Automatic verification of ventricular stimulation: fusion management algorithm

BACKGROUND: Ventricular stimulation with automatic control and back-up pulse warrants maximum safety for the patient and increases device longevity. Fusion phenomenon may hinder evoked response (ER) detection and cause unnecessary back-up stimulation. We evaluated an automatic fusion beat management algorithm and its relationship with atrioventricular (AV) interval programming in a DDD/R pacemaker. METHODS: We analyzed 45 Holter registrations of patients implanted with an Insignia Ultra DR. Fusion beat classification, as performed automatically by the Fusion Management Algorithm, was compared to visual inspection by the analyzing physician. Fusions were classified as loss of capture (LOC), true fusions, or fusions classified as captured beats. Patients were divided into two groups according to AV interval programming: long AV delay (AV(l))(>150 ms) short AV delay (AV(s))(相似文献   

Automatic Capture Verification by Charge-Neutral Sensing

Automatic capture verification can prolong pulse generator longevity and increase patient safety. However, the detection of evoked response following pacing is complicated due to afterpotentials caused by polarization of electrodes. This study describes a new capture verification scheme, which neutralizes the charges between the pacing electrodes. The hypothesis of the charge-neutral sensing is that the afterpotentials in the ring and the tip are opposite in polarity when pacing in a bipolar mode between ring and tip. Summing the unipolar signals sensed at the tip and the ring should effectively cancel the afterpotentials. This scheme was implemented in an external computer based system and tested during pacemaker implant/replacement on 23 patients during VVI pacing (17 acutely implanted leads and 6 chronic leads). Surface ECG was recorded to provide a marker for capture and noncapture. The pacing voltage was gradually decreased until a noncapture beat was noted. To avoid fusion beats, the pacing rate was programmed ˜50% higher than the intrinsic rate. The evoked response was high pass filtered and the integral average was calculated for both capture and noncapture beats. The system signal to noise ratio (SNR) was expressed as ratio of the minimum integral average of all capture beats to the maximum integral average of all noncapture beats. The system SNR was 8.6 ± 1.3 (mean ± S.E.M; range 1.5–22.8), indicating that the charge-neutral sensing method has, on average, a ninefold safety margin in providing capture verification. Further, evaluation is needed to fully assess this feature in patients with chronic leads.     

Impact of fusion avoidance on performance of the automatic threshold tracking feature in dual chamber pacemakers: a multicenter prospective randomized study

The Autocapture algorithm enables automatic capture verification on a beat-by-beat basis by recognizing the evoked response signal following each pacemaker stimulus. The algorithm intends to increase patient safety while decreasing energy consumption. However, the occurrence of fusion beats, particularly during dual chamber pacing, may limit the energy saving effect of Autocapture. The aim of this multicenter, prospective, randomized study was to evaluate the impact of the Fusion Avoidance (FA) algorithm on the incidence of fusion beats. Thirty-eight patients (mean age 69 +/- 13 years) with intrinsic AV conduction who were implanted with an Affinity DR were studied. After programming a PV/AV delay of 120/190 ms, patients were randomized to FA On or Off. Each group was further randomized with respect to activation of the AutoIntrinsic Conduction Search (AICS) algorithm. The total number of beats, ventricular paced beats, fusion beats, backup pulses, and threshold searches were analyzed from 24-hour Holter recordings. The number of total beats was comparable in both FA groups. The number of total ventricular paced beats, fusion beats, backup pulses, and threshold searches were significantly reduced in the FA On group (% reduction: 68% P < 0.001, 75% P < 0.01, 95% P < 0.01, and 94% P < 0.05, respectively). The number of ventricular paced beats with full capture was significantly reduced when AICS was activated (P < 0.05). In conclusion, the FA algorithm substantially reduces the amount of ventricular paced beats, fusion beats, unnecessary backup pulses and threshold searches, and therefore, provides added benefits in energy saving obtained by Autocapture.     

AutoCapture with Dual-Coil Leads of Implantable Cardioverter Defibrillator

AutoCapture™ (AC) can confirm ventricular capture with true bipolar single coil leads of implantable cardioverter defibrillators (ICD). The compatibility of AC with a new, true bipolar, dual-coil ICD lead needed to be evaluated. This multicenter study enrolled 46 patients (69 ± 10 years, 37 men) undergoing ICD implantation. All patients received a true bipolar, dual-coil lead. Evoked response (ER) sensitivity and AC threshold tests were performed using a pulse generator with the AC algorithm. Mean capture threshold was 0.85 ± 0.67 V, pacing impedance 612 ± 225 Ω, R wave amplitude 13.85 ± 6.17 mV, and defibrillation threshold 14.4 ± 5.1 J. AC was recommended in 45 patients (97.8%) with ER and polarization values of 14.86 ± 7.32 mV and 0.87 ± 0.69 mV, respectively. The AC algorithm was highly compatible with true bipolar, dual-coil ICD leads. An AC algorithm specifically designed for an ICD may improve the generator longevity. Further examination of AC compatibility with other leads is warranted.     

Importance of ventricular rate after mode switching during low intensity exercise as assessed by clinical symptoms and ventilatory gas exchange

Automatic mode switching from DDD(R) to DDI(R) or VVI(R) pacing modes has improved dual chamber pacing in patients at high risk for supraventricular tachyarrhythmias. However, little is known about the effect of ventricular pacing rate adaptation after mode switching. We conducted a single-blinded, crossover study in 15 patients (58 +/- 21 years) with a DDD pacemaker who had AV block and normal sinus node function to investigate the influence of pacing rate adaptation to intrinsic heart rate during low intensity exercise. Patients performed two tests (A/B) of low intensity treadmill exercise (0.5 W/kg) in randomized order. They initially walked for 6 minutes while paced in DDD mode. The pacing mode was then switched to VVI with a pacing rate of either 70 beats/min (test A) or matched to the intrinsic heart rate (95 +/- 11 beats/min test B). Respiratory gas exchange variables were determined and patients classified the effort before and after mode switching on a Borg scale from 6 to 20. Percentage changes of respiratory gas exchange measurements were significantly larger (O2 consumption: -8.2 +/- 5.0% vs. -0.6 +/- 7.2%; ventilatory equivalent of CO2 exhalation: 5.3 +/- 4.9% vs. 1.5 +/- 4.3%; respiratory exchange ratio: 7.0 +/- 2.2% vs. 3.5 +/- 3.0%; end-tidal CO2: -5.7 +/- 2.9% vs. -1.8 +/- 2.7%; all P < 0.01) and the increase in subjective assessment of the effort tended to be higher (mean increase on Borg scale: 1.6 +/- 1.9 vs. 1.1 +/- 1.8, P = 0.07) after heart rate unadjusted than after adjusted mode switching. Mode switching from DDD to VVI pacing is better tolerated and gas exchange measurements are less influenced if ventricular pacing rate is adjusted to the level of physical activity. Thus, pacing rate adjustment should be considered as part of automatic mode switch algorithms.     

A New Algorithm for Minimizing Pacemaker Polarization Artifact: Universally Applicable in Permanent Pacing Systems

Polarization artifacts that result from pacing may interfere with analysis of paced evoked responses during, e.g., automatic threshold tracking. We have developed a method for reduction of such artifacts that relies on the introduction of pacing stimuli during the refractory period of unipolar or bipolar paced captured beats after previous identification of a refractory period "template" or baseline. The refractory pacing stimuli cannot capture the heart, and thus any deviation from the template is due to polarization artifact alone. The artifact amplitude is measured and the precharge duration of the triphasic stimulus waveform is changed each time until artifact is minimized, as detected by repeated reversals in the polarily of the polarization artifact. In a series of 11 patients with unipolar and bipolar permanent pacing leads, mean initial artifact before balancing was 1.44 ± 0.84 mV, which was reduced to 0.44 ± 0.30 mV after balancing (P = 0.001). Initial precharge duration was 3.2 msec by design; mean final precharge duration was 3.30 ± 0,34 msec. This algorithm is universally applicable in permanent pacing systems, as it is valid in unipolar and bipolar pacing and it does not require an intrinsic cardiac rhythm.     

Use of the AutoCapture Pacing System with Implantable Defibrillator Leads

MARENCO, J.P., et al.: Use of the AutoCapture Pacing System with Implantable Defibrillator Leads. Introduction: Previous studies using various bipolar pacemaker leads have shown that the AutoCapture (AC) Pacing System is able to verify ventricular capture and regulate pacing output, increasing patient safety with respect to unexpected threshold changes and potentially prolonging device longevity. An increasing number of patients with implantable cardioverter defibrillators (ICDs) require ventricular pacing that contributes to a shortening of longevity of these systems. This prospective study tested the compatibility of the AC system with bipolar ICD leads. Methods: The AC algorithm was evaluated prior to ICD testing in 30 ICD recipients. A single coil, active fixation, true bipolar ventricular lead was implanted in 21 patients, and a dual coil, passive fixation, integrated bipolar ventricular lead was implanted in 9 patients. A ventricular evoked response sensitivity test and an AC threshold test were performed using a pacemaker with the ventricular AC algorithm. Results: AC was recommended in 22/30 (73.3%) of implants, including 20/21 (95.2%) with the single coil and 2/9 (22.2%) with the dual coil lead. Mean polarization was lower (   1.23 ± 0.95 mV   vs   3.70 ± 2.33 mV, P = 0.013   ) while the mean evoked response was higher (   18.04 ± 8.29 mV   vs   10.13 ± 4.22 mV, P = 0.002   ) with the single coil leads. Conclusion: Automatic threshold tracking using the AC is compatible with ICD leads. Leads with lower polarization and greater evoked response are more likely to result in recommendation of AC use. Use of this system offers the potential for increasing ICD generator longevity and improving patient safety in response to late unexpected threshold increases. (PACE 2003; 26[Pt. II]:471–473)     

Clinical experience with an automatic threshold tracking algorithm study

The automatic threshold tracking pacing system algorithm developed by St. Jude Medical, verifies ventricular capture beat by beat by recognizing the evoked response (ER) following each pacemaker stimulus. The present automatic threshold tracking function requires a bipolar ventricular lead with low polarization. The aim of this study was to evaluate a new algorithm developed to use with unipolar leads with different levels of polarization. An external pacemaker with the ability to sense intrinsic R waves and measure ER signals, as well as deliver stimulus, was used. An algorithm for detecting the true ER in a unipolar sensing configuration (tip-case) was developed. Based on the assumption that the true evoked R wave amplitude is independent of the stimulation amplitude, the algorithm calculates and subtracts the polarization present at any pacing stimulus from the measured ER. The resulting signal is analyzed to verify capture. This study comprises 35 patients of which 26 were new implants and 9 had chronic leads. The automatic threshold-tracking algorithm was calibrated for each patient and pacing was performed at different pulse amplitudes and pulse duration. Capture was verified for each paced beat. The recordings were stored for later comparison with the tape-recorded intracardiac heart signals. The new algorithm correctly verified capture or loss of capture for every single analyzed beat at the different pacing outputs in every individual patient. The results from this initial study suggests that the new ER detection principle will allow automatic threshold tracking to be used not only with low polarization bipolar leads but with most leads. (PACE 2003; 26:2219–2224)     

Determination of Pacing Capture in Implantable Defibrillators: Benefit of Evoked Response Detection Using RV Coil to Can Vector

SPLETT, V., et al. : Determination of Pacing Capture in Implantable Defibrillators: Benefit of Evoked Response Detection Using RV Coil to Can Vector. Automatic detection of capture in ICDs would be useful for ensuring normal pacing function and lead integrity and may increase device longevity. Evoked response detection can be difficult due to postpace polarization. Polarization on the RV coil to can vector, however, should be absent when pacing with a true bipolar lead (pace tip to ring). Polarization on the RV coil to can vector should be low in an integrated bipolar lead due to the large surface area of the coil. Ventricular-paced responses were prospectively recorded in 20 patients during ICD implantation or replacement. Capture and loss of capture responses were noted during threshold searches with electrograms recorded between the RV coil and can. A detector was designed to discriminate between capture and noncapture-paced responses using data from the first 11 patients and validated on the remaining 9. The detector had a sensitivity of 99.9% (detected capture on capture beats), and had a specificity of 100% (detected no capture on noncapture beats) for all lead configurations. There was no measurable polarization with true bipolar leads. In integrated bipolar leads, maximum polarization ranged from 0.0 to 16.7mV. In conclusion, paced evoked responses can be detected in ICDs using the RV coil to can vector using standard pacing waveforms. Special polarization reducing pacing waveforms are not required. These observations could be used to design ICDs with automatic pacing threshold detection.     

The Effect of Posture on the Response to Atrioventricular Synchronous Pacing in Patients with Underlying Cardiovascular Disease

In order to determine whether the hemodynamic benefit of atrioventricular synchronous pacing is maintained in the upright position, 14 patients with dual chamber pacemakers were paced in VVI mode and DDD mode in both the supine and standing position. The hemodynamic response was assessed by measuring the velocity time integral derived from the pulsed-wave Doppler signal in the left ventricular outflow tract during VVI pacing and dual chamber pacing at three different AV delays (125, 200, 250 ms). In the supine position, the velocity time integral during VVI pacing was 14.6 ± 3.0 cm and this increased during DDD pacing at all three AV delays (17.7 ± 3.3, 17.9 ± 3,0, 17.5 ± 3.5 cm). In the upright position, the velocity time integral during VVI pacing was 12.9 ± 3.5 cm and this increased with DDD pacing (15.5 ± 3.3, 15. 1 ± 4.0, 15.1 ± 3.9 cm). It was concluded that although stroke volume decreases when assuming the upright position, the beneficial response to dual chamber pacing is maintained and equals that observed in the supine position.     

Bipolar ventricular far-field signals in the atrium

In an attempt to evaluate the prevalence and predisposing factors of bipolar ventricular far-field oversensing, 57 patients were studied who had a Medtronic dual chamber pacemaker implanted (models 7940: n = 6; 7960i: n = 41; 401: n = 3; 8968i: n = 7) and bipolar atrial leads with a dipole spacing from 8.6 to 60 mm attached to various parts of the atrial wall (lateral/anterior: n = 30; appendage: n = 10; atrial septum: n = 10; floating: n = 7). Median bipolar sensing threshold for P waves was 4.0 mV (2.8-4.0 mV, lower and upper quartile) with standard leads and 0.35 (0.25-1.4) mV with single pass (VDD) devices. At the highest sensitivity available, 43 of 50 DDD pacemakers but only two of seven VDD systems detected intrinsic R waves in the atrium (P < 0.01). Ventricular far-field oversensing occurred at 0.5 mV in 28 (56%) and at 1.0 mV in 16 of 50 DDD units (32%), respectively, and there was one observation in a septal implant at a sensitivity of even 2.8 mV. With ventricular pacing, VDD systems were as susceptible to far-field signals as DDD pacemakers. Outside the postventricular blanking period (100 ms), evoked R waves were detected by 27 of 57 systems (47%) at maximum atrial sensitivity, by 10 (18%) at 0.5 mV, and by 2 (4%) at a setting of 1.0 up to 1.4 mV, respectively. There was no definite superiority of any lead position, there was a trend in favor of the atrial free wall for better intrinsic R wave rejection, but just the opposite was the case for paced ventricular beats. Bipolar signal discrimination tended to be higher with short tip-to-ring spacing (1 7.8 mm) but the difference to larger dipole lengths (30-60 mm) was not significant in terms of the R to P wave ratio and the overall far-field susceptibility. In summary, bipolar ventricular far-field oversensing in the atrium is common with short postventricular blanking times and high atrial sensitivity settings that may be warranted for tachyarrhythmia detection and mode switching. A potentially more discriminant effect of shorter dipole lengths (< or = 10 mm) remains to be tested.     

Spatial Resolution and Role of Pacemapping During Ablation of Accessory Pathways

The objectives of this study were: (1) to evaluate quantitatively the spatial resolution of pacemapping: and (2) to assess the predictive value and role of pacemapping for the catheter ablation of overt APs. Sixty-three unipolar leads were used instead of the standard 12-lead ECG to acquire more information and assess the intrinsic accuracy of pacemapping. Spatial resolution was evaluated in 19 patients for whom data were recorded during bipolar ventricular pacing near the AV ring using the three electrode pairs of a quadripolar ablation catheter with a 5mm interelectrode spacing. The predictive value was assessed in 27 patients with overt APs who underwent HF ablation: their data were recorded during pacing at the site of successful ablation and at one or two sites where HF energy delivery was ineffective. Data from different beats were compared visually by using body surface potential maps and quantitatively by computing average correlation coefficients (r). Heproducibility was high for paced beats (r = 0.98 ± 0.02). Displacements of 5 mm of the pacing site could be detected with a sensitivity of 90% and a specificity of 87%. Correlation between pacing at successful ablation sites and preexcited sinus rhythm was low (r = 0.79 ± 0.11) and the ablation outcome could be predicted with a negative prediction accuracy of 87% and a positive prediction accuracy of 49%. Despite an excellent spatial resolution, pacemapping is of limited value for the identification of successful AP ablation sites, probably because APs can be interrupted at some distance from their ventricular insertion point.     

Single versus dual chamber pacing in the young: noninvasive comparative evaluation of cardiac function

The advantages of atrial synchrony over asynchronous ventricular pacing remain unclear in the young, chronically right ventricular (RV) - paced patient. This is in contrast to the older patient with inherent diastolic dysfunction who has been shown to benefit from atrial synchrony with dual chamber (DDD,R/VDD), over single chamber rate response (VVI,R) ventricular pacing. The goal of this study was to noninvasively assess cardiac function in a group of young, RV-paced patients before and after establishment of atrial synchrony. Echocardiographic data were retrospectively analyzed from 10 patients with congenital or acquired complete AV block, who were VVI,R paced for 10.2 +/- 2 years (mean age at study 19.2 +/- 8.9 years), and were subsequently converted to DDD,R/VDD pacing (mean age at study 20.7 +/- 9.5 years). Paired t-test analysis of left ventricular (LV) systolic and diastolic function during VVI,R versus DDD,R/VDD pacing did not result in any short-term difference in LV short axis fractional area of change or FAC (53% +/- 7.5% vs 56.8% +/- 8.7%) or mitral maximal velocity (E) normalized to mitral flow velocity time integral (VTI) (5.2/s +/- 1.5 vs 4.4/s +/- 1.5). A decrease in mitral flow E/A ratio was observed after short-term DDD,R/VDD pacing (2.2 +/- 0.5 vs 1.9 +/- 0.3). Atrial synchronous dual chamber pacing in young patients with complete AV block does not lead to any appreciable early change in global LV function over single-site RV pacing. Therefore, early establishment of atrial synchrony in the young asymptomatic VVI,R-paced patient with normal intrinsic ventricular function may not be warranted.     

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.     

Symptoms, Cardiovascular Risk Profile and Spontaneous ECG in Paced Patients: A Five-Year Follow-Up Study

GRIMM, W., ET AL.: Symptoms, Cardiovascular Risk Profile and Spontaneous ECG in Paced Patients: A Five-Year Follow-Up Study. Only few data are available about the course of symptoms, cardiac diseases, and spontaneous rhythm in pacemaker patients. Therefore, we followed the course of 308 paced patients (age 72 ± 11 years) with a mean implantation time of 63 ± 45 months. Results: The symptom triad of syncope, dizziness, and dyspnea improved remarkably in 93% of patients. Thirty-nine percent suffered from coronary heart disease. The risk factors of hypertension (47%), nicotine (37%), and diabetes mellitus (25%) were found significantly more often than in a normal population with the same age and sex profile. In VVI paced patients with sick sinus syndrome (SSS, n = 67) atrial fibrillation (AF) occurred significantly more often (42%) than in patients with AV block (n = 80, 23%, p < 0.05). Only one out of 41 DDD paced patients showed AF at follow-up. VVI stimulation seems to favor AF due to retrograde conduction in SSS. Only 3% of patients with SSS developed second- or third-degree AV block. Therefore, atrial pacing is preferable in most patients with SSS.     

Sensing Through the Esophagus for Temporary Atrial Synchronous Ventricular VDD Pacing

The purpose of this study was to evaluate the effectiveness and safety of temporary VDD pacing using an esophageal electrode for sensing of the atrial electrogram. We studied 15 patients, 8 men and 7 women, aged 77 ± 2 years (mean ± SE, range 61–90), with severe atriovenfricular (AV) conduction disturbances. A 24-hour beat-to-beat ECG analysis was used to evaluate the effectiveness of the pacing system and special tests were performed to test the stability of pacing and sensing. The system performed satisfactorily in 12 of the 15 patients. The 24-hour Holter ECG monitoring revealed the following percentages of beats: 96.32 ± 0.5 VDD, 2.92 ± 0.6 VVI, and 0.14 ± 0.05 paced beats resulting from pseudosensing. All the latter were single, with no bigeminy or salvos. The results of the stability tests were as follows: the percentage of VDD beats was significantly lower than the 24-hour mean when the patient lay on his right side (92.8 ± 0.5, P < 0.001), during the swallowing of liquids (91.26 ± 0.4, P < 0.001) and soft foods (84.2 ± 1.4, P < 0.001), and during coughing (94.2 ± 0.6, P < 0.001). The percentage of VVI type beats increased in these four cases (6.7 ± 0,5, 7.2 ± 0.3, 13.2 ± 1.2 and 4.8 ± 0.4, respectively, P < 0.001 in each case). The percentage of ectopic beats due to pseudosensing did not change significantly during any of the tests. These results indicate that the method described is a safe and effective technique for temporary VDD pacing.     

The Value of DDD Pacing in Patients with an Implantable Cardioverter Defibrillator

Although the beneficial effects of DDD pacing are well known, currently available ICDs provide only fixed rate ventricular antibradycardia pacing. In a consecutive series of 139 patients with ICDs, we have analyzed the need for antibradycardia pacing and the indications for DDD pacing. We also report our initial experience with the Defender 9001 (ELA Medical, France) DDD-ICD. Out of 139 patients, 25 (18%) were in need of antibradycardia pacing. Ten patients already had a pacemaker at the time of ICD implantation and ten other patients had a conventional pacemaker indication at that time. Five patients became pacemaker dependent during a follow-up of 20 ± 8 months. The disorders necessitating pacemaker therapy were high degree AV conduction disturbances in 72%, sick sinus syndrome in 12%, and AF with a slow ventricular response in 16% of patients. Based upon current indications, DDD pacing was indicated in 20 (80%) of 25 patients. The Defender 9001 DDD-ICD (ELA Medical) was used in two patients with ischemic cardiomyopathy and pacemaker syndrome with VVI pacing. Cardiac output during DDD pacing increased by 36% in one patient with an increase in VO₂ max during exercise of 29%. The other patient showed an increase in cardiac output of 50% with DDD pacing, and, while unable to exercise with VVI pacing, had a VO_2max of 24 mL/kg per minute during DDD pacing. Up to 18% of our ICD patients are in need of antibradycardia pacing. Of these pacemaker dependent patients, 80% have an indication for DDD pacing. Our first clinical experience with a DDD-ICD confirms the hemodynamic benefit of AV synchronous pacing in ICD patients with pacemaker syndrome.     

Full Ventricular Capture Indicated by the QT Interval Function

The atrioventricular (AV) interval is critical in dual chamber (DDD) pacing in patients with hypertrophic obstructive cardiomyopathy (HOCM) to obtain full ventricular capture (FVC) with maximal reduction of the left ventricular (LV) outflow gradient and optimal LV diastolic filling. We studied the relationship of FVC, fusion, spontaneous AV conduction, and the QT interval. Methods: 11 patients with various cardiac diseases and stable AV conduction received a QT sensing Diamond (tm) Vitatron, DDD pacemaker. Software was downloaded into the pacemaker. In the DDD pacing mode, with the QT interval measured from the ventricular pacing stimulus to the end of the T wave, the AV interval was shortened from 400 ms, in 20-ms steps, to 90 ms. At 90 ms the stimulation rate was increased by 30 beats/mm and the AV interval was increased stepwise. FVC and fusion was examined on the surface ECG, Results: At 400 ms interval, spontaneous AV conduction inhibited the pacemaker. Shortening the AV interval resulted in pacing with a short QT interval. Further reduction of the AV interval resulted in a longer QT interval up to a point where the QT interval became stable. This point, the bending point in the plot of measured QT interval versus shortened AV intervals, coincided with the point of FVC. The relation of the QT-AV interval plot and the point of fusion was comparable when lengthening the AV interval at a 30 beats/mm faster stimulation rate. Conclusion: The bending point in the QT interval versus AV interval plots showed a good correlation with the FVC and fusion points observed on ECG. The results suggest that automatic discrimination between fusion and full capture using QT interval measurements may be feasible.     

Maximizing biventricular pacing in patients with rate‐controlled atrial fibrillation using ventricular sense response

In patients with atrial fibrillation (AF), cardiac resynchronization therapy (CRT) is challenging because the ventricular rate of conducted AF exceeds the biventricular pacing rate. In the current report, we present a patient who received a CRT device that was programmed to ventricular sense response (VSR) on with VVI 40 beats per minute to allow the AF to be paced as fusion beats. We found that the pacing configuration resulting in the narrowest QRS in this patient was VVI 40 with VSR biventricular fusion pacing during AF. VSR mode allows for CRT delivery without the need to artificially increase heart rate.     

Inappropriate Sensing of Atrial Stimuli in Patients with Third-Generation Defibrillators and DDD Pacemakers

Although the problem of ICD sensing of paced ventricular stimuli has been resolved by incorporation of VVI pacing into current ICDs, many patients require separate DDD pacemakers. We report a problematic PM-ICD interaction: the inability to prevent sensing of paced atrial stimuli (atrial sensing) leading to double-counting in DDD-PM-requiring patients with transvenous (TV) ICDs with aggressive autogain sensing (CPI Ventak® PRxII or III). Four of eight patients receiving both transvenous DDD PMs and ICDs (CPI Endotak® lead, at the RV apex), had atrial sensing, leading to double counting, despite intraoperative testing of multiple atrial locations with an active fixation lead. Five patients had a PRxlI/III ICD, four with atrial sensing (80%), and three a PRx without atrial sensing. Patients with atrial sensing were not distinguished by any clinical or device related variable. In patients with atrial sensing (all with heart block), the PM was programmed to VDD mode. No patient has received inappropriate therapy or failed to sense VP in follow-up. In many patients with TV ICDs who require DDD pacing, no atrial position can be found without ICD sensing of atrial stimuli. While in patients with heart block this problem can be circumvented by programming to the VDD mode, in patients with sinus incompetence it may only be resolved by the combination ICD-DDD PM, currently in development.