Acute effects of a class IA antiarrhythmic drug on the ventricular evoked response amplitude in patients with cardiac pacemakers

Some newer cardiac pacemakers are able to control the efficacy of the ventricular pacing pulse beat by beat and to adjust the ventricular output to the actual pacing threshold. This capture verification is based on the detection of the ventricular evoked response amplitude, which has to be detected immediately after the pacing pulse. The sensitivity of the pacemaker to detect the evoked response amplitude must be adjusted individually to avoid the simultaneous detection of lead polarization. The aim of the present study was to evaluate the acute effects of a class IA antiarrhythmic drug on the evoked response amplitude and polarization in 13 pacemaker patients. The implanted pacemaker was the VVIR pacemaker Regency (St. Jude Medical), which provides the automatic capture verification algorithm Autocapture. The patients received 50 mg of ajmaline intravenously within 1 min. The evoked response amplitude and polarization were measured before and 2, 4, 6 and 8 min after ajmaline injection. The evoked response amplitude significantly decreased from 8.0 +/- 4.0 mV to a minimum value of 6.4 +/- 3.1 mV 2 min after drug administration. The decrease remained significant from the end of the application up to 6 min. The recommended sensitivity setting for the evoked response significantly (p < 0.05) decreased from 4.0 +/- 2.3 mV before to 3.1 +/- 1.3 mV 2 min after administration. No significant changes were observed for polarization. After the ajmaline application in 2 patients, the pacemaker recommended the deactivation of Autocapture for 9 min in 1 patient and 12 min in the other. The reasons were a decrease in the evoked response amplitude from 3.1 to 1.9 mV and from 9.0 to 5.7 mV, respectively, with a polarization ranging to about 3.0 mV. In conclusion, the ajmaline injection decreased the evoked response amplitude for some minutes. These findings indicate that antiarrhythmic drugs can alter the automatic capture verification function.     

Reduction of the pace polarization artefact for capture detection applications by a tri-phasic stimulation pulse.

This study investigated the ability to minimize pace polarization artefacts (PPA) by adjusting the post-stimulus pulse duration of a tri-phasic stimulation pulse. Adjustment of the stimulation pulse was enabled by downloading special study software into an already implanted pacemaker. Tests were performed in a total of 296 atrial leads and 311 ventricular leads. Both chronic and acute leads were included in the study. Statistically significant differences were found in the initial PPA (without any adjustment of the stimulus pulse) between atrial and ventricular leads. In addition, significant differences were observed among various lead models with respect to changes over time in the initial ventricular PPA. Successful PPA reduction was defined as a reduction of the PPA below 0.5 mV for atrial leads and below 1 mV for ventricular leads. Results show a success rate for ventricular and atrial PPA reduction of 97.8% and 98.7%, respectively. Threshold tests showed that after reduction of the PPA loss of ventricular capture can be reliably detected. However, atrial threshold tests showed many false positive evoked response detections. In addition, unexpectedly high evoked response amplitudes were observed in the atrium after reduction of the PPA. Results from additional measurements suggest that these high atrial evoked response amplitudes come from the influence of the input filter of the pacemaker.     

Myocardial stimulation threshold in patients with cardiac pacemakers: effect of physiologic variables, pharmacologic agents, and lead electrodes

Many factors affect the threshold for myocardial stimulation in patients with cardiac pacemakers. The acute local tissue reaction at the electrode-myocardium interface accounts for early threshold rises and may be minimized by choice of specific electrodes (steroid-eluting or carbon-tip). Physiologic variations due to changes in autonomic tone (including eating, sleeping, and exercise) account for day-to-day fluctuations in pacing threshold. Electrolyte and metabolic abnormalities, especially hyperkalemia, alkalosis, acidosis, and hyperglycemia, increase the pacing threshold. Commonly used antiarrhythmic drugs (quinidine and procainamide) also increase pacing threshold. Patients with pacemakers who require antiarrhythmic agents or who have coincident metabolic or electrolyte disturbances should be observed closely for failure to capture. Management of failure to capture is directed at removing the inciting cause and attempting to lower the pacing threshold with isoproterenol, if the situation is urgent. Acute increases in pacing threshold immediately following pacing system implantation can be treated with corticosteroids. Increasing the energy output of programmable pacemakers, in specific circumstances, or insertion of a temporary pacemaker capable of delivering higher energy output than the implanted generator may also be successful.     

Advances in Cardiac Pacing: Beyond the Transvenous Right Ventricular Apical Lead

While for decades right ventricular (RV) apical pacing has been the standard of care for patients requiring pacemaker or defibrillator lead placement, investigators have sought alternatives to achieve more physiologic electrical activation of the heart and reduce long‐term pathologic effects of nonphysiologic apical pacing. These investigations have included attempts at identifying superior pacing sites within the right atrium and RV and development of new leads to enhance specificity of sensing and capture. This review focuses on recent advances in alternative sites for pacing and developments in novel pacing technology ranging from intramyocardial electrodes to leadless pacemakers. First, there have been several studies demonstrating potential benefits of site‐specific pacing, including His bundle pacing and RV outflow tract pacing in potentially attenuating electromechanical dyssynchrony and long‐term functional decline seen with RV apical pacing. Available options for lead placement have been enhanced by development of intramyocardial electrodes that may significantly reduce far‐field oversensing and nonchamber specific capture. With development of intramyocardial electrodes, the potential for atrioventricular septal pacing has recently been described, making synchronous activation of both ventricles with a one‐lead system possible without crossing the tricuspid valve and offering an alternative to modern cardiac resynchronization therapy (CRT). Finally, recent advances in leadless pacemaker systems using ultrasound or magnetic fields are briefly discussed. The results of these studies suggest that there may be options to the RV apex, made possible by novel lead and pacemaker technology. These advances can potentially aid in reducing long‐term negative effects of chronic pacemaker therapy.     

心脏再同步化治疗的特殊病例处理

目的观察心室再同步化治疗的特殊病例处理。方法对2例扩张型心肌病因冠状静脉畸形、左心室起搏电极不能达到理想起搏位置的患者采用心外科微创手术植入左心室心外膜起搏电极。结果2例患者三腔起搏器各起搏电极植入过程顺利，起搏器工作良好，起搏心率为80次/min。左心室收缩同步性均较术前改善。术后1周心功能均恢复至NYHA心功能分级Ⅲ级。无并发症。结论对经导管径路植入左心室电极失败的患者应用微创开胸左心室心外膜起搏电极植入进行心脏再同步化治疗是可行、安全且有效的。     

Combined automatic implantable cardioverter-defibrillator and pacemaker systems: implantation techniques and follow-up

The automatic implantable cardioverter-defibrillator (AICD) effectively prevents death due to ventricular tachycardia or ventricular fibrillation. Some patients who need an AICD also require cardiac pacing to treat symptomatic bradycardia, bradycardia after defibrillation, or to provide a rate floor to reduce the frequency of bradycardia-related ventricular arrhythmias. Some patients also can benefit from antitachycardia pacing. A mapping technique to implant a pacemaker and AICD sensing leads is presented. For patients with a pacemaker who later need an AICD, the left ventricle is mapped with use of the AICD rate-sensing electrodes to identify a site at which the minimal pacemaker stimulus and maximal ventricular electrogram amplitudes are recorded. An external cardioverter-defibrillator that has amplifiers similar to those in the AICD is used to monitor the rate-sensing electrogram. For patients with an implanted AICD, pacemaker implantation is undertaken by mapping the right ventricle with the pacemaker lead while the AICD is in standby mode; the AICD beep monitor is then used to determine a site where pacemaker stimulus detection by the AICD does not occur. Eight patients underwent implantation of a combined AICD-pacemaker system (four ventricular antitachycardia pacemakers, three ventricular demand pacemakers and one atrial demand pacemaker). Neither inhibition of AICD arrhythmia detection nor double counting occurred. Satisfactory AICD-pacemaker function was shown in all patients postoperatively, and no pacemaker malfunction was observed. Thus, with currently available technology, a combined AICD-pacemaker system can be implanted with satisfactory function of both devices and without adverse device-device interactions.     

Left ventricle automatic pacing threshold management in CRT systems: A comprehensive review

Modern cardiac resynchronization therapy (CRT) device‐based threshold detection enables capture management and voltage output adjusting to combine consistent left ventricular (LV) pacing with acceptable battery drainage. The current technologies available for LV capture automatic confirmation in most cases require the evoked response, as well as “LV pace to right ventricular sense” algorithms. The LV pacing percentage counter may overestimate the CRT delivery which may be reduced due to pacing inhibition (by sensed LV activation) or inadequate capture due to subthreshold current or pacing into refractory tissue. Moreover, the LV threshold at implant and its behavior over time (as a marker of electrical viability) and the ineffective CRT issues (subthreshold stimulation or concealed loss of capture) are discussed. The purpose of the present review is to explore these new challenges regarding LV pacing automatic management.     

Clinical Validation of New Pacing-Sensing Configurations for Atrial Automatic Capture Verification in Pacemakers

INTRODUCTION: This study evaluated an atrial automatic capture verification scheme based on atrial evoked response (AER). Atrial pacing was between Atip and Can (Atip-Can) using different coupling capacitances (CCs). Independent pairs of sensing electrodes between Aring and Vtip (Aring-Vtip) or between Aring and a separate indifferent electrode (Aring-Indiff) were used to reduce pacing-induced afterpotentials. METHODS AND RESULTS: A custom-made external pacing system was used to perform automatic step-up and step-down pacing (0.1 to 7.1 V at 0.5 msec, step size of 0.1 V) using different CCs (2 or 15 microF). Intracardiac signals from Aring-Indiff and Aring-Vtip were independently recorded and analyzed both in real time and off-line to detect AER. Every paced beat also was visually inspected and compared with surface ECG to verify the captures. With the intracardiac signals properly filtered, AER detection was based on the signal within a window of 12 to 65 msec after the stimulus. Data from 27 patients (4 chronic and 23 acute implantations; age 65.6+/-13.9 years) were analyzed. Bipolar atrial lead measurements using a standard pacing system analyzer were as follows (mean +/- SD): impedance 695+/-227 ohms, P wave amplitude 4.2+/-2.3 mV, slew rate 1.1+/-0.9 V/sec, and pacing threshold at 0.5 msec 1.0+/-0.5 V. The results with CC = 2 microF showed that of 9,500 atrial paced beats, correct capture verification rates were 99.8% (Aring-Indiff) and 99.4% (Aring-Vtip). Similar results were achieved with CC = 15 microF (99.7% and 99.5%, respectively). CONCLUSION: AER can be reliably detected using independent pacing (Atip-Can) and sensing (Aring-Vtip or Aring-Indiff) electrodes. Therefore, atrial automatic capture verification by AER detection is feasible.     

Uni- and bipolar pacing threshold measurements with capturecontrol, a new automatic pacemaker function for capture verification. Comparison of the automatic and the manual pacing threshold measurement

It is mandatory in pacemaker patients to determine the pacing threshold at each follow-up visit. To facilitate the pacing threshold measurements, complete automatic pacemaker tests are being developed. A new pacemaker algorithm for automatic capture verification (Capturecontrol) detects the presence of the evoked response signal 70-100 ms after the pacing pulse. The aim of this study was to determine the uni- and bipolar pacing thresholds using this automatic pacemaker function and compare them with the manually determined threshold. The study included 14 patients with the DDD pacemaker Logos (Biotronik) connected to the high-ohmic ventricular pacing lead Synox SX 60-BP (Biotronik). At predischarge and 8, 14, 20 and 26 weeks after implantation the uni- and bipolar pacing thresholds were assessed manually and with the automatic pacemaker function at 0.4 ms duration. Mean pacing thresholds determined with the automatic pacemaker function were not different from the manually measured values. This applied to uni- and bipolar pacing. Seventy percent of all unipolar and 67% of all bipolar measurements had no deviation. A deviation of 0.1 V between manual and automatic threshold measurement was observed in 25% (unipolar) and 28% (bipolar), respectively. A 0.2-volt difference occurred in 3% in the unipolar measurements. Deviations >/=0.3 V were found in 2% of all unipolar and in 5% of all bipolar measurements. In conclusion, automatic pacing threshold measurements using the Capturecontrol algorithm were similar compared to the manually determined thresholds. The excellent agreement between the two methods was observed for bipolar as well as unipolar pacing and on condition that all patients had a high-ohmic ventricular pacing lead. Therefore, fewer requirements are necessary for Capturecontrol than for presently available systems. Such pacemaker functions can help to speed up the measurements during follow-up visits.     

Left ventricular pacing by automatic capture verification.

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.     

Temporary coronary guidewire pacing during percutaneous coronary intervention.

Temporary pacing is occasionally required during percutaneous coronary artery interventions. This can be accomplished by the insertion of a temporary transvenous pacemaker wire into the right ventricle, but there is some risk and inconvenience associated with this approach. Temporary pacing using the coronary artery guidewire was described in 1985 but is used infrequently. Using currently available equipment, we evaluated guidewire pacing in 26 patients. Guidewire pacing was successful in all patients, but not with all coronary guidewires at acceptable ventricular capture thresholds. No complications occurred from guidewire pacing. Bench testing of multiple different wires showed several with very high resistances likely unsuitable for clinical use. Temporary guidewire pacing is easily performed and should be considered as an alternative to the separate placement of a temporary transvenous pacemaker.     

Reversible atrial lead dysfunction of DDD pacemaker after recent inferior myocardial infarction--a case report

A patient with DDD pacemaker had pacing dysfunction following an inferior myocardial infarction. The threshold of that implanted right atrial pacing lead was abnormally high but the generator was normal. A temporary lead was inserted into the high right atrium near the appendage and near the low atrium for testing of threshold, which was abnormally high in these 2 places. Forty days after stent implantation in the proximal segment of the right coronary artery, the threshold spontaneously returned to normal. The change threshold of electrode-tissue interface in the right atrium was suspected due to hibernation of right atrium ischemia.     

Electrophysiologic endocardial mapping from a noncontact nonexpandable catheter: a validation study of a geometry-based concept

INTRODUCTION: The need for high-resolution simultaneous mapping of cardiac excitation and arrhythmias on a beat-by-beat basis is widely recognized. Here we validate a noncontact mapping approach that combines a spiral catheter design with mathematical reconstruction to generate potential maps, electrograms, and activation maps (isochrones) on the entire left ventricular endocardial surface during a single beat. The approach is applicable to any heart chamber. METHODS AND RESULTS: The catheter is 3 mm (9 French) in diameter and carries 96 electrodes. Reconstruction accuracy is evaluated through direct comparison with endocardial data measured with 95 needle electrodes. Results show that endocardial potentials, electrograms, and isochrones are reconstructed with good accuracy during pacing from single or multiple sites (simulating ectopic activity). Pacing sites can be located to within 5 mm of their actual position, and intersite distances of 17 mm can be resolved during dual pacing. The reconstructed potential pattern reflects the intramural depth of pacing. The reconstructions are robust in the presence of geometric errors, and the accuracy is minimally reduced when only 62 catheter electrodes are used (32 are sufficient for pacing site localization). CONCLUSION: The study demonstrates that simultaneous endocardial mapping can be accomplished during a single beat from a spiral-shaped noncontact catheter with good accuracy.     

RR间期散点图评价VVI及AAI起搏的价值

研究旨在明确RR间期散点图 (RR图 )评价VVI和AAI起搏功能的价值。起搏器专用记录仪记录 2 1例患者的 2 4h动态心电图 (DCG)用以人工逐搏分析判断起搏功能 ,并与RR图的评价结果进行对比。 2 1例人工与RR图起搏功能的判断结果相符。虽然 14例起搏功能正常者的RR图与起搏心搏的比例不一而分为三型 :起搏优势型、部分起搏型、快速自身心搏优势型 ,但共同的特点是不显示低于起搏器所定的逸搏心率的缓慢心搏点。 7例起搏功能异常者均示异常的RR图 ,5例证明缓慢心搏存在 ,2例分别提示双重起搏频率或起搏和感知障碍。结论 :DCG的RR图可快速、准确判定VVI和AAI的缓慢性起搏异常     

Relation between QT interval and heart rate. New design of physiologically adaptive cardiac pacemaker.

The relation between QT interval and heart rate has been studied in a group of patients undergoing physiological exercise, in a group undergoing atrial pacing without exercise, and in a group with complete heart block undergoing exercise at a fixed ventricular rate controlled by cardiac pacing. The expected shortening in QT interval during physiological exercise is only in part the result of the intrinsic effect of increased rate, since patients undergoing atrial pacing to comparable rates show only a small decrease in measured QT interval and patients exercising at fixed rates in heart block exhibit a decreasing QT interval related to the independent atrial rate. QT interval changes appear mainly to be governed by factors extrinsic to heart rate. The physiological control of QT interval has been used to construct a cardiac pacemaker which senses the interval between the delivered stimulus and the evoked T wave, and uses the stimulus-evoked T wave interval to set the subsequent pacemaker escape interval. Thus physiological control of cardiac pacing rate, independent of atrial activity, using conventional unipolar lead systems is possible.     

The influence of atrial activity on ventricular capture by failing artificial pacemakers. I. Report of two new cases and review of the literature.

Atrial activity can influence the ability of a failing artificial pacemaker to excite the heart. An appropriately timed atrial beat may cause failure in excitation by pacemaker stimuli which are usually successful in ventricular capture. Conversely, stimuli which usually fail in excitation may be made to succeed by an appropriately timed atrial beat. Two case reports and a review of the literature are presented. Alternative mechanisms for this influence of atrial activity are electrotonic effects (Wedensky facilitation or inhibition) and mechanical effects (motion of the pacing catheter or ventricular myocardium). The authors consider the latter mechanism preferable.     

The influence of atrial systole on ventricular capture by failing artificial pacemakers. II. Experimental observations

The mechanism by which atrial systole influences the efficacy of ventricular capture by a failing pacemaker was investigated in 12 dogs with atrioventricular heart block. Atrial systole caused facilitation of ventricular capture in eight dogs, and inhibition of capture in 10 dogs. Interpolating atrial extrasystoles caused an enhancement or depression of the hemodynamic performance of the atrial systole that affected the efficacy of the pacemaker stimulus. These interpolation experiments showed that atrial systole influenced the efficacy of capture by a mechanical mechanism and not by an electrotonic mechanism. Atrial systole probably caused motion of the endocardial pacing catheter and/or ventricular myocardium. This motion increased or decreased the contact between the pacing electrode and the endocardium with subsequent changes in the efficacy of capture. In three dogs with pacing through epicardial electrodes, atrial systole had no effect on the efficacy of capture.     

Impact of anti-tachycardia pacing on atrial fibrillation burden when added on top of preventive pacing algorithms: results of the prevention or termination (POT) trial.

AIMS: The efficacy of preventive pacing algorithms (PPA) and anti-tachycardia pacing (ATP) in reducing atrial fibrillation (AF) burden remains controversial. The aim of this study was to assess whether ATP on top of PPA decreases AF burden. METHODS AND RESULTS: A series of 199 consecutive patients, with conventional indications for pacing, and documented AF, received a DDDR (rate adaptive dual chamber pacemaker) pacemaker with ATP capabilities (AT 500 Medtronic). After 3 months of conventional DDDR pacing at 70 b.p.m., AF burden was analysed. If patients had >30 min/week of AF, they were randomized to PPA or to PPA+ATP for 3 months (period 1). They were then crossed to the alternative therapy (period 2) and followed three additional months with a 1-month wash out period in-between. A group of 85 patients were randomized. Mean age 68 +/- 8 years, 61% men. Both groups showed a significant decrease in AF burden at the end of period 1 (64 and 81%, respectively). CONCLUSIONS: Atrial pacing with PPA decreases AF burden in patients with pacing indication. We did not observe a further decrease in AF burden or in the number of episodes when adding ATP on top of PPA.     

Quantitative study of the supernormal phase of ventricular excitability in man.

The supernormal phase of excitability of the human heart was studied by means of fixed rate endocardial pacing in 11 patients with acute and chronic bradyarrhythmias. Ten of the eleven patients manifested a supernormal phase. The duration of the phase increased with increasing intensity of subthreshold stimuli and ranged from 91 to 148 percent of the Q-T interval. Subthreshold stimuli of a wide range of intensity could elicit a full response. Two types of supernormal phase, early and late in relation to the cardiac cycle, were observed. The latter was attributed to the summation of subthreshold stimuli with either spontaneous phase 4 depolarization of a ventricular ectopic pacemaker or atrial depolarization potentials. Its possible connection with Wedensky facillitation was suggested. The ventricle was less excitable after an ectopic beat than after a normally conducted beat.     

Chest wall stimulation in evaluation of patients with implanted ventricular-inhibited demand pacemakers.

Chest wall electrical stimuli, too weak to affect the heart, act as electrical signals to an implanted ventricular-inhibited (QRS blocking) demand pacemaker which interprets them as originating from the heart and consequently responds according to its specifications. Rapid external stimulation permits diagnostic interpretation of the spontaneous electrocardiogram by completely inactivating the implanted pacemaker. The slow random delivery of external stimuli throughout the cardiac cycle delineates the pacemaker refractory period after the emission of a pacing stimulus and after the sensing of a spontaneous beat. During apparent fixed-rate pacing the demand capability of the pacemaker may be easily seen by appropriately timed chest wall stimulation which induces the pacemaker to sense a spontaneous QRS complex. This simple technique may reveal subtle changes in pacemaker performance, and contributes to the understanding of pacemaker arrhythmias.