[Cardiac resynchronization therapy: preoperative screening. How can we reliably predict response to CRT?]. / Kardiale Resynchronisationstherapie: Präoperatives Screening. Wie sicher können wir Therapieresponder erfassen?

Cardiac resynchronization therapy (CRT) is an established therapy for patients with advanced heart failure, depressed left ventricular function, and wide QRS complex. However, about 30 to 45% of patients do not respond to CRT. Assuming that the main therapeutic action of CRT is the correction of dyssynchronous myocardial contraction, a plethora of echocardiographic dyssynchrony parameters have been proposed to improve the prediction of response to CRT. However, one multicenter study has recently questioned the utility of any of these indexes. This review delineates the various causes of non-response to CRT, explains the different levels and mechanisms of dyssynchrony and gives a critical overview of currently available echocardiographic techniques for assessment of dyssynchrony. Based upon a discussion of the evidence coming from randomized multicenter studies and against the background of national and international cardiac societies' guideline recommendations on CRT, a rational basis for the evaluation of patients for CRT is proposed.

[His-bundle stimulation and alternative RV stimulation sites]. / HIS-Bündel-Stimulation und alternative rechtsventrikuläre Stimulationsorte.

The increasing evidence that right ventricular (RV) apical stimulation is detrimental for cardiac mechanics and increases the risk of new onset heart failure and mortality promotes strategies to avoid ventricular pacing and - if not applicable due to atrioventricular block - stipulates the search for alternative techniques of pacing the heart from the right ventricle. Despite more than 15 years of clinical research it remains unclear whether pacing from the right ventricular outflow tract or septum, dual site RV stimulation or selective pacing of the His bundle results in hemodynamic and prognostic benefit over the traditional method of apical RV pacing. The article reviews pertinent literature and tries to demonstrate pathophysiological mechanisms.

[Is resynchronization therapy necessary when optimizing right ventricular stimulation?]. / Ist bei Optimierung der rechtsventrikulären Stimulation eine Resynchronisationstherapie überhaupt erforderlich?

Cardiac resynchronization therapy (CRT) using biventricular stimulation is hampered by coronary venous imponderabilities, complex implantation procedures, technical malfunctions and complications as well as disappointing responder rates. Despite its pathophysiological soundness and some initial success, the use of AV sequential pacing for the treatment of heart failure has been abandoned because right ventricular (RV) apical stimulation may be detrimental for cardiac mechanics, may worsen heart failure and may increase mortality. Attempts at avoiding desynchronizing effects and improving hemodynamics by pacing from alternative RV sites have been numerous but not convincing. Whether patients with left ventricular dysfunction or overt heart failure may benefit from pacing the RV outflow tract or septum, from dual site RV or His bundle stimulation instead of left ventricular based resynchronization is the topic of this review.

[Peculiarities in the follow up of resynchronization therapy]. / Besonderheiten der Nachsorge nach kardialer Resynchronisationstherapie.

While resynchronization therapy (CRT) is based on conventional pacemaker- and ICD technology, its main intention is to minimize inter- and intraventricular asynergy and to establish optimal AV timing if sinus rhythm is preserved. The focus of this contribution is a series of conditions which jeopardize the therapeutic goal of CRT and should be recognized and hopefully corrected during follow up of CRT systems. These scenarios include uncertainties about left ventricular capture, double sensing in the ventricles, inhibition of the ventricular output (and loss of resynchronization), atrial and ventricular tachycardia and rate adaptation. Technical issues of following rhythm management devices are only discussed in the context of CRT requirements.

Rejection of atrial sensing artifacts by a pacing lead with short tip-to-ring spacing.

AIMS: The ability of a new pacing lead design, with a 10 mm tip-to-ring spacing, to facilitate rejection of sensed far field R-waves and myopotentials was evaluated. METHODS AND RESULTS: Measurements were performed in 66 patients. The occurrence of far field R-wave sensing and myopotential sensing was determined by means of the surface ECG and the ECG markers provided by the pacemaker. At an atrial sensitivity of 0.25 mV and an atrial blanking of 50 ms far field R-wave sensing was observed in 12 patients (18.2%) and at an atrial sensitivity of 1.0 mV no far-field R-wave sensing was observed. Myopotentials were sensed in 3 patients. In all patients the measured P-wave amplitude was at least twice the estimated amplitude of the far field R-wave at an atrial blanking of 50 ms. CONCLUSION: The results from this study show that a small tip-to-ring spacing allows for programming of a high atrial sensitivity and short atrial blanking with an acceptably low risk for atrial artifact sensing.

[The role of cardiac pacing in atrial arrhythmia prevention]. / Stellenwert der Herzschrittmacher-Therapie bei der Vorhofflimmer-Prophylaxe.

Pathophysiological considerations, animal data and acute clinical tests suggest some benefit of cardiac pacing in the prevention of paroxysmal atrial tachyarrhythmia. While early clinical studies confirm this notion, data of randomized prospective trials at least are mixed. The equivocal effects of using alternative atrial pacing sites and/or dedicated preventive pacing algorithms leaves the question of how to predict the beneficial effect of antitachycardia pacing strategies in the individual patient. Since the answer is lacking, the mere intention to prevent atrial arrhythmias is not a valid pacing indication. Pacing for the bradycardia tachycardia syndrome, however, may benefit from preventive techniques in individual cases.

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.

Defining the optimum upper heart rate limit during exercise: a study in pacemaker patients with heart failure.

AIMS: There is no non-invasive method to determine the individual optimum of maximum exercise heart rate. Knowledge of this value is of particular interest in patients with structural heart disease who are prone to tachycardia intolerance. The purpose of this study was to define the optimal maximum heart rate using cardiopulmonary exercise testing and exercise Doppler echocardiography and to compare the results of both approaches. METHODS AND RESULTS: In 49 pacemaker patients with chronotropic incompetence, the optimum upper heart rate limit was determined using cardiopulmonary exercise testing and exercise Doppler echocardiography. The optimum upper rate limit was given by the highest pacing rate which still produced an increase in oxygen consumption, or by that pacing rate which was linked to the lowest value for the Doppler-derived myocardial performance index. In patients with normal left ventricular ejection fraction (>or=55%) the optimum upper rate limit was 86% of age-predicted maximum heart rate, in patients with left ventriuclar dysfunction (ejection fraction

Do battery depletion indicators reliably predict the need for pulse generator replacement?

The aim of this study was to test the validity of battery depletion indicators to forecast end of service (EOS) in dual chamber pulse generators (PG). Two additional approaches for prediction of EOS were evaluated as well: the real-time telemetry of cell impedance and a battery stress test (BST) that used a transitory increase in pacing rate. The study population consisted of 119 patients with Intermedics dual chamber PG models Cosmos II and Relay, in which cell impedance had exceeded 2.5 k omega. The patients were followed in 6-month intervals. If the interrogation of the PG or the BST prompted the appearance of the intensified follow-up indicator (IFI), the next follow-up was scheduled within 2 months. PG replacement was performed on physician's discretion or immediately on appearance of the elective replacement indicator (ERI), regardless of the method of ERI provocation. During a period of 2 years/and 9 months, 33 patients underwent PG replacement. Out of 21 patients with positive ERI indicators, only 5 had positive warning indicators of approaching battery depletion in the preceding follow-up (IFI during BST, n = 4; ERI during BST n = 1). The majority of patients (n = 16, 76%) revealed ERI without prior activation of IFI, neither spontaneous nor during the BST. Four of these 16 ERI-positive patients had cell impedance values far below the ERI limits of the manufacturer. Based on battery depletion indicators, an exact prediction of EOS of dual chamber pacemakers is not possible. Measuring battery impedance allows for a statistical estimation of remaining service life but it may be misleading in the individual case. A BST that is based on a temporary increase of pacing rate is invalid in forecasting battery depletion. As activation of the ERI can trigger an abrupt change to the VVI backup mode, pacemaker dependent patients with low programmed basic pacing rates may be hemodynamically compromised by an unexpected activation of ERI. Close monitoring intervals and PG replacement before appearance of the ERI is recommended in those patients.

Longevity of dual chamber pacemakers: device and patient related determinants.

In 382 patients with three different dual chamber pulse generators, the median time interval to battery depletion was 98.3 months. Cox regression analysis revealed the following variables as significant predictors of battery longevity: programmed pacing rate, energy of the stimulation output, mode of stimulation (i.e., proportion of paced cycles in one or two chambers), battery capacity, and internal sensing current of the pacemaker. Although 27% of all patients died before the service life of the pacemaker was over and despite a rate of premature reoperations of 8.6%, the majority of pacemaker patients (55%) fully used the expected battery life span of the pulse generator. Patients who died before the pacemaker had reached its end of service were significantly older at implantation than patients who survived until pacemaker replacement. The vast majority (92%) of patients received another dual chamber pulse generator when replacement was required. These data underline the need for long-lasting dual chamber devices.

Safety and efficiency of pulse charge multiplication for chronic ventricular output programming.

Fifty-one patients with Intermedics pacemakers and different chronic (> or = 12 months) ventricular lead models were investigated. Ventricular charge thresholds (microC) were measured telemetrically at 1.0, 2.0, 2.5, and 3.5 V, respectively. Then pulse duration was increased until charge per pulse (microC) was twice the threshold value in patients not being pacemaker dependent (n = 39) and three times the threshold in pacemaker dependent patients (n = 12), thus giving a 2:1 or 3:1 safety factor in terms of charge ("safety charge"). At safety charge settings, the battery current was measured telemetrically for all four pulse amplitudes (PA) in VVI mode at 70 beats/min. For safety purposes, only pulse amplitudes were considered that fulfilled two conditions: (1) pulse duration threshold (PDT) < or = 0.30 ms at PA and (2) PDT < or = 1.00 ms at a pulse amplitude of (PA-0.5 V). The combination of pulse amplitude and pulse duration that yielded the safety charge at the lowest battery current was defined as optimized ventricular output (Copt). It was found at 1.0 V in 27 patients and at 2.0 V in 24 patients. The safety pulse duration (SPD) that yielded a 2:1 safety charge in patients who were not pacemaker dependent was 0.32 +/- 0.12 ms for both, 1.0 V (n = 23) and 2.0 V (n = 16), respectively. In pacemaker dependent patients, the SPD for the 3:1 safety charge was 0.61 +/- 0.25 ms (at 1.0 V, n = 4) and 0.47 +/- 0.11 ms (at 2.0 V, n = 8), respectively. The safety factor for conversion of PDT into SPD was 3.15 (range 3.00-3.38) for pacemaker dependent patients and 2.04 (range 2.00-2.43) for patients who were not pacemaker dependent, respectively. Charge thresholds measured at study entrance, after 24 hours, and again after 6 months showed a median variation of 14% and a maximum individual variation of 55%. On day 0 and 180, 24-hour Holter recordings were obtained from all patients and revealed constant ventricular capture at output settings Copt. When the output was changed from a fixed setting (2.5 V at 0.50 ms) to Copt, the battery current decreased by 17.5% (P < 0.0001). In conclusion, pacing thresholds in patients with chronic ventricular leads are stable enough to permit programming battery-saving low output settings, if pacemakers are followed on a regular basis. Titration of a 2:1 safety charge (a 3:1 safety charge in pacemaker dependent patients) by prolongation of pulse duration is safe, provided that pulse amplitude is chosen carefully. Using this approach, current consumption can significantly be reduced without jeopardizing patient's life.

Septal lead implantation for the reduction of paced QRS duration using passive-fixation leads.

In 120 consecutive patients with standard pacing indications, we tested the feasibility of RV septal lead implantation technique guided by surface ECG and the degree to which this technique reduces paced QRS duration compared to RV apical stimulation when passive-fixation leads are used. During implantation, an ECG was recorded with a paper speed of 100 mm/s using the orthogonal Frank leads, and QRS was measured from the earliest to the latest deflection in any of the Frank leads. Pace-mapping of the septum was performed until QRS was minimal. The lead was attached, where QRS, pacing threshold, lead impedance, and EGM amplitude provided the best compromise. An average of 3.7 +/- 2.5 attempts (range 1-18, median 7) was needed until a final implantation site was found. There were no technical problems during implantation. QRS could be reduced by 5-55 ms (mean delta QRS 19 +/- 11 ms) in 83 (69%) of 120 patients. In 22 (18%) patients, QRS was identical with apical and septal pacing, and in 15 (13%) patients, QRS was 5-20 ms (10 +/- 4) longer despite septal stimulation. Average QRS was significantly shorter during septal pacing compared with apical pacing (151 +/- 20 vs 162 +/- 23 ms, P < 0.001). There was a tendency towards greatest QRS reduction when the high septum was stimulated (22 +/- 11 ms reduction) as compared with mid- (18 +/- 11 ms) or apical parts of the RV septum (16 +/- 10 ms). QRS reduction was most likely if apical QRS width was > 170 ms (P = 0.0002), and there was an inverse correlation between apical QRS and delta QRS (r = 0.53, P < 10(-7)). During a mean follow-up of 14 months, there was no pacing or sensing problem and no lead dislodgment occurred.

AAIR versus DDDR pacing in the bradycardia tachycardia syndrome: a prospective, randomized, double-blind, crossover trial.

In 19 patients paced and medicated for bradycardia tachycardia syndrome (BTS), AAIR and DDDR pacing were compared with regard to quality of life (QoL), atrial tachyarrhythmia (AFib), exercise tolerance, and left ventricular (LV)function. Patients had a PQ interval < or = 240 ms during sinus rhythm, no second or third degree AV block, no bundle branch block, or bifascicular block. In DDDR mode, AV delay was optimized using the aortic time velocity integral. After 3 months, QoL was assessed by questionnaires, patients were investigated by 24-hour Holter, cardiopulmonary exercise testing (CPX) was performed, and LV function was determined by echocardiography. QoL was similar in all dimensions, except dizziness, showing a significantly lower prevalence in AAIR mode. The incidence of AFib was 12 episodes in 2 patients with AAIR versus 22 episodes in 7 patients with DDDR pacing (P = 0.072). In AAIR mode, 164 events of second and third degree AV block were detected in 7 patients (37%) with pauses between 1 and 4 seconds. During CPX, exercise duration and work load were higher in AAIR than in DDDR mode (423+/-127 vs 402+/-102 s and 103+/-31 vs 96+/-27 Watt, P < 0.05). Oxygen consumption (VO2), was similar in both modes. During echocardiography, only deceleration of early diastolic flow velocity and early diastolic closure rate of the anterior mitral valve leaflet were higher in DDD than in AAI pacing (5.16+/-1.35 vs 3.56+/-0.95 m/s2 and 69.2+/-23 vs 54.1+/-26 mm/s, P < 0.05). As preferred pacing mode, 11 patients chose DDDR, 8 patients chose AAIR. Hence, AAIR and DDDR pacing seem to be equally effective in BTS patients. In view of a considerable rate of high degree AV block during AAIR pacing, DDDR mode should be preferred for safety reasons.

[High impedance electrodes]. / Hochohm-Elektroden.

The concept of small surface high impedance pacing electrodes is based on three major arguments: 1) tip size reduction increases the field strength at the electrode surface; 2) a micro-porous coating allows for downsizing the geometric surface area to about 1 mm(2) without increasing the voltage pacing threshold; and 3) small electrodes exhibit high pacing impedance hence reduce the charge transfer from the battery through the electrode-tissue interface. This design does not compromise sensing if the input impedance of the amplifier used is adequate (>30kΩ). In the long term (2 up to 5 years post-implant), typical impedance values range between 900 and 1200Ω, pacing thresholds are below 1.0V @ 0.5 ms, and the minimum charge delivered per pulse is around 0.2µC. Careful implantation is a prerequisite of good long term performance and does not bear additional risks of myocardial perforation or excessive threshold rise as compared to the normal (5.8 mm(2)) electrode size. The benefit in terms of battery drain is maximum with nominal output parameters (≥2.5 volt); when pacing below the battery voltage, however, the difference in pacemaker longevity is marginal between normal and high impedance "low threshold electrodes". This energy balance may change in favor of high impedance leads if the current drain of the circuitry will be lowered in next generation pacing devices.

Evolution of an active fixation atrial pacing lead.

UNLABELLED: Three bipolar atrial pacing leads from one manufacturer differing in a single electrode design characteristic were compared. Each lead had nonretractable screw and a microporous electrode tip made of activated carbon. Model S84F had a tip surface area of 8 mm2. In model S44F, the tip surface area was reduced to 4 mm2 by insulation of the screw, and in model BS45D, steroid elution was added to the 4 mm2 tip. Ten patients in each group received identical pulse generators. During implantation, atrial potentials (5.4 +/- 2.0, 4.2 +/- 2.0, 4.6 +/- 2.1 mV), pacing thresholds at 0.5 ms (0.47 +/- 0.14, 0.41 +/- 0.15, 0.55 +/- 0.33 V) and lead impedance at 2.5 V/0.5 ms (515 +/- 80, 575 +/- 152, 546 +/- 131 omega) were comparable among groups. The early postoperative threshold peak was significantly lower with the BS45D than with the S84F and S44F lead models. One year after implantation, charge threshold was significantly lower with the BS45D lead than with the S84F and the S44F model (0.34 +/- 0.11 vs. 0.68 +/- 0.20 and 0.56 +/- 0.21 microC; P < 0.05). Lead impedance at 2.5 V/0.5 ms (557 +/- 90, 549 +/- 36, 524 +/- 72 omega) and atrial sensing (4.3 +/- 2.1, 4.7 +/- 1.9, 4.7 +/- 0.9 mV) were not significantly different. One year postimplant, current drain of the pacing system was measured by pacemaker telemetry at chronic output settings in AAI mode/70 beats/min. Battery current measured among the three atrial lead models did not differ significantly (S84F: 11.9 +/- 0.90, S44F: 12.2 +/- 1.8, BS45D: 11.5 +/- 0.26 microA). IN CONCLUSION: reduction of the tip surface area by insulation of the screw did not improve pacing performance. Addition of steroid elution to the 4 mm2 tip significantly lowered the early threshold peak and the long-term pacing threshold. Lowering of the pacing threshold, however, did not lower the current drain of the pacing system.