A Method of Esophageal Electrogram Recording for Diagnostic Atrial and Ventricular Pacing

This study evaluates improvement of the electrogram sensed via an esophageal catheter with the sensing electrode adjacent to the stimulating electrode with and without a specialized artifact suppression system. In 100 patients (65 men and 35 women) aged 16-60 years (mean 48 years), esophageal recordings of left atrial activity were obtained during simultaneous transesophageal atrial pacing. Transesophageal ventricular pacing was performed in an additional 34 patients. Without the suppression system, ventricular paced activity, recorded from the esophagus, was not suitable for interpretation. About 10% of the atrial electrogram response could be recorded and evaluated during atrial pacing. With the stimulus artifact suppression system, interpretable recordings were obtained 100% of the time during atrial and ventricular recordings. The method described allows use of transesophageal diagnostic testing where previously only the intracardiac route was possible.     

Autonomic Function during Closed Loop Stimulation and Fixed Rate Pacing: Heart Rate Variability Analysis from 24‐Hour Holter Recordings

Aim: Aim of this retrospective study was to analyze the effect of closed‐loop stimulation (CLS) and DDD pacing mode on autonomic balance, and to evaluate heart rate variability (HRV) during CLS stimulation. Methods and Materials: Autonomic balance was estimated by a 24‐hour HRV analysis of paced and spontaneous beats in patients implanted with a dual‐chamber pacemaker (Inos²⁺ CLS—Biotronik GmbH, Berlin, Germany) and randomly assigned to CLS or DDD pacing mode. Patients underwent two 24‐hour electrocardiogram Holter recordings at the end of each 3‐month pacing mode period. Each Holter recording was automatically scanned to extract sequences of consecutive beats of the same type [atrial paced (Ap)‐sequence and atrial spontaneous (As)‐sequence], lasting at least 130 beats. Results: Eight hundred and ten sequences were extracted from 15 patients, and the following spectral parameters were evaluated during both CLS and DDD mode: the total power (variance), the absolute and percentage (relative to the total power) powers of the low frequency (LF, 0.04–0.15 Hz) and high frequency (HF, 0.15–0.4 Hz) components, as well as the LF/HF power ratio. Discussion: The two main findings of this study were: in all the patients, CLS seems to mimic short‐term physiological HRV, although the variability (total power) was lower than that relative to the spontaneous beats; the HRV of the spontaneous beats had an higher LF/HF when the pacemaker was programmed as DDD respect to CLS, consistent with a shift toward sympathetic predominance. PACE 2010; 33:337–342)     

A Double-Blind Study of Submaximal Exercise Tolerance and Variation in Paced Rate in Atrial Synchronous Compared to Activity Sensor Modulated Ventricular Pacing

To assess the variation in paced rate during everyday activity and the importance of atrioventricular synchronization (AV synchrony) for submaximal exercise tolerance, atrial synchronous (DDD) and activity rate modulated ventricular (VVI,R) pacing were compared in 17 patients with high degree AV block. The patients were randomly assigned to either mode and evaluated by treadmill exercise to moderate exertion and by 24-hour Holter monitoring after 2 months in the DDD and VVI,R modes, respectively. At the end of the study, the patients were programmed to the pacing mode corresponding to the preferred study period. During the treadmill test, the mean exercise time to submaximal exertion (Borg 5/10), exertion ratings and respiratory rate did not differ between pacing modes despite a significantly lower ventricular rate in the VVI,R mode. The atrial rate during VVI,R pacing was significantly higher than the ventricular rate, but did not differ from the ventricular rate during DDD pacing. There was a diurnal variation in paced rate in both pacing modes. Paced ventricular rate was, however, higher and variation in paced rate greater in DDD compared to VVI,R pacing. Nine patients preferred the DDD mode, three patients preferred the VVI,R mode, while five subjects did not express any preference. The results from this study indicate that the variation in paced rate during activity sensor-driven VVI,R pacing does not match that during DDD pacing neither during everyday activities nor during submaximal treadmill exercise. Nevertheless, no differences in exercise time, Borg ratings, and respiratory rate during submaximal exercise were found. Thus, for most patients with high degree AV block, DDD and VVI,R pacing seem equally satisfactory for submaximal exercise.     

Closed Loop Stimulation is Effective in Improving Heart Rate and Blood Pressure Response to Mental Stress: Report of a Single-Chamber Pacemaker Study in Patients with Chronotropic Incompetent Atrial Fibrillation

Introduction: Closed-loop stimulation (CLS) is a form of rate-adaptive pacing capable of providing an effective pacing rate profile not only during physical exercise but also during mental stress. To test its effectiveness, CLS and accelerometer sensor (AS) rate response were compared intraindividually during a mental stress test (MST). Methods: Thirty-six patients (mean age 78.9 ± 6.4 years) implanted with a pacemaker with the CLS algorithm (Cylos, Biotronik, Berlin, Germany) underwent MSTs in different pacing configurations: nonrate-adaptive mode (VVI), AS mode (VVIR), and CLS mode, respectively. A modified Stroop test was used in order to induce mental stress. Heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure, and pacing percentage burden were collected for 5 minutes before, during, and 5 minutes after the test. Results: Mean peak-HR during MST was significantly higher in CLS configuration than in VVIR and VVI modes (92.8 ± 12.6 vs 78.9 ± 6.5 vs 77.8 ± 7.5; P ≤ 0.001). The average HR increase during MST was also higher in CLS configuration than in VVIR and VVI modes (22.7 ± 16.7 vs 8.2 ± 8.6 vs 6.6 ± 6.3; P ≤ 0.001). The percentage of pacing beats during MST was higher in CLS configuration than with the other two algorithms (48.4 ± 17.9 vs 27.4 ± 17.5 vs 25.8 ± 17.6; P ≤ 0.001). The average peak-SBP was significantly higher during MST in CLS mode than in VVIR and VVI configurations (172.6 ± 15.5 vs 156.7 ± 12.2 vs 145.5 ± 13.7; P ≤ 0.001). The mean SBP increase showed a similar behavior (51.8 ± 24.7 vs 18.4 ± 13.7 vs 16.4 ± 10.3; P ≤ 0.001). Conclusion: CLS algorithm in a single-chamber device is more effective than AS in detecting an hemodynamic demand due to an emotional stress and supplying a proper HR increase. These results are even more surprising compared to previous data in dual-chamber pacemakers, because they imply that CLS algorithm can provide an appropriate rate-modulation in patients with AF and chronotropic incompetence. (PACE 2012; 35:990-998).     

Permanent Overdrive Atrial Pacing in the Chronic Management of Recurrent Postoperative Atrial Reentrant Tachycardia in Patients with Complex Congenital Heart Disease

This study investigated the value of permanent atrial pacing as an adjunct to the current therapy in the chronic management of recurrent postoperative atrial reentrant tachycardia in patients with complex congenital heart disease. We studied the postpacing clinical course in 18 patients with recurrent atrial reentrant tachycardias unresponsive to conventional therapy who had an implanted atrial pacemaker. The pacemaker was programmed at a lower pacing rate 20% faster than the spontaneous mean daily rate previously determined with 24-hour Holter monitoring. Serial Holter recordings and pacemaker programming sessions were subsequently performed trying to mantain a paced atrial rhythm overdriving the spontaneous rhythm as long as possible. Twenty-four hour Holter monitoring documented a prevalent (> 80%) paced rhythm during the daily hours in all patients during the follow-up; all patients, however, required at least once a variation In programmed mode and pacing rate. Antiarrhythmic medications were discontinued after 6 months if the patient remained arrhythmia free while on pacing. Recurrences of atrial reentrant tachycardia occurred in five patients (29%) during the initial 6 months interval after the pacemaker implantation, while late recurrences occurred in only two patients (11 %). One patient died suddenly 10 months after the pacemaker implant. At the end of the follow-up, 15 patients (83%) were arrhythmia-free and only 2 of them were still on antiarrhythmic drugs. We conclude that permanent atrial overdrive pacing can be an important tool in the management of patients with atrial reentrant tachycardia following repair of congenital heart disease.     

Antiarrhythmic Effects of VVI Pacing at Physiologic Rates: A Crossover Controlled Evaluation

Ventricular pacing can prevent bradycardia-dependent ventricular ectopic activity (VEA) and is helpful in some cases of drug-refractory venfricuiar tachycardia (VT). This study is a prospective evaluation of VVI pacing for the control of VEA not related to underlying bradycardia, drug side-effects, or prolonged QT interval syndromes. Twenty-nine patients undergoing serial electrophysioiogic-pharmacoiogic testing for VT control were studied. Eighteen of these patients (12 men; meon age = 60.1) both completed ihe protocol and had sufficient VEA for analysis. Coronary disease was present in 13 patients, cardiomyopathy in two patients, and one patient each had myocarditis, mitral valve prolapse, and no structural heart disease. Ambulatory (Holter) monitor recordings during VVI pacing were compared with control recordings made in the absence of pacing, VVI pacing rates were 10–15 bpm above the mean daily heart rate (mean = 92 bpm; range = 63–110). Hours from paced recordings were paired with hours from control (prior to analysis) according to time of day to reduce the effects of spontaneous variability in VEA frequency. Overall, VVI pacing reduced ventricular premature complexes (VPGs) 26% from 331 to 245/hour (p < 0.001). During pacing, couplets (pairs, successive VPGs) were reduced from 6.95 to 1.03/hour (p < 0.000001) and VT (≥3 successive VPCs) from 0.89 to 0.045 episodes/hour (p < 0.003). Of 13 patients with couplets, 11 had ≥50% reduction and five had ≥90% reduction. Baseline VT was eliminated in four out of nine patients during pacing. Pacing did not increase VEA significantly in any patient. In this group of patients, reduction of VEA by VVI pacing was significant and was comparable to pharmacologic interventions. Higher forms of VEA fcouplets and VT) appeared to respond better than single VPCs. Further studies may define patients with VEA who can benefit from pacing     

Clinical Interest of a Sensor Driven Algorithm Limiting Ventricular Pacing Rate During Supraventricular Tachycardia in Dual Chamber Pacing

A sensor driven algorithm limiting ventricular pacing rate during supraventricular tachycardia (SVT) is included in a dual chamber rate modulated pacemaker sensitive to acceleration forces (Relay, 294-03, Intermedics Inc.). According to the intensity of concomitant exercise, the ventricular pacing rate is limited either to the programmed maximum pacing rate (MPR) or to an interim lower limit, called "conditional ventricular tracking limit" (CVTL). The MPR prevails over the CVTL when the sensor calculated pacing rate exceeds the minimal rate by more than 20 beats/mm. The purpose of the study is to determine the clinical safety and efficacy of this algorithm in patients with intermittent SVT. Method: a Relay was implanted in four patients with a bradycardia/tachycardia syndrome and in four patients with complete atrioventricular block (CAVB). All had episodes of paroxysmal atrial tachycardia. The units were programmed in DDDR: rate responsive parameters were adjusted by simulating the rate response during three levels of exercise to let the MPR override the CVTL only during strenuous exercise. Holter monitors and exercise testings were performed at 3-month follow-up. Results: in seven patients, Holter recordings showed Supraventricular arrhythmias at rest with a ventricular pacing rate limited to the CVTL. Appropriate rate increases during exercise testings were also demonstrated. Three devices had to be reprogrammed in DDIR tone patient suffering from nearly permanent atrial flutter and two patients not tolerating the CVTL pacing rate at rest). Conclusion: the CVTL algorithm is effective in protecting against high ventricular pacing rates during Supraventricular arrhythmias. It allows the selection of the DDDR mode even with a high MPR in patients with intermittent SVT.     

Paradoxical AV Delay Shortening of a Pacemaker

Barold, S.S., et al. : Paradoxical AV Delay Shortening of a Pacemaker. Paradoxical shortening of the paced AV delay (atrial paced-ventricular paced or Ap-Vp interval) was observed at rest in the DDD and DDDR modes in three patients with implanted CPI Vigor DR pacemakers programmed with a long AV delay and a relatively narrow difference between the lower and upper rates. This behavior is related to the VA extension algorithm designed to prevent the sensor-driven atrial pacing rate from exceeding the programmed upper rate whenever a sensed conducted QRS complex continually follows an atrial stimulus. We found that this algorithm also becomes manifest at rest and may cause shortening of the Ap-Vp intervals. The VA extension algorithm is best conceptualized in terms of a separate atrial upper rate that functions on exercise and at rest. The atrial and ventricular upper rates are equal but the atrial upper rate is initiated by an atrial-paced or sensed event and the ventricular upper rate is initiated by a paced or sensed ventricular event. Under certain circumstances delay in the release of the atrial stimulus Ap to conform to the atrial upper rate interval produces variable abbreviation of the paced AV (Ap-Vp) delays with resultant variation in the duration of the atrial escape intervals despite fundamental ventricular-based lower rate timing.     

Septal His-Purkinje Ventricular Pacing in Canines: A New Endocardial Electrode Approach

Ventricular activation sequences and cardiac performance are influenced by pacing sites. Stimulation of or close to the specialized a trioventricular (AV) conduction system optimizes paced ventricular function compared to alternative epi- or endocardial muscle conduction sites. This study reports a new endocardial electrode implant approach to approximate septal His-Purkinje ventricular pacing. Five 6-month-old beagles were used, A custom, platinum-iridium, exposed helical screw electrode (Medtronic, Inc.), 4.5-mm long, with a 17.8-mm² surface area, was designed with a polyurethane covered 4 filar MP35N nickle conductor lead. An 8 French sheath (USCI, Inc.) was modified as introducer to permit simultaneous implant intracardiac pressure and electrogram recordings. Following a thoracotomy, the introducer was inserted through the right atrial appendage and advanced to record optimal His-bundle electrogram while maintaining atrial pressure along the septal tricuspid valve annulus. After electrode implant, ECG demonstrated narrow paced QRS morphology. Mean implant values showed sensed R wave 6,3 mV, slew rate 0.65 V/sec, pacing impedance 319 ohms, and threshold 0.9 V/3.3 mA at 0.5-msec output. Necropsy showed implant above the tricuspid annulus with electrode extension into and contained within the proximal ventricular septum. This study demonstrates that an endocardial septal approach to His-Purkinje ventricular pacing to optimize paced ventricular function is feasible with a new electrode design and precise septal implant technique. Alternative introducer designs may permit tranvenous application of this approach.     

Initial Experience with Mode Switching in a Dual Sensor, Dual Chamher Pacemaker in Patients with Paroxysmal Atrial Tachyarrhythmias

Mode switching algorithms have been developed to avoid tracking of atrial fibrillation (AF) or flutter (AFL) during DDD(R) pacing. Upon recognition of AF or AFL, the mode is switched to a nontracking, sensor driven mode. The Vitatron Diamond model 800 pacemaker does this on a beat-to-beat basis. Atrial events occurring within a “physiological range” (± 15 beats/min) calculated from a running average of the atrial rate are tracked. When atrial events are not tracked the escape interval is either determined by the sensor(s) or by a fallback algorithm thereby preventing large increases in V-V interval during mode switching. Loss of atrioventricular (AV) synchrony by atrial premature beats and after an episode of AF or AFL is prevented by atrial synchronization pulses (ASP), which are delivered after a safe interval (timed out from the sensed premature atrial event) has expired and before delivery of the next ventricular stimulus. We implanted 26 such devices in 18 men and 8 women with symptomatic second- or third-degree AV block and paroxysmal AF or AFL. Their ages ranged from 18–84 years (mean 60), and the follow-up ranged from 2–13 months (mean 8). During pacemaker check-up, exercise testing or 24-hour Holter monitoring one or more episodes of mode switching was documented in 8 patients. In these 8 patients a smooth transition (ventricular rate) from sinus rhythm to AF or AFL was documented on one or more occasions, without inappropriate increase in ventricular rate in the DDDR mode. None of the patients complained of palpitations. Appropriate rate response was seen in all patients during Holter monitoring and exercise. Restoration of AV synchrony with ASP was documented many times. In 2 patients the DDIR mode was programmed due to intermittent synchronization of ventricular stimuli to near incessant supraventricular tachycardia, which sometimes gave rise to asymptomatic slightly irregular ventricular paced rhythms below WO beats/min. Recognition of AF or AFL was reliable. No inappropriate increases in ventricular pacing rate were seen at the onset of or during AF or AFL. ASP is an effective method of maintaining AV synchrony and avoiding competitive atrial pacing.     

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.     

Efficacy and Safety of Ventricular Rate Responsive Pacing in Children with Complete Atrioventricular Block

Single chamber rate responsive pacing offers many potential advantages over the more complex dual chamber atrial tracking pacing mode in children, and the preservation of atrioventricular synchrony could be unnecessary in selected groups of pediatric patients. Twenty-two pediatric patients (age range 9 months to 12 years; mean 6.5 years) had implantation of ventricular rate responsive (VVIR) pacemakers over a 2-year period. All patients had chronic third-degree atrioventricular block, and a normal ventricular function at rest. During the follow-up each patient underwent a 24-hour Holter monitoring, and ten performed a graded treadmill test in both ventricular fixed rate (VVI) and rate responsive (VVIR) pacing mode. Paced ventricular rates were found to be normal for age in all 22 patients; maximum rate did not reach the higher programmed rate during daily activities in any patient. Comparing the mean paced ventricular rate to the mean rates of blocked P waves, six patients showed a difference of more than 20 beats/min, which induced the pacemaker parameters to be reprogrammed. In all patients a significant correlation was found between variations of paced ventricular rate and variations of spontaneous blocked atrial rhythm (P < 0.05); this correlation persisted in the subsequent Holter controls in the ten patients with longer follow-up. Exercise tolerance resulted normal in the ten patients who performed a treadmill test either in VVIR or VVI mode, with increased maximal heart rates and maximal systolic blood pressure in VVIR mode (P < 0.0013). Rate responsive ventricular pacemakers seem to adequately respond to the physiological needs of daily life of this selected group of children requiring permanent pacing.     

Evaluation of Rate-Responsive Pacemakers by Transesophageal Holter Monitoring of Spontaneous Atrial Rate

BONGIORNI, M.G., ET AL.: Evaluation of Rate-Responsive Pacemakers by Transesophageal Holter Monitoring of Spontaneous Atrial Rate. One of the most important problems in rate responsive (RR) pacing is the clinical experimental evaluation of the reliability of various sensors. In particular, it is difficult to test their sensitivity and specificity during daily activity of the patients. Atrial rate, when present and normal, is the most physiological marker of metabolic requirements, but sometimes it is impossible to analyze the P wave in ventricular paced rhythm during routinely performed tests (e.g., ergometric test and 24-hour Holter monitoring). During various physical activities, we monitored atrial electrograms on an esophageal lead on the first channel of a standard Holter tape recorder; on the second channel a surface ECG lead was recorded. We selected 10 patients with high grade heart block and normal sinus node function paced in RR-VVI mode. RR pacing was obtained using various sensors (body activity, blood temperature, spike-T interval, minute ventilation). The good quality of recording allowed an easy evaluation of atrial and ventricular rates. In four cases an appropriate increase in heart rate was documented; sensitivity threshold and/or rate response slope were reprogrammed when indicated. The pacing rate of one patient did not parallel the atrial rate during walking only. In three cases, we observed a delay in the ventricular rate increase, with ventricular rate decreasing at peak exercise despite further atrial rate increase. In the last two patients, we observed inappropriate pacing response; pacing rate increased later and to a lower level than the atrial one. This new method is applied easily and appears reliable to evaluate the response of RR pacemakers to individual metabolic needs. Its applicability is, however, limited by the need for a normal sinus node function. In conclusion, transesophageal atrial rate recording is a useful tool for the clinical evaluation of RR pacemakers, and it can be proposed as a new method for testing new sensors.     

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.     

Heart rate changes during acute mental stress with closed loop stimulation: report on two single-blinded, pacemaker studies

BACKGROUND: Mental stress affects hemodynamic properties of the heart in patients indicated for a pacemaker, therefore highlighting the need for a rate-adaptive sensor that responds to mental loads. One such sensor utilizes Closed Loop Stimulation (CLS), which translates right ventricular contractility into patient specific pacing rates. Clinical studies utilizing CLS [Emotional Response (ER) and Emotional Response 2 (ER2) studies] have been performed to confirm CLS provides appropriate heart rate response to acute mental stress. The objective of these studies was to compare heart rates during a mental stress test, with the patient's pacemaker programmed to a CLS pacing mode and an accelerometer pacing mode. METHODS: Patients were implanted with a BIOTRONIK Protos/CLS pacemaker (Berlin, Germany) and subjected to mental stress testing. The stress test consisted of a relaxation period followed by a color-word test and an arithmetic challenge test. The ER2 study utilized a randomized study design, in which pacing mode testing order was randomized. RESULTS: Analysis included patients who exhibited at least 80% sensor-driven heart rates during stress testing. Results for both studies demonstrated that CLS provided a statistically significant higher increase in heart rate during testing compared with an accelerometer pacing mode. The studies also showed that CLS provided a statistically significant higher peak heart rate during testing compared with an accelerometer pacing mode. CONCLUSIONS: The ER and ER2 studies demonstrate that the CLS algorithm responds with an appropriate heart rate response to acute mental stress in patients exhibiting a high percentage of sensor-driven pacing.     

Benefits and Limitations of Rate Adaptive Pacing Under Laboratory and Daily Life Conditions in Patients with Minute Ventilation Single Chamber Pacemakers

Rate adaptive pacing has been shown to improve hemodynamic performance and exercise tolerance during acute testing. However, there remain concerns about its benefit in daily life and possible complications incurred by unnecessary pacing. This double-blind crossover study compared the benefit of rate adaptive (SSIR) versus fixed rate (SSI) pacing under laboratory and daily life conditions in 20 rate incompetent patients with minute ventilation single chamber pacemakers (META II). The heart rate (HR) response during three different exercise tests (treadmill, bicycle ergomctry, walking test) was correlated with the Holler findings during daily life in either pacing mode. The maximal HR was significantly higher in the SSIR-mode compared to the SSI-mode, both during laboratory testing (treadmill: 123 ± 15 vs 93 ± 29 beats/min: ergometry: 118 ± 15 vs 89 ± 27 beats/min; walking test: 127 ± 9 vs 95 ± 26 beats/min, all P values < 0.01) as well as during daily life (Holter: 126 ± 13 vs 103 ± 24 beats/min, P < 0.01). On Holter, the average HR (71 ± 14 vs 71 ± 8 beats/min) and the percentage of paced rhythm (54 % vs 62%, SSI- vs SSIR-mode, P = NS) were not different in either mode. However, despite a 30% rate gain in the SSIR-mode, the exercise capacity remained unchanged, and only 38% of patients preferred the SSIR-mode. Minute ventilation pacemakers provide a physiological rate response to exercise. Irrespective of the protocol used, the findings of laboratory testing are comparable to those during daily life. However, patient selection for rate adaptive single chamber pacing should be made with caution, since the objective benefit of restoring normal chronotropy may subjectively be negligible for most patients.     

Usefulness of Echocardiography to Predict Inappropriate Atrial Sensing in Single-Lead VDD Pacing

Reliable atrial sensing is the prerequisite for restoration of atrioventricular synchrony in patients with single-lead VDD pacing systems. To determine echocardiographic variables associated with inappropriate atrial sensing, 21 consecutive patients with symptomatic second- or third-degree AV block and normal sinus node function were studied. Prior to implantation echocardiographic measurements of end-systolic and end-diastolic dimensions and volumes of the right atrium and right ventricle were performed. All patients underwent implantation of a Medtronic Thera VDD(d) pacemaker with a bipolar Medtronic Capsure electrode. A minimal amplitude of the unfiltered atrial electrocardiogram of > or =0.5 mV was required for permanent lead position and the atrial sensitivity was programmed below the lowest recorded value. Appropriate atrial sensing (atrial triggered ventricular paced complexes/total number of ventricular paced complexes) was assessed during 24-hour Holter monitoring and treadmill exercise testing 3 to 6 weeks after implantation. Inappropriate atrial sensing (<95% correct atrial synchronization during Holter registration and/or <97.5% during exercise testing) was present in nine patients. Right atrial volumes and the right ventricular end-diastolic volume was significantly higher, as compared to patients without inappropriate sensing (12 patients). The right atrial and diastolic volumes had the highest correlation with correct atrial sensing r = 0.83, P<0.0001). Using a postdefined cut-off value of > or =80 mL for the end-diastolic right atrial volume, sensitivity and specificity for inappropriate sensing was 100% and 92%, respectively. These findings show that preimplant echocardiography can identify patients with inappropriate sensing during VDD pacing, in whom DDD pacing should be considered.     

Programming a Long Paced Atrioventricular Interval May Be Risky in DDDR Pacing

In patients with intermittent AV block and dual chamber pacemakers, a long paced AV interval of 200 msec or more can be selected to prolong pulse generator life (by avoiding the ventricular pace output) and to enable a more physiological and hemodynamically superior activation sequence. This case report describes the potential risks of programming a long paced AV interval in a patient with a DDDR pacemaker. T wave pacing, as described here, can occur if the conducted QRS complex is not sensed because it occurs during the ventricular blanking period (delivery of the atrial stimulus). This can be initiated by the mechanisms that induce apparent and actual P wave undersensing of the conducted QRS complex. In this case report apparent P wave undersensing and subsequent T wave pacing with ventricular capture (in a patient with intermittent AV block) occurred frequently during an exercise test done in the DDDR mode with a paced AV interval of 200 msec, according to the clinical evaluation protocol.     

Interatrial conduction correlates with optimal atrioventricular timing in cardiac resynchronization therapy devices

Background: Echocardiographic optimization of the atrioventricular delay (AV) may result in improvement in cardiac resynchronization therapy (CRT) outcome. Optimal AV has been shown to correlate with interatrial conduction time (IACT) during right atrial pacing. This study aimed to prospectively validate the correlation at different paced heart rates and examine it during sinus rhythm (Sinus). Methods: An electrophysiology catheter was placed in the coronary sinus (CS) during CRT implant (n = 33). IACT was measured during Sinus and atrial pacing at 5 beats per minute (bpm) and 20 bpm above the sinus rate as the interval from atrial sensing or pacing to the beginning of the left atrial activation in the CS electrogram. P‐wave duration (PWd) was measured from 12‐lead surface electrocardiogram, and the interval from the right atrial to intrinsic right ventricular activation (RA‐RV) was measured from device electrograms. Within 3 weeks after the implant patients underwent echocardiographic optimization of the sensed and paced AVs by the mitral inflow method. Results: Optimal sensed and paced AVs were 129 ± 19 ms and 175 ± 24 ms, respectively, and correlated with IACT during Sinus (R = 0.76, P < 0.0001) and atrial pacing (R = 0.75, P < 0.0001), respectively. They also moderately correlated with PWd (R = 0.60, P = 0.0003 during Sinus and R = 0.66, P < 0.0001 during atrial pacing) and RA‐RV interval (R = 0.47, P = 0.009 during Sinus and R = 0.66, P < 0.0001 during atrial pacing). The electrical intervals were prolonged by the increased atrial pacing rate. Conclusion: IACT is a critical determinant of the optimal AV for CRT programming. Heart rate‐dependent AV shortening may not be appropriate for CRT patients during atrial pacing. (PACE 2011; 34:443–449)     

Is the Atrial High Rate Episode Diagnostic Feature Reliahle in Detecting Paroxysmal Episodes of Atrial Tachyarrhythmias?

The atrial high rate episode diagnostic in The Thera® pacemaker reports frequency, duration, and date/time of atrial tachyarrbytbmias according to programmed criteria. The aim of The study was to validate The atrial high rate episode diagnostic feature. Episodes of atrial fibrillation recorded by Holter monitoring were compared to episodes detected by the pacemaker. Eorty five ambulatory (Holter) recordings were used for evaluation. Thirty of 45 ambulatory (Holter) recordings showed sinus rhythm. On 4 of these 30 ambulatory (Holter) recordings, The Thera® detected 12 episodes of atrial tachyarrbythmias as false-positives (sinus rhythm was detected as atrial tacbyarrbytbmia). The main reason was far-field R and T wave oversensing. On 15 of 45 ambulatory (Holter) recordings, 125 episodes of atrial tachyarrhytbmias were recorded. Ninety-three of these events also were detected by the pacemaker, while for 32 events the Thera® reported sinus rhythm. The main reason was that the episodes were of too short duration. Therefore, the Thera® (programmed with detection rate 160 beats/min, detection beats 40, termination beats 10) was unable to detect atrial tachycardias. Software simulation of The diagnostic algorithm under several programming settings using the digitized Holter files demonstrated highly reliable detection of atrial tachyarrhythmias (sensitivity 98%, specificity 100%) when programmed as follows: detection rate 220 beats/min, detection beats 10, termination beats 20. It can be concluded that Thera®'s high rate episode monitor is a reliable tool for detection of a trial tachyarrhythmias, if programmed as recommended.