Quantitation of chronotropic response: comparison of methods for rate-modulating permanent pacemakers

Tachy-brady syndrome: Electrophysiology and evolving principles of management

Sudden alterations in the heart rate may be associated with diverse symptoms. Sinus node dysfunction (SND), also known as sick sinus syndrome, is a sinoatrial (SA) node disorder. SND is primarily caused by the dysfunction of the pacemaker, as well as impaired impulse transmission resulting in a multitude of abnormalities in the heart rhythms, such as bradycardia-tachycardia, atrial bradyarrhythmias, and atrial tachyarrhythmias. The transition from bradycardia to tachycardia is generally referred to as "tachy-brady syndrome" (TBS). Although TBS is etiologically variable, the manifestations remain consistent throughout. Abnormal heart rhythms have the propensity to limit tissue perfusion resulting in palpitations, fatigue, lightheadedness, presyncope, and syncope. In this review, we examine the physiology of tachy-brady syndrome, the practical approach to its diagnosis and management, and the role of adenosine in treating SND.

Design and rationale of the MODULAR ATP global clinical trial: A novel intercommunicative leadless pacing system and the subcutaneous implantable cardioverter-defibrillator

Background

The subcutaneous implantable cardioverter-defibrillator (S-ICD) has demonstrated safety and efficacy for the treatment of malignant ventricular arrhythmias. However, a limitation of the S-ICD lies in the inability to either pace-terminate ventricular tachycardia or provide prolonged bradycardia pacing support.

Objective

The rationale and design of a prospective, single-arm, multinational trial of an intercommunicative leadless pacing system integrated with the S-ICD will be presented.

Methods

A technical description of the modular cardiac rhythm management (mCRM) system (EMPOWER leadless pacemaker and EMBLEM S-ICD) and the implantation procedure is provided. MODULAR ATP (Effectiveness of the EMPOWER™ Modular Pacing System and EMBLEM™ Subcutaneous ICD to Communicate Antitachycardia Pacing) is a multicenter, international trial enrolling up to 300 patients at risk of sudden cardiac death at up to 60 centers trial design. The safety endpoint of freedom from major complications related to the mCRM system or implantation procedure at 6 months and 2 years are significantly higher than 86% and 81%, respectively, and all-cause survival is significantly >85% at 2 years.

Results

Efficacy endpoints are that at 6 months mCRM communication success is significantly higher than 88% and the percentage of subjects with low and stable thresholds is significantly higher than 80%. Substudies to evaluate rate-responsive features and performance of the pacing module are also described.

Conclusion

The MODULAR ATP global clinical trial will prospectively test the safety and efficacy of the first intercommunicating leadless pacing system with the S-ICD. This trial will allow for robust validation of device-device communication, pacing performance, rate responsiveness, and system safety.

Rate adaptive pacing in people with chronic heart failure increases peak heart rate but not peak exercise capacity: a systematic review

Rate adaptive cardiac pacing (RAP) allows increased heart rate (HR) in response to metabolic demand in people with implantable electronic cardiac devices (IECD). The aim of this work was to conduct a systematic review to determine if RAP increases peak exercise capacity (peak VO₂) in line with peak HR in people with chronic heart failure. We conducted a systematic literature search from 1980, when IECD and RAP were first introduced, until 31 July 2021. Databases searched include PubMed, Medline, EMBASE, EBSCO, and the Clinical Trials Register. A comprehensive search of the literature produced a total of 246 possible studies; of these, 14 studies were included. Studies and subsequent analyses were segregated according to comparison, specifically standard RAP (RAPON) vs fixed rate pacing (RAPOFF), and tailored RAP (TLD RAPON) vs standard RAP (RAPON). Pooled analyses were conducted for peak VO₂ and peak HR for RAPON vs RAPOFF. Peak HR significantly increased by 15 bpm with RAPON compared to RAPOFF (95%CI, 7.98-21.97, P < 0.0001). There was no significant difference between pacing mode for peak VO₂ 0.45 ml kg^-1 min^-1 (95%CI, - 0.55-1.47, P = 0.38). This systematic review revealed RAP increased peak HR in people with CHF; however, there was no concomitant improvement in peak VO₂. Rather RAP may provide benefits at submaximal intensities by controlling the rise in HR to optimise cardiac output at lower workloads. HR may be an important outcome of CHF management, reflecting myocardial efficiency.

Heart rate score, a measure related to chronotropic incompetence in pacemaker patients

BACKGROUND

Heart rate score (HrSc) ≥70% in cardiac resynchronization therapy defibrillator and implantable cardioverter-defibrillator subjects predicts 5-year mortality risk. A high HrSc suggests few sensed cardiac cycles above the programmed lower rate.

OBJECTIVE

To determine if HrSc is related to chronotropic incompetence (CI) in pacemaker (PM) subjects.

METHODS

HrSc is the percentage of all atrial-paced and sensed events in the single tallest 10 beats/min histogram bin programmed to DDD 60/min. The prospective LIFE study of PM subjects examined multiple treadmill-based measures of CI. The 1-month postimplant DDD 60/min PM rate histogram prior to treadmill was retrospectively analyzed for HrSc. Measures of CI were applied to submaximal treadmill data in the DDD mode. HrSc was compared to these CI measures and to clinical indications for PM.

RESULTS

The 1-month histogram demonstrated HrSc ≥70% in 43% of subjects. HrSc ≥70% correlated with a clinical diagnosis of sick sinus syndrome (P < .001). CI was present in 34%-88% of subjects by treadmill-based measures. Agreement between treadmill-based measures for CI was poor and varied from 39% to 83%. HrSc ≥70%, as a measure of CI, was most highly correlated with unpaced heart rate <70% of age-predicted maximum heart rate (67%) (odds ratio 3.7, P < .001).

CONCLUSIONS

HrSc ≥70% correlates with treadmill measures of CI and clinical sick sinus syndrome. HrSc ≥70% is a measure of CI in PM subjects that is inexpensive, repeatable, and quantitative.

A new algorithm for optimization of rate-adaptive pacing improves exercise tolerance in patients with HFpEF

AIM

To develop an algorithm for optimization of rate-adaptive pacing settings in heart failure patients with preserved ejection fraction (HFpEF) and permanent cardiac pacing.

METHODS

This is a prospective randomized controlled study. A total of 54 patients with HFpEF, permanent atrial fibrillation (AF), and VVIR pacing were randomized to an intervention group with optimization of rate-adaptation parameters by using cardiopulmonary exercise testing (CPET) and pacemaker stress echocardiography (PASE), and to a control group with conventional programming. CPET, 6-min walk test (6-mwt), echocardiography (echo), Duke Activity Status Index (DASI), and Minnesota questionnaire (MLHFQ) were performed at baseline and after 3 months. PASE was used to exclude exercise-induced ischemia and to determine safe upper sensor rate. Pacing parameters were corrected to achieve optimal heart rate increments of 3-6 bpm for 1 mL/min/kg of VO₂ (oxygen uptake).

RESULTS

After 3 months, the intervention group demonstrated significant improvement of VO₂ peak by 1.64 ± 1.6 mL/min/kg, anaerobic threshold by 1.33 ± 1.3 mL/min/kg, exercise time by 170 ± 98 s, 6-mwt distance by 75 ± 63 m (P < .0001 for all), DASI by 5.23 points (P = .009), MLHFQ-score (reduction by 9 points, P < .0001), and echo parameters (decrease in LA volume from 108 (84; 132) to 95 (85; 130) mL, P = .026; E/e' from 11.7 ± 3.2 to 10.4 ± 2.9, P = .025; systolic pulmonary artery pressure (SPAP) from 44 ± 14 to 39 ± 12 mm Hg, P = .001) compared to the control group.

CONCLUSION

An algorithm incorporating CPET and PASE for optimal programming of rate-adaptation parameters is a valuable tool to improve exercise capacity in HFpEF patients with permanent AF and VVIR pacing who remain exercise intolerant after conventional programming.

A blended sensor restores chronotropic response more favorably than an accelerometer alone in pacemaker patients: the LIFE study results

BACKGROUND

Adaptive rate sensors used in permanent pacemakers incorporate an accelerometer (XL) to increase heart rate with activity. Limited data exists regarding the relative benefit of a blended sensor (BS) (XL and minute ventilation) versus XL alone in restoring chronotropic response (CR) in chronotropically incompetent (CI) patients.

METHODS

One thousand five hundred thirty-eight patients from the limiting chronotropic incompetence for pacemaker recipients (LIFE) study were implanted with a pacemaker and 1,256 patients had data collected at 1 month. Patients performed a treadmill test 1-month postimplant while programmed in nonrate responsive mode (DDD-60) to determine CI. Only patients who completed at least three exercise stages and achieved a peak perceived exertion >or=16 were included in the analyses. The metabolic chronotropic relationship (MCR) slope was used to evaluate CR in 547 patients. Patients were randomized to XL or BS with a conservative fixed rate response factor (XL = 8, MV = 4). CI patients performed a follow-up 6-month treadmill test.

RESULTS

CI prevalence in this patient population (n = 547) was 34%. No differences in baseline characteristics existed between groups. Although both groups showed significant within-group improvements in MCR slope from 1 to 6 months (both P < 0.001), the BS group had a significantly higher MCR slope at 6 months compared to the XL group (P = 0.011). Improvement in quality of life (QOL) did not differ between groups.

CONCLUSIONS

In this general pacemaker population with CI, a BS programmed empirically restores CR more favorably than an XL sensor programmed nominally. Further studies are needed to determine if individual sensor optimization would lead to improvement in functional capacity, higher MCR slopes, and QOL.

Development of Implantable Devices for Continuous Ambulatory Monitoring of Central Hemodynamic Values in Heart Failure Patients

BACKGROUND

Care and management of patients with congestive heart failure (CHF) is a major health-care challenge. The value of acute hemodynamic data in assessing heart failure has been questioned in some studies, while more intensive hemodynamic monitoring has been reported to improve patient care in others. A series of patient studies are reported here that were conducted to identify device requirements and verify the feasibility of continuous hemodynamic monitoring in CHF patients and devices for remote transfer and use of these data.

METHODS AND RESULTS

The results of four separate studies in 68 CHF patients who received systems for chronic hemodynamic monitoring between 1992 and the present are reviewed. One early study was with five patients followed for 7-16 months and another study was with nine patients followed for 4-22 months. A third study included 21 patients followed up to 39 months, and the fourth study included 32 patients implanted in 1998-99 with many of them still in follow-up. These studies support the technical feasibility of implanted devices and the external instrumentation required to transfer and manage the collected data. They also support the long-term stability and accuracy of these systems. Three additional acute studies conducted with 30 patients and chronic data from 53 of the 68 patients with the implanted systems are presented that support the feature included in the newer monitors--the ability to reliably estimate pulmonary artery diastolic pressures from the right ventricular pressure signal.

CONCLUSIONS

Development of implantable technology to measure several hemodynamic variables in ambulatory CHF patients is feasible. External instrumentation needed to remotely acquire data from the implanted devices has been verified. The potential to eliminate the uncertainties associated with the use of acute, invasive hemodynamics and the ability to evaluate long-term ambulatory hemodynamic patterns is provided. These findings set the stage for determining the potential clinical value of these systems in impacting the care of chronic CHF patients.

Individual optimization of pacing sensors improves exercise capacity without influencing quality of life

INTRODUCTION

Programmable pacemaker sensor features are frequently used in default setting. Limited data are available about the effect of sensor optimization on exercise capacity and quality of life (QOL). Influence of individual optimization of sensors on QOL and exercise tolerance was investigated in a randomized, single blind study in patients with VVIR, DDDR, or AAIR pacemakers.

METHODS

Patients with > or =75% pacing were randomized to optimized sensor settings (OSS) or default sensor setting (DSS). Standardized optimization was performed using three different exercise tests. QOL questionnaires (QOL-q: Hacettepe, Karolinska, and RAND-36) were used for evaluation of the sensor optimization. One month before and after optimization, exercise capacity using chronotropic assessment exercise protocol and the three QOL-q were assessed.

RESULTS

Fifty-four patients (26 male, 28 female) with a mean age of 65 +/- 16 years were enrolled in the study. In each group (OSS and DSS) 27 patients were included. One month after sensor optimization, the achieved maximal heart rate (HR) and metabolic workload (METS) were significantly higher in OSS when compared with DSS (124 +/- 28 bpm vs 108 +/- 20 bpm, P = 0.036; 7.3 +/- 4 METS vs 4.9 +/- 4 METS, P = 0.045). Highest HR and METS were achieved in patients with pacemakers with accessible sensor algorithms. In patients with automatic slope settings (33%), exercise capacity did not improve after sensor optimization. QOL did not improve in OSS compared with DSS.

CONCLUSION

After 1 month of individual optimization of rate response pacemakers, exercise capacity was improved and maximum HR increased, although QOL remained unchanged. Accessible pacemaker sensor algorithms are mandatory for individual optimization.

Direct Comparison of a Contractility and Activity Pacemaker Sensor During Treadmill Exercise Testing

There are limited data about the chronotropic capacity of the peak endocardial acceleration (PEA) sensor. This study directly compared the chronotropic function from the PEA and the activity (ACT) sensor. The study included 18 patients (age 73 +/- 7 years) with > or = 75% pacemaker-driven heart rate (HR) and a PEA sensor and 11 healthy controls (age 67 +/- 7 years) underwent a chronotropic assessment exercise protocol (CAEP) exercise test with the pacemaker patients in VVIR mode after programming the sensors in the default setting with adjustment of the upper sensor rate as an age related maximum value (220-age). The ACT sensor was externally strapped on the thorax. Achieved exercise duration for the patients and controls was, respectively, 9.2 +/- 3 vs 18.4 +/- 4 minutes (P <0.001). The maximal achieved HR with the PEA sensor was 124 +/- 25 beats/min, versus the ACT with 140 +/- 23, versus the controls with 153 +/- 26 beats/min (P <0.001 between the groups). For the PEA, ACT, and controls, the time to peak HR was, respectively, 11 +/- 3, 7 +/- 3.6, and 18 +/- 4 (P <0.001 between groups) and HR after 10 minutes recovery was, respectively, 80 +/- 20, 65 +/- 15, and 82 +/- 4 beats/min (P <0.001 between groups). The PEA sensor functions hypochonotroop during exercise programmed as a single sensor system. It is, therefore, preferable to combine the PEA sensor with an activity-based sensor in a dual sensor system. Although both groups had normal left ventricular functions, the exercise capacity of pacemaker patients is significantly lower than in the controls.

Comparison of the cardiopulmonary response to exercise in recipients of dual sensor DDDR pacemakers Versus a Healthy control group

The authors previously have shown in healthy subjects that age related loss of muscular strength did not alter the chronotropic response during treadmill exercise, whether with sudden onset of effort, as in the chronotropic assessment exercise protocol (CAEP) or more gradual effort as in the Harbor exercise protocol. This study was performed to verify that in patients suffering from chronotropic insufficiency, and in absence of other effort-limiting disorders, "physiologic" pacing enables a cardiorespiratory response comparable to that of age-matched healthy subjects. Furthermore, the aim of the study was to confirm that the response of a new dual sensor-based pacing system was properly adapted to the metabolic demand, whether during CAEP or during Harbor test, by subjecting patients to both protocols. All study participants were able to undergo treadmill exercise testing, had normal cardiopulmonary function tests at rest, and no cardiac, muscular, or pulmonary disease. A healthy group (control) included 16 subjects (mean age 70.4 +/- 3.9 years), and the test group (pacemaker [PM] included 9 subjects (mean age 67.1 +/- 10.8 years) permanently paced for isolated chronotropic insufficiency with a dual sensor pacing system. All subjects underwent CAEP and Harbor tests with measurements of gas exchange, 24 hours apart, in randomized order. All subjects reached an appropriate level of exercise, as expressed by mean lactate plasma concentrations, which were slightly higher in the control than the PM group during CAEP (4.9 +/- 1.9 vs 3.7 +/- 1.9 mmol/L, NS) and Harbor (5.3 +/- 1.9 vs. 3.8 +/- 1.8 mmol/L, P < 0.05) tests. No statistical difference was observed in VO2 and VE at peak exercise between the two groups during either test. In the PM group, heart rate at peak exercise and metabolic reserve slope were higher during the CAEP than the Harbor protocol. These two measurements were significantly lower than in the control group. The PM group also had lower plasma lactate concentrations and dyspnea/fatigue scores. The Harbor test seems less suitable than the CAEP test to study the chronotropic response of pacemakers with dual sensors during exercise. A high performance of the new dual sensor-based pulse generator was confirmed in this physically fit patient population, whose peak heart rate was considerably higher than in other similar studies.

Current status of dual-sensor pacemaker systems for correction of chronotropic incompetence

Rate-adaptive pacing has been shown to improve exercise capacity in patients with chronotropic incompetence. However, all sensors used to adapt the pacing rate to meet metabolic demands show typical limitations. To overcome these, concepts using 2 sensors for rate adaptation have been developed, combining an unspecific but fast-reacting sensor with a specific but slower-reacting one. Clinical performance of these dual-sensor pacemaker systems is related to 3 factors: (1) choice of sensors, (2) mode of sensor integration, and (3) algorithms for automatic optimization of the integrated sensor response. Clinical studies using dual-sensor rate-adaptive pacing systems have demonstrated their ability to mimic normal sinus rate during different forms of exercise, avoiding inadequate or delayed rate response. However, to avoid combining the disadvantages of both single sensors, dual-sensor rate-adaptive systems need effective automatic algorithms. Sensor cross-check should be quick and combine fast reactivity and high specificity, particularly so as to prevent overpacing. Programmable rate response-related parameters should continuously be optimized. The pacemaker should provide diagnostic facilities during exercise to simulate short-term sensor performance at different settings and memory functions to evaluate long-term sensor performance. Assessment and eventually deactivation of all automatic functions should be possible. Finally, even with automatic algorithms for sensor optimization, maximal benefit from a dual-sensor system can only be achieved if the physician is able to identify and correct pitfalls of each system.

Programming of sensor driven pacemakers

The chronotropic response is the most important means by which cardiac output is increased and oxygen delivery is maintained in response to increased oxygen consumption during exercise or stress. When the chronotropic response is suboptimal or absent, exercise intolerance results. This condition, called chronotropic incompetence can be treated effectively with a sensor-driven rate-responsive pacemaker. The effectiveness of this therapy assumes that the pacemaker is programmed appropriately. This article focuses on the programming of sensor-driven pacemakers and provides additional suggestions for follow-up testing to ensure maximal benefit from these devices.

Oxygen uptake to work rate relation throughout peak exercise in normal subjects: relevance for rate adaptive pacemaker programming

The oxygen uptake to work rate (VO2/WR) relationship observed throughout peak exercise testing is already being applied for rate adaptive pacemaker programming. However, the detailed curve design of VO2/WR with respect to the anaerobic threshold (AT) has not yet been investigated. It was the purpose of this study to determine the VO2/WR slope below and above the AT in a healthy control group. Seventy-eight healthy control subjects (45.9 +/- 17.4 years; 34 women: 49.9 +/- 18.6 years 44 men: 43.6 +/- 16.6 years) were exercised on a treadmill with "breath-by-breath" gas exchange monitoring using the symptom limited "ramping incremental treadmill exercise" (RITE) protocol. The slope of the VO2/WR relationship from rest to peak exercise (r-p), rest to AT (slope A), and AT to peak exercise (slope B) in mL oxygen uptake per watt of external treadmill work was determined by linear regression analysis. [table: see text] The oxygen uptake to work rate relationship throughout peak exercise in the entire study group generated a significant slope change at the AT (31%, P < 0.0001) with a decreasing slope during higher work load intensities. Female subjects demonstrated a greater percentage of slope change at AT (43%), as compared to men (22%, P < 0.01). When using the oxygen uptake to work rate relationship for the programming of the pacemaker's rate response to exercise, the significant slope change at the AT should be considered to more appropriately pace during higher work intensities supported by anaerobic metabolism. Female pacemaker patients should be programmed to generate a steeper VO2/WR slope below AT with a greater slope change at AT, as compared to men. Abnormally high oxygen uptake to work rate ratios above the AT may be possibly used as an indicator of overpacing.

Cardiac output is a sensitive indicator of difference in exercise performance between single and dual sensor pacemakers

Although multisensor pacing may compensate the inadequacy of rate adaptation in a single sensor system, the clinical role of multisensor driven rate adaptive pacing remains unclear. We compared the performance between single sensor and dual sensor driven pacemakers using exercise cardiac output (CO) as a marker of cardiac performance. Eight patients with a mean age of 63 +/- 3 years implanted with a dual sensor pacemaker driven by combined activity (ACT) and QT interval sensors were studied in the ACT-, QT- only and the dual QT + ACT-VVIR modes. Patients performed submaximal and maximal exercise tests with CO assessed by carbon dioxide rebreathing method. Comparing the HR response based on the change in metabolic workload, the ACT-VVIR "overpaced," the QT-VVIR "underpaced," and the QT + ACT-VVIR achieved the best approximation to normal. The percentages of CO increase in ACT-VVIR and QT + ACT-VVIR modes over resting CO were higher at 1 minute of exercise (295 +/- 85% and 165 +/- 49%, respectively) compared to the QT-VVIR mode (81 +/- 40%, P < or = 0.05). During exercise, stroke volume changes from baseline were similar between ACT-VVIR and QT + ACT-VVIR modes, but a compensatory increase in stroke volume occurred in the QT-VVIR mode during submaximal exercise (50 +/- 11 mL vs 24 +/- 17 mL in the QT + ACT-VVIR and 14 +/- 4 in ACT-VVIR, P < or = 0.003). There was no difference in the maximal exercise workload, exercise duration and CO at the submaximal and maximal exercise between the 3 sensor modes. Thus, exercise capacity is a poor indicator of sensor performance while CO measurement is a sensitive indicator of sensor mode differences especially at low workload exercise. The ACT-VVIR gave the fastest increase in CO at start of exercise at the expanse of overpacing, whereas the "under-paced" QT-VVIR compensated for the slower rate increase by utilizing contractility reserve during submaximal exercise. Dual sensor pacing, by achieving the best heart rate to workload relationship, provided a CO response without overpacing or using contractility reserve during exercise.

A prospective multicenter study demonstrating clinical benefit with a new accelerometer-based DDDR pacemaker. Dromos Dr Investigators Group

From November 1994 to October 1995, 63 patients (average age 66 years; 41 men) from 15 centers implanted with the Biotronik Dromos DR and Ergos TC 03 pulse generators were prospectively screened with an exercise test in the DDD mode for the presence of chronotropic incompetence (CI). Both pulse generators incorporate an identical accelerometer-based motion sensor. CI was defined as a maximum heart rate < 60% of age predicted maximum heart rate or 100 beats/min. Twenty-five patients (40%) met the criteria for CI. Two weeks later, CI patients were required to complete paired metabolic exercise testing in the DDD and DDDR modes on consecutive days with a 24-hour rest period. The order of testing was randomized and performed double blinded to minimize potential biases. Three patients who did not reach the anaerobic threshold (AT) and one patient who was unable to perform the metabolic testing were excluded from the analysis. Compared to the DDD mode, there were statistically significant improvements in the DDDR mode for all five endpoints: heart rate (84 +/- 3.6 vs 113 +/- 3.5 beats/min; P < 0.0001); total exercise time (8.23 +/- 0.71 vs 9.15 +/- 0.65 min; P = 0.0005); maximum VO2 (17.76 +/- 1.36 vs 20.43 +/- 1.75 mL/kg per min; P = 0.0001); VO2 at AT (13.1 +/- 0.87 vs 14.59 +/- 0.79 mL/kg per min; P < 0.01); and exercise time to AT (5.65 +/- 0.61 vs 6.33 +/- 0.53 min; P = 0.02). In conclusion, the results of paired metabolic exercise tests with the Dromos DR and Ergos TC 03 pulse generators demonstrate a clear clinical benefit using the accelerometer-based sensor in the CI patient.

Heart rate to work rate relation throughout peak exercise in normal subjects as a guideline for rate-adaptive pacemaker programming

We investigated the physiologic heart rate (HR) to work rate (WR) relation throughout peak exercise in normal subjects as a guideline for rate-adaptive pacemaker slope programming. The study group consisted of 41 middle-aged subjects (22 men and 19 women) without evidence of cardiopulmonary disease. Peak-exercise stress tests were performed on a calibrated treadmill by using the symptom-limited "ramping incremental treadmill exercise" (RITE) protocol. The HR response, oxygen uptake, and treadmill workload increments were assessed simultaneously. The HR/WR slope, as determined using linear regression analysis, was 0.37 +/- 0.13 beats/min/W for the entire study group, which indicates an upper range increase of 5 beats/10 W increase of external treadmill work performed, using the mean value +/- 1 SD. Men generated an HR/WR slope of 0.32 +/- 0.09 beats/min/W, and women, 0.43 +/- 0.15 beats/min/W, indicating a significant sex-related difference in the HR/WR relation (p < 0.01). Thus, to achieve an appropriate matching of HR with patient effort, rate-adaptive pacemakers should generate an average increase of approximately 5 beats per increase in 10 W of external treadmill work. The HR/WR relation can easily be determined to provide the clinician with a minimal check system to avoid a hyper- or hypochronotropic paced response to exercise.

Rate adaptive cardiac pacing using right ventricular venous oxygen saturation: quantification of chronotropic behavior during daily activities and maximal exercise

Central venous oxygen saturation (SvO2) closely reflects cardiac output and tissue oxygen consumption. In the absence of an adequate chronotropic response during exercise, SvO2 will decrease and the extent of desaturation may be used as a parameter for rate adaptive cardiac pacing. Eight patients with sinoatrial disease received a DDDR pacemaker capable of DDDR pacing by sensing either SvO2 or piezoelectric detected body movement. Both sensors were programmed to attain a rate of about 100 beats/min during walking, and with the lower and upper rates set at 50% and 90% of age predicted maximum, respectively. Chronotropic behavior of the two sensors were compared in the DDD mode with measurement of sensor responses, during everyday activities (walking, stair climbing, postural changes, and physiological stresses) and at each quartile of workload during a continuous treadmill exercise test. During walking at 2.5 mph, both sensors showed no significant difference in delay time (both react within 15 secs) or half-time (SvO2 = 36 +/- 12 sec and activity 24 +/- 3 sec; P = NS), although SvO2 driven pacing achieved 90% target rate response slower than activity sensing (124 +/- 16 sec vs 77 +/- 10 sec; P < 0.02). SvO2 pacing was associated with a more physiological rate response during walking upslope (68 +/- 12 beats/min vs 57 +/- 10 beats/min; P < 0.05), ascending stairs (59 +/- 10 beats/min vs 31 +/- 6 beats/min; P < 0.05), and standing (34 +/- 7 beats/min vs 9 +/- 2 beats/min; P < 0.05). The SvO2 sensor significantly overpaced in the first quartile of exercise (51.8 +/- 25.6% in excess of heart rate expected from workload), but the rate was within 20% of expected for the remainder of exercise. "Underpacing" was observed with the activity sensor at the higher workload. In conclusion, the SvO2 sensor demonstrated a more physiological response to activities of daily living compared with the activity sensor. Using a quantitative method, the speed of onset of rate response of the SvO2 sensor was comparable to activity sensing, and was more proportional in rate response. Significant overpacing occurs at the beginning of exercise during SvO2 driven pacing, which may be improved with the use of a curvilinear algorithm.

Effect of chronotropic response pattern on oxygen kinetics

BACKGROUND

The sinus node is considered to be the model of chronotropic response for pacemakers that use artificial rate modulating sensors. Maximal metabolic exercise testing with measurement of oxygen consumption (VO2) is frequently used to evaluate chronotropic response. Since activities of daily living are generally transient and involve submaximal effort, maximal exercise testing may not provide the most clinically relevant method of assessing rate modulation. The purpose of this study was to determine if an abrupt increase in heart rate (HR) at the onset of submaximal exercise provides improved oxygen kinetics compared with a linear response.

METHODS AND RESULTS

Thirteen patients with complete heart block and permanent rate modulating pacemakers implanted following catheter ablation of the atrioventricular junction for refractory atrial fibrillation were chosen for study. The patients first completed a maximal treadmill exercise test using the chronotropic assessment exercise protocol with breath-by-breath analysis of expired gases. The expected HR at 50% of metabolic reserve was calculated for each patient. Three submaximal constant workload exercise tests were then performed at 50% of each patient's metabolic reserve, with the pacemaker randomly programmed to provide three different patterns of chronotropic response: linear (in which HR increased from 70 beats/min to the expected HR at 50% of metabolic reserve), fast (in which HR was abruptly increased to the expected HR at 50% of metabolic reserve), and slow (VVI at 70 beats/min). Oxygen kinetics were compared for the three patterns of chronotropic response. Cumulative oxygen (O2) consumption was significantly greater for the fast pattern (3610 mL) as compared with the linear (3487 mL, P = 0.004) or slow pattern (3277 mL). The O2 deficit was lower for the fast (361 +/- 139 mL) than for the linear (539 +/- 225 mL, P = 0.003) or slow chronotropic pattern (559 +/- 194). Similar improvements in the rate constant of O2 uptake and Borg perceived exertion scores were observed with the fast chronotropic response pattern.

CONCLUSION

A rapid increase in pacing rate at the onset of exercise improves oxygen kinetics and results in less perceived exertion as compared to a more gradual rate increase that is more characteristic of sinus node behavior.

Clinical study of a new activity sensor for rate adaptive pacing controlled by electrical signals generated by the kinetic energy of a moving magnetic ball

A new rate adaptive pacemaker (Sensorithm) controlled by an activity sensor providing electrical signals induced by a magnetic ball moving freely in an elliptical cavity surrounded by two copper coils, was implanted in ten patients; mean age of 75 years (range 64-89). Six patients had atrioventricular block and four had sinus node disease. In auto-set testing procedure during a 1-minute walk in the corridor, a slope resulting in a maximum rate of 95 beats/min was selected in every patient, and a medium reaction time was programmed. During graded treadmill exercise tests the heart rate increased 63 +/- 7 beats/min to 135 +/- 6 beats/min in rate adaptive pacing mode (VVIR), and 15 +/- 6 beats/min (P < 0.0001) in ventricular pacing mode (VVI). The symptom-limited exercise time was 9.1 +/- 1.1 minutes and 8.2 +/- 1.2 minutes (P = NS), and the exercise distance was 501 +/- 95 meters and 428 +/- 92 meters (P < 0.05) in VVIR and VVI pacing mode, respectively. The maximum oxygen uptake was 20.6 +/- 2.6 mL/kg per minute in VVIR pacing and 18.1 +/- 2.1 mL/kg per minute (P < 0.05) in VVI pacing. The delay time until the pacing rate increased 10% of the total rate increase at onset of treadmill exercise was 4.4 +/- 0.7 seconds.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative comparison of rate response and oxygen uptake kinetics between different sensor modes in multisensor rate adaptive pacing

Although multisensor pacing may mitigate the inadequacy of rate adaptation in a single sensor system, the clinical role of multisensor driven rate adaptive pacing remains unclear. The cardiopulmonary performance of six patients (mean age 63.5 +/- 10 years) who had undergone the implant of combined QT and activity VVIR (Topaz) pacemakers was assessed during submaximal and maximal treadmill exercise with the rate response sensor randomly programmed to either single sensor mode, QT and activity (ACT), or dual sensor mode, with equal contribution of QT and ACT (QT = ACT). The rate of response, the proportionality, oxygen kinetics, and maximal exercise performance of the various sensor modes during exercise were measured and compared. The ACT sensor mode "overpaced" and the QT and QT = ACT sensor modes "underpaced" during the first three quartiles of exercise (P < 0.05). The ACT sensor mode also gave the fastest rate of response with the shortest delay (13 +/- 1.5 sec vs 145 +/- 58 sec and 41 +/- 17 sec, P < 0.05), time to 50% rate response (39 +/- 2.7 sec vs 275 +/- 48 sec and 203 +/- 40 sec, P < 0.05), and time to 90% of rate response (107 +/- 21 sec vs 375 +/- 34 sec and 347 +/- 34 sec, P < 0.05) and a smaller oxygen debt (0.87 +/- 0.16 L vs 1.10 +/- 0.2 L and 1.07 +/- 0.18 L, P < 0.05) compared to the QT and QT = ACT sensor modes, respectively. These differences were most significant at low exercise workloads. Thus, different sensor combinations result in different rate response profiles and oxygen delivery, especially during low level exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Rate modulated pacing based on right ventricular dP/dt: quantitative analysis of chronotropic response

Right ventricular contractility increases in response to catecholamine stimulation and greater ventricular preload, factors that increase with exercise workload. Thus, the maximum systolic dP/dt may be a potentially useful sensor to control the pacing rate of a permanent pacing system. The present study was designed to test the long-term performance of a permanent pacemaker that modulates pacing rate based on right ventricular dP/dt and to quantitatively analyze the chronotropic response characteristics of this sensor in a group of patients with widely varying structural heart diseases and degrees of hemodynamic impairment. A permanent pacing system incorporating a high fidelity pressure sensor in the lead for measurement of right ventricular dP/dt was implanted in 13 patients with atrial arrhythmias and AV block, including individuals with coronary artery disease, hypertension, severe obstructive pulmonary disease with prior pneumonectomy, atrial septal defect, dilated cardiomyopathy, restrictive cardiomyopathy, and mitral stenosis. Patients underwent paired treadmill exercise testing in the VVI and VVIR pacing modes with measurement of expired gas exchange and quantitative analysis of chronotropic response using the concept of metabolic reserve. The peak right ventricular dP/dt ranged from 238-891 mmHg/sec with a pulse pressure that ranged from 19-41 mmHg. There was a positive correlation between the right ventricular dP/dt and pulse pressure (r = 0.70, P = 0.012). The maximum pacing rate and VO2max were 72 +/- 6 beats/min and 12.61 +/- 4.0 cc O2/kg per minute during VVI pacing and increased to 124 +/- 18 beats/min and 15.89 +/- 5.9 cc O2/kg per minute in the VVIR pacing mode (P < 0.0003 and P < 0.002, respectively). The integrated area under the normalized rate response curve was 96.7 +/- 45.7% of expected during exercise and 100.1 +/- 43.4% of expected during recovery. One patient demonstrated an anomalous increase in pacing rate in response to a change in posture to the left lateral decubitus position. Thus, the peak positive right ventricular dP/dt is an effective rate control parameter for permanent pacing systems. The chronotropic response was proportional to metabolic workload during treadmill exercise in this study population with widely varying forms of structural heart disease.