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Peak endocardial acceleration (PEA) measured by an implantable acceleration sensor inside the tip of a pacing lead reflects ventricular filling and myocardial contractility. The contribution of the plateau phase of PEA as an indicator of optimal ventricular filling, hence of the appropriate atrioventricular interval (AVI) at rest and during exercise, was studied in 12 patients (age 69 +/- 6 years) with complete AV block and a PEA sensing DDDR pacemakers (Living 1 Plus, Sorin Biomedica). At a mean resting heart rate of 79 +/- 15 beats/min, the mean AVI optimized by PEA versus Doppler echocardiography (echo) were identical (142 +/- 37 vs 146 +/- 26 ms, P = 0.59). During submaximal exercise at a mean heart rate of 134 +/- 6 beats/min, AVI optimized by PEA was 135 +/- 37 ms. Cardiac output at rest, measured by the CO2 rebreathing method, was comparable with AVI determined by echo versus PEA (4.3 +/- 2.9 and 3.7 +/- 2.4 L/min, respectively), and increased to the same extent (8.0 +/- 3.9 vs 8.3 +/- 5.2 L/min) during submaximal exercise. In patients with AV block, AVI automatically set by PEA was comparable with AVI manually optimized by Doppler echocardiography and was associated with comparable exercise induced hemodynamic changes.

Automatic mode switching (AMS) is a useful means to avoid rapid ventricular response during atrial fibrillation (AF), but AMS cannot occur if the detected atrial rate during AF is below the mode switching criteria. This may be the result of antiarrhythmic medications, or when the atrial events fall within the atrial blanking period, or if the atrial amplitudes during AF are too small to be sensed. We hypothesize that the addition of an automatic rate switching (ARS) algorithm may complement AMS response during AF with different detected atrial rates. We studied the Marathon DDDR pacemaker (Model 294-09, Intermedics Inc.) with the AMS and ARS algorithms that are independently programmable but can also operate in combination. AF sensed above the AMS rate (160 beats/min) will lead to VDIR pacing, whereas AF below AMS rate will be tracked at an interim rate as dictate by the ARS, at a ventricular response that is 20 beats/min above the sensor indicated rate. Atrial tachyarrhythmias were simulated by chest wall stimulation (CWS). CWS was applied to 33 patients (16 men, 17 women, mean age 69 +/- 11 years) with a Marathon DDDR pacemaker using an external pacer to simulate AF occurring at two rate levels: above the AMS rate (programmed at 160 beats/min) at 180 beats/min and below the AMS rate at 120 beats/min. The maximum, minimum, and mean ventricular rates during CWS in DDDR mode with AMS alone, ARS alone, and their combination were compared. During CWS at 120 beats/min, the AMS plus ARS setting showed a mean ventricular rate of 79 +/- 3 beats/min and 124 +/- 14 beats/min in the AMS setting alone (P < 0.01). With CWS at 180 beats/min, the mean ventricular rate in the AMS plus ARS setting compared to the AMS setting alone was not significantly different. However, the variation in ventricular pacing rate was 7 +/- 14 beats/min in the AMS plus ARS setting and 40 +/- 42 beats/min in the AMS setting (P < 0.05). In conclusion, AMS is effective for simulated atrial tachyarrhythmias sensed above the AMS rate. Combined AMS with ARS is useful to handle simulated atrial tachyarrhythmia at a slower rate and to avoid rate fluctuation during AMS. There is also a possibility that this can be applied to the naturally occurring atrial tachyarrhythmias.

The use of single lead for atrial synchronous ventricular (VDD) pacing in patients with high grade atrioventricular (AV) block and normal sinus node function is an acceptable alternative to dual chamber (DDD) pacing. Implantation and follow up procedures are simplified, and cost is usually reduced by more than the cost of an additional atrial lead. With the use of either diagonally arranged dipole or closely spaced ring electrodes, reliable atrial sensing can be achieved using differential atrial amplifier and high atrial sensitivity. Also oversensing is infrequently observed using provocation tests and dynamic recordings, clinical undersensing is unusual and minimized by programming to the highest atrial sensitivity. However, as atrial pacing is not possible, loss of AV synchrony and rate response may occur for unrecognized or progressive sinus node disease and lower rate limit. The development of single lead dual chamber pacing system may overcome this limitation. Recent studies have demonstrated that atrial pacing can be effective either with the use of a special pacing lead configuration or via floating atrial electrode with a novel stimulation method. Overlapping biphasic impulse (OLBI) can reduce atrial pacing threshold. Early clinical experience suggested that this new pacing method can provide effective and reliable atrial pacing with a relatively low incidence of diaphragmatic pacing. Thus the problem of atrial sensing is solved with a single pass lead but further long term evaluation is required to assess the efficacy and feasibility of new instrumentation for single lead dual chamber pacing.

The use of single lead, atrial synchronous ventricular (VDD) pacing in patients with high grade atrioventricular (AV) block and normal sinus node function is an acceptable alternative to dual chamber (DDD) pacing. Implantation and follow up procedures are simplified, and cost is usually reduced by more than the cost of an additional atrial lead. With the use of either diagonally arranged dipole or closely spaced ring electrodes, reliable atrial sensing can be achieved using differential atrial amplifier and high atrial sensitivity. Also oversensing is infrequently observed using provocation tests and dynamic recordings, clinical undersensing is unusual and minimized by programming to the highest atrial sensitivity. However, as atrial pacing is not possible, loss of AV synchrony and rate response may occur for unrecognized or progressive sinus node disease and lower rate limit. The development of single lead dual chamber pacing system may overcome this limitation. Recent studies have demonstrated that atrial pacing can be effective either with the use of a special pacing lead configuration or via floating atrial electrode with a novel stimulation method. Overlapping Biphasic Impulse (OLBI) can reduce atrial pacing threshold. Early clinical experience suggested that this new pacing method can provide effective and reliable atrial pacing with a relatively low incidence of diaphragmatic pacing. Thus the problem of atrial sensing is solved with a single pass lead but further long term evaluation is required to assess the efficacy and feasibility of new instrumentation for single lead dual chamber pacing.

Long-term atrial pacing with overlapping biphasic impulse stimulation using floating atrial electrodes is limited in its use by the high rate of intermittent failure to capture the atrium and by the occurrence of diaphragmatic stimulation in ambulatory patients.

Objective: To investigate the platelet activation in different modes of pacing in patients implanted with dual chamber rate adaptive pacemaker (DDDR) for bradyarrhythmias, and to explore the possible underlying mechanism of the higher thromboembolic incidence in single chamber ventricular rate adaptive (VVIR) pacing., Design: Platelet activation was determined in chronically paced patients during three different pacing modes (VVIR, DDD, and DDDR) in a randomised crossover fashion., Setting: Pacemaker clinic at a university teaching hospital., Patients: 15 patients with complete heart block, mean (SD) age 63 (10) years, and 12 patients with sick sinus syndrome, mean age 68 (9) years, implanted with DDDR pacemakers., Main Outcome Measures: Platelet activation was assessed by measuring the plasma concentrations of platelet factor 4 (PF4) and beta thromboglobulin using an enzyme linked immunosorbent assay (ELISA). Mean log plasma PF4 and beta thromboglobulin values were compared in paced patients during different pacing modes and with controls., Results: Compared with controls, patients paced in DDDR, DDD, and VVIR modes had higher mean log plasma concentrations of PF4 (0.90 (0.32), 0.92 (0.29), and 1.12 (0.33) v 0.61 (0.29) log IU/ml, all p < 0.05, respectively) and beta thromboglobulin (1.55 (0.20), 1.59 (0.16), and 1.71 (0.18) v 1.40 (0.12) log IU/ml, all p < 0.05, respectively). In paced patients, VVIR pacing was associated with higher plasma concentrations of PF4 and beta thromboglobulin than either DDDR or DDD pacing (all p < 0.05). There was no significant difference in plasma PF4 and beta thromboglobulin between patients with complete heart block and sick sinus syndrome in the corresponding pacing mode. Holter monitoring showed no difference in mean pacing rate and occurrence of cardiac arrhythmias to account for the increased platelet activation during VVIR pacing. There was no relation between the percentage of ventricular pacing on Holter during DDDR, DDD, and VVIR modes and the log mean plasma concentrations of PF4 (r = 0.002, 0.001, and 0.001, respectively, all p > 0.05) and beta thromboglobulin (r = 0.007, 0.01, and 0.001, respectively, all p > 0.05)., Conclusions: Single chamber ventricular pacing was associated with enhanced spontaneous systemic platelet activation compared with physiological dual chamber pacing. This was related to the loss of atrioventricular synchrony rather than to the underlying cause of bradycardia, lack of rate response, or coexisting arrhythmia. This abnormality may be associated with increased thromboembolism and was correctible by an appropriate pacing mode prescription and possibly antiplatelet treatment.

Objectives: The purpose of this study was to investigate the effect of long-term ventricular pacing on myocardial perfusion and function in patients receiving such pacing., Background: The long-term effect of ventricular pacing on myocardial perfusion and function in humans is unclear, although animal studies have suggested that it may be adverse., Methods: Forty-three patients with complete heart block and dual-chamber rate-adaptive (DDDR) pacing were studied. All underwent thallium-201 (Tl-201) exercise myocardial scintigraphy to assess myocardial perfusion and radionuclide ventriculography to determine left ventricular function and regional wall motion. Coronary angiography was also performed in patients with abnormal findings on Tl-201 study., Results: There was no significant difference in mean age, gender, percent ventricular pacing, pacing threshold, ventricular pacing output and metabolic equivalents on exercise testing between patients with or without perfusion defects on exercise Tl-201 scintigraphy. However, the duration of pacing tended to be longer in patients with than in those without perfusion defects (43.9 +/- 49.7 vs. 20.1 +/- 9.8 months, p = 0.05). Tl-201 perfusion defects were noted in 28 (65%) of 43 of patients (inferior 78% [n = 22], apical 67% [n = 17], septal 21% [n = 6], anterior 7% [n = 2], lateral 3% [n = 1)]. Of 16 of 28 patients with abnormal Tl-201 findings who underwent coronary angiography, only 3 (19%) had significant coronary artery disease. Patients with an abnormal perfusion defect had a significantly lower left ventricular ejection fraction (48.5 +/- 9.9% vs. 59.6 +/- 8.9%, p < 0.001) and a higher percent of wall motion abnormalities (57% vs. 20%, p = 0.026), mainly over apical regions., Conclusions: Long-term right ventricular apical pacing resulted in a high incidence of myocardial perfusion defects that increased with the duration of pacing. These myocardial perfusion abnormalities were associated with apical wall motion abnormalities and impaired global left ventricular function.

By cross-checking the relative sensor activation between a nonspecific and specific sensor during extraneous interference, a multisensor rate adaptive pacemaker may be able to limit inappropriate rate responses. The effects of activity (ACT) sensor programming on rate response kinetics of a QT and ACT dual sensor VVIR pacemaker with sensor cross-checking algorithm were studied in four patients with atrial fibrillation and complete heart block. The rate adaptive setting of each sensor was individually optimized, and an equal rate contribution for the QT and ACT sensors (QT = ACT) was used in the dual sensor VVIR mode. Three maximal treadmill exercise tests were performed in random order in three different VVIR modes driven by QT only, QT = ACT, and in the dual sensor mode with the most sensitive (low threshold) ACT setting. In the two dual sensor modes, the time for onset of rate response (delay time) was reduced (both < 15 sec) compared with QT only VVIR mode (233 +/- 70 sec). However, the time to 50% of rate response in the low ACT threshold dual sensor mode was delayed compared with to QT = ACT (450 +/- 110 [95% confidence interval 234-666] vs 311 +/- 103 [109-513]sec, P < 0.05) and was similar to the QT only mode (401 +/- 120 [166-636]sec). The time to reach 90% of rate response was similar in the three modes tested. The resting activity counts registered by the ACT sensor were < 5 and 16 +/- 2 counts/min in the optimally programmed and low threshold ACT settings, respectively. This resulted in sensor cross-checking at rest in the overprogrammed dual sensor VVIR mode, thereby limiting the rate response. Thus, the combined sensor system provides a faster initial response to exercise than the QT only sensor. Programming the ACT threshold to low will prevent this faster response because of sensor cross-checking.

Although ventricular rate adaptive pacing (VVIR) improves exercise capacity and cardiac output compared to constant rate ventricular pacing (VVI), this pacing mode does not provide benefit of atrioventricular (AV) synchrony. We evaluated the use of a custom-built VDDR pacing system using a single pass, ventricular lead, which detects endocavity P wave using a pair of diagonally arranged atrial bipolar (DAB) electrodes. In the VDDR mode, AV synchrony is enabled and the P wave rate is used in conjunction with an accelerometer based activity sensor for rate adaptive pacing. A VDDR pacemaker was implanted in three patients with complete AV block (mean age 63 +/- 1 year) and the mean implantation time was 29 minutes. Mean P wave amplitude was 2.4 mV (1.2-4.2 mV) at implantation and telemetered P wave amplitude was stable over a follow-up of 6 months. At a sensitivity of 0.2 mV, stable P wave sensing was observed during breathing maneuvers, arm swinging, myopotential induction, and Holter recording. Paired exercise tests performed in the VDDR and VVIR modes showed higher cardiac output at rest, during exercise, and in the recovery period in the VDDR pacing mode. Thus VDDR pacing using a single pass lead is superior to VVIR pacing by enabling P synchronous ventricular pacing without adding to the complexity of implantation.

Although a long postventricular atrial refractory period (PVARP) may prevent the occurrence of pacemaker mediated tachycardias and inadvertent tracking of atrial arrhythmias in dual chamber (DDD) pacing, the maximum upper rate will necessarily be compromised. We tested the feasibility of using minute ventilation sensing in a dual chamber rate adaptive pacemaker (DDDR) to shorten the PVARP during exercise in 13 patients with bradycardias (resting PVARP = 463 +/- 29 msec) to avoid premature upper rate behavior. Graded treadmill exercise tests in the DDD and DDDR modes at this PVARP resulted in maximum ventricular rates of 98 +/- 8 and 142 +/- 3 beats/min, respectively (P < 0.0001), due to chronotropic incompetence and upper rate limitation in the DDD mode, both circumvened with the use of sensor. In order to stimulate atrial arrhythmias, chest wall stimulation was applied for 30 seconds at a rate of 250 beats/min at a mean unipolar atrial sensitivity of 0.82 mV. Irregular ventricular responses occurred in the DDD mode (the rates at a PVARP of 280 and 463 +/- 29 msec were, respectively 92 +/- 5 and 66 +/- 3 msec; P < 0.0001). In the DDDR mode at a PVARP of 463 +/- 29 msec, regular ventricular pacing at 53 +/- 2 beats/min occurred due to mode switching to VVIR mode in the presence of repetitive sensed atrial events within the PVARP. One patient developed spontaneous atrial fibrillation on follow-up, which was correctly identified by the pacemaker algorithm, resulting in mode switch from DDDR to regular VVIR pacing and preservation of rate response. In conclusion, sensor controlled PVARP allows a long PVARP to be used at rest without limiting the maximum rate during exercise. In addition, to offer protection against retrograde conduction, a long PVARP and mode switching also limit the rate during atrial arrhythmias and allow regular ventricular rate responses according to the physiological demands.

The rate adaptive characteristics and pacemaker mediated tachycardia protection algorithm of an accelerometer based DDDR pacemaker were evaluated in 11 patients with bradycardia (seven atrioventricular block, four sick sinus syndrome). Rate adaptive programming was effected by collecting the acceleration level during a 3-minute moderate exercise ("tailoring" of sensor). In comparison with an externally attached piezoelectric sensor, the accelerometer sensor showed lower rate changes during external tapping of the pacemaker (16 +/- 3 vs 29 +/- 4 ppm, P less than 0.02) and applied direct pressure (1 +/- 1 vs 40 +/- 3 beats/min, P less than 0.001) on the pacemaker. At nominal setting, the accelerometer sensor showed improved rate stability and higher rate response to jogging and standing, although responses to other daily activities and treadmill exercise were similar. Apart from changing the rate responsive slope, rate response could be improved by repeat "tailoring" of the sensor at a lower exercise level, resulting in better overall rate response characteristics. The ability of the rate monitoring software to collect acceleration levels for an activity and profile the projected rate response at different rate responsive settings allowed programming to be effected with the minimum amount of exercise testing. The pacemaker also discriminated atrial tachyarrhythmias from normal sinus response using the sensor to judge the appropriateness of the atrial rate, which correctly identified and prevented rapid ventricular tracking in two patients during atrial flutter/fibrillation.

The relative hemodynamic profile between dual chamber pacing (DDD) and activity sensing rate responsive pacing (VVIR) was compared in ten patients with dual chamber rate responsive pacemakers (Synergist II). With a double blind, randomized exercise protocol, DDDR pacemakers were programmed into VVI, VVIR, and DDD (AV interval 150 msec) modes and in seven patients the test in the DDD mode was repeated with the AV interval programmed at 75 msec. A treadmill exercise test of 6-minutes duration (2 stages, Stage I at 2 mph, 0% gradient and Stage II at 2 mph, 15% gradient) was performed at each of the programmed settings, with a rest period of 30 minutes in between tests. Cardiac output was assessed using continuous-wave Doppler sampling ascending aortic flow and expressed as a percentage of the value achieved during VVI pacing. During exercise, pacing rate between DDD and VVIR pacing was similar but was higher with DDD at the first minute of recovery (91 +/- 4 vs 81 +/- 3 beats/min, respectively). Cardiac output was significantly higher at rest, during low level exercise, and recovery with DDD pacing compared with VVIR pacing (resting: 21 +/- 14 vs -2 +/- 7%; Stage I: 36 +/- 6 vs 16 +/- 7%; Stage II: 25 +/- 15 vs 10 +/- 8%; recovery: 26 +/- 12 vs 4 +/- 9%; P less than 0.05 in all cases). Systolic blood pressure was significantly higher during low level of exercise in the DDD mode. Shortening of the AV interval to 75 msec did not significantly affect cardiac output during exercise, but cardiac output after exercise was reduced (2 +/- 6 vs 23 +/- 6% at an AV interval of 150 msec, P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of heart rate changes on the recovery of cardiac hemodynamics and lactate clearance after exercise was studied in nine patients with complete atrioventricular (AV) block treated with programmable pacemakers. A preliminary treadmill exercise test in which the pacing rate was externally increased stepwise from 70 to 130 bpm was performed to determine the maximum exercise duration. Two exercise tests involving an equal amount of exercise load were performed, the pacing rate was either programmed to the basic rate (abrupt decay) or gradually (modulated decay) immediately after exercise termination. Compared with abrupt decay, modulated decay resulted in a higher mean arterial pressure (100 +/- 4 mmHg vs 91 +/- 5 mmHg, P less than 0.05) and diastolic pressure (76 +/- 4 mmHg vs 59 +/- 4 mmHg, P less than 0.001) immediately on exercise termination. Immediately after exercise and during modulated decay, cardiac output (represented by Doppler derived minute distance) declined gradually and was determined mainly by a higher pacing rate without significant changes in stroke volume. On the other hand, minute distance fell abruptly during abrupt decay (996 +/- 107 m at peak exercise and 561 +/- 88 m immediately after a rate change at exercise termination, P less than 0.01) with a corresponding abrupt increase in systemic vascular resistance. This was later compensated by a gradual increase in stroke volume during the recovery period. The cumulative cardiac output between the two rate changes equalized at the 4th minute of recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of an abrupt reduction in atrial pressures on atrial natriuretic peptide (ANP) secretion was studied in four patients with complete atrioventricular block with a dual-chamber pacemaker when the pacing mode was changed from the VVI to the DVI mode at an equal rate of 70/min. Simultaneous continuous hemodynamic monitoring was performed using a balloon-tipped thermodilution catheter. With DVI pacing, there was an immediate decrease of right atrial pressure from 4.5 +/- 0.9 to 1.8 +/- 1.1 mm Hg, and a reduction of pulmonary arterial wedge pressure from 7 +/- 0.8 to 4.5 +/- 0.9 mm Hg, together with a rise in cardiac output from 3.1 +/- 0.2 to 3.7 +/- 0.2 L/min. However, despite a constant hemodynamic status after dual-chamber pacing, the arterial ANP level steadily decreased from 151 +/- 26 pg/ml to a steady low level of 78 +/- 15 pg/ml after 20 minutes of dual-chamber pacing (percentage reduction- 48 +/- 8%, p less than 0.05). This persisted until the end of the study at 60 minutes. The time-dependent decay in ANP secretion after an abrupt and constant change in hemodynamic status should be considered when interpreting ANP levels.

A minute ventilation sensing rate responsive pacemaker was implanted in a 29-week pregnant woman with symptomatic complete atrioventricular (AV) block under echocardiographic and electrocardiographic (ECG) guidance. Satisfactory rate responses during a submaximal treadmill exercise test and daily activities were achieved. The course of pregnancy and cesarean section is discussed. During the cesarean section and after the delivery of the baby, changes in the ventilator settings confirmed that the pacing rate was closely correlated with both the tidal volume (r = 0.94, P less than 0.01) and the respiratory rate (r = 0.93, P less than 0.05).

Symptomatic myopotential interference was observed in a patient with a respiratory-dependent rate modulated pacemaker (RDP3). During treadmill exercise, prolonged interference suspended the rate responsive function and resulted in reversion to the interference mode with the pacing rate falling back to the basic frequency during the interference. This loss of rate response resulted in severe impairment of exercise tolerance and reduction in cardiac output during exercise. The unit was replaced with a bipolar activity sensing rate modulated pacemaker.

Most studies evaluating the rate response of adaptive-rate pacemakers have been based on treadmill or bicycle exercise. These studies disregard the fact that few pacemaker recipients voluntarily undertake such activities. The rate responses of nine patients (mean age 62 years, range 33-79 years) with implanted minute ventilation sensing (Meta) pacemakers were studied. The indications for pacing were complete heart block (seven patients), sick sinus syndrome (one patient), and five nodal disease (one patient). Significant improvement in maximum distance covered during a 12-minute walking test was observed in the rate adaptive compared to the VVI pacing mode (989 +/- 104 vs 921 +/- 90 m, P less than 0.02). The rate responses of this pacemaker during daily activities were recorded with telemetry during a variety of structured daily activities. The rate responses were also compared to those of an externally attached Activitrax pacemaker in each patient and to a group of ten age and sex matched volunteers. For less strenuous activities such as walking, descending stairs, washing, and bed making, both pacemakers achieved adequate rate responses compared to normal subjects. For more strenuous activities, the Activitrax pacemaker failed to achieve an adequate rate response. For example, the pacing rate achieved on ascending stairs was lower than that achieved on descending stairs (92 +/- 3 vs 102 +/- 3 bpm, P less than 0.02). The direction of rate responses was more appropriate for the Meta pacemaker. Similar to the normal subjects, the maximum rate was reached before the end of an activity with the Activitrax pacemaker.(ABSTRACT TRUNCATED AT 250 WORDS)

Two unusual cases of Wenckebach-like conduction block in the infranodal tissues which developed after an intravenous dose of a Class I antiarrhythmic drug are presented. The first case shows infra-Hisian Wenckebach during sustained atrioventricular nodal reentrant tachycardia. The second case demonstrates rate-dependent Wenckebach-like exit block between the pacing catheter and the right ventricular tissues during pacing.

A 67-year-old male patient with previous history of pulmonary tuberculosis presented with syncope due to complete heart block. Collapse of the right lung and deviation of the heart to the right chest had prevented visualization of the cardiac silhouette by fluoroscopy. Successful endocardial permanent pacing using a passive fixation electrode was achieved with the help of ultrasonic visualization of the cardiac chambers.

The rate of QT adaptation to abrupt changes in pacing rate was studied in seven patients with newly diagnosed complete heart block with a ventricular escape rate of less than 40 beats.min-1. Their median age was 70 (range 36-84) years, and none was taking any cardioactive medication known to affect the QT interval. From a baseline pacing rate of 50 or 110 beats.min-1 the ventricular rate was increased or decreased to a new level. The time taken for the ventricular paced QT interval to complete 90% of the change secondary to the change in rate was found to be 136(16) s (mean(SEM] when the rate was increasing and 189(25) s when the rate was decreasing (p less than 0.01). This time interval was independent of the magnitude of the rate change and the baseline heart rate from which the change occurred. Furthermore, the time course of QT adaptation was found to be exponential and was characterised by a time constant of 49.1(2.2) s when the rate was increasing and 60.4(2.0) s when the rate was decreasing (p less than 0.01). It is concluded that QT measurements in response to a change in pacing rate should take into account the time dependent nature of QT changes.