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Biomedical subjects

G Fröhlig

Publications and source records attributed to G Fröhlig.

At least 19 recordsLinked to original sources
PubMed2005

[The role of cardiac pacing in atrial arrhythmia prevention].

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.

Algorithms↗
PubMed2005

[Peculiarities in the follow up of resynchronization therapy].

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.

Arrhythmias, Cardiac↗
PubMed2005

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.

Aged↗
PubMed2004

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.

Aged↗
PubMed2002

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 <or=45%) it was 75% of the age-predicted maximum rate (P=0.004). The optimum upper rate limit, as defined by cardiopulmonary exercise testing and exercise Doppler echocardiography, were closely correlated (P<0.0001) with a mean deviation of 6+/-6 beats x min(-1). CONCLUSION: Cardiopulmonary exercise testing and exercise Doppler echocardiography are valuable tools which help to determine the optimum upper rate limit in order to avoid excess heart rates in heart failure patients. The application of these methods is not limited to pacemaker patients but may be helpful in therapeutic interventions with chronotropic drugs.

Adult↗
PubMed2001

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.

Aged↗
PubMed2001

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.

Aged↗
PubMed2001

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.

Aged↗
PubMed2001

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.

Electric Impedance↗
PubMed2001

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.

Aged↗
PubMed2000

The influence of right atrial septal pacing on the interatrial contraction sequence.

UNLABELLED: Right atrial septal pacing yields shorter interatrial conduction delays than conventional right atrial pacing at the free wall or the right atrial appendage. However, the hemodynamic effects of right atrial septal pacing are less well known. This study measured the delay between right and left atrial contractions during right atrial septal pacing (n = 21), conventional right atrial pacing (n = 32) and atrial multisite pacing (n = 6) by pulse Doppler echocardiography of transtricuspidal and transmitral blood flow. The effects of right atrial septal pacing (n = 14) versus conventional right atrial pacing (n = 22) on the optimal AV delay during dual chamber pacing was examined in patients with high degree atrioventricular (AV) block. Compared to sinus rhythm, conventional right atrial pacing increased P wave duration from 119 +/- 21 ms to 137 +/- 24 ms (P < 0.001), whereas both right atrial septal pacing (119 +/- 10 ms before, 106 +/- 13 ms during pacing, P = 0.002) and atrial multisite pacing (123 +/- 20 ms before, 112 +/- 11 ms during pacing, P = 0.5) shortened P wave duration. Atrial pacing caused a significant (P < 0.002) prolongation of atrial contraction [corrected] delays from 24 +/- 21 ms to 41 +/- 26 ms during conventional right atrial pacing, and reversed the right-to-left into a left-to-right contraction sequence in 20 of 21 patients during right atrial septal pacing (atrial conduction delay during sinus rhythm: 34 +/- 23 ms vs -37 [corrected] +/- 26 ms during atrial pacing, P < 0.0001). Atrial multisite pacing caused a nonsignificant shortening of the usual right-to-left contraction delay from 22 +/- 34 ms to 11 +/- 18 ms. The optimal left heart AV delay during AV sequential pacing was significantly (P = 0.002) shorter during right atrial septal pacing (108 +/- 38 ms) than during conventional right atrial pacing (152 +/- 33 ms). During conventional right atrial pacing the optimal right heart AV delay was significantly (P = 0.029) shorter than the optimal left heart AV delay. The opposite relation was observed for right atrial septal pacing (P = 0.033). CONCLUSIONS: Interatrial septal pacing does not synchronize right and left atrial contractions. It reverses the atrial mechanical timing from a right-to-left to a left-to-right contraction sequence, and requires the setting of shorter AV delays during dual chamber pacing if based on the optimization of left heart timing. Interatrial septal pacing is a technique which allows pacing of the left atrium from a right atrial site, rather than a single site approach to biatrial pacing.

Adolescent↗
PubMed1999

Influence of right ventricular stimulation site on left ventricular function in atrial synchronous ventricular pacing.

OBJECTIVES: The study investigates the correlation between left ventricular function and QRS duration obtained by alternate right ventricular pacing sites. BACKGROUND: 1. Right ventricular apical pacing is associated with alterations of left ventricular contraction sequence. 2. A stimulation producing narrow QRS complexes is supposed to provide for better left ventricular contraction patterns. METHODS: Fourteen patients with third degree AV block received one ventricular pacing lead in apical position. The alternate lead was attached to that site on the septum that produced the smallest QRS complex as measured from the earliest to the last deflection in any of the orthogonal Frank leads (xyz). During atrial synchronous ventricular pacing, the AV delay was optimized individually and for each stimulation site using mitral valve doppler or impedance cardiography. By radionuclide ventriculography, the phase distribution histogram of left ventricular contraction was evaluated as area under the curve (AuC); systolic function was determined as ejection fraction (EF) and as absolute ejected counts (EC) in random order. The difference (delta) in QRS duration between apical and septal stimulation (deltaxyz) was correlated with the difference in phase distribution (deltaAuC) and ejection parameters (deltaEF, deltaEC). RESULTS: QRS duration was shorter with septal than with apical pacing in 9 out of 14 patients (64%); it was longer in 4 (29%), and no difference was seen in 1 patient. There was a significant positive correlation between the change in QRS duration (deltaxvz) and phase distribution (deltaAuC: r = 0.66393, p = 0.010) and a significant negative correlation to systolic function (deltaEF: r = 0.70931, p = 0.004; deltaEC: r = 0.74368, p = 0.002). CONCLUSIONS: In atrial synchronous right ventricular pacing, if the AV delay is adapted individually, decreased QRS duration obtained by alternate pacing sites is significantly correlated with homogenization of left ventricular contraction and with increased systolic function in acute tests.

Aged↗
PubMed1999

Dissociating beliefs about heart rates and actual heart rates in patients with cardiac pacemakers.

Performance on heartbeat counting tasks is usually interpreted in terms of cardiac sensitivity. We tested the hypothesis that heartbeat counting is influenced by beliefs about heart rates by dissociating beliefs about heart rates and actual heart rates. In a within-subjects design, heart rates of 50 patients with cardiac pacemakers were set to a low (50 bpm), medium (75 bpm), or high (110 bpm) pacing rate unknown to the patients via remote control while they performed a heartbeat tracking task. Results showed that patients' heartbeat counting did not follow the shifts in their actual heart rates adequately, although their overall performance was comparable to that of young and healthy control participants. As a result, tracking scores decreased significantly in the high pacing rate condition where beliefs about heart rates and actual heart rates were most extremely dissociated. The findings suggest that tracking scores reflect beliefs about heart rates rather than cardiac sensitivity.

Adult↗
PubMed1999

AV conduction with atrial rate adaptive pacing in the bradycardia tachycardia syndrome.

AV conduction with atrial rate adaptive pacing (AAIR) during exercise was investigated in 43 patients (28 men, 15 female, mean age 68 +/- 7 years) who were paced and medicated with antiarrhythmic drugs for the bradycardia tachycardia syndrome (BTS). Patients were included if they had no second- or third-degree AV block, no complete bundle branch or bifascicular block, and a PQ interval < or = 240 ms during sinus rhythm at rest. The interval between the atrial spike and the following Q wave (SQ) was measured in the supine position at rest (R) with maximum AAI pacing rate (Fmax) achieved below the Wenckebach point (SQ-R-Fmax). Bicycle ergometry was performed using the Chronotropic Assessment Exercise Protocol, and AAI pacing rate was increased stepwise by programming load-adapted increments. Seven patients showed intrinsic rhythm during exercise. In those 36 patients who were atrially paced throughout ergometry (E), SQ was measured with 70 beats/min on the lowest CAEP stage (SQ-E-70) and with Fmax at maximum work load (SQ-E-Fmax). During exercise, no second-degree AV block was observed, but 28 of 36 patients (78%) showed a nonphysiological increase of the SQ interval, and the average SQ-E-Fmax was significantly longer than SQ-E-70 (250 +/- 31 versus 228 +/- 32 ms, P < 0.01). There was only a weak correlation between SQ-R-Fmax and SQ-E-Fmax (r = 0.35824, P < 0.05). When Fmax obtained during exercise was kept during recovery, 14 patients (39%) developed a second-degree AV block between 15 and 240 seconds after ergometry, 8 patients within 90 seconds. Patients who had exhibited a P on T wave in the ECG with Fmax at the end of exercise (11 of 36 patients) were reevaluated by Doppler echocardiography. Using the same exercise protocol and identical, load-adapted rate increments, only 3 of 11 patients showed premature mitral valve closure. It is concluded that patients paced and medicated for BTS are prone to a nonphysiological prolongation of AV conduction with AAIR pacing during and after exercise. As this risk can hardly be predicted by rapid atrial pacing at rest, the pacing system should be dual chamber in this subset of patients. This especially applies to the patients in whom mechanical AV timing is affected by the conduction delay.

Aged↗