P Wave Tracking Above the Maximum Tracking Rate in a DDDR Pacemaker

Dual-chamber, rate-modulated pacemakers have recently become available. These devices, whose rate response is determined by the combined input from the intrinsic atrial rate and the sensor-driven rate, have led to some unexpected upper rate behaviors. In the case presented, with the maximum sensor pacing rate at 150 ppm, multiple episodes of apparent P wave tracking occurred above the maximum P wave iracking rate of 100 ppm. This behavior is explained by P waves thai inhibit sensor-driven atrial output; inhibition may result in variable maximum tracking rates that are equal to the current sensor-driven rate. This effect appears to have minimal physiological consequence. Its importance lies in its recognition as normal DDDR function so that searches for pacemaker malfunction will not be made.     

Reliability of the Evoked Response in Determining the Paced Ventricular Rate and Performance of the QT or Rate Responsive (TX) Pacemaker

The TX pacemaker uses a conventional transvenous electrode to sense T-waves of paced ventricular complexes and it adapts the pacing rate to varying physiological demands by responding to changes in the QT or, more correctly, the stimulus artifact-to-T-wave (stimulus-T) interval. This pacing system was assessed in 13 patients. The relation between heart rate and stimulus-T interval and the effect of programming on the performance of this pacemaker were studied on several occasions in each patient. Treadmill exercise performance during TX pacing mode was compared with atrial synchronized ventricular (VAT) and asynchronous ventricular demand (VOO and VVI--70 beats per minute) pacing modes. T-wave sensing problems arose in three patients. In one, this was overcome by reducing the pulse amplitude from 5.0 to 2.5 V. In another patient, spontaneous recovery of T-wave sensing occurred 5 months after pacemaker implantation. T-wave sensing deteriorated with the passage of time in most patients. Satisfactory rate response as assessed by treadmill exercise testing and Holter monitoring was achieved in 12 patients through adjustments of two programmable parameters: the slope that defines the alteration in heart rate in response to a millisecond change in stimulus-T interval and the "sensing window" that is the interval during which T-waves can be sensed and a rate response is possible. Exercise performance was significantly better during rate responsive pacing (TX) mode as compared with VVI pacing but was comparable to that during VAT pacing. The resting heart rate/stimulus-T interval can be described by the following linear regression equation: stimulus-T interval = 466 - 1.68 X paced-rate, r2 = -0.62. This relation, however, was subject to wide inter- and intra-patient variation. Consequently, given identical programmed parameters and exercise protocol, the chronotropic response differed significantly from patient to patient and in the same patient from one occasion to another. Our results show that a physiologically beneficial chronotropic response can be achieved in most patients. However, reprogramming, based on results of exercise tests and Holter monitoring, may be necessary to adjust for changes in T-wave sensing and the heart rate/stimulus-T interval relation and, thus to ensure that the pacemaker continues to function optimally.     

Dual Device Therapy in the Setting of Changing ICD Technology: Device-Device Interaction Revisited

This case report concerns an adverse device-device interaction between a replacement ICD and a dual chamber rate responsive pacemaker. It was observed that subtle changes in the design of sensing circuits between an older first-generation ICD and the newer third-generation ICD device led to unexpected and dramatic changes in the interactive behavior of a dual device system. The new ICD was connected to chronically implanted hardware. The sensing behavior of the newer ICD included a shorter time constant in the decay of the automatic gain control function, resulting in triple sensing of both the atrial and ventricular paced stimuli and the evoked QRS complex. Physicians should be aware of new design changes in the future so as to anticipate such interactions. In the setting of rapidly changing technology, extra caution must be exercised when choosing to implant two devices in the same patient.     

Comparison of Sinus Node Response to Exercise with Responses From Two Different Activity-Based Rate Adaptive Pacemakers in Healthy Subjects of Different Age Groups

The pacing rates from accelerometer-based (Excel™) and piezoelectric-based (Legend™) activity sensing rate adaptive pacemakers, both strapped externally in the pectoral position, were compared with sinus rate response in normal volunteers of two different age groups (group 1, mean age 35 ± 16 years; group 2, mean age 72 ± 9 years) during various physical activities. Both pacemakers were programmed in manufacturers' nominal rate adaptive settings. Both types of activity sensing pacemakers programmed in this way showed chronotropic deficiencies to metabolic demand in healthy young subjects and in those matching the usual age of pacemaker implant, especially during "burst" activities. These data suggest that present recommended activity sensing rate response algorithms for accelerometer and piezoelectric pacemakers are inappropriate for many physical activities.     

Impaired Activity Rate Responsiveness of an Atrial Activity-Triggered Pacemaker: The Role of Differential Atrial Sensing in its Prevention

The physiological benefit of rate responsive, single-chamber cardiac pacing is well documented. We studied the activity response of nine atrially placed Activitrax II pacemakers. Seven patients were noted to have an inadequate activity-rate response with maximal pacing rates of 85 to 101 beats/min. Marker Channel analysis revealed that the upper rate timeout was reset by far-field R wave sensing, even when sensing occurred in the atrial refractory period. These 9 pacemakers were tested by atrial sensitivity adjustment for ability to exclude far-field R wave sensing, while preserving P wave sensing. Unipolar implantation data were then examined for predictors of this differential far-R and P-wave sensing. Differential atrial sensing occurred in 4/9 pacemakers (2/2 bipolar in the right atrial appendage; 0/1 bipolar in the coronary sinus; and 4/9 unipolar). An empirically developed index utilizing unipolar implant parameters discriminated outcomes for 8/9 unipolar pacemakers. We conclude that: (1) the rate responsiveness of the atrial Activitrax II pacemaker is limited by far-field R wave sensing even when this occurs during atrial channel refractoriness; (2) reprogramming atrial sensitivity to differentially sensed P and far-field R waves may restore appropriate rate responsiveness; and (3) although a unipolar implant discriminant index may correctly identify adequacy of future rate responsiveness, the atrial application of the Activitrax II pacemaker is cautioned until further validation is forthcoming, particularly when used in unipolar and coronary sinus applications.     

Rate responsive pacing using the evoked QT principle. A physiological alternative to atrial synchronous pacemakers

We have evaluated clinically a rate-responsive pacemaker which uses the evoked QT principle as indicator of physiological demand. This pacemaker is microprocessor-based and fully programmable noninvasively through radiofrequency coupling to an external microcomputer. To date this system has been implanted in 15 patients. With this QT sensing pacemaker the rate response to exercise was smooth and progressive, and gradually returned to the basic paced rate after termination of activity. Physiologic rate responsive pacing resulted in significant improvement in exercise tolerance and a 40% increase in cardiac output when compared to fixed-rate pacing in 8 patients. This initial experience confirms the possibility of obtaining a physiological response to exercise using a pacing system dependent only on a unipolar electrode which is independent of the problems of atrial activity and sensing. Rate responsive pacing might prove to be a useful alternative to atrial synchronous systems, and particularly advantageous in those patients whose sinoatrial function is abnormal or who suffer from atrial arrhythmias.     

The Range of Sensors and Algorithms Used in Rate Adaptive Cardiac Pacing

Implantable sensors play an important role in physiological cardiac pacing. Sensors can be classified according to the technical methods in which sensing is achieved: the sensing of the evoked ventricular response, intrathoracic impedance and body acceleration forces, and the incorporation of special sensors on pacing electrodes. These sensors differ in their relative merits in terms of speed, proportionality, sensitivity, and specificity of rate response. The efficacy of a sensor can be significantly modified by the algorithm used in relating sensor signal to a pacing rate change. The currently available types of sensors and algorithms are summarized and compared in this review article. The relative merits of these sensors and algorithms form the basis for designing a multisensor pacing system.     

Clinical Observations with a Dual Sensor Rate Adaptive Single Chamber Pacemaker

The Topaz model 515 (Vitatron B.V.) is a dual sensor rate responsive pacemaker for single chamber stimulation. It can be driven by activity counts (ACT) and QT interval measurements. Inappropriate rate modulation due to one sensor can be corrected by "sensor cross-checking." It was implanted in ten patients (20-86 years) of whom seven had complete heart block and atrial arrhythmias. After implantation T-wave amplitude ranged from 0.9mV-3.5 mV. T-wave sensing ranged from 88%–99% in 9/10 patients at the follow-up of 3 weeks. Eight patients remained in default setting of the activity threshold, after evaluation with a short walking test. An exercise test was performed on all patients. In one test, QT sensing was marginal because of lead implantation in the right ventricular outflow tract. Therefore, this pacing rate was only modulated by ACT sensing. All others were tested with equal contribution of information from both sensors (ACT = QT). In 7/9, rate response was satisfactory. When the treadmill was repeated with ACT in five of these seven patients, rate generally accelerated too fast. In one patient the setting was adjusted to "QT > ACT," because of inappropriate acceleration due to activity sensing, in another it was adjusted to "QT < ACT" because of delayed response to activity. The pacing rate and the ACT during treadmill tests in "QT = ACT" mode were more closely correlated in the first 3 minutes, compared with the last 3 minutes. We feel that rate modulation with this new pacemaker is adequate. Sensor blending and sensor cross-checking are of clinical importance.     

The Use of Exercise Testing in Children to Evaluate Abnormalities of Pacemaker Function not Apparent at Rest

The purpose of this study was to evaluate the use of exercise testing in identifying abnormalities of pacemaker function and in confirming set parameters not apparent at rest in children with implanted atrial synchronous physiologic pacemakers. Maximal exercise tests were performed on 24 children (15 boys, 9 girls) from 4.5 to 18 years of age (median = 15) with physiologic pacemakers. The lower rate limit was observed before or following testing in 19 of 24 cases. In each case this correlated with the set lower rate limit. The upper rate limit was reached in 10 of 24 cases and was found to be lower than that programmed in one case in which a long atrial refractory period had limited the upper rate limit. Six children reached the maximum upper rate limit to which their pacemaker could be programmed. No abnormalities of atrial capture or ventricular capture occurred during exercise testing. Ventricular sensing was normal in each case. Atrial sensing was observed to be normal in 15 of the 24 cases. Two patients had decreased atrial sensing with exercise. Reversion to the "noise rate" due to myopotential inhibition was found in seven other cases. Subsequent tests on two of these children showed normal sensing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lower incidence of unexpected in-hospital death after interprofessional implementation of a bedside track-and-trigger system

Background

In-hospital patients may suffer unexpected death because of suboptimal monitoring. Early recognition of deviating physiological parameters may enable staff to prevent unexpected in-hospital death. The aim of this study was to evaluate short- and long-term effects of systematic interprofessional use of early warning scoring, structured observation charts, and clinical algorithms for bedside action.

Methods

A prospective non-randomized controlled study of unexpected in-hospital death before and after implementation of a clinical intervention in a medical and surgical ward setting at an urban Danish university hospital. Information was obtained over three four-month study periods – a pre-interventional one in 2009 (1st March–30th June), and two postinterventional ones in 2010 (1st September–31st December) and 2011 (1st March–30th June). The incidence of unexpected patient death, the primary study outcome, was calculated as the rate of unexpected patient mortality based on in-hospital risk time.

Result

The adjusted unexpected patient mortality rate was significantly lower during the second postinterventional study period than before the intervention, 17 versus 61 per 100 adjusted patient years (P = 0.013), corresponding to a rate ratio of 0.271 (95% confidence interval (CI) 0.097–0.762). A tendency to reduced unexpected mortality was found during the first postinterventional study period (25 versus 61 per 100 adjusted patient years, P = 0.053; rate ratio 0.404, CI 0.161–1.012).

Conclusion

Clinical intervention comprising systematic monitoring practice, early warning scoring, an observation chart, and an algorithm for bedside management, implemented by interprofessional teaching, training, and optimization of communication and collaboration, may significantly reduce unexpected in-hospital mortality.     

Relationship Between Right Atrial and Mixed Venous Oxygen Saturation and Heart Rate During Exercise in Normal Subjects and Patients with Cardiac Disease

FRENCH, W.J., ET AL.: Relationship Between Right Atrial and Mixed Venous Oxygen Saturation and Heart Rate During Exercise in Normal Subjects and Patients with Cardiac Disease. An ideal sensing variable for use in rate responsive pacemakers should measure a physiological parameter that closely correlates with heart rate during various activities in a diverse group of subjects. Nineteen patients, 12 normal and 7 patients with heart disease, were studied to assess the relationship between mixed venous oxygen saturation and heart rate. In patients with heart disease right atrial oxygen saturation and heart rate were also compared. Each subject underwent pulmonary artery catheterization and performed seated cycle ergometer exercise. Gas exchange and heart rate were measured continuously and blood sampled at frequent intervals. Normal patients were studied at rest and during steady-state exercise (mean work rate 149 watts). Patients were studied at rest, steady-state exercise [mean work rate 37 watts), and during incremental exercise (5–10 wattsimin) to tolerance. There were 248 paired right atrial or mixed venous oxygen saturation/heart rate observations obtained. Changes in mixed venous oxygen saturation and heart rate were not substantially altered by fitness or cardiac disease. Rate responsive pacemakers sensing changes in oxygen saturation may be a superior sensing variable for both normal and patients with heart disease.     

Evaluation of a New Rate Adaptive Ventricular Pacemaker Controlled by Double Sensors

The LEGEND-PLUS, a new rate adaptive pacemaker that combines activity and minute ventilation sensing for automatic rate adaptation was implanted in the right ventricle (VVIR) in 11 patients (mean age 62 ± 9 years). Initial programming was performed using the Programmer Exercise Protocol (a 3-minute walk). This programming was evaluated by treadmill tests, up-stairs and down-stairs walking, and Holier recordings. Results: Following the final programming of LEGEND-PLUS, the mean upper activity rate was 102 ± 7 beats/rain (range 90–120 beats/min), while the mean upper minute ventilation rate was 125 ± 16 beats/min (range 100–150 beats/min). The mean rate responses during the exercise protocol and the final programming in minute ventilation and activity sensing modes were 5.4 ± 2.3 (range 1–9), versus 4 ± 2.4 (range 1–8; P < 0.01) and 7.6 ±1.1 (range 5–9), versus 7.5 ± 0.8 (range 6–9; P = 0.8), respectively. In the combined sensing mode, the acceleration rate was identical to the activity rate response and the deceleration rate mimicked the minute ventilation. Conclusion: Dual sensor VVIR pacemakers have the potential to improve rate adaptation to exercise. The rate response to exercise in patients fitted with activity and minute ventilation sensors, VVIR pacemakers closely mimics the physiological rate response.     

Initial Clinical Experience with Rate Adaptive Cardiac Pacing Using Two Sensors Simultaneously

LANDMAN, M.A.J., ET AL.: Initial Clinical Experience with Rate Adaptive Cardiac Pacing Using Two Sensors Simultaneously. In the rate adaptive pacemakers, all presently available sensors show one or more drawbacks. Combining two sensors in a single pacemaker, we tried to optimize its rate responsive characteristics. In this study, we present the rate adaptive behavior of a two sensor pacemaker system, using both QT interval and activity sensing. In addition, we compared the rate response with that of each sensor alone. Nine patients with an implanted QT interval sensing pacemaker, and an externally attached activity sensing pacemaker performed three exercise stress tests on treadmill. The QT interval, measured by the implanted pacemaker, and the activity level, were transmitted to an external computer. This computer contained the two sensor rate adaptive algorithm, and reprogrammed the implanted pacemaker on beat-to-beat basis. Conclusion: In the two sensor mode the rate increases immediately at the onset of exercise, caused by the prompt response of the activity sensor. Further rate increase is driven by the QT interval sensor and therefore proportional to the level of exercise. Furthermore, the rate decay during the recovery phase is more physiological.     

QT Sensing Rate Responsive Pacing and Myocardial Infarction:

A 65-year-old man, treated with the QT sensing rate responsive pacemaker required to manage high degree AV block, sustained a transmural inferior wall myocardial infarction 6 months after the pacemaker implant. The rate response of the pacemaker during the acute phase of the infarction was physiological as evidenced by increased pacing rate during pain and with the gradual decrease in rate during the first postinfarction days. The underlying mechanisms are discussed.     

Inverted Pacemaker Mediated Tachycardia Induced During Noninvasive Electrophysiology Testing

This report describes a case in which an implanted pacemaker programmed to perform noninvasive electrophysiology testing resulted in an unusual form of pacemaker mediated tachycardia. The method of chest wall stimulation was used by programming a unipolar, triggered pacing mode with a short refractory period. In the AAT mode, far-field R wave sensing occurred beyond the physiological atrial refractory period. The triggered atrial response resulted in a single chamber, pacemaker mediated tachycardia.     

Apparent P Wave Underselling in a DDD Pacemaker Post Exercise

Wencke-bach behavior of DDD pacemakers occurring when the P-P interval varies between the programmed upper rate interval and the total atrial refractory period is symmetrical in a sense that the pacemaker response during atrial rate acceleration is similar to the pacemaker response during atrial rate deceleration. This phenomenon can be observed in all patients with persistent AV block in whom a DDD pacemaker is implanted, during exercise testing when the spontaneous atrial rate exceeds the selected upper rate, i.e., the programmed upper rate interval. However, this phenomenon will not be observed in all patients with intermittent intact AV conduction during exercise. In this case report we describe a patient who showed an asymmetrical response during a bicycle exercise test. There was 1:1 atrial sensing ventricular pacing until the atrial rate exceeded the upper rate of 140 ppm, while atrial sensing was restored during recovery when the conducted sinus rhythm had decreased to 105 beats/min.     

Upper Rate Lockout: An Unexpected Feature of Rate Adaptive Atrioventricular Delay

We present a case in which use of rate adaptive AV delay resalted in unexpected pacemaker 2:1 AV block when the patient's atrial rate exceeded the pacemaker maximum tracking rate but was below the predicted multiblock rate. "Lockout" of normal upper rate behavior was accompanied with the requirement of a slower atrial rate for reassociation than loss of atrial tracking, a form of upper rate hysteresis. The mechanism of upper rate lockout is discussed, along with potential ways to avoid the problem. The use of software based pacemakers with an extended range of programmable options allows the most flexibility in optimizing pacemaker performance in an individual patient.     

Knowledge of diabetes among personnel in home‐based care: how does it relate to medical mishaps?

OBJECTIVE: To assess the influence of knowledge about diabetes on the performance of diabetes care for the elderly involving insulin treatment, with special attention to aspects of patient safety in home care. DESIGN: A questionnaire was administered to nurse's aides and assistant nurses (n = 3144). Answers to questions about knowledge of diabetes were related to "relevant" or "risky measures" as judged from a hypothetical diabetes case. A 94% response rate was obtained. The study took place in January 1997 in 15 of Sweden's 289 municipalities. RESULTS: Insufficient theoretical knowledge about how the blood sugar is related to an insulin reaction led to an almost threefold increased risk of taking a "risky measure". Insufficient knowledge about reasons for an insulin reaction also resulted in a higher risk, as was the case for personnel working in home based care in contrast to those working solely in Institutional care. In addition, the risk that a nurse's aide would take a "risky measure" was higher than that for an assistant nurse. This may indicate that the basic theoretical knowledge of nurse's aides is inadequate. CONCLUSION: Deficiencies in basic knowledge of diabetes among nurse's aides and assistant nurses constitute a major cause of potentially serious mishaps in home care of elderly diabetic patients treated with insulin.     

The Ventricular Endocardial Paced Evoked Response

The endocardial ventricular evoked response which follows delivery of a unipolar stimulus down the sensing electrode is remarkably uniform, and is of slightly longer duration at the base than at the apex of the heart. As the same lead is used for both pacing and sensing, it is possible to record the evoked T wave representing dominantly local repolarization which follows a pacing-induced depolarization from the same site. Studies of the pacing evoked response following administration of drugs with class 3 mode of action are similar to those obtained by monophasic action potential recordings, and suggest that myocardial repolarization can be accurately assessed by this technique. The stimulus to evoked T wave timing has been used to design a pacing system which offers the advantage of physiological control of pacing rate, independent of atrial activity, using a conventional endocardial electrode lead system. The potential advantages of this system are reviewed.     

Analysis of Atrial Sensed Far-Field Ventricnlar Signals: A Reassessment

Accurate detection of the spontaneous far-field ventricular signal may be used to determine the ventricular activation, and hence, the interval from atrial stimulus to the ventricular R wave (AR interval) using a standard atrial pacing lead. This can be useful in developing a physiological atrial rate responsive (AAIR) pacemaker and in further improving DDD(R) pacing algorithms. In order to better characterize the atrial sensed far-field ventricular signal, 200 consecutive patients undergoing pacemaker implantation were studied. The amplitude of the far-field ventricular signal was significantly smaller than that of the atrial deflection. In all recordings, the slew rate of the atrial deflection was larger than that of the far-field ventricular signal. Subdivision of the recordings by electrode position, pocket location, or QRS duration on the surface ECG resulted in significantly different signal characteristics. The amplitude and slew rate of the far-field ventricular signal were significantly smaller in bipolar versus unipolar sensing. Atrial sensed far-field ventricular recordings could also be obtained in the case of ventricular pacing. Our results indicate that accurate sensing of the far-field ventricular signal from an atrial pacing lead is conceivable in most patients. The different signal characteristics in relation to parameters, such as electrode position, sensing mode, and pocket location, may be useful in determining the optimal conditions for signal sensing.