An approach in the assessment of pacing hemodynamics: a comparison of VVI and DDD

Previous methods for assessment of pacemaker hemodynamics have been limited to a rigid hospital environment. An alternative is the ambulatory ventricular function monitor (C-VEST) that, with a single injection of technetium-99m, permits the continuous measurement of relative ejection fraction (EF) and cardiac output (CO) during the activities of daily living. A study of reproducibility and a comparison of dual chamber (DDD) and fixed rate ventricular (VVI) pacing are presented. Reproducibility was assessed in six patients (4 males; mean age 58, range 27-78 years) with a mean EF of 48.5% (range 34%-62%) and DDD pacemakers, implanted for conduction abnormalities. In addition, 11 patients (7 males; mean age 55.5, range 34-75 years) with a mean EF of 48.5% (range 34%-65%), chronic complete heart block, and DDD pacemakers were used for the comparative study. After an initial multigated scan, the monitor was positioned over the left ventricle and kept in place with the plastic C-VEST. The patients undergoing the reproducibility study performed three shuttle walking tests with 20 minutes of rest in between. The patients in the comparative study were randomized to either VVI or DDD mode and performed one shuttle walking test in each pacing mode. The results confirmed that the C-VEST produces reproducible results with no significant difference in peak CO between the three shuttle walks. In addition, it confirmed previous hemodynamic studies showing that DDD pacing was superior to VVI pacing both at rest (P < 0.004) and at exercise (P < 0.002). These findings show the C-VEST to be an extremely useful tool for the hemodynamic assessment of pacemaker patients.     

Neuropsychological function in adults with attention-deficit hyperactivity disorder

Pacemaker therapy in patients with atrial fibrillation means the best current pacemaker therapy for patients with bradycardias with the aim to avoid the onset of atrial fibrillation and to establish DDD pacing despite of a history of atrial tachyarrhythmias. The newer application of pacing is the suppression of atrial arrhythmias in patients with medical refractory atrial tachyarrhythmias. Patients with slow ventricular rates and permanent atrial fibrillation should receive a VVI-pacemaker, if the bradycardias causes syncope, dizziness or a decrease of their exercise tolerance. In case of chronotropic incompetence the pacemaker should provide rate responsive pacing. Patients with sick sinus syndrome should receive an atrial (AAI) or dual-chamber (DDD) pacemaker, because patients with these in contrast to VVI-pacemakers develop less often atrial fibrillation and subsequent complications such as atrial thromboembolism. A dual-chamber or VDD-pacemaker--the latter connected to a VDD-single-lead--is indicated in patients with advanced AV-block. Atrial fibrillation occurs in 3 to 6% of the patients with no history of arrythmia and is, if pacemakers have no automatic mode switch, an often reason to program the devices to the VVI-pacing mode. Nowadays, most DDD(R)-pacemakers provide an automatic mode switch: During an atrial tachycardia the pacemaker switches to a VVI/VVIR mode and restores the initial DDD(R)-pacing mode with termination of the arrhythmia. In respect to the newer applications, one approach to prevent atrial tachyarrhythmias is permanent atrial pacing. As lower pacing rates of 80 to 90 ppm are usually needed and many patients hardly tolerate these pacing rates, new algorithms are under clinical investigation. Another approach is the simultaneous depolarization of the right and left atrium. Biatrial pacing is performed with one lead in the high right atrium and another lead in the coronary sinus. Another solution is bifocal atrial pacing with leads placed in the high right atrium and in the coronary sinus ostium. One effect of the new pacing techniques is to shorten interatrial conduction times. Therefore, biatrial pacing has become a therapy to prevent atrial arrhythmias deriving from delayed interatrial conduction times. As atrial reentry circuits seem to be important in atrial fibrillation, multisite atrial pacing is also performed in patients with medical refractory paroxysmal atrial fibrillation. Preliminary results suggest a more effective prevention of atrial fibrillation; nevertheless, these techniques should be still restricted to patients enrolled in clinical studies.     

Vertebral artery injury in C1-2 transarticular screw fixation: results of a survey of the AANS/CNS section on disorders of the spine and peripheral nerves. American Association of Neurological Surgeons/Congress of Neurological Surgeons

OBJECTIVES: The goal of this study was to investigate the possible role of transesophageal echocardiography in the evaluation of patients with clinical pacemaker syndrome. BACKGROUND: Several reports on transthoracic echocardiographic features of ventricular pacing were described; however, no previous study of transesophageal echocardiography has been undertaken in patients at the severe end of pacemaker syndrome who need reprogramming of dual-chamber pacing for symptom relief. METHODS: Twelve patients with ventricular-inhibited pacemakers (VVI) with clinical symptomatic pacemaker syndrome (group I) and 10 patients with VVI without pacemaker syndrome (group II) were prospectively studied. The two groups were pacemaker dependent and had persistent ventriculoatrial conduction. Transesophageal echocardiographic parameters were assessed in group II and within 6 hours before reprogramming to the DDD mode in group I. Follow-up transesophageal echocardiographic study was performed 28+/-5 days after reprogramming in group I. RESULTS: All patients in group I had subjective improvements of symptoms after DDD reprogramming. The atrial reverse flow velocities of pulmonary veins in group I before reprogramming were significantly higher in group II (39.3+/-11.4 versus 15.7+/-13.5 cm/sec, p < 0.0001). Spontaneous echo contrast in the descending aorta was detected in all patients from group I before reprogramming. The prevalence of significant mitral regurgitation (> or = moderate) was significantly higher in group I before reprogramming than in group II (67% versus 8%, p = 0.01). Significant mitral regurgitation and spontaneous echo contrast in the descending aorta in group I disappeared after reprogramming to the DDD mode. CONCLUSIONS: Transesophageal echocardiography provides physiologic, pacemaker-related hemodynamic changes in paced patients. Significantly higher atrial reverse flow velocities of pulmonary veins, increased frequency of spontaneous echo contrast in the descending aorta, and significant mitral regurgitation are peculiar echocardiographic findings in patients with VVI with clinical pacemaker syndrome.     

A 7-day activity diary for assessment of daily energy expenditure validated by the doubly labelled water method in adolescents

Several authors have reported the single atrioventricular (AV) electrode, comprising an atrial dipole floating in the right atrium, to be a system capable of providing results which are just as satisfactory as those of conventional systems (DDD). Between August 1992 and March 1995, a VDD single electrode pacemaker was implanted in 65 patients (mean age: 73 years +/- 17.2). The indication for implantation was isolated high degree AVB with no apparent sinus dysfunction. Four pacemakers were used: Vitatron (n = 24), Intermedics (n = 23), Medico (n = 13), Biotronik (n = 5). Intraoperative atrial endocavitary recording was 1.8 mV +/- 0.74. 17 patients died from a cause unrelated to pacemaker dysfunction. 4 patients were lost to follow-up. The remaining 44 patients were reviewed in our centre with a mean follow-up of 14.5 months +/- 7 months. Seven pacemakers (16%) were reprogrammed in VVI or VVI (R) mode, because of permanent atrial fibrillation in 3 cases, complete loss of atrial reception in 2 cases and late onset sinus dysfunction in 1 case. In the 41 patients in sinus atrial rhythm, the atrioventricular synchronization rate was greater than 90% in 88% of patients, equal to 76.3% in 2.4% of patients and atrioventricular synchronization was impossible in 9.6% of cases. CONCLUSION: The overall results of our preliminary experience of VDD mode single electrode pacemaker are moderate. The poor results essentially concerned patients with paroxysmal atrial arrhythmias prior to pacing.     

Triple chamber pacemaker for end-stage heart failure in a patient with a previously implanted automatic defibrillator

A 63-year-old man with an ischemic dilated cardiomyopathy previously implanted with an implantable cardioverter defibrillator (ICD) received a triple chamber pacemaker as an ultimate therapeutic resort for end-stage congestive heart failure. After implant, the tolerance to physical exercise increased and NYHA class decreased from III to II. Echocardiography assessed ventricular contraction resynchronization during DDD biventricular pacing as compared to VVI pacing. No major pacemaker-ICD interaction was noted during testing or follow-up. We conclude that sequential biventricular pacing is feasible in the presence of an ICD.     

DDD pacemaker implantation--cardiac pacemaker tips in the left atrium and ventricle by the left thoracotomy

Recently DDD pacemaker implantation for the children has undergone trials world wide; though regarding the approach, ways and positions of the epicardial lead, a few problems are still remained to be discussed. Now we report 9 cases (5 males, 4 females) of DDD pacemaker implantations by the left anterolateral thoracotomy approach. The 9 patients weighing 6.5 to 33 kg, were aged 11 months to 12 years (mean 6 years) of whom male 5, female 4 with degree of Block; 2 and 7. To all patients the stab-in type epicardial tips were implanted in the left atrium, the screw-in type ventricular epicardial tips were in the left ventricle by the 4th intercostal thoracotomy, and the pacemaker generators were beneath the fascia of the abdominal rectus muscle. We have no sensing and pacing failure, all pacemakers are working in the DDD mode well.     

AAIR versus DDDR pacing in patients with impaired sinus node chronotropy: an echocardiographic and cardiopulmonary study

The aim of this study was to compare AAIR and DDDR pacing at rest and during exercise. We studied 15 patients (10 men, age 65 +/- 6 years) who had been paced for at least 3 months with activity sensor rate modulated dual chamber pacemakers. All had sick sinus syndrome (SSS) with impaired sinus node chronotropy. The patients underwent a resting echocardiographic evaluation of systolic and diastolic LV function at 60 beats/min during AAIR and DDDR pacing with an AV delay, which ensured complete ventricular activation capture. Cardiac output (CO) was also measured during pacing at 100 beats/min in both pacing modes. Subsequently, the oxygen consumption (VO2AT) and VO2AT pulse at the anaerobic threshold were measured during exercise in AAIR mode and in DDDR mode with an AV delay of 120 ms. The indices of diastolic function showed no significant differences between the two pacing modes, except for patients with a stimulus-R interval > 220 ms, for whom the time velocity integral of LV filling and LV inflow time were significantly lower under AAI than under DDD pacing. At 60 beats/min, CO was higher under AAI than under DDD mode only when the stimulus-R interval was below 220 ms. For stimulus-R intervals longer than 220 ms, and also during pacing at 100 beats/min, the CO was higher in DDD mode. The stimulus-R interval decreased in all patients during exercise. The time to anaerobic threshold, VO2AT, and VO2AT pulse showed no significant differences between the two pacing modes. Our results indicate that, at rest, although AAIR pacing does not improve diastolic function in patients with SSS, it maintains a higher CO than does DDDR pacing in cases where the stimulus-R interval is not excessively prolonged. On exertion, the two pacing modes appear to be equally effective, at least in cases where the stimulus-R interval decreases in AAIR mode.     

Oral clonidine premedication enhances the pressor response to ephedrine during spinal anesthesia

Magnetic resonance imaging (MRI) generates potent electromagnetic forces in the form of a static, gradient, or pulsed radiofrequency magnetic field that can result in pacemaker malfunction. This report documents a case of rapid cardiac pacing during MRI in a patient with a dual chamber pacemaker. Although the mechanism of rapid cardiac pacing is unclear, it was directly related to radiofrequency pulsing. We postulated that the lead acts as an antenna for radiofrequency energy that interacts with the pacemaker's output circuit, thus, causing cardiac pacing at a cycle length representing a multiple of the repetition time; or perhaps rapid pacing is related to induced currents generated between the MRI unit and the pacing lead.     

Results of atrioventricular synchronous pacing with optimized delay in patients with severe congestive heart failure

To verify that atrioventricular (AV) synchronous pacing (DDD) with short AV delay improves the condition of patients with severe congestive heart failure, we implanted DDD pacemakers in 10 patients with severe heart failure (New York Heart Association [NYHA] class III to IV). One day after pacemaker implantation, the AV delay was optimized by Doppler echocardiographic measurements over the aortic outflow tract. Patients were evaluated regarding NYHA class, stroke volume, cardiac output, ejection fraction, and quality of life at 1, 3, and 6 months after pacemaker implantation. Although the optimized AV delay was associated with short-term improvement in stroke volume and cardiac output (baseline stroke volume = 22 +/- 7 ml, day 1 = 28 +/- 12 ml; p = 0.03: baseline cardiac output = 1.9 +/- 0.6 L/min, day 1 = 2.2 +/- 1.1 L/min; p = 0.10), the mean stroke volume, cardiac output, NYHA class, and ejection fraction did not change significantly after 1, 3, and 6 months of pacing compared with baseline values. Three patients improved in NYHA class during the follow-up. A consistent improvement in stroke volume, cardiac output, NYHA class, and ejection fraction was observed in only 1 patient. In conclusion, we found no beneficial effects of AV-synchronous pacing with optimized AV delay in patients with severe heart failure.     

Sex differences in selection of pacemakers: retrospective observational study

OBJECTIVE: To evaluate the effect of patients' sex on selection of pacemakers. DESIGN: Retrospective univariate and multivariate analysis of a large database. SETTING: German central pacemaker register. SUBJECTS: Records collected at the register for 1992 and 1993 (n=31 913), covering 64% of all implantations in Germany. MAIN OUTCOME MEASURE: Probability of receiving a single chamber, dual chamber, or rate responsive pacemaker in relation to sex. RESULTS: Univariate analysis showed that women were more likely to receive single chamber pacemakers and less likely to receive dual chamber or rate responsive systems than men. After demographic and clinical variables were controlled for, women were still more likely to receive a single chamber system (atrial pacing: odds ratio 0.89, 95% confidence interval 0.74 to 1.07; ventricular pacing: 0.85, 0.80 to 0.92) and less likely to receive a dual chamber (1.20, 1.12 to 1.30) or a rate responsive system (1.26, 1.17 to 1.37) than men. CONCLUSIONS: The data suggest sex differences in the selection of a pacemaker system which cannot be explained by the underlying cardiac disorder. Further research is needed to evaluate why guidelines for implanting pacemakers are not better adhered to.     

A gastroesophageal electrode for atrial and ventricular pacing

Temporary transvenous cardiac pacing requires technical expertise and access to fluoroscopy. We have developed a gastroesophageal electrode capable of atrial and ventricular pacing. The flexible polythene gastroesophageal electrode is passed into the stomach under light sedation. Five ring electrodes, now positioned in the lower esophagus, are used for atrial pacing. A point source (cathode) on the distal tip of the electrode, now positioned in the gastric fundus, is used for ventricular pacing. Two configurations of atrial and ventricular pacing were compared: unipolar and bipolar. During unipolar ventricular pacing the indifferent electrode (anode) was a high impedance chest pad. For bipolar ventricular pacing the indifferent electrode was a ring electrodes placed 2 cm proximal to the tip. Unipolar atrial pacing was performed with 1 of 5 proximal ring electrodes acting as cathode ("cathodic") or as anode ("anodic") in conjunction with a chest pad. Bipolar atrial pacing was performed using combinations of 2 of 5 ring electrodes. Atrial capture was obtained in all 55 subjects attempted. When all electrode combinations were compared, atrial capture was significantly more frequent using the bipolar approach (153/210 bipolar, 65/210 unipolar; t = 7.37, P < 0.001). For unipolar atrial pacing, cathodic stimulation (from esophagus) was more successful than anodic stimulation (cathodic 62/105, anodic 20/105; t = 5.81, P < 0.001). In 43 subjects attempted unipolar ventricular pacing resulted in a higher frequency of capture than the bipolar approach (unipolar 41/43 (95.3%), bipolar 19/43 (44.2%); P < 0.001). In conclusion, atrial pacing was optimal using pairs of ring electrodes ("bipolar") while ventricular pacing was optimal using the distal electrode tip (cathode) in conjunction with a chest pad electrode ("unipolar"). This gastroesophageal electrode may be useful in the emergency management of acute bradyarrhythmias and for elective electrophysiological studies.     

Inhibition and triggering of heart pacemakers by muscle potentials

The unipolar pulse generator systems were tested in 220 patients (96 VVIM, 97 VVIO, 27 physiological systems) to determine the incidence of sensing interference with muscle potentials. 23% exhibited oversensing, with a sex distribution of 32% for males and 15% for females. The interference was observed more often in VVIM pacemakers at nominal setting (35%) than in VVIO pacemakers (11%). In DDD pacemakers both inhibition and triggering of ventricular stimulation was observed. Among the 23 patients with persisting syncope or dizziness after implantation of the pacemaker, the symptoms were observed during physical activity only in 5. In these 5 the underlying arrhythmia was tachycardia in 3 and inhibition of the pacemaker by muscle potentials in only one patient.     

An optimized AV delay algorithm for patients with intermittent atrioventricular conduction

Detection and promotion of an intermittent atrioventricular (AV) conduction is the objective of an AV delay hysteresis algorithm in dual chamber pacemaker (DDD) pacing. The AV delay following an atrial event is automatically extended by a programmable interval (AV hysteresis interval) if the previous cycle showed spontaneous AV conduction, i.e., a ventricular event was detected within the previous AV delay. An automatic search mode scans for spontaneous ventricular events during the hysteresis interval: a single AV delay extension (equal to the programmed AV delay hysteresis) will occur after a successive, programmable number of AV cycles with ventricular pacing. If a spontaneous AV conduction is present, the AV delay will remain extended by the hysteresis interval. Our first results in 17 patients with intermittent AV block disclosed a satisfactorily working algorithm with effective reduction of ventricular stimuli. In relation to the underlying conduction disturbance and pacemaker settings, the majority of our patients showed a reduction of ventricular pacing events up to 90% without any adverse hemodynamic or electrophysiological changes. Based on clinical (promotion of a physiological activation and contraction sequence) and technical (reduction of power consumption) advantages, the AV hysteresis principle could be of incremental value for future dual chamber pacing in patients with intermittent complete heart block.     

Pacemaker upgrade for recurrent pacemaker syndrome using a redundant contralateral electrode in a patient with bilateral venous stenoses

Following His-bundle ablation and VVIR pacemaker implantation, severe pacemaker syndrome developed and was treated with DDDR pacing, in a 70-year-old woman. Due to bilateral subclavian vein stenoses, DDDR pacing could not be maintained and an unusual method of restoring atrioventricular synchrony is described using the contralateral redundant atrial electrode connected to the ipsilateral dual chamber pacemaker and ventricular electrode.     

Cardiac pacemaker infection: surgical management with and without extracorporeal circulation

BACKGROUND: Pacemaker infections are rare, but serious complications of pacemaker therapy. The generator pocket, the pacing leads, or both may be involved. METHODS: We report on 12 patients with infected pacemaker systems. Four patients suffered from localized generator pocket infections, 6 had infected leads, and 2 patients had both. Pacemaker systems were completely removed in all patients. When the infection was limited to the generator pocket, the pacemaker system was removed at the original implantation site. Extracorporeal circulation was employed for the explantation of infected pacing leads. RESULTS: No complications occurred in patients with localized generator pocket infections. One patient with infected leads who was preoperatively already in a serious clinical condition died of septic shock in the early postoperative period; another patient died of pulmonary complications after tricuspid valve replacement 14 months after pacemaker explantation. No recurrent infections were observed. CONCLUSIONS: Explantation of the complete pacemaker system has proved a reliable method to eradicate infection. Complications have been rare, except in patients in a critically ill state who undergo cardiopulmonary bypass.     

A self-control approach to inefficient spending

Endocardial pacemaker electrodes rely in part upon endocardial fixation proximal to the electrode tip to prevent ejection of the tip from the ventricular apex. Fixation of these electrodes to the superior vena cava and tricuspid valve, in particular, has been reported. Infection of endocardial electrodes necessitates their removal. This report concerns avulsion of a tricuspid valve leaflet during traction on an infected electrode. With the availability of new methods of apical fixation, the utilization of electrode sheathing materials which discourage endocardial fixation would increase the safety of their removal under the circumstances reported herein.     

Acute hemodynamic effects of biventricular DDD pacing in patients with end-stage heart failure

OBJECTIVES: The aim of this study was to assess the potential acute benefit of multisite cardiac pacing with optimized atrioventricular synchrony and simultaneous biventricular pacing in patients with drug-refractory congestive heart failure (CHF). BACKGROUND: Prognosis and quality of life in severe CHF are poor. Various nonpharmacological therapies have been evaluated but are restricted in their effectiveness and applications. In the early 1990s, dual chamber pacing (DDD) pacing was proposed as primary treatment of refractory CHF but results were controversial. Recently, tests to evaluate the effect of simultaneous pacing of both ventricles have elicited a significant improvement of cardiac performance. METHODS: Acute hemodynamic study was conducted in 18 patients with severe CHF (New York Heart Association class III and IV) and major intraventricular conduction block (IVCB) (QRS duration = 170+/-37 ms). Using a Swan-Ganz catheter, pulmonary artery pressure, pulmonary capillary wedge pressure (PCWP) and cardiac index (CI) were measured in different pacing configurations: atrial pacing (AAI) mode, used as reference, single-site right ventricular DDD pacing and biventricular pacing with the right ventricular lead placed either at the apex or at the outflow tract. RESULTS: The CI was significantly increased by biventricular pacing in comparison with AAI or right ventricular (RV). DDD pacing (2.7+/-0.7 vs. 2+/-0.5 and 2.4+/-0.6 l/min/m2, p < 0.001). The PCWP also decreased significantly during biventricular pacing, compared with AAI (22+/-8 vs. 27+/-9 mm Hg; p < 0.001). CONCLUSIONS: This acute hemodynamic study demonstrated that biventricular DDD pacing may significantly improve cardiac performance in patients with IVCB and with severe heart failure, in comparison with intrinsic conduction and single-site RV DDD pacing.     

Mitochondrial encephalomyopathy (Kearns-Sayre syndrome) with complete atrioventricular block: a case report

A pacemaker was implanted into a 17-year-old man with cardiac failure due to complete atrioventricular block complicated by mitochondrial encephalomyopathy (Kearns-Sayre syndrome). Due to the possible complication of latent myocardial dysfunction, it was decided to implant the dual chamber pacemaker (DDD) and the operation mode was set to DDD 70 ppm 1 year after implantation; this alleviated the cardiac failure. In this case, the necessity of preventive pacemaker implantation in the early stage of cardiac failure was recognized.     

Two-year experience with rate-modulated pacing controlled by mixed venous oxygen saturation

Mixed venous oxy-hemoglobin saturation (MVO2) is a physiological variable with several features that might be desirable as a control parameter for rate adaptive pacing. Despite these desirable characteristics, the long-term reliability of the MVO2 sensor in vivo is uncertain. We, therefore, designed a study to prospectively evaluate the long-term performance of a permanently implanted MVO2 saturation sensor in patients requiring VVIR pacing. Under an FDA approved feasibility study, eight patients were implanted with a VVIR pulse generator and a right ventricular pacing lead incorporating an MVO2 sensor. In order to accurately assess long-term stability of the sensor, patients underwent submaximal treadmill exercise using the Chronotropic Assessment Exercise Protocol (CAEP) at 2 weeks, 6 weeks, and 3, 6, 9, 12, 18, and 24 months following pacemaker implantation. Paired maximal exercise testing using the CAEP was also performed with the pacing system programmed to the VVI and VVIR modes in randomized sequence with measurement of expired gas exchange after 6 weeks and 12 months of follow-up. During maximal treadmill exercise the peak exercise heart rate (132 +/- 9 vs 71.5 +/- 5 beats/min, P < 0.00001) and maximal rate of oxygen consumption (1,704 +/- 633 vs 1382 +/- 407 mL/min, P = 0.01) were significantly greater in the VVIR than in the VVI pacing mode. Similarly, the duration of exercise was greater in the VVIR than the VVI pacing mode (8.9 +/- 3.6 min vs 7.6 +/- 3.7 min, P = 0.04). The resting MVO2 and the MVO2 at peak exercise were similar in the VVI and VVIR pacing modes (P = NS). However, the MVO2 at each comparable treadmill exercise stage was significantly higher in the VVIR mode than in the VVI mode (CAEP stage 1 (P = 0.005), stage 2 (P = 0.04), stage 3 (P = 0.008), and stage 4 (P = 0.04). The correlation between MVO2 and oxygen consumption (VO2) was excellent (r = -0.93). Telemetry of the reflectance of red and infrared light and MVO2 in the right ventricle during identical exercise workloads revealed no significant change over the first 12 months of follow-up (ANOVA, P = NS). The chronotropic response to exercise remained proportional to VO2 in all patients over the first 12 months of follow-up. The time course of change in MVO2 during maximal exercise was significantly faster than for VO2. At the 18- and 24-month follow-up exercise tests, a significant deterioration of the sensor signal with attenuation of chronotropic response was noted for 4 of the 8 subjects with replacement of the pacing system required in one patient because of lack of appropriate rate modulation. Rate modulated VVIR pacing controlled by right ventricular MVO2 provides a chronotropic response that is highly correlated with VO2. This parameter responds rapidly to changes in workload with kinetics that are more rapid than those of VO2. Appropriate rate modulation provides a higher MVO2 at identical workloads than does VVI pacing. Although the MVO2 sensor remains stable and accurate over the first year following implantation, significant deterioration of the signal occurs by 18-24 months in many patients.     

Pacing impedance variability in tined steroid eluting leads

The aim of the study was to investigate pacing impedance (PI) behavior in ambulatory patients. Eighteen atrial and 18 ventricular tined steroid eluting leads with 1.2-mm2 and 5.6-mm2 electrodes were implanted in 20 patients. At 9-27 months after implantation PI was measured automatically by means of additional algorithms downloaded via telemetry links into implanted Thera pulse generators. PI was determined based on the voltage drop on the output capacitor during the 5 V-1 ms pacing impulse, at the programmable sampling rates from 1 second to 30 minutes. The study examined in particular: (1) PI trends and variations associated with different breathing patterns, body postures, provocative maneuvers, bike exercise, and during 24 hours; (2) impact of pacing rate and AV-delay on PI; (3) correlation between PI variability and pacing threshold, lead configuration, absolute PI value, age, gender, disease, and cardiac chamber. The most important findings were: (1) large PI variations of up to 450 omega were observed in properly functioning leads, (2) PI variability exhibited a weak negative correlation with pacing thresholds as if electrode positional stability was not a major factor underlying PI variations, (3) unipolar and bipolar PI variations were equivalent to each other (correlation factor = 0.93) implying that PI was mostly dependent on the circumstances around the lead tip.