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.

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.

Five-year follow-up of a bipolar steroid-eluting ventricular pacing lead

Steroid-eluting pacing leads are known to attenuate the threshold peaking early after implantation. Long-term performance, however, is not yet settled. The lead design tested in this prospective study combines a 5.8-mm2 tip of microporous platinum-iridium with elution of 1.0 mg of dexamethasone sodium phosphate and tines for passive fixation (model 5024, Medtronic Inc.). In 50 patients (mean age 69 +/- 10 years), the electrode was implanted in the right ventricular apex. Follow-up was performed on days 0, 2, 5, 10, 28, 90, 180 and every 6 months thereafter for 5-years postimplant. At each visit, pacing thresholds were determined as pulse duration (ms) at 1.0 V and as the minimum charge (microC) delivered for capture. Lead impedance (omega) was telemetered at 2.5 V-0.50 ms, and sensing thresholds (mV) were measured in triplicate using the automatic sensing threshold algorithm of the pacemaker implanted (model 294-03, Intermedics Inc.). On the day of implantation, mean values were 0.10 +/- 0.03 ms, 0.12 +/- 0.03 microC, 758 +/- 131 omega, and 13.1 +/- 1.8 mV, respectively. Beyond 1-year postimplant, pacing thresholds did not vary significantly. Sensing thresholds and lead impedance values were stable during long-term follow-up. Five years after implantation, mean values were 0.23 +/- 0.11 ms, 0.24 +/- 0.07 microC, 670 +/- 139 omega, and 11.6 +/- 3.1 mV for pulse width and charge threshold, lead impedance, and sensing threshold, respectively, and all leads captured at 1.0 V with the longest pulse duration available (1.50 ms). It is concluded that the bipolar steroid-eluting tined ventricular lead showed stable stimulation thresholds, lead impedance values, and sensing thresholds for 5 years after implantation.

[Which cardiologic diagnosis in patients with cerebral ischemia?]

There are few scenarios which need urgent clarification for the acute therapy of stroke. Normally, the patient's history, clinical findings, an electrocardiogram and a limited number of blood tests are suitable to govern precise management. Additional questions can be answered by transthoracic echocardiography (TTE) which gives information on left ventricular function, the development of thrombi after myocardial infarction, valvular lesions or vegetations. Transesophageal imaging (TEE) is required if TTE remains technically inadequate or if specific questions (e.g. the suspicion of a mitral valve prosthetic vegetation) shall be answered. The procedure is indicated only if therapeutic implications can be anticipated. Outside scientific protocols, the same criterion has to be applied when screening for potential sources of emboli (patent foramen ovale, atherosclerotic lesions of the ascending aorta) which can only be detected by TEE with adequate sensitivity and may be shown to require secondary prophylaxis in the near future.

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.

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.

Rate adaptive atrial pacing in the bradycardia tachycardia syndrome

In 42 patients (26 men, 16 women; mean age 69 +/- 10 years), who were paced and medicated with antiarrhythmic drugs for the bradycardia tachycardia syndrome, chronotropic response and AV conduction with rapid atrial pacing during exercise were studied. 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 with an AAI pacing rate of 5 beats/min above the sinus rate (SQ-R + 5), and at the end of exercise with 110 beats/min (SQ-E110). Bicycle ergometry was performed using the Chronotropic Assessment Exercise Protocol with the pacemakers being programmed to AAI with a fixed rate of 60 beats/min. Chronotropic incompetence was defined as peak exercise heart rate: (1) < 100 beats/min; (2) < 75% of the maximum predicted heart rate; or (3) the heart rate at half the maximum workload < 60 + 2 beats/min per mL O2/kg per minute (calculated O2 consumption). During exercise, one patient developed atrial fibrillation. Chronotropic incompetence was present in 71% (29/41) of the patients according to definition 2, and in 76% (31/41) according to definition 1 or 3. Ten out of 41 patients (24%) exhibited a second-degree AV block with atrial pacing at 110 beats/min at the end of exercise. Only 9 out of the remaining 31 patients (29%) showed a physiological adaptation of the SQ-E110, and 21 patients (68%) exhibited a paradoxical increase of the SQ interval with rapid atrial pacing at the end of exercise as compared to the SQ-R + 5. These observations indicate that the pacing system to be used in most patients paced and medicated for the bradycardia tachycardia syndrome should be dual chamber, and the option of rate adaptation should be considered.

Telemetry guided pacemaker programming: impact of output amplitude and the use of low threshold leads on projected pacemaker longevity

In a prospective study, a low threshold screw-in electrode (Medtronic 5078, group I, n = 9) was compared to a conventional active fixation lead (Biotronik Y60BP, group II, n = 9) to investigate whether lower pacing thresholds really translate into longer projected service life of the pacemaker. The leads were implanted in the atrium and were connected to a dual chamber pacing system which included the same ventricular lead (Medtronic 5024) and the same pulse generator model (Intermedics 294-03) in both groups. Eighteen months after implantation, atrial and ventricular pacing thresholds were measured as the charge delivered per pulse [microC] at 0.5, 1.0, 1.5, 2.0, and 3.5 V, respectively. For chronic output programming in both channels, patients capturing at 0.5 V were set to 1.0 V, those capturing at 1.5 V were permanently programmed to 2.0 V with the double of the charge threshold as the safety margin for pacing ("safety charge"). A combination of atrial and ventricular output settings was optimal, if it resulted in minimum battery current drain (microA] as measured by pacemaker telemetry. In both groups, current consumption [microA] decreased significantly as output amplitude was decreased, exhibiting its lowest value at 1.0 V in either channel. All ventricular leads could be programmed to the optimum output amplitude of 1.0 V in groups 1 and 2. As the 2:1 "safety charge" values were almost identical, the ventricular channel essential contributes the same amount to the battery drain of the pacing system in both groups. In the atrium, all patients of group 1 could be programmed to the optimum output amplitude of 1.0 V with an average pulse duration of 0.42 +/- 0.15 ms. In group 2, however, all patients had to be programmed to 2.0 V with a mean pulse width of 0.52 +/- 0.15 ms. With the atrial and ventricular output being optimized, the average battery drain of the whole pacing system was 12.19 +/- 0.63 microA in group 1 versus 14.42 +/- 0.32 microA in group 2 (P < 0.001). As patients were chronically programmed to these output settings, this difference translates into a clinically relevant gain in projected pacemaker longevity of 17 months or 18.3% (121 +/- 4 vs. 104 +/- 2 months; P < 0.001). Thus, programming a 2:1 safety margin in terms of charge and optimizing the output parameters by real-time telemetry of the battery current is a useful approach to reduce battery current drain. Making the most of modern lead technology with a different performance in only one channel of an otherwise identical DDD pacing system translates into a significant prolongation of projected pacemaker service life which is of great importance with the increasing awareness of health care expenditures. The gain in projected longevity is mainly due to the option of reducing the output amplitude which is still significantly beneficial well below the nominal voltage of the power source.

Bipolar active fixation atrial leads: comparison of two new lead models

The purpose of the study was to examine the pacing and sensing characteristics of two bipolar active fixation atrial leads with a coaxial and a coradial conductor design, respectively. One group of ten patients received the ELA model S44F (4 mm2 vitreous carbon tip, coaxial multifilar coils, silicone). Nine other patients received the Intermedics ThinLine EZ 438-10 (8 mm2 iridium oxide-coated titanium tip, parallel-wound bifilar coil, polyurethane). Both lead models had electrically insulated corkscrews. Intraoperatively, pacing threshold (PT) at 0.50 ms, unfiltered atrial potential (AP), slew rate (SR) and pacing impedance (Z) at 2.5 V, 0.50 ms were measured using a Medtronic 5311 PSA. On the day of implant, and 2, 5, 10, 28, 90, 180, and 360 days after implant, minimum charge threshold (delta Qmin), atrial sensing threshold (Asen) and Z were measured via telemetry of the pacemaker (Intermedics 294-03 and 294-09). Z was significantly lower (P < 0.01) in the ThinLine EZ group at implant (419 omega vs 576 omega, mean values, 438-10 vs S44F) and at each follow-up (317-426 omega vs 492-613 omega). Five of nine patients with the 438-10 lead had Z values < 300 omega during follow-up (minimum 234 omega). There was no significant difference between the two leads with respect to PT (0.42 V vs 0.41 V), AP (3.75 mV vs 4.25 mV), SR (0.56 vs 1.06), delta Qmin (0.19-1.23 microC vs 0.18-1.35 microC) and Asen (3.4-4.5 mV vs 2.7-4.7 mV), respectively. Two patients developed pericardial effusions after implantation of a ThinLine EZ lead. One of them, who had a transient drop of blood pressure during implant, subsequently developed acute exsudative pericarditis. Therefore, both leads had acceptable sensing and pacing thresholds, but the 438-10 lead developed unusually low long-term lead impedance values. The high incidence of perforations in our small group of 438-10 patients has not been observed, thus far, in other studies.

Atrial lead implantation during atrial flutter or fibrillation?

In patients with sinoatrial disease, unexpected atrial flutter (Af) or fibrillation (AF) is a common problem during implantation of atrial-based pacing systems. As an alternative approach to blind atrial lead placement, lead positioning could be optimized by atrial electrogram mapping. It was the object of this study to evaluate if atrial lead implantation according to this approach and during ongoing arrhythmia is reasonable or if it should be postponed until restoration of sinus rhythm (SR). Twenty-nine consecutive patients (group I) with sick sinus syndrome received a dual-chamber pacemaker during an episode of Af (n = 11) or AF (n = 18). All but two atrial leads were of the screw-in type and had bipolar sensing. Atrial lead position was optimized by mapping the electrogram under fluoroscopy to find locations with high potential amplitudes. The patients were followed for 15.1 +/- 9.8 months, and atrial sensing threshold (AST), atrial pulse width threshold (PWT) at 2.0 V, the pacing mode programmed, and the clinical outcome (OUT) were recorded. The control group consisted of 30 patients (group II) who equally had a history of AF or Af, but were in SR during implantation. The atrial peak-to-peak potential (APEAK) after final lead placement was lower for AF (median value 2.5 mV, lower-upper quartile: 1.7-3.1 mV) as compared to Af (3.8 mV, 2.7-4.9 mV, P < 0.05) and SR (4.1 mV, 3.3-6.2 mV, P < 0.001). There was a correlation (P < 0.01) between APEAK during Af/AF and the postoperative AST immediately after restoration of SR. No lead in any group had to be corrected due to improper sensing in the postoperative course. Median chronic AST was 2.8 mV (2.0-4.0 mV) in group I and 4.0 mV (2.8-4.0 mV) in group II. Median chronic PWT at 2.0 V was 0.15 ms (0.12-0.26 ms) in group I and 0.15 ms (0.09-0.20 ms) in group II. There was no significant difference in chronic AST and PWT between both groups. All but two patients in group I preserved SR as the basic rhythm. A stable SR was observed in 10 of 29 patients, intermittent Af/AF was documented in 17 of 29 patients, seven of whom were asymptomatic. There was no significant difference in OUT between group I and II. Hence, sinus rhythm is not a prerequisite of atrial lead implantation. Mapping the Af or AF waves appears to be useful to guide lead placement and to achieve sufficient sensing and pacing conditions after conversion to sinus rhythm.

A fractally coated, 1.3 mm2 high impedance pacing electrode

Minimizing the geometric surface area of pacing electrodes increases impedance and reduces the current drain during stimulation, provided that voltage (pulse-width) thresholds remain unchanged. This may be feasible by coating the electrode surface to increase the capacity of the electrode tissue interface and to diminish polarization. Ten unipolar, tined leads with a surface area of 1.3 mm2 and a "fractal" coating of iridium (Biotronik SD-V137) were implanted in the ventricle, and electrogram amplitude (unfiltered), slew-rate, pacing threshold (0.5 ms), and impedance (2.5 V; 0.5 ms) were measured by the 5311 PSA (Medtronic). On days 0. 2. 5. 10, 28, 90, 180, 360 postimplant, sensing threshold (up to 7.0 mV, measuring range 1-14 mV on day 360 only) and the strength duration curve (0.5-4.0 V; 0.03-1.5 ms; steps: 0.5 V; 0.01 ms, respectively) were determined, the minimum charge delivered per pulse (charge threshold), and the impedance were taken from pacemaker telemetry (Intermedics 294-03). Data were compared with those of an earlier series of 20 unipolar, tined TIR-leads (Biotronik) with a surface area of 10 mm2 and a @actal" coating of titanium nitride. With the model SD-V137 versus TIR, intraoperative electrogram amplitudes were 15.1 +/- 6.1 versus 14.4 +/- 3.9 mV (NS), slew rates 3.45 +/- 1.57 versus 1.94 +/- 1.06 V/s (P < 0.05), pacing thresholds 0.16 +/- 0.05 versus 0.52 +/- 0.15 V (P < 0.01) and impedance measurements 1,136 +/- 175 versus 441 +/- 73 omega (P < 0.0001), respectively. During follow-up, sensing thresholds were the same with both leads. Differences in pulse width thresholds lost its significance on day 28 but resumed on day 360 (SD-V137; 0.08 +/- 0.04 ms; TIR: 0.16 +/- 0.06 ms at 2.5 V; P < 0.01). With an electrode surface of 1.3 mm2, charge per pulse and impedance consistently differed from control, being 0.15 +/- versus 0.66 +/- 0.20 microC (P < 0.001) and 1,344 +/- 376 versus 538 +/- 79 omega respectively, one year after implantation (P < 0.0001). In summary, "fractally" coated small surface electrodes do not compromise sensing; by more than doubling impedance against controls they offer pacing thresholds (mainly in terms of charge) that are significantly lower than with the reference electrode.

[Effect of programmed safety margin on function time of modern dual chamber pacemakers]

In 55 consecutive patients with the same dual chamber pacemaker (Relay, Intermedics) and different pacing leads, the influence of different safety margins for pacing on battery current was investigated. 2.8 +/- 0.9 years after implantation, atrial and ventricular pulse-width thresholds (tRS) (ms) were determined at 0.5, 1.0, and 2.0 V, and the charge delivered at threshold was telemetered. If tRS was < 1.50 ms at 0.5 V, an amplitude of 1.0 V was programmed in the atrium and the ventricule; if tRS was < 1.50 ms at 1.0 V, then an amplitude of 2.0 V was chosen. Two times the charge threshold (2 x QRS), two times the voltage threshold (2 x URS), and three times the pulse-width threshold (3 x tRS) were programmed as the safety margins for pacing. With every safety margin, battery current (IBat) (microA) was averaged from 5 telemetric readings in D00 mode with 70 bpm. IBat was significantly lower with 2 x QRS as compared with 2 x URS (13.43 +/- 1.0 vs. 14.20 +/- 1.2 microA, p < 0.01) and as compared with 3 x tRS (13.99 +/- 1.2 microA, p < 0.05). Pacemaker longevity derived from these current data was significantly longer with 2 x QRS (112 +/- 8 months) as compared with 2 x URS (106 +/- 9, p < 0.01) and as compared with 3 x tRS (108 +/- 8, p < 0.05). If current consumption is compared intraindividually in dependance on the programmed amplitude, battery current is significantly lower at 1.0 V as compared with 2.0 V resulting in a mean reduction of 0.63 microA (-4.9%, p < 0.05) and an average gain in longevity of 5 months. This applies to every safety margin tested. Differences in battery current caused by the safety margins will translate into a greater gain in longevity in future pacemaker models with reduced internal current consumption.

Femoral injection of echo contrast medium may increase the sensitivity of testing for a patent foramen ovale

OBJECTIVE

The diagnosis of a patent foramen ovale (PFO) as a cause of stroke is of increasing interest especially in young (<45 years) patients.

METHODS

We studied potential right-to-left shunting using transesophageal echocardiography (TEE) and bilateral transcranial Doppler sonography (TCD) of the middle cerebral artery (MCA) simultaneously in 44 patients. All patients were younger than age 45 years and suffered from an acute ischemic stroke or transient ischemic attack. Other possible etiologies were excluded. Echo contrast medium was injected in an alternating mode via antecubital or femoral veins. Tests were performed with and without the Valsalva maneuver. The criteria for a PFO were that the contrast pass from the right to the left atrium (TEE) and early detection (<10 seconds) of more than 10 micro air bubbles in at least one MCA by TCD.

RESULTS

A PFO was diagnosed in 22 patients (50%). The detection rate with TEE/TCD was 11.4%/4.5% via antecubital injection, 18%/13.6% via antecubital injection plus the Valsalva maneuver, 38.6%/36% via femoral injection alone, and 50%/50% via femoral injection plus the Valsalva maneuver. The difference between femoral and antecubital injections was significant with and without the Valsalva maneuver (p < 0.01, chi2 test). There were no differences between TEE and TCD after femoral injection with the Valsalva maneuver. The brain transit time was 4.6 +/- 2.1 seconds for femoral injection and 6.3 +/- 4.1 seconds for antecubital injection.

CONCLUSIONS

The sensitivity in detecting a PFO was markedly increased by femoral injection. This may be caused by different inflow patterns to the right atrium: inferior vena caval flow is directed to the right atrial septum, whereas superior vena caval flow is directed to the tricuspid valve. Thus, femoral injection may help to improve the detection of PFO and may explain the differences between TEE and TCD findings in previous studies.

Optimizing the AV delay in DDD pacemaker patients with high degree AV block: mitral valve Doppler versus impedance cardiography

In DDD-pacemaker patients with high degree AV block, Doppler echocardiography of transmitral blood flow can be used to find the individually optimal AV delay (AVO) for left heart AV synchronization. This study tried to validate a Doppler method (ECHO) recently proposed to optimize left ventricular filling by comparing it to stroke volume data derived from impedance cardiography (ICG). It should be further elucidated if optimizing the AV delay (AVD) by means of this method is superior to fixed AVD settings and which differential AVD (pace-sense-offset) should be programmed for atrially triggered (ATP) and AV sequential (AVP) pacing, respectively. AVO as measured in 53 patients showed a linear correlation between ECHO and ICG for both ATP (r = 0.66, P < 0.00001) and AVP (r = 0.53; P < 0.005). The mean deviation in AVO between ECHO and ICG was +/- 26 ms (ATP) and +/- 30 ms (AVP), respectively, with a tendency to longer AVDs with the Doppler method. ECHO limitations could mainly be attributed to: (1) restrictions of AVD programming options (which may be compensated for by slight modification of the proposal); and (2) to pathophysiological mechanisms that alter mitral valve dynamics. Optimization of the AVD by Doppler produced a stroke volume that was significantly higher (19%) than with a fixed AVD (150 ms in ATP; 200 ms in AVP). There was a wide scatter in pace-sense-offsets between-7 and 134 ms, which was reflected by both methods. It is concluded that AVO determinations by ECHO are valid provided that methodological pitfalls and limitations caused by the disease are recognized. Tailoring AVD with respect to diastolic filling improves systolic function and is superior to nominal AVD settings. Fixed differential AVDs as offered by some manufacturers are far from being physiological. Thus modern pulse generators should offer free programmability over a wide range of AV delays.

Chronic ventricular pacing using an output amplitude of 1.0 volt

Thirty-seven patients (21 male, 16 female, mean age 71 years) received identical DDD pacemakers. They also received the same bipolar ventricular passive fixation electrode, which has a microporous tip of platinum-iridium, a surface area of 5.8 mm2, and steroid elution. Eighteen months after implantation the ventricular charge threshold [microC] was measured telemetrically at 0.5, 1.0, and 2.0 V, respectively. For the 1.0 and 2.0 V amplitudes the pulse duration was increased until the charge per pulse [microC] was twice the threshold value, thus giving a 100% safety margin in terms of charge ("safety charge"). Patients who had ventricular capture at 0.5 V were permanently programmed to 1.0 V (30/37 patients), while those who did not capture at 0.5 V were set to 2.0 V (7/37 patients). In both cases, the pulse duration was programmed according to the rationale of "safety charge." During a routine follow-up period of 6 months, no complications were observed and none of the patients suffered from symptoms indicating loss of ventricular capture. Twenty-four-hour Holter recordings, obtained from all patients at the end of the follow-up with the output parameters unchanged, revealed constant ventricular capture. In patients with chronic stable pacing thresholds and steroid-eluting low threshold leads who have capture at 0.5 V, chronic ventricular pacing at an output amplitude of 1.0 V is feasible, and it seems to be safe if the pacing threshold is measured as charge delivered per pulse and a 100% safety margin in terms of charge is programmed. Reducing the output amplitude to well below the battery voltage may increase pacemaker longevity.

[Biatrial stimulation in therapy of paroxysmal atrial tachycardia: a case report]

A biatrial pacemaker was inserted in a 68-year-old female with paroxysmal atrial fibrillation and atrial flutter refractory to antiarrhythmic drugs based on a sick-sinus-syndrome and concomitant interatrial conduction delay. One electrode positioned in the right atrium and another electrode located in the coronary sinus were connected to a dual-chamber pacemaker. The electrode in the right atrium was connected to the atrial channel, the electrode in the coronary sinus to the ventricular channel. The pacemaker was programmed in DDD-mode with an AV-delay of 30 ms. Under a chronic antiarrhythmic medication with 160 mg sotalol per day there was no evidence for recurrent episodes of atrial tachyarrhythmias in the patient's history, 24-h-Holter-ECG, nor in the memory of the pacemaker during a follow-up of 8 months.

[Initial clinical experiences with low energy internal cardioversion of chronic atrial fibrillation after unsuccessful external cardioversion]

Between January and September 1995, 54 consecutive patients (male: 34, age: 66 +/- 10 years) with symptomatic chronic atrial fibrillation (median duration: 4.5 months) were referred for external electrical cardioversion to our hospital. Mean left atrial diameter was 49 +/- 9 mm, heart disease was apparent in 81%. All patients were under antiarrhythmic drugs (class III: 85%). In 49 patients (91%) sinus rhythm was achieved. In five patients atrial fibrillation persisted after delivery of 360 Joules. These five patients were characterized by a significantly higher body weight in comparison to patients with successful external cardioversion. All five patients underwent low energy internal cardioversion the following day: biphasic R-wave synchronous shocks were delivered through catheters positioned in the right atrium and the coronary sinus using stepwise increased energy levels. Internal cardioversion was successful in all patients resistant to external cardioversion: stable sinus rhythm was established at a mean energy level of 13 +/- 6.7 Joules. No complications were observed. During the follow-up, each patient revealed a relapse of symptomatic atrial fibrillation within 2 weeks after internal cardioversion despite antiarrhythmic therapy, whereas only 16 patients (33%) lost sinus rhythm during the same period of time after external cardioversion (p < 0.01). During a mean follow-up of 283 +/- 72 days 21 patients (43%) preserved stable sinus rhythm after external cardioversion. Internal low energy cardioversion seems to be effective and safe in conversion of chronic atrial fibrillation resistant to external cardioversion. The clinical value of this invasive, time- and material-consuming therapy seems to be limited in this setting because of the high early relapse-rate in the investigated patient population. Further clinical studies in a larger cohort of patients are necessary.

A new steroid-eluting screw-in electrode

A new lead design was tested that combined a small microporous steroid-eluting electrode with an insulated, exposed helix for active fixation. This lead (model 5078, Medtronic, Inc., group I, n = 10) was compared to a conventional model (model Y 60 BP, Biotronik) with a larger surface of polished platinum-iridium, equipped with a fixed, noninsulated screw but without steroid elution (group II, n = 10). The two lead models were studied in the atrial position of dual chamber pacing systems, which all had a tined ventricular lead (model 5024, Medtronic, Inc.), with essentially the same steroid-eluting tip as the new active fixation lead design. Sensing and pacing data were recorded acutely and during 1 year of follow-up, via the telemetry of a Relay pulse generator (Intermedics, Inc.). Intraoperatively, unfiltered atrial electrogram amplitudes did not differ between groups (group I: 7.12 +/- 2.56 mV vs group II: 6.42 +/- 1.87 mV; P > 0.05), nor did sensing thresholds 1 year after implantation (group I: 5.33 +/- 1.70 mV vs group II: 4.26 +/- 1.40 mV; P > 0.05). Atrial pacing thresholds as measured during surgery at a pulse width of 0.5 msec were lower in group I (0.49 +/- 0.15 V) than in group II (0.68 +/- 0.19 V; P < 0.05). From day 5 through day 360 of follow-up, the difference in atrial pacing thresholds was highly significant (P < 0.01), with a smaller peaking of early thresholds and a much lower scattering of data for the steroid screw-in leads than for controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Cineradiography for determination of normal and abnormal function in mechanical heart valves

To determine the diagnostic value of cineradiography of mechanical heart valves, 112 cinefluoroscopic studies were performed in 76 patients with 95 valve prostheses (caged ball or disk valves, tilting disk and bileaflet valves). A patient group (n = 45) presenting with clinical or echocardiographic findings suggestive of valve-related complications was compared with a control group (n = 31) without such symptoms. Disk-opening angles (mean +/- SD) for Medtronic Hall aortic valves were found to be significantly smaller (62.8 +/- 11.1 degrees) in patients than in control subjects (73.9 +/- 1.6 degrees; p < 0.05). Tissue ingrowth or thrombus formation, or both, demonstrated in 3 patients on subsequent reoperation, are considered as the main cause of incomplete or asymmetric disk opening. Opening and closing times did not differ significantly between patients and control subjects. Besides abnormal valve motion, structural defects such as strut fracture or leaflet escape could be rapidly detected by cineradiography if x-ray projections according to the particular valve design were used. Together with quantitative Doppler echocardiographic and clinical data, this method can help to give specific answers if the question is to either confirm or exclude imminent or acute valve malfunction. Thus, modern cineradiography is a highly valuable noninvasive diagnostic tool for both rapid management of emergency cases and routine follow-up of patients with mechanical heart valves.

Threshold and polarization properties of modern active fixation atrial leads

The purpose of the study was to compare the stimulation characteristics of two modern active fixation leads (Ela 583F, vitreous carbon tip [ELA] and Intermedics 82-0008-1601, iridium oxide tip [IROX]) with a standard lead (Osypka KY 67 VC, carbon-covered elgiloy tip [OSY]). In three groups of ten patients each, minimum charge threshold delta Qmin and polarization properties were determined via charge telemetry of the pacemaker (Intermedics Cosmos II and Relay) 0, 2, 5, 10, 28, 90, and 180 days after implant (dai). The polarization parameters global capacitance Cg, global resistance Rg, polarization voltage U(p), and a time constant t* (t* = Cg.Rg) were obtained by nonlinear regression. U(p) was always significantly (sig) lower in ELA and IROX (0.04-0.10 V) compared to OSY (0.54-0.76 V). Rg was sig lower in ELA (330-437 omega) compared to OSY and IROX (414-588 omega) from 0 to 28 dai. From 2 to 10 dai, Cg was sig higher in ELA and IROX (3.8-4.2 microF) compared to OSY (3.3-3.4 microF). In the three groups, delta Qmin reached a comparable maximum (1-1.2 microC) at 5 dai. Therefore, vitreous carbon and iridium oxide atrial fixation leads exhibit low chronic polarization effects compared to a standard elgiloy lead, but do not show a sig reduction in charge threshold.

Reliability of an automatic sensing algorithm

Automatic adaptation of the atrial sensitivity was evaluated in 18 patients with dual chamber pacemakers (Intermedics, Inc., Relay) in the unipolar mode. After atrial sensitivity was stabilized in the upright position, patients underwent a 1.0 W/kg body weight exercise for 5 minutes. A 24-hour Holter ECG was recorded, and the maximum and minimum atrial sensitivity values reached were stored in the memory of the pulse generator. In a second series of 12 patients, Holter ECGs were recorded twice, starting with the same sensitivity but with automatic adaptation alternately switched "on" or "off." Results of the exercise test: mean atrial sensitivity declined from 2.30 +/- 0.77 mV to 2.03 +/- 0.68 mV. There was no change in five patients, a slight increase in two patients, and lowering of the atrial sensitivity was observed in 11 patients, the difference ranging from 0.2 to 1.0 mV. A total of two P waves in two patients were missed by the atrial amplifier. The minimum and maximum sensitivity reached during Holter monitoring averaged 2.31 +/- 0.67 mV versus 1.72 +/- 0.71 mV (difference 0-1.7 mV). Normal pacemaker function was found in six patients, including one patient without any intrinsic atrial activity. Malsensing of less than five P waves occurred in four patients. More than 50 sensing defects resulted from ectopic atrial beats (four patients). We observed atrial oversensing in three cases; one patient showed atrial over- and undersensing. The comparison between fixed and variable sensitivity did not reveal any superiority of automatic adaptation.(ABSTRACT TRUNCATED AT 250 WORDS)