Increasing Cardiac Rate by Measurement of Right Ventricular Temperature

Un stimulateur qui augments sa Fréquence en fonction de l'exercice permet au patient d'améliorer son état de bien-être. Les capteurs pourraient utiliser la fréquence auriculaire, l'espace QT, le pH, la saturation d'oxygène du sang veineux, la fréquence ventilatoire, le débit cardiaque, les mouvements du corps et la température sanguine. Afin de déterminer l'éfficacité de la reconnaissance de l'exercice par utilisant la température du sang du ventricule droit, un stimulateur expérimental a été développé et évalué chez le chien. Un algorithme a été incorporé dans un stimulateur VVI comportant un microprocesseur, qui pourrait détecter l'exercice et le repos à partir de la température sanguine Deux fréquences de stimulation étaient done possibles pour améliorer le débit cardiaque. Des etudes sont en cours peur démontrer la fisabilité d'un tel systéme chez l'homme.     

The Central Venous Blood Temperature as a Guide for Rate Control in Pacemaker Therapy

True physiologic pacing is only feasible in patients with heart block and normal sinus rhythm using atrial synchronized pacing. In sick sinus syndrome (SSS) or atrial fibrillation no adequate sensing possibility is present. For these conditions something other than electrical signals must be found to guide rate control. In clinical experiments a thermistor integrated in a bipolar pacing lead was implanted in one of the authors as well as in a pacemaker patient. Treadmill tests at 3, 6, and 10 km per hour have shown no substantial increase of the central venous temperature (CVT) in the lower effort range; an increase of 0.6-0.75 degrees Celsius (degrees C) in the medium range; and an increase of 1.35 degrees C in the higher range, respectively. External pacing in the author, or rate variations by programming the VVI, M unit in the patient at rest do not influence CVT. CVT correlates well in the medium-range group, which mostly reflects the capabilities of the average pacemaker patient. In the higher effort range a delay between rate increase and increase of CVT is noticed. There is no increase in CVT beyond the physiologic variations in the lower effort range.     

A Central Venous Temperature Sensing Lead

Pacemaker rate responsiveness derived from changing central venous blood temperature requires the development of sensor leads that are stable and reliable. The relevant characteristics of one such design are described. Temperature response time, data acquisition time, temperature sensitivity, and long-term sensor shunt impedance have been studied both in vitro and in vivo. These parameters are analyzed with respect to the intrinsic temperature signal and to pacemaker implementation problems.     

Measurement of Right Ventricular Blood Temperature During Exercise as a Means of Rate Control in Physiological Pacemakers

Several biological parameters have been suggested for rate control in physiological pacemakers in the past. Up to now, measurements of central venous blood temperature have been mostly done on dogs. We studied central venous blood temperature and heart rate in 14 healthy volunteers under conditions of treadmill and bicycle exercise with different workloads. A custom made 5F lead with a thermistor incorporated near the tip was placed at the right ventricle under fluoroscopic control. Temperature was recorded with an accuracy of 1/100°C on a digital memory device at a sampling rate of 5–10 s. We found the increase in blood temperature to be not only a function of absolute workloads but also a function of the individual's maximum exercise tolerance. Independent of the absolute increase in heart rate and temperature at a given workload, the individual's relation of increase in temperature and heart rate was found to be highly correlating (r = 0.9095). At a load of 100 W, we found a mean increase in heart rate of 52 beats and of temperature of 0.57°C, at 750 W of 74 beats/min and 0.84°C. During, as well as after, the exercise, heart rate and temperature have a parallel course. According to our data, control of physiological pacemakers by means of central venous blood temperature is possible.     

Subclavian Venogram as a Guide to Lead Implantation

Recent reports have raised doubts regarding the safety and efficacy of the blind subclavian venipuncture technique for intra-cardiac lead implantation. To permit a more lateral entry, we used a simple subclavian venogram performed through the brachial vein of the ipsilateral arm of 22 consecutive unselected patients undergoing had implantation (19 permanent pacemakers and 3 intracardiac defibriUators). A total of 35 leads were implanted (31 left pectoral and 4 right pectoral). Lead insertion by venogram technique was used successfully in all patients. Two inconsequential arterial punctures occurred. There were no pneumotho-races, infections, or other complications. Lateral placement should facilitate lead manipulation and minimize "subclavian crush." The method of ipsilateral venogram guided lead insertion appears to be safe and reliable and deserves consideration in patients who require permanent lead placement via the subclavian vein approach.     

Overnight Heart Rate and Cardiac Function in Patients with Dual Chamber Pacemakers

Animal data indicate that chronic, overnight pacing at normal evening heart rates impairs cardiac function. We examined the relationship of pacing rate and cardiac function in nine patients with dual-chamber pacemakers. We investigated two, 3-week pacing regimens (80 and 50 ppm: DDD mode) in a cross-over design. Doppler echocardiograms were performed at 1700 hours (PM) and 0600 hours (AM) at the end of each regimen. Ventricular function and preload decreased overnight (PM vs AM) with both pacing regimens. Compared to the morning values, the ratio of preejection to ejection time (PEP/ET) rose (0.43 vs 0.46), while the mean velocity of circumferential fiber shortening (V_cf) fell (1.16 cm/s vs 1.11 cm/s). Stroke volume (SV) (61 mL vs 53 mL) and ejection fraction (EF) also fell (0.56 vs 0.53) in the morning, End-diastolic volume (EDV) (94 mL vs 88 mL) decreased in the morning, as did the ratio of passive to active filling (E/A) (1.06 vs 0.96). Iscvolumic relaxation time(91 msvs 101 ms) increased overnight at both pacing rates. Systolic function decreased at 80 ppm relative to 50 ppm at both times of day. SV fell (54 mL vs 61 mL), while both EDV (92 mL vs 90 mL) and end-systolic volume (ESV) increased (43 mL vs 40 mL). Contractility measured by V_cf(1.09 cm/s vs 1.18 cm/s) and PEP/ET (0.49 vs 0.41) was reduced at 80 ppm. The heart needs to rest at night by slowing its rate of contraction. Pacing at 80 ppm impairs systolic and diastolic ventricular function compared to 50 ppm. Longer term consequences of ostensibly physiological pacing rates merit inquiry, particularly in those with preexisting cardiac dysfunction.     

Standardized Informal Exercise Testing for Programming Rate Adaptive Pacemakers

t is essential that patients with pacemakers capable of rate modulation undergo some form of exercise testing to assure appropriate rate modulation, Informal exercise testing is a reasonable and Jess expensive alternative to formal treadmill testing. Empiric adjustment of the rate response parameters by assessing the patient's rate response while walking at a self-determined casual and brisk pace has been used. However, no normals exist to determine the appropriate rate response for a "casual" and "brisk" walk. Volunteers were tested with metronome-guided casual and brisk walks in an effort to standardize the informal exercise and determine expected heart rate response for these levels of activity, Results of the metronome-guided rate response in normal volunteers may be useful in determining the appropriate rate response for pacemaker patients when tested in such an informal manner.     

Right Ventricular Blood Temperature Profiles for Rate Responsive Pacing

To establish the efficacy of a temperature-based pacemaker control algorithm, right ventricular temperature and heart rate were measured for 12–70 hours in eight patients (51 ± 17 years) and in one normal volunteer (28 years) during a variety of activities including exercise, rest, sleeping, eating, drinking, and bathing. A diurnal variation in heart rate and temperature was observed. Drinking caused transient temperature changes (less than one minute); during eating, increases of 0.07–0.36°C over 3–12 minutes were observed. An increase of 0.24°C over 8.5 minutes was observed in one patient during bathing. An abrupt drop in temperature was typically observed at the onset of exercise, followed by a steady temperature rise. During treadmill exercise, after a drop (0.13–0.48°C, Bruce n - 4; 0A6–0.34°C, Naughton, n = 3) during the first 1–2 minutes, temperature rose steadily through the end of peak exercise (0.45–1.01°C, Bruce; 0.28–0.47°C, Naughton). A temperature dip was also observed when a patient was told exercise would start but the treadmill failed to turn on. The dip is probably secondary to changes in blood flow from the peripheral circulation to the central system at the onset of exercise. Repeated exercise separated by short rests caused progressive blunting of the initial dip. Right ventricular temperature changes in a predictable manner with daily activity, allowing a temperature algorithm to detect rest and exercise.     

Effects of Body Constitution and Age on Maximum Pacing Rate of Activity-Modulated Rate Responsive Pacemakers

The pacing rate of activity-modulated pacemakers is triggered by vibrations running through the body. Whether the body constitution predicts maximum pacing rate and may facilitate rate response programming was studied in 16 patients with Activitrax pacemakers. Rate response parameters were programmed to a fixed setting in VVIR/VOOR mode (lower pacing rate 60 ppm, upper pacing rate 125-130 ppm, activity threshold medium/7). Body vibrations were induced by a treadmill exercise test with increasing speed. Maximum pacing rates were measured at the stage of symptom-limited tolerance. Exercise tests with a duration of 7.3 +/- 2.9 minutes resulted in a maximum pacing rate of 98 +/- 22 ppm ranging from 60-122 ppm. Maximum pacing rates did not differ between male (n = 10; 102 +/- 21 ppm) and female (n = 6; 92 +/- 24 ppm). Correlations between maximum pacing rates and body constitutional factors were not significant with r = -0.15 (weight), r = 0.39 (height), r = 0.07 (body surface area), and r = -0.27 (skin-fold thickness). The correlations with body mass index (r = -0.53) and age (r = -0.53) were initially significant, but not after Bonferroni-Simes-Hommel correction. The age-dependent relationship may be caused by the shorter exercise duration of older patients indicated by the correlation between exercise duration and maximum pacing rate (r = 0.77), as well as with age (r = -0.73). Conclusions: body constitution did not modify body vibrations and did not allow prediction of maximum pacing rates; therefore, it is no aid for the programming of rate response parameters.     

Should a VVIR Pacemaker Increase the Heart Rate with Standing?

To assess the usefulness of incorporating a posture sensor into a ventricular inhibited rate modulated pacemaker, the hemodynamic effects of increasing the ventricular pacing rate with standing were studied in 15 pacemaker dependent patients aged 55 +/- 3.5 years. In a randomized cross-over design, the pacing rate remained at 70 or was increased to 100 beats/min immediately prior to standing. Blood pressure was monitored continuously and forearm blood flow was measured by venous occlusion plethysmography. There was no difference in supine blood pressure (117 +/- 4/63 +/- 3 compared to 118 +/- 5/64 +/- 4 mmHg) or forearm blood flow (2.88 +/- 0.36 vs 2.94 +/- 0.32 mL/100 mL/min) before the 70 or 100 pacing rate intervention. With standing, blood pressure fell to an equivalent degree at the two pacing rates (fall in mean blood pressure at 70 beats/min 6 +/- 4 and at 100 beats/min 8 +/- 2 mmHg, P = 0.7). After 1 minute of standing differences in blood pressure were similar, but after 2.5 minutes of standing the increase in mean blood pressure was less at 70 than at 100 beats/min (increase from control 28 +/- 2 compared to 36 +/- 3 mmHg, P = 0.002). Forearm blood flow decreased after standing for 1 and 2.5 minutes but there was no difference between the 70 and 100 pacing rates (fall in forearm blood flow at 2.5 minutes 0.50 +/- 0.24 and 0.59 +/- 0.25 mL/100 mL/cm2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiac Pacemaker Regulated by Respiratory Rate and Blood Temperature

A new method using respiratory rate and temperature as the guides for optimal pacing is proposed. A pacemaker was fabricated which senses these two parameters simultaneously. The pacemaker functions by calculating the cardiac rate, which would be derived from the respiratory rate and the blood temperature. The higher of the two rates is adopted as the cardiac pacing rate, i.e., at which stimuli will be delivered. The operation was tested in a mongrel dog with complete atrioventricular block. After the induction of anesthesia, a thermistor temperature probe was inserted into right atrium and a respiratory rate sensor was attached around the chest. After administration of a pyrogenic drug, both respiratory rate and blood temperature increased. The pacing rate was increased from 178 beats/minute(bpm) at 36.4 degrees C, blood temperature, and 26.5 acts/minute(apm), respiratory rate, to 233 bpm at 40.1 degrees C and 40.0 apm. Cardiac output was increased from 2.15 liters/minute(l/pm) at the beginning to 2.50 l/pm at maximum. The transition of the guide from respiratory rate to temperature was observed at about 38 degrees C.     

Clinical Evaluation of a Dual Sensor, Rate Responsive Pacemaker

Dual sensor pacemakers should respond more appropriately during differing exercise modes than a single sensor device. The Topaz™ models 515 (QT and activity count [ACT] sensing) pacemaker shows appropriate rate response during treadmill exercise testing. We postulated that adjustments to relative sensor contribution should allow fine tuning of the onset of rate response. Eleven patients with this pacemaker were studied. Three standard exercise tests were performed with adjustment of sensor blending and activity threshold between each one. We also assessed the response to isometric exercise and a false positive activity signal. Results : Times to 100 ppm (3.7 ± 1.3, 4.4 ± 2.0, 5.3 ±1.5 mins), times to peak rate (6.1 ± 1.6, 5.6 ± 1.4, 6.5 ± 1.3 mins) and accelerations to peak (9.0 ± 2.4, 9.2 ± 5.3, 7.7 ± 2.8 ppm/min) were measured in all three different sensor settings (QT = ACT, QT 相似文献   

Atrial Rate Adaptive Pacing: What Happens to AV Conduction?

To investigate if an nonphysiological prolongation of the AV inteii-al is common during activity sensor modulated atrial rate adaptive (AAIR) pacing, 21 patients witb sinus node disease treated with fixed rate atrial (AAI) or AAIR pacemakers were examined. Spike-Q intervals were compared at different beaii: rates obtained by overdrive pacing at rest and during exercise (Study I), measured during exercise at unresponsive (AAI), optimal (AAIR) and over responsive programming (AAIR +) of the activity sensor (Study II), and finally examined by 24-hour Holter recording in AAI and AAIR pacing modes (Study III). Study I: The spike-Q interval increased significantly with increasing heart rate at rest, but not during exercise. At rest the spike-Q interval was significantly higher at all heart rates compared to exercise. There was a significant positive correlation between the maximal spike-Q interval at rest and the maximal spike-Q inteival during exercise (r = 0.63). Study II: The spike-Q interval was shortest in the AAI and longest in the AAIR+ mode in all patients. Study III: During AAI or AAIR pacing the spike-Q interval was longest at night and shortest in the morning. The mean spike-Q interval was longer in AAIB than in AAI pacing. No statistical difference between the maximal spike-Q intervals observed during the two modes was, however, found. Variations in spike-Q interval are generally caused by changes in autonomic tone or medication with drugs with antiarrhythmic effect. Our results indicate that the risk for an nonphysiological prolongation of the AV interval during AAIR pacing is rather small and can be predicted by studying the spike-Q interval at rest during overdrive pacing.     

Correlation of Impedance Minute Ventilation with Measured Minute Ventilation in a Rate Responsive Pacemaker

Although rate responsive pacing based on impedance minute ventilation (IMV) is now standard, there is almost no data confirming the relationship between IMV from an implanted pacemaker and measured minute ventilation (VE) during exercise. Nineteen completely paced adults implanted with Medtronic Kappa 400 pacemakers underwent symptom-limited maximal metabolic treadmill testing using a modified Minnesota Pacemaker Response Protocol. Minute ventilation (VE, L/min) was simultaneously measured using the flowmeter of a respiratory metabolic gas analysis system and the transthoracic impedance minute ventilation circuitry of the pacemaker. Correlation coefficients (r) were used to find the best fit line to describe the relationship between the two measurements. Mean (+/- SD) r values for the first, second, and third order polynomial equations and for log and exponential equations were: 0.92 +/- 0.08, 0.94 +/- 0.04, 0.95 +/- 0.04, 0.91 +/- 0.06, and 0.91 +/- 0.07, respectively. None of the r values were statistically different from the first order equation. Transthoracic IMV as measured by the Medtronic Kappa 400 is closely correlated to measured minute ventilation and is represented well by a first order (linear) equation.     

Physiologic Benefits of Rate Responsiveness

?augmenfation du besoin métabolique ou cours de ?exercice est fournie par une hausse du débit cardiaque et de ?apport ?oxygène. Les malades porleurs ?un stimuluteur à fréquence fixe ne peuvent pas augmenter la fréquence cardiaque dont dépend ?augmentation du débil systolique. Nous décrivons un stimulateur capable ?augmenter sa fréquence suivant ?uctivité auriculaire. Par cette méthode nous avons observé un meilleur débit cardiaque, de ?ordre de 55 ± 3.7%. Ce stimulafeur améliore donc la performance cardiaque pendant ?exercice. Increases in metabolic demand in response lo routine activities and exercise are met througb grealer cardiac output ond oxygen delivery. Putienls with fixedrate pacemakers cannot increase heart rate and must rely solely on increases in stroke volume to provide the necessary adjustments in cardiac output. These compensatory strofte volume increases limit the fixedrate pacemaker patient's ability to meet the demand of their daily routine. A physiological, rate responsive pacemaker was studied and it was found to increase maximum exercise tolerance from 4.4 ± .62 METS paced VVI at 65 ppm to 8.1 ± .71 METS when the same patients were paced rate responsively at an average rate of 91 ± 3.8 ppm. Animal studies were used lo quantify the limitation in stroke volume reserve. Maximum increases of 55.8 ± 3.7% over resting vulues were seen in animals in complete heart block at pacing rates of 100 ppm during strenuous exercise. Higher pacing rates increased cardiac output at the same exercise intensity, from 4.94 ± .72 Ipm at 100 ppm lo 7.66 ± 1.02 Ipm at 250 ppm. A pacemaker that increases pacing rate in response to grealer metabolic demand will maintain stroke volume and enddiastolic volume at near normal voiues while providing significant improvement in cardiac output and work capacity.     

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.     

Doppler Echocardiographic Assessment of the Hemodynamic Benefits of Rate Adaptive AV Delay During Exercise in Paced Patients with Complete Heart Block

To determine if rate adaptation of the atrioventricular (AV) delay (i.e., linearly decreasing the AV interval for increasing sinus rate) improves exercise left ventricular systolic hemodynamics, we performed paired maximal semi-upright bicycle exercise tests (EXTs) on 14 chronotropically competent patients with dual chamber pacemakers. Nine patients with complete AV block (CAVB) and total ventricular pacing dependence during exercise comprised the experimental group. Pacemakers in these patients were programmed randomly to rate adaptive AV delay (AVDR) for one EXT and fixed AV delay (AVDF) for the other EXT. AVDF was 156 msec; AVDR decreased linearly from 156–63 msec from rates of 78–142 beats/min. The other five patients had intact AV conduction and comprised the control group who were exercised in identical fashion while their pacemakers were inhibited throughout exercise io assure reproducibility of hemodynamic measurements between EXTs. Cardiac hemodynamics were calculated using measured Doppler echocardiographic systolic aortic valve flows recorded suprasternally with an independent 2-MHz Doppler transducer during a graded ramp exercise protocol. For analysis, exercise was divided into four phases to compare Doppler measurements at submaximal and maximal levels of exercise, rest, early exercise (1st stage), late exercise (stage preceding peak), and peak. Patients achieved statistically similar heart rates between EXTs at each phase of exercise. Although at lower levels of exercise cardiac hemodynamics did not differ, experimental patients (with CAVB) showed a statistically significant benefit to cardiac output at peak exercise with heart rates of 129 ± 13 beats/min (AVDR: 9.4 ± 2.8 L/min; AVDE: 8.2 ± 2.6 L/min, P = 0.002), stroke volume (AVDR: 74.1 ± 25.6 mL; AVDF: 64.3 ± 24.4 mL, P = 0.0003), and aortic ejection time (AVDR: 253.3 ± 35.7 msec; AVDF: 226.7 ± 35.0 msec, P = 0.002). Duration of exercise, peak rate pressure product, peak aortic flow velocities, and acceleration times did not differ. In contrast, control group patients (intact AV conduction throughout exercise) showed no statistical differences between any hemodynamic parameters measured at any phase of exercise from the first to second exercise test. These data demonstrate that systolic cardiac hemodynamics measured echocardia-graphically at the high heart rates achieved with peak exercise are improved with AVDR compared to AVDF in chronofropically competent patients with complete AV block. This is due primarily to improved stroke volume and a longer systolic ejection time with AV delay rate adaptation.     

Pacemaker-Mediated Tachycardia from a Single Chamber Temperature Sensitive Pacemaker

This report describes a case of pacemaker-mediated tachycardia from a single chamber temperature sensitive rate modulated pacemaker. The patient experienced diaphragmatic pacing that produced an increase in right ventricular blood temperature. This temperature increase was sensed by the pacemaker and led to sustained upper rate limit pacing. Decreasing the ventricular output to prevent diaphragmatic capture eliminated further episodes of pacemaker-mediated tachycardia.     

Temperature Dependent Pulse Generator Dysfunction

Malfunction of a lithium-powered R-wave inhibited unipolar pulse generator (CPI Model 0505) necessitated removal 15 months after implantation. Examination of the pulse generator in a water bath revealed abnormal function at temperatures above 31.5 degrees C and normal function at temperatures below 31.5 degrees C. CPI suggested that the failure was caused by the 10 kHz timing crystal in the generator.     

A Rate-responsive Pacemaker Controlled by Right Ventricular Blood Temperature

To demonstrate the capabilities of a rate-responsive pacemaker controlled by right ventricular blood temperature, a prototype pacemaker was developed and tested in dogs with complete atrioventricular (AV) block. Using a previously obtained data base of right ventricular blood temperature recorded both during rest and during treadmill exercise from dogs with either induced AV block or normal AV conduction, a control algorithm which identified periods of exercise was developed. This algorithm was implemented in a microprocessor-based, rate-responsive pacemaker which generates two pacing rates: a basal rate (86 bpm) during rest and a higher rate (113 bpm) during moderate exercise. With repeated trials of submaximal treadmill exercise (2.25, 3.0, 5.0 mph, 16% grade) the pacemaker correctly detected the onset and cessation of exercise with latencies ranging from 35 to 124 seconds. Pacemaker rate increase latency decreased as the exercise level was increased. Pacemaker response latency was not affected by the choice of resting or exercise pacing rate. These preliminary data indicate that right ventricular blood temperature can provide a reliable index to control pacemaker rate. An implantable temperature-controlled pacemaker using this algorithm is presently under long-term evaluation in dogs performing untethered exercise.