Is Local Myocardial Contractility Related to Endocardial Acceleration Signals Detected by a Transvenous Pacing Lead?

The availability of sensors monitoring cardiac function parameters may offer many interesting new applications in cardiac pacing. A microaccelerometer sensor (BEST, Biomechanical Endocardial Sorin Transducer) located at the tip of a pacing lead (PL) has been developed by Sorin Biomedica. The signal detected by the accelerometer, peak Endocardial acceleration (PEA), was shown to reflect cardiac contractility and to be related to the dP/dt signal. Whether the PEA detected by the BEST sensor in different cardiac locations is the expression of local acceleration forces or reflects the whole heart contractility has not yet been demonstrated in humans. Endocardial acceleration and PEA were evaluated in five patients (4 males, 1 female, mean age 68 years) who underwent cardiac catheterization. Sinus rhythm was present in four patients and chronic atrial fibrillation was present in one. The BEST PL was introduced through the left subclavian vein and PEA signals were recorded: (1) at the apex of the right ventricle (RV), (2) within the coronary sinus (CS), (3) at the right atrial appendage (RAA), and (4) floating in the right atrium. The PEA signals were recorded simultaneously with surface ECG, intracardiac electrograins, and RV pressure. At each recording site, PEA signals with significant amplitude were always recorded during the preelection period, during the isovolumic contraction phase, independently of the recording site and cardiac rhythm. The PEA amplitude was higher in the RV (mean value 1.32 g) and it decreased in the RAA and CS (0.75 and 0.45 g, respectively). The same behavior of PEA was observed during sinus rhythm or atrial fibrillation. The amplitude and the timing of the PEA signals detected by the BEST accelerometer were independent of the recording site and atrial rhythm; they appeared to be strictly related to the global ventricular contractility. These results suggest that the BEST could be used either as an effective sensor in closed loop pacing systems, or primarily as a diagnostic hemodynamic sensor.     

Dual Chamber Rate Responsive Pacing System Driven by Contractility: Final Assessment After 1-Year Follow-up

The aim of this study was to assess the long-term performance of a new dual chamber rate responsive pacing system based on the dynamic measurement of the peak endocardial acceleration (PEA) index of cardiac contractility. Seventy patients who participated in the Multicenter European Clinical Evaluation were studied 1 year after implantation by continuously recording the PEA and the heart rate (HR) during exercise stress testing and during 24 hours of usual activities. A complete examination of standard parameters was also performed to assess the pacing/sensing lead characteristics. Statistical comparisons were performed with the data recorded with the same protocol at 1 month after implant for each patient. A linear correlation coefficient was calculated between PEA and sinus rate when the patient showed predominant atrial tracked rhythm. There were no significant differences between PEA values measured at 1 month and 1 year (PEA = 0.41 ± 0.26 g vs 0.45 ± 0.29 g at rest and PEA = 1.63 ± 0.77 g vs 1.72 ± 0.83 g during peak exercise). The correlation coefficient remained stable (0.67 ± 0.15 vs 0.65 ± 0.14 during daily life and 0.74 ± 0.14 vs 0.77 ± 0.11 during exercise). The PEA signal detected by the sensor was reliable and stable. No long-term complications or adverse effects were observed, and the lead performance was comparable to that of a standard lead.     

A Sensor-based Evaluation of Heart Contractility in Patients with Head-up Tilt-induced Syncope

Studies using the head-up tilt test (HUT) suggest that a reflex increase in sympathetic activity resulting in vigorous myocardial contractions precedes neurally-mediated syncope (NMS), The aim of this study wax to evaluate heart contractility changes during positive HUT. Ten patients with recurrent NMS and positive HUT were investigated. Before HUT we temporarily placed a standard right ventricular pacing electrode incorporating in its tip a recently developed microaccelerometer (Sorin Biomedica, Italy) that measures the peak endocardial acceleration (PEA) during the isovolumetric phase as an index of heart contractility. PEA potential amplitude, heart rate and mean blood pressure were continuously studied during HUT. Syncope occurred 16.7 ± 10.3 min after 60° till, either at baseline (8 patients) or after sublingual nitrate administration (2 patients). PEA value was stable at 0.62 ± 0.34 (1G = 9.8 m/sec²) during the supine phase. It slightly increased to 0.72 ± 0.44 G (p = NS) during the first minutes of 60° tilt and then remained unchanged until a further increase of 71 ± 79% (range 10 to 266 %) as compared to tilt value (p = 0.004) at 2.8 ± 2.4 min (range 0.25 to 6.5 min) before the syncope in 9 patients. The latter increase was not observed in the patient with dilated cardiomyopathy. In conclusion, a significant increase in heart contractility was observed in 9 patients in the minutes preceding HUT-induced NMS. These changes might be used for driving a rate adaptive pacemaker when cardiac pacing is indicated to prevent NMS.     

An Implantable Intracardiac Accelerometer for Monitoring Myocardial Contractility

As the myocardium contracts isometrically, it generates vibrations that are transmitted throughout the heart. These vibrations can be measured with an implantable microaccelerometer located inside the tip of an otherwise conventional unipolar pacing lead. These vibrations are, in their audible component, responsible for the first heart sound. The aim of this study was to evaluate, in man, the clinical feasibility and reliability of intracavity sampling of Peak Endocardial Acceleration (PEA) of the first heart sound vibrations using an implantable tip mounted accelerometer. We used a unidirectional accelerometer located inside the stimulating tip of a standard unipolar pacing lead: the sensor has a frequency response of DC to 1 kHz and a sensitivity of 5 mV/G (G - 9.81 m/s^?2). The lead was connected to an external signal amplifier with a frequency range of 0.05–1,000 Hz and to a peak-to-peak detector synchronized with the endocardial R wave scanning the isovolumetric contraction phase. Following standard electro-physiological studies, sensor equipped leads were temporarily inserted in the RV of 15 patients (68 ± 15 years), with normal regional and global ventricular function, to record PEA at rest, during AAI pacing, during VVI pacing, and during dobutamine infusion (up to 20 |mg/kg per min). PEA at baseline was 1.1 G ± 0.5 (heart rate = 75 ± 14 beats/rain) and increased to 1.3 G ± 0.9 (P = NS vs baseline) during AAI pacing (heart rate = 140 beats/min) and to 1.4 G ± 0.5 (P = NS vs baseline) during VVI pacing (heart rate = 140 beats/min). Dobutamine infusion increased PEA to 3.7 G ± 1.1 (P < 0.001 vs baseline), with a heart rate of 121 ± 13 beats/min. In a subset of three patients, simultaneous hemodynamic RV monitoring was performed to obtain RV dP/dt_max, whose changes during dobutamine and pacing were linearly related to changes in PEA (r = 0.9; P < 0.001). In conclusion, the PEA recording can be consistently and safely obtained with an implantable device. Pharmacological inotropic stimulation, but not pacing induced chronotropic stimulation, increases PEA amplitude, in keeping with experimental studies, suggesting that PEA is an index ofmyocardial contractility. Acute variations in PEA are closely paralleled by changes in R V dP/dt_max, but are mainly determined by LV events. The clinical applicability of the method using RV endocardial leads and an implantable device offers potential for diagnostic applications in the long-term monitoring of myocardial function in man.     

Detecting Incipient Vasovagal Syncope: Intraventricular Acceleration

The peak endocardial acceleration (PEA) caused by ventricular isometric contraction can be measured with an implantable microaccelerometer located inside the tip of a normal unipolar pacing lead. It has been shown that PEA correlates with myocardiai contractility and the maximum rate of rise of ventricular pressure (peak dP/dt) of the left ventricle. A PEA measuring system was temporarily inserted into the apex of the right ventricle in seven patients affected by syncope of uncertain origin. Each patient subsequently underwent 60 tilt testing with three different protocols: without pharmacological challenge (baseline); potentiated with sublingual trinitroglycerin (at a dose of 0.3 mg); and with isoproterenol infusion (at a dose of 3 μg/min). Each phase lasted 20 minutes. Syncope was induced in 1 patient during the baseline phase, in 3 patients during the trinitrin phase, and in 4 patients during the isoproterenol phase. Six patients had a negative response during the baseline phase and served as a control group. From the beginning of upright posture to the time of maximum heart rate, PEA increased by about the same amount in both positive and negative patients, but absolute values were from two- to three fold higher with isoproterenol (from 1.2 ± 0.5 G to 1.6 ± 0.8 G, from 0.8 ± 0.2 G to 1.2 ± 0.4 G, and from 2.8 ± 1.8 G to 3.6 ± 1.8 G, respectively, for negative, positive baseline or trinitrin, and positive isoproterenol tests). At the time of syncope, PEA values fell to baseline values. PEA changes were inversely correlated with blood pressure changes and directly correlated with heart rate changes. Thus, tilt induced syncope occurred both at low and high levels of left ventricular contractility. Whether spontaneous syncopes occur at low or high PEA behavior remains to be established. Since heart rate correlates well with changes in PEA and is far easier to measure, it is unlikely that a PEA measurement system or, in general, a contractility-based system, might become an ideal sensing parameter for the introduction of devices to combat vasovagal syncope.     

Interindividual Comparison of Different Sensor Principles for Rate Adaptive Pacing

In recent years a multitude of rate adaptive sensor systems based on different sensor signals have been developed to adapt the pacing rate to the physical load of the patient. In contrast to those systems the closed loop stimulation (CLS) represents a new concept, which regards the pacemaker as part of the cardiocirculatory system. The pacemaker converts the regulating information of the circulatory center into a heart rate. This study compares the closed loop stimulation and the different sensor systems that evaluate external parameters for rate adaptive pacing with a control group. To this end, 27 patients and 15 patients with a healthy sinus node (control group) were subjected to physical and mental stress tests. The recorded results were analyzed with regard to the maximum rates reached during stress. The results show that none of the studied sensor-controlled systems was able to determine an adequate pacing rate under all of the various load states. The dual sensor systems experience problems in balancing the input of the two sensor signals when calculating the pacing rate. The evaluation of a single external parameter, such as the acceleration of the upper body with the accelerometer, also failed to provide an adequate pacing rate in many stress situations. In contrast to all sensor systems, CLS achieved a heart rate in agreement with those of the reference group in all physical and mental stress situations.     

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 ≥ 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.     

Heart rate changes during acute mental stress with closed loop stimulation: report on two single-blinded, pacemaker studies

BACKGROUND: Mental stress affects hemodynamic properties of the heart in patients indicated for a pacemaker, therefore highlighting the need for a rate-adaptive sensor that responds to mental loads. One such sensor utilizes Closed Loop Stimulation (CLS), which translates right ventricular contractility into patient specific pacing rates. Clinical studies utilizing CLS [Emotional Response (ER) and Emotional Response 2 (ER2) studies] have been performed to confirm CLS provides appropriate heart rate response to acute mental stress. The objective of these studies was to compare heart rates during a mental stress test, with the patient's pacemaker programmed to a CLS pacing mode and an accelerometer pacing mode. METHODS: Patients were implanted with a BIOTRONIK Protos/CLS pacemaker (Berlin, Germany) and subjected to mental stress testing. The stress test consisted of a relaxation period followed by a color-word test and an arithmetic challenge test. The ER2 study utilized a randomized study design, in which pacing mode testing order was randomized. RESULTS: Analysis included patients who exhibited at least 80% sensor-driven heart rates during stress testing. Results for both studies demonstrated that CLS provided a statistically significant higher increase in heart rate during testing compared with an accelerometer pacing mode. The studies also showed that CLS provided a statistically significant higher peak heart rate during testing compared with an accelerometer pacing mode. CONCLUSIONS: The ER and ER2 studies demonstrate that the CLS algorithm responds with an appropriate heart rate response to acute mental stress in patients exhibiting a high percentage of sensor-driven pacing.     

Multicenter Clinical Evaluation of a New SSIR Pacemaker

A multicenter clinical evaluation of Sorin Swing 100, a new SSIR pacemaker with a gravimetric sensor, was performed by seven different centers enrolling a total of 89 patients, 56 men and 33 women, mean age 73.1 years, for pacemaker implantion (73 patients) or pacemaker replacement (16 patients). Pacing mode was VVIR in 73 patients and AAIR in 16. The behavior of pacing rate was evaluated 3 months after the implant by performing a 24-hour Holter monitor, an exercise stress test, and tests for the assessment of mechanical external interference (MEI). A physiological behavior of the paced rate was always observed during Holter monitoring. In 52 completely paced patients mean diurnal, nocturnal, and maximal heart rate were, respectively, 74.9 ± 5.7 ppm, 58.1 ± 5.8 ppm, and 113.4 ± 12.7 ppm; a paced rate exceeding 100 ppm was reached on the average 5.6 times/Holter monitor. In all but two patients the sleep rate (55 ppm) was reached during the night or long resting time. During exercise stress test a direct correlation between the increase in pacing rate and the increase in workload was observed; the mean maximal heart rate reached in 49 completely paced patients was, respectively, 102.8 ± 9 ppm in 17 patients who accomplished stage 1, 116.2 ± 13.6 ppm in 28 patients who accomplished stage 2, and 133 ± 6.7 ppm in 10 patients who accomplished stage 3 of the Bruce protocol. MEI testing never increased the pacing rate over the noise rate (10 ppm over the basic rate). In only seven patients the results obtained suggested to change the nominal set up of the pacemaker. Our experience clearly indicates that Swing 100 is an effective, reliable, and easy to use SSIR pacemaker. The availability of the sleep rate allows a more physiological pattern of pacing rate and can lead to significant energy saving.     

Atrioventricular Interval Optimization in the Right Atrial Appendage and Interatrial Septum Pacing: A Comparison Between Echo and Peak Endocardial Acceleration Measurements

PADELETTI, et al. : Atrioventricular Interval Optimization in the Right Atrial Appendage and Interatrial Septum Pacing: A Comparison Between ECHC and Peak Endocardial Acceleration. Interatrial septum pacing (IASP) reduces interatrial conduction time and consequently may interfere with atrioventricular delay (AVD) optimization. We studied 14 patients with an implanted BEST Living system device able to measure peak endocardial acceleration (PEA) signal. The aims of our study were to compare the (1) optimal AVD (OAVD) in right atrial appendage pacing (RAAP) and IASP, and (2) OAVD derived by the PEA signal versus OAVD derived by Echo/Doppler evaluation of the left ventricular filling time (LVFT) and cardiac output (CO). Measurements were performed in DDD VDD modes Eight patients (group A) had RAAP and six patients (group B) had IASP. In group A, OAVD measured by LVFT, CO, and PEA was 185 ± 23 ms , 177 ± 19 ms , and 192 ± 23 ms in DDD and 147 ± 19 ms , 135 ± 27 ms , and 146 ± 20 ms in VDD, respectively. OAVD measured by LVFT, CO, and PEA was significantly longer in DDD mode than in VDD (P < 0.01, P < 0.01, P < 0.001 ). In group B, OAVD measured by LVFT, CO, and PEA was 116 ± 19 ms , 113 ± 10 ms , and 130 ± 30ms in DDD and 106 ± 16 ms , 96 ± 15 ms , and 108 ± 26 ms in VDD, respectively. No statistical differences were observed between DDD and VDD. Significant correlations between OAVDs PEA derived and OAVDs LVFT and CO derived were observed (r = 0.71, r = 0.69, respectively ). When new techniques of atrial stimulation, as IASP, are used an OAVD shorter and similar in VDD and DDD has to be considered. The BEST Living system could provide a valid method to ensure, in every moment, the exact required OAVD to maximize atrial contribution to CO.     

Detection of acute myocardial ischemia during percutaneous transluminal coronary angioplasty by endocardial acceleration

The first heart sound is generated by vibrations from the myocardium during isovolumic contraction. Peak endocardial acceleration (PEA) has been used previously to measure these vibrations in humans and correlates with myocardial contractility during inotropic interventions. It is unknown if changes in PEA can be used to characterize a reduction in contractility during ischemic episodes. This study was designed to evaluate the use of an endocardial accelerometer for the detection of acute myocardial ischemia. Thirteen patients undergoing routine percutaneous transluminal coronary angioplasty (PTCA) consented to having a single-axis, lead-based accelerometer positioned in the right ventricular apex. PEA was defined as the maximum peak-to-peak amplitude during a window 50 ms before to 200 ms following the peak R wave. Time of endocardial acceleration (TEA) was defined as the time from the peak R wave to the maximum accelerometer signal within this window. To obtain a more robust estimate of the strength of vibrations, a 100-beat template of the accelerometer signal was constructed at baseline and applied as a matched filter during ischemia. The peak magnitude of the filtered endocardial accelerometer signal (Max Filtered EA) was used as an index of signal intensity. Median baseline PEA, TEA, and Max Filtered EA were 0.91 +/- 0.35 g, 75.2 +/- 16.2 ms, and 0.40 +/- 0.20 g, respectively. PEA and Max Filtered EA significantly decreased by 7% during ischemia (0.91 to 0.85 g and 0.40 to 0.37 g, both P < 0.05, respectively). TEA did not significantly change from baseline (77.0 ms, P = ns). The results of this study suggest that acute ischemia can be detected with an endocardial accelerometer in humans.     

A Rate Responsive Pacemaker that Physiologically Reduces Pacing Rates at Rest

Current rate responsive pacemakers incorporate sensors such as minute ventilation (MV) for adapting to changing patient conditions during exercise and periods of exertion. However, for sleep and/or rest periods, the only pacemakers currently on the market that slow the pacing rate utilize an internal timer to determine a decrease in pacing rate. It would be advantageous if the pacing rate could be automatically lowered during periods of sleep or rest. This study utilized a rate responsive sensor, MV, to track the patient's sleeping and resting periods and to decrease the pacing rate at such times. A total of eight patients implanted with Sentri 1210 single chamber MV sensor pacemakers were studied. A sleep rate (SH) of 45 beats/min was selected. A sleep rate response function, which indicated the relationship between changes in MV and corresponding heart rate, was initially set at a value of 16 and continually and automatically updated in a 3-month study. Adaptation was based on the premise that 3 hours per day should be spent at the SR. The average decrease in pacing rates from onset to 3 month for the eight patients was 12.4%± 5.3%. Correspondingly, the histograms of the lowest datalog histogram (40–59 beats/min) increased from 0% to 15.4%± 0.9% of paced beats. Correlation between the patients' 24-hour diary and Holter recordings showed that the pacing rates during sleep were consistently lower than when the patients were awake and active. This was also the case with a patient whose nocturnal and daily routine was intentionally altered. In conclusion, the MV sensor has shown to be an accurate sensor for the automatic determination of periods of sleep or rest. Data demonstrates that the decreased average pacing rate will increase pacer longevity as well as potentially provide more physiological pacing rates at night.     

Relationship between Amplitude and Timing of Heart Sounds and Endocardial Acceleration

Objective: To study the correlation between heart sounds and peak endocardial acceleration (PEA) amplitudes and timings, by modulation of paced atrioventricular (AV) delay in recipients of dual chamber pacemakers.
Methods: Ten recipients of dual chamber pacemakers implanted for high-degree AV block were studied. Endocardial acceleration (EA) and phonocardiographic and electrocardiographic signals were recorded during performance of an AV delay scan in VDD and DDD modes.
Results: First PEA (PEA I) and first heart sound (S1) changed similarly with the AV delay. A close intrapatient correlation was observed between S1 and PEA I amplitudes in all patients (P < 0.0001). The interpatient normalized PEA I to S1 amplitudes correlation was r = 0.89 (P < 0.0001) in DDD mode, and r = 0.81 (P < 0.0001) in VDD mode. The mean cycle-by-cycle PEA I to S1 delay was −4.3 ± 22 ms and second PEA (PEA II) to second heart sound (S2) delay was −7.7 ± 15 ms.
Conclusions: A close correlation was observed between PEA I and S1 amplitudes and timings, and between PEA II and S2 timings. These observations support the hypothesis that PEA and heart sounds are manifestations of the same phenomena. EA might be a useful tool to monitor cardiac function.     

Peak endocardial acceleration reflects heart contractility also in atrial fibrillation

Previous studies demonstrated that peak endocardial acceleration (PEA) in sinus rhythm is related to LV dP/dtmax. Until now, PEA was never evaluated during R-R interval variations in AF. The aim of this study was to establish the behavior of PEA in AF and the relationship of PEA versus LV dP/dtmax. Six sheep (65 +/- 6 kg) were instrumented with a LV Millar catheter and with an accelerometer lead. AF was induced and PEA, LV dP/dtmax, and ECG were monitored. AF persisted for 5 +/- 1.3 minutes. From sinus rhythm to AF, the heart rate went from 92 +/- 3 to 130 +/- 35 beats/min (P < 0.05), LV dP/dtmax from 684 +/- 18 to 956 +/- 344 mmHg/s (P = NS) and PEA from 0.82 +/- 0.06 to 0.94 +/- 0.33 g (P = NS). The correlation between PEA and LV dP/dtmax was significative in sinus rhythm (r = 0.7, P < 0.05) and in AF (r = 0.8, P < 0.05). A positive relationship was found between the preceding interval and PEA (r = 0.4 +/- 0.07, P < 0.05) and LV dP/dtmax (r = 0.61 +/- 0.08, P < 0.05), while a negative one was found between the prepreceding interval and both PEA (r = -0.39 +/- 0.11, P < 0.05) and LV dP/dtmax (r = -0.64 +/- 0.05, P < 0.05). At the onset of AF, LV dP/dtmax and PEA showed similar changes: beat-to-beat correlation between PEA and LV dP/dtmax was high. As for LV dP/dtmax, PEA is positively related to the preceding interval and negatively related to the prepreceding interval. These data confirm that PEA reflects heart contractility also during AF and hold promise for the use of this sensor in therapeutic implantable devices.     

Endocardial pacemaker implantation in infants weighing < or = 10 kilograms

Epicardial pacemaker implantation is the most common approach for small children requiring pacemaker implantation, though it is not free from complications. This article reviews the experience with endocardial pacemaker implantation, as an alternative approach, in children < or =10 kg at two centers. Thirty-nine children, median age 3.8 months (2 days-35 months), weight 4.6 kg (2.3-10 kg) underwent endocardial permanent pacing (VVI/R in 38, DDDR in 1). Indications for pacing were complete heart block (CHB) in 34 (congenital in 21, postsurgical in 12, congenitally corrected transposition of the great arteries 1), long QT syndrome in 3, and sinus bradycardia in 2 children. Two children with postsurgical CHB died 7 days and 3 weeks after implantation, respectively, due to heart failure and septicemia, despite appropriate pacemaker therapy. Over a median follow-up of 4.3 years (9 months-15.3 years), 12 patients underwent 18 generator replacements. Five patients were upgraded to physiological pacing. Ten patients underwent 12 ventricular lead advancements. Ventricular lead extraction was attempted 11 times in nine patients and succeeded 10 times. Two patients were converted to epicardial dual chamber systems. Two prepectorally placed generators required resiting due to threatened skin necrosis. Infective endocarditis on the lead, 9 months postimplant required removal of the system in one patient. The subclavian vein was found to be asymptomatically thrombosed in four patients. Endocardial permanent pacing is feasible and effective in children < or = 10 kg and an acceptable alternative to epicardial pacing.     

Comparison of Normal Sinus Rhythm and Pacing Rate in Children with Minute Ventilation Single Chamber Rate Adaptive Permanent Pacemakers

Rate adaptive pacemakers are used to achieve a better cardiac performance during exercise by increasing the heart rate and cardiac output. The ideal rate adaptive sensor should be able to mimic sinus node modulation under various degrees of exercise and other metabolic needs. Minute ventilation sensing has proven to be one of the most accurate sensor systems. In this study, alterations in sinus rhythm and pacing rates during daily life conditions in 11 children (median age 11 years, range 6–14 years) with minute ventilation single chamber pacemakers were investigated. Correlation of sinus rhythm with pacing rates was assessed. ECG records were obtained from 24–hour Holter monitoring. Average rates of five consecutive P waves and pace waves were determined every half hour. The average of the two values was then used to determine hourly rates. Correlation coefficients between the sinus rhythm and pacing rates were calculated. In nine patients, pacing rates correlated well to sinus rhythm (range 0.6793–0.9558. P < 0.001 and P < 0.05), whereas in two cases correlation was not sufficient (P > 0.05). Most of the patients, in whom rate response factor (RRF) measurements during peak exercise by treadmill with cnronotropic assessment exercise protocol were performed and pacemakers were programmed to these parameters, had more appropriate ventricular rates compared to spontaneous sinus rates. In these patients mean RRF value was 15.3 ± 2.7 (range 12–20, median 15). This study shows that during daily activities minute ventilation rate adaptive pacemakers can achieve pacing rates well correlated to sinus rhythm that reflects the physiological heart rate in children.     

Recording of Peak Endocardial Acceleration in the Atrium

Background: The important role played by peak endocardial acceleration (PEA or sonR) in hemodynamic monitoring of cardiac resynchronization therapy (CRT) was recently highlighted in several studies with the sensor embedded in a right ventricular (RV) lead tip. This study examined the short- and long-term reliability of a right atrial (RA) sonR sensor.
Methods: RA and RV sonR signals were measured from RA and RV leads respectively, at implant and up to 12 months of follow-up, in 19 recipients of either single chamber pacemakers or CRT systems. At 1 month of follow up, RA sonR signals and heart rate were simultaneously recorded during exercise.
Results: A reliable RA sonR signal amplitude was measured at implant, proportional to the RV amplitude. We observed in both the right atrium and right ventricle (1) a similar signal noise ratio at implant, (2) a similar evolution of the sonR signal amplitude up to 12 months of follow-up, and (3) a high correlation between heart rate and RA sonR signal amplitude during exercise.
Conclusions: The RA sonR signal was reliable and proportional to the RV signal on the short and long term, and reflected changes in activity. These observations suggest that the sonR sensor could be placed in the atrium for the hemodynamic monitoring of CRT system recipients.     

Achieving Permanent Left Ventricular Pacing—Options and Choice

Cardiac resynchronization therapy (CRT) requires permanent left ventricular (LV) pacing. Coronary sinus (CS) lead placement is the first line clinical approach but can be difficult or impossible; may suffer from a high LV pacing threshold, phrenic nerve stimulation, and dislodgement; and produces epicardial LV pacing, which is less physiological and hemodynamically effective and potentially more proarrhythmic than endocardial LV pacing. CS leads can usually be extracted with direct traction but may require use of extraction sheaths. Half of CS side branches previously used for lead placement may be unusable for the same purpose after successful lead extraction, and 30% of CS lead reimplantation attempts may fail due to exhaustion of side branches. Surgical epicardial LV lead placement is the more invasive second line approach, produces epicardial LV pacing, and has a lead failure rate of ≈15% in 5 years. Transseptal endocardial LV lead placement is the third line approach, can be difficult to achieve, but produces endocardial LV pacing. The major concern with transseptal endocardial LV leads is systemic thromboembolism, but the risk is unknown and oral anticoagulation is advised. Among the new CRT recipients in the United States and Western Europe between 2003 and 2007, 22,798 patients may require CS lead revisions, 9,119 patients may have no usable side branches for CS lead replacement, and 1,800 patients may require surgical epicardial LV lead revision in the next 5 years. The CRT community should actively explore and develop alternative approaches to LV pacing to meet this anticipated clinical demand.     

Clinical Observations with a Dual Sensor Rate Adaptive Single Chamber Pacemaker

The Topaz model 515 (Vitatron B.V.) is a dual sensor rate responsive pacemaker for single chamber stimulation. It can be driven by activity counts (ACT) and QT interval measurements. Inappropriate rate modulation due to one sensor can be corrected by "sensor cross-checking." It was implanted in ten patients (20-86 years) of whom seven had complete heart block and atrial arrhythmias. After implantation T-wave amplitude ranged from 0.9mV-3.5 mV. T-wave sensing ranged from 88%–99% in 9/10 patients at the follow-up of 3 weeks. Eight patients remained in default setting of the activity threshold, after evaluation with a short walking test. An exercise test was performed on all patients. In one test, QT sensing was marginal because of lead implantation in the right ventricular outflow tract. Therefore, this pacing rate was only modulated by ACT sensing. All others were tested with equal contribution of information from both sensors (ACT = QT). In 7/9, rate response was satisfactory. When the treadmill was repeated with ACT in five of these seven patients, rate generally accelerated too fast. In one patient the setting was adjusted to "QT > ACT," because of inappropriate acceleration due to activity sensing, in another it was adjusted to "QT < ACT" because of delayed response to activity. The pacing rate and the ACT during treadmill tests in "QT = ACT" mode were more closely correlated in the first 3 minutes, compared with the last 3 minutes. We feel that rate modulation with this new pacemaker is adequate. Sensor blending and sensor cross-checking are of clinical importance.     

Safety and Imaging Quality of MRI in Pediatric and Adult Congenital Heart Disease Patients with Pacemakers

Background: Magnetic resonance imaging (MRI) is a standard of care in evaluating many disease processes. Given concerns about device damage or movement, programming changes, lead heating, inappropriate pacing, and image artifact, MRI is contraindicated in pacemaker patients. Despite this, studies have demonstrated safety and efficacy of MRI in adults with acquired heart disease and endocardial pacing leads. We sought to evaluate MRI use in congenital heart disease (CHD) patients with predominantly epicardial pacing leads.
Methods: From July 2007 to October 2008, MRI (1.5 Tesla) was performed in 11 patients without alternative imaging modality who were not pacemaker dependent or possessing abandoned leads. Pacing was disabled during MRI. An electrophysiologist monitored electrocardiogram and hemodynamic parameters throughout each study. Device and lead function were evaluated before and after MRI, and at subsequent clinic visits.
Results: Eleven MRIs (four cardiac, seven noncardiac) were performed in eight patients. Mean patient age was 16.5 ± 9.2 years (range 1.7–24.5) with five patients under the age of 16 years. Diagnoses included structural CHD in six patients and long QT syndrome and congenital heart block in one each. There were three dual- and five single- (three atrial, two ventricular) chamber devices, two endocardial, and nine epicardial leads. No inappropriate pacing or significant change in generator or lead parameters was noted. All MRI studies were of diagnostic quality.
Conclusion: Diagnostic quality MRI can be performed safely in nonpacemaker-dependent CHD patients with predominantly epicardial leads. Further studies will define safe practice measures in this population, as well as in CHD patients with pacemaker dependency.