Europace Advance Access first published online on October 11, 2007
This version published online on October 17, 2007
Europace, doi:10.1093/europace/eum225
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Left ventricular pacing by automatic capture verification
Institute of Cardiology, University of Bologna, Via Massarenti 9, 40138 Bologna, Italy
Manuscript submitted 7 May 2007. Accepted after revision 18 September 2007.
* Corresponding author. Tel: +39 051 345898; fax: +39 051 344859.E-mail address: mauro.biffi{at}aosp.bo.it, mbiffi{at}aosp.bo.it
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Abstract |
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Aims: To investigate the feasibility of transvenous left ventricular (LV) pacing by autocapture at long term. A reliable measurement of LV evoked response (ER) is the pivotal requirement for beat-to-beat detection of ventricular capture and automatic output adjustment.
Methods and results: Seven patients with accepted class I indication to permanent cardiac pacing received a DDDR pacemaker with automatic output adjustment based on beat-to-beat capture verification (Insignia Ultra 1290, Guidant), whose ventricular port was connected to a LV lead placed in a branch of the coronary sinus. The device allows LV threshold trending, performing a threshold test every 21 h, and diagnoses acute and non-acute issues of ER detection during follow up. Average follow up after implantation was 34 ± 6 months (range 28–45, median 34). Left ventricular pacing threshold showed an increase from implantation (1.2 ± 0.4 V at 0.4 ms) that peaked at week 4 (1.6 ± 0.7 V at 0.4 ms), and returned to baseline (1.1 ± 0.5 at 0.4 ms) by the end of the 7th week. Autocapture performance at long term, as assessed by the trend of LV threshold and of ER diagnostic issues, did not show any pitfall.
Conclusions: Our observations support the feasibility and safety of capture verification during LV pacing alone. A possible application of this pacing technology could be biventricular stimulation.
Key Words: Left ventricular pacing, Automatic capture verification, Pacing threshold, Evoked response
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Introduction |
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TopAbstractIntroductionPatients and methodsStatistical analysisResultsDiscussionReferences |
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The results of cardiac resynchronization therapy in patients with advanced heart failure and the evidence that unnecessary right ventricular pacing may be unpredictably detrimental in patients with standard indications to cardiac pacing have prompted the search to novel modalities for ventricular pacing.1
–3
In patients with left ventricular (LV) dysfunction and intraventricular conduction delay LV pacing could be an alternative pacing site, as observed in patients with advanced heart failure.4,5 Because of the issue of lead stability, an approach to LV pacing alone has never been tried in patients with high degree atrio-ventricular block (AVB); recent improvement in lead manufacture has set the premises to start this type of investigation.
The release of a DDDR pacemaker capable of automatic adjustment of the ventricular output based on beat-to-beat capture verification (Insignia Ultra 1290, Guidant) regardless of lead polarity, impedance, and polarization at the electrode-tissue interface,6,7 prompted our Centre to evaluate the feasibility of transvenous LV pacing by automatic capture verification.
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Patients and methods |
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TopAbstractIntroductionPatients and methodsStatistical analysisResultsDiscussionReferences |
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Seven patients, four females and three males, aged 70 ± 9 years (range 46–85) with accepted indications to a DDDR pacemaker received an Insignia Ultra unit connected to an active fixation bipolar atrial lead, and to a unipolar lead for LV pacing (Attain OTW 4193, Medtronic) placed in a branch of the coronary sinus. By the time we started this evaluation, this was the only IS-1 LV pacing lead that could be handled either over-the-wire or stylet-driven, hence was used throughout the study. Clinical characteristics of the patients as well as indications for pacemaker implantation are reported in Table 1.
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Autocapture was tested at completion of the implant. The pacing algorithm provides beat-to-beat verification of ventricular stimulation at outputs only 0.5 V above threshold, with 3.5–5 V backup pulse in case of failure. To achieve this feature, the device automatically monitors the evoked response (ER) elicited by each impulse delivered: detection of LV ER is hence the pivotal point of this algorithm performance. ER needs to be reliably distinguished by the polarization induced by the pacing pulse at the tissue-electrode surface: this goal was achieved in all the patients thanks to the reduced coupling capacitor technology of the Insignia pacemaker. Compared with 10 µF capacitors, the reduced coupling capacitor (2.2 µF) speeds the rate decay of post pacing artifact, thus allowing ER detection regardless of pacing configuration and pacing lead technical characteristics.6
,7 Autocapture was turned on in all the patients, and the patients were then followed on an outpatient basis at 3, 5, 12 months and yearly thereafter. Measurements of pacing threshold, pacing impedance, intrinsic signal amplitude, and recording of arrhythmias were obtained at each follow up visit. Insignia Ultra 1290 checks ventricular stimulation threshold either every 21 h or in case of failure of the low-energy stimulus, and adjusts ventricular output to maintain effective low-energy pacing. A detailed trending of LV threshold became hence available during follow up of these patients. In case of failure of ER detection, pacemaker-generated diagnostic is also available.
Left ventricular threshold was checked either manually or by auto capture after skin closure, and at follow up visits, so that direct comparison of device-calculated and operator-performed LV threshold are available. Manual determination of LV pacing threshold preceded commanded automatic determination. Blinded determination was not possible at follow up because ventricular threshold trending is displayed as soon as the pacemaker is interrogated. Ventricular pacing output was managed by the automatic algorithm as far as LV pacing threshold was reliably detected and <3 V at 0.4 ms (limit of the reduced coupling capacitor technology). Manual reprogramming was deemed necessary when these requirements were unmet.
Ventricular sensitivity was adapted by the algorithm for automatic adjustment of sensitivity.
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Statistical analysis |
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TopAbstractIntroductionPatients and methodsStatistical analysisResultsDiscussionReferences |
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Descriptive parameters are reported as mean±standard deviation.
Measurements of LV pacing lead (intrinsic amplitude, pacing impedance, and threshold) were obtained by the device and compared at implant, peak of LV threshold increase, and during the chronic phase by Friedman test.
Measurements of RA pacing lead (intrinsic amplitude, pacing impedance, and threshold) were compared at implant, and at follow up visits by Friedman test.
Linear regression of pacemaker-calculated and physician-performed LV threshold values at implant and follow up visits, was calculated.
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Results |
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TopAbstractIntroductionPatients and methodsStatistical analysisResultsDiscussionReferences |
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Average follow up was 34 ± 6 months (range 28–45, median 34). Left ventricular lead placement site was anterolateral midway to distal (4 patients with LVEF>50%), lateral midway from base to apex (2 patients with LVEF<50%), lateral distal (patient 2). None of these patients had lead dislodgement during follow up. No unusual behaviour of any pacing lead was observed, as reported in Table 2.
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Autocapture was tested successfully at skin closure in all the patients (Figure 1), and LV pacing was completely managed by this feature during follow up (Table 2, Figure 2). Diaphragmatic stimulation occurred at 7 V in patient 3, at 5.5 V in patient 5, and was not observed in the remaining patients up to 10 V at implantation. Due to intrinsic atrioventricular conduction, LV pacing occurred at different extent of fusion in patients 1,3,4,7 depending on heart rate, intrinsic conduction behaviour, and programming of AV delay rate-responsiveness. The fusion phenomenon may result in decreased ER amplitude, possibly leading to capture underdetection with inappropriate back-up pulse delivery, and eventually turning off the algorithm. Thanks to beat-to-beat detection and update of ER amplitude, the autocapture algorithm was never turned off because of fusion, in agreement with the observations by Sperzel et al.8
Moreover, an autocapture algorithm feature based on localization of the minimum of ER signal can detect fusion beats: back-up pulse delivery is thus withheld. Automatic measurement of pacing threshold is not affected by fusion because it occurs at 60 ms AV delay, so that fusion is avoided (Figure 1). Acute and non-acute issues of ER detection, such as those related to frequent fusion beats or insufficient ER amplitude, were not observed in our patients; in particular, inability to detect loss of LV capture during threshold search never occurred.
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Left ventricular pacing threshold had a slight increase compared with implantation, that peaked within the 4th week, and returned to values comparable to implantation within the 7th week (Table 2, Figure 2). Thereafter, LV threshold showed only fluctuations
0.2 V above or below the average value (Figure 2). Changes of LV threshold were observed from implantation to follow up; threshold at last follow up visit (median 34 months) was significantly lower when compared with its peak value (P = 0,012 at Friedman test, Table 2).
The comparison of pacemaker-calculated and physician-performed LV threshold values at implant and at follow up visits did not show any significant difference. The average of LV threshold values calculated by the device was 1.11 ± 0.47 V when compared with 1.09 ± 0.49 V detected by the physician (p = NS). A highly significant correlation between device- and physician-operated threshold test was observed: r = 0.98, P < 0.001 (Figure 3). Pacing output was continuously managed by autocapture throughout all the follow-up period, manual reprogramming was never needed.
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Discussion |
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TopAbstractIntroductionPatients and methodsStatistical analysisResultsDiscussionReferences |
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This is the first study to report the feasibility of transvenous LV pacing in patients requiring ‘conventional’ dual chamber pacing, aside from cardiac resynchronization therapy. The relative interest is the possibility to use the same autocapture technology currently employed in right ventricular endocardial pacing for this peculiar pacing site, left epicardial.
Our observations show that no special requirement is needed to reliably detect LV ER respect to right ventricular ER, and that long-term LV pacing by autocapture can be achieved.
The performance of autocapture was validated by physician-operated threshold testing, which proved a reliable function of the algorithm (Figure 3). A practical application of LV pacing by automatic verification of stimulation is biventricular pacing. Its feasibility has been demonstrated in a pioneering acute study.9 Goetze et al.10 have recently reported the possibility to achieve LV pacing in CRT patients by two different methods. The method used in our study, based on the reduced coupling capacitor technology, could effectively work in 86% of patients throughout all the pacing settings currently employed in CRT therapy with any LV pacing lead.10 In the same study, a method based on independent vectors for LV pacing and ER detection proved superior (96% of patients applicability), but a bipolar LV lead is mandatory for this purpose.10 Although manufacturers have considerably improved lead technology, bipolar LV leads may occasionally prove difficult to handle at sharp bends or in thin vessels. Thus, each method may result useful in the individual patient. The implementation of LV pacing by autocapture could significantly increase device longevity, particularly when suboptimal pacing thresholds are to be accepted to achieve optimal LV synchronization, or to avoid phrenic stimulation. In the event of a narrow gap between myocardial and diaphragmatic threshold, a pacing output as threshold+0.5 V results in 99.8% effective stimulation,8 thus providing adequate pacing at low output while decreasing the risk of diaphragmatic stimulation. In the situation of a high or unstable pacing threshold, automatically adjusting LV output helps to maintain the benefit of CRT (which is an on/off phenomenon) while improving device longevity compared with a fixed 100% safety margin programming.
Avoiding the use of voltage multipliers by automatic verification of stimulation is the main way to prolong device longevity and reduce the cost of pacing therapy, as observed in right ventricular pacing.11–14 This aspects have relevant economic implications when expensive devices as biventricular defibrillators are considered.
Our study aimed to demonstrate the safety and feasibility of transvenous LV pacing, but it was underpowered to assess the haemodynamic and clinical effect of LV pacing compared with RV endocardic pacing. The haemodynamic effects of LV pacing may indeed be quite different among our patients, depending on extent of fusion (related to underlying intrinsic AV conduction), coexistent LBBB (two patients), AV delay programming, baseline EF, and LV pacing site. In fact, 4/7 patients had normal systolic LV function, and LV lead pacing site differed among patients, so that no conclusion is possible. Prospective, numerically powered studies are required to assess the safety and efficacy of LV pacing for established pacing indications. The assessment of the most appropriate pacing site for ventricular stimulation requires prospective studies based on patients clinical outcome, and is beyond the scope of this small pilot study. This experience simply discloses the potential of available technology to achieve LV stimulation by automatic verification.
Conflict of interest: none declared.
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Footnotes |
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Additional corrections for this paper were received from the author after first publication in Advance Access. This version includes all corrections and is therefore final.
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References |
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[1] Bristow MR, Saxon LA, Boehmer J, Krueger S, Kass DA, De Marco T, et al. Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) Investigators. Cardiac-resynchronization therapy with or without an implantable defibrillator in advanced chronic heart failure. N Engl J Med (2004) 20:2140–50.
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