Veronique Mahaux

Cardiac arrhythmias and risk stratification after myocardial infarction: results of the CARISMA pilot study.

HUIKURI, H.V., et al .: Cardiac Arrhythmias and Risk Stratification After Myocardial Infarction: Results of the CARISMA Pilot Study. CARISMA is a multicenter study enrolling patients with a left ventricular ejection fraction ≤40% after acute myocardial infarction (AMI), in whom an electrocardiogram (ECG) loop recorder (ILR) is implanted to measure the incidence of tachyarrythmia and bradyarrhythmia episodes. The value of 24 hour ambulatory ECG, signal‐averaged ECG late potentials, QT dispersion, T wave alternans, and electrophysiologic testing as predictors of life‐threatening arrhythmias is examined. The study tested the automatic documentation of arrhythmias by the ILR in 30 post‐AMI patients. Results: At a mean follow‐up of 47 days, the ILR had detected atrial tachyarrhythmias in 8 of 28 patients, nonsustained ventricular tachycardias in 2, and transient third degree atrioventricular block in 3. An indication for implantation of an implantable cardioverter defibrillator (ICD) or permanent pacemaker (PM) was observed in 9 out of 29 patients (31%). An average of 2.3 events stored by the ILR were due to inappropriate triggering. Because its memory size is limited to a maximum of 14 episodes, the ILR was unable to store arrhythmias 28% of the follow‐up time. False events rate and monitoring time were improved by suturing the device within its pocket. Conclusions: The ILR allowed the automatic detection of brady‐ and tachyarrhythmias in post‐AMI patients, though a high incidence of false activations were observed. Clinically significant arrhythmias were recorded in a large number of patients with depressed left ventricular function early after AMI. This prompted the implantation of ICD or PM in nearly one third of patients. (PACE 2003; 26[Pt. II]:416–419)

Risk markers of late high-degree atrioventricular block in patients with left ventricular dysfunction after an acute myocardial infarction: a CARISMA substudy

AIMS High-degree atrioventricular block (HAVB) after acute myocardial infarction (AMI) is associated with increased risk of mortality. Risk markers and predictors of HAVB occurring after AMI are largely unknown. The aim of this study was to assess the predictive value of risk markers derived from a series of non-invasive and invasive tests for the development of HAVB documented by an implantable loop recorder (ILR) in late convalescent phases of an AMI. METHODS AND RESULTS The study included 292 patients with AMI and subsequent left ventricular dysfunction without prior HAVB or implanted pacemaker. An ILR was implanted for continuous arrhythmia surveillance. Risk stratification testing was performed at inclusion and 6 weeks after AMI. The tests included echocardiography, electrocardiogram (ECG), 24 h Holter monitoring, and an invasive electrophysiological study. High-degree atrioventricular block was documented in 28 (10%) patients during a median follow-up of 2.0 (0.4-2.0) years. Heart rate variability (HRV) measures and non-sustained ventricular tachycardia occurring at the week 6 Holter monitoring were highly predictive of HAVB. Power law slope <-1.5 ms(2)/Hz was the most powerful HRV parameter (HR = 6.02 [2.08-17.41], P < 0.001). CONCLUSION Late HAVB development in post-AMI patients with left ventricular dysfunction can be predicted by risk stratification tests. Measures of HRV reflecting autonomic dysfunction revealed the highest predictive capabilities.

Clinical Experience with a New Activity Sensing Rate Modulated Pacemaker using Autoprogrammability

Sensolog 703 is a new single chamber activity sensing rate modulated pacemaker that offers an automatic adjustment of settings called Autoset. Units were implanted in 11 patients (mean age: 67 years) for atrioventricular block (two patients), sinoatrial block (three patients), sick sinus syndrome (four patients), chronotropic incompetence (one patient), and atrial fibrillation with slow ventricular response (one patient). The devices were programmed in VVIR mode using Autoset. The accuracy of the settings was verified by the built‐in histogram function. In 6/11 patients, these settings were not satisfactory. Autoset was repeated at 6 months (nine patients) and 10 months (five patients) after implantation. External telemetric recordings daring daily life activities, Holter monitoring, bicycle or treadmill stress tests helped in the evaluation of the rate response obtained with the automatic programming. The following problems were encountered: maximum pacing rate for a low level of exercise (four patients), insufficient rate increase (four patients), higher pacing rate daring low than daring heavy exercises (four patients). A time‐consuming (15 to 48 minutes) manual programming was necessary in eight out of nine patients (6 months) and five out of five patients (10 months). In our study, Sensolog 703 algorithm tended to behave as an on/off system; automatic programming was time consuming and only indicative.

Clinical Interest of a Sensor Driven Algorithm Limiting Ventricular Pacing Rate During Supraventricular Tachycardia in Dual Chamber Pacing

A sensor driven algorithm limiting ventricular pacing rate during supraventricular tachycardia (SVT) is included in a dual chamber rate modulated pacemaker sensitive to acceleration forces (Relay, 294‐03, Intermedics Inc.). According to the intensity of concomitant exercise, the ventricular pacing rate is limited either to the programmed maximum pacing rate (MPR) or to an interim lower limit, called “conditional ventricular tracking limit” (CVTL). The MPR prevails over the CVTL when the sensor calculated pacing rate exceeds the minimal rate by more than 20 beats/mm. The purpose of the study is to determine the clinical safety and efficacy of this algorithm in patients with intermittent SVT. Method: a Relay was implanted in four patients with a bradycardia/tachycardia syndrome and in four patients with complete atrioventricular block (CAVB). All had episodes of paroxysmal atrial tachycardia. The units were programmed in DDDR: rate responsive parameters were adjusted by simulating the rate response during three levels of exercise to let the MPR override the CVTL only during strenuous exercise. Holter monitors and exercise testings were performed at 3‐month follow‐up. Results: in seven patients, Holter recordings showed Supraventricular arrhythmias at rest with a ventricular pacing rate limited to the CVTL. Appropriate rate increases during exercise testings were also demonstrated. Three devices had to be reprogrammed in DDIR tone patient suffering from nearly permanent atrial flutter and two patients not tolerating the CVTL pacing rate at rest). Conclusion: the CVTL algorithm is effective in protecting against high ventricular pacing rates during Supraventricular arrhythmias. It allows the selection of the DDDR mode even with a high MPR in patients with intermittent SVT.

In Vitro Evaluation of a Sensor Sensitive to Acceleration Forces Included in a New Rate Modulated Pacemaker

The characteristics of the sensor and rate adaptive algorithm included in a new dual chamber rate responsive pacemaker (Relay 294–03, Intermedics, Inc.) were studied by submitting the device to calibrated to‐and‐fro movements of specific frequencies and peak accelerations by means of a mechanical arm connected to a speed adapter. Atrial pacing rate was continuously recorded on a Holter monitor. The influences of the frequency, the magnitude, and the axis of the acceleration forces as well as the reproducibility of the rate response were evaluated. Results: (1) the sensor was sensitive to frequencies ranging from 0.5 to 7 Hz with a peak sensitivity at 3 Hz; (2) the pacing rate was not affected during movements at frequencies > 6 Hz, commonly presented as nonactivity related signals fear, bus transportation, drilling); (3) the pacing rate increased as a function of the acceleration magnitude up to 0.5 G (0.3 G for 3 Hz), then remained constant. This level of acceleration usually corresponds to high degrees of activity; (4) rate response was maximum when acceleration was directed in the anteroposterior direction; (5) reproducibility of the rate response was excellent (R2: 0.999; slope of the regression line: 0.999). Conclusion: Relay 294‐03 is a low frequency signal sensing rate modulated pacemaker using an accelerometer sensitive to motion, mainly in the anteroposterior direction.

Computerized heart rejection monitoring using high resolution pacemaker telemetry

Although the survival of heart transplant recipients markedly improved since the introduction of cyclosporin, early detection of rejection episodes remains a major challenge. Allograft rejection is not a steady phenomenon but occurs in sporadic waves, extending over a few days or weeks. The patient usually remains asymptomatic until a significant myocardial damage results in heart failure. To initiate a successful therapy at early stage, the diagnosis must be made before clinical features of cardiac failure occur. Endomyocardial biopsy is the gold standard of rejection monitoring. Nevertheless, this procedure is invasive, expensive and cannot be repeated too frequently to optimally control immunosuppression. Those limitations have spurred the search for reliable, non-invasive and easily repeated monitoring rejection tools. Acute rejection results in cellular infiltrates, edema and eventually myocardial necrosis. Those factors are considered to alter the electrophysiological properties of the myocardium. Before the introduction of cyclosporine A, those diffuse and massive lesions allowed the detection of rejection by monitoring the amplitude of the surface ECG. Immunosuppression with cyclosporine A resulted in more focal lesions with minimal edema making standard ECG inaccurate for the detection of rejection. Epicardial ECG monitoring, already suggested by Sewell et al. [1] in 1968, regained interest. Preliminary studies showed a significant relation between intramyocardial electrogram amplitudes and endomyocardial biopsy results [2-5]. Nevertheless, attention progressively focused of the repolarization phase of the paced QRS. Indeed, ionic abnormalities due to cell necrosis, and alterations of transmembranic ionic transportation could alter repolarization. The monitoring of the evoked T-wave amplitude using an externalized QT-driven pacemaker exhibited a significant fall of this parameter preceding by an average of 2 days the diagnosis of rejection by endomyocardial biopsy [6]. Long-term monitoring of ventricular evoked response and evoked T-wave amplitude by means of an implanted pacemaker implemented with high resolution telemetry capabilities con-

Atrial flutter: historical background.

Atrial Flutter. For five decades, the mechanism of atrial flutter remained controversial, with protagonists and antagonists of circus movement versus ectopic focus theories. The development of clinical electrophysiologv in the 1970s and the observations made by many authors in various canine heart models supported the concept of atrial flutter as a reentrant wave confined to the right atrium. It was established that, in the common type of atrial flutter, the activation wavefront proceeds in a cranial direction over the right atrial septum and descends on the right atrial free wall in the caudal direction. A zone of slow conduction was identified interiorly and posteriorly in the right atrium, target of the modern ablative techniques. The history of atrial flutter clearly illustrates the bidirectional flow of information and the mutual stimulation between the basic and the clinical levels, leading both to a better understanding of the nature of the arrhythmia and to new therapeutic approaches.

Stepwise analysis of the calibration procedure of an accelerometer-based pacemaker.

The rate modulation of Relay™ 294–03 is individually adjusted during a 3‐minute calibration test corresponding to the collection of moderate acceleration signals (MAL), which are related to a programmable moderate pacing rate (PR). Those rate/acceleration values form a calibration point in the flat part of the rate response curve (HRC). To help in a more clinically oriented analysis of this feature, the stimulator was first calibrated while strapped on a volunteer who remained seated (low MAL), walked (medium MAL), or jogged (high MAL). The device was then mechanically submitted to three calibrated to and fro movements corresponding to the sensitivity spectrum of the sensor. Each movement was repeated ten times to test the influence of the slope (1–10). Results: (1) One‐way ANOVA showed a significant effect of the MAL recorded during the calibration test on subsequent rate modulation (P = 0.0001); (2) The sensor amplifier gain was inversely related to the MAL: high MAL induced lower amplifier gain and lower PR for identical accelerations; (3) Lower amplifier gain allowed to discriminate highest acceleration magnitudes before reaching an overflow of the sensor; (4) The maximum achievable PR increased not only with the programmed slope, but also with decreasing MAL (P = 0.0055): a low MAL shifts to the left calibration point located on the part of the RRC and makes the last steep part of the RRC start earlier, thus leading to higher maximum achievable PR. In conclusion the calibration procedure is crucial not only in defining a moderate acceleration intensity but also in determining the sensor amplifier gain and the maximum achievable PR.

Programming the upper rate behaviour and the atrial escape interval in paced patients with unstable atrium

Since the introduction of dual chamber pacing for treatment of patients with sick sinus syndrome, much data showed a decreased incidence of heart failure, stroke and atrial fibrillation.

Usefulness and Adequacy of Sensor Data Storage and Retrieval for Rate Response Simulation

The usefulness of sensor data storage for rate response simulation was evaluated using a new dual chamber rate modulated pacemaker sensitive to acceleration forces (Relay 294–03 [lntermedics Inc.]). The pacemaker can store the sensor output during routine exercise and those values can be used to simulate rate profiles for other rate response settings. The predictive value of this feature was evaluated in three studies (mechanical, external pacemaker, and implanted pacemaker). In the first study, the pacemaker was submitted to three runs of eight different mechanical calibrated to‐and‐fro movements. In the second study, nine external pacemakers were strapped on healthy volunteers who performed three jogging tests. Finally, the predictive value of the simulation was studied in five implanted patients during three successive walking tests. In each study, the pacemaker was submitted three times to the same activity. The responsiveness was successively set to 5, 1, and 10, and the pacemaker outputs were continuously recorded on a Holter monitor. At the end of the first run, rate profile simulations for slopes 1 and 10 were performed; slope 5 rate response was simulated after the second run. A regression analysis was used to establish the correlation between predicted and achieved pacing rates for each study. The coefficients of correlation between predicted and measured pacing rates for the mechanical, external, and clinical studies were 0.999, 0.985, and 0.823, respectively. The corresponding slopes of regression lines were 1.005, 0.971, and 0.935. Calculated rate profile has a high predictive value and could be used to optimize rate responsive settings without serial exercise testings.