), and at the point at which the waveform's first major, rapid transient crossed baseline (BI-TRN). Occurrences of discrete diastolic activations were also quantified from the unipolar and bipolar tracings. From a total of 415 unipolar electrograms, 301 unambiguous signals were identified as suitable for comparison with the bipolar signals. Both BI-PK and BI-TRN criteria for the determination of local activation were highly correlated with and not significantly different from the local activation from the unipolar electrogram. From 85 ambiguous unipolar electrograms, it was possible to determine local activation from the corresponding bipolar signal in 33% of the occurrences. From the eight patients, 64 diastolic potentials were recorded of which 42 were seen only in bipolar mode, 7 in only unipolar mode, and 15 were evident in both tracings. The prevalence of diastolic potentials was significantly greater in recordings made using bipolar mode. The results demonstrate that complementary information regarding local activations and diastolic potentials can be derived from unipolar and bipolar recordings and suggest that both electrode configurations should be used in multichannel cardiac mapping systems.     

Inappropriate ICD Shocks caused by T-wave Oversensing due to Acute Alcohol Intoxication

T-wave oversensing can be a serious problem that often results in inappropriate device therapy. We report here a patient with binge alcohol use who received multiple, inappropriate ICD shocks due to T-wave oversensing from repolarization changes induced by acute alcohol intoxication and no other relevant metabolic derangements. Following recovery from his alcohol intoxication a few days later, the T-wave amplitude decreased so the device no longer inappropriately sensed or delivered therapies. This case represents an uncommon, but reversible, cause of T-wave oversensing that should be considered before more aggressive measures are taken to correct the abnormality. (PACE 2012; 35:e267-e271).