Analysis of rhythm variation during spontaneous cardioinhibitory neurally-mediated syncope. Implications for RDR pacing optimization: an ISSUE 2 substudy.

BACKGROUND: Little is known of the variations of the heart rate during spontaneous cardioinhibitory neurally-mediated syncope. Their knowledge has both academic and practical implications for the optimization of rate drop response (RDR) pacing mode. METHODS AND RESULTS: We describe variations of the rhythm occurring during 48 syncopal episodes documented by implantable loop recorder. The presyncopal phase of 18 s (interquartile range 9-65) was characterized by a fall in heart rate from 83 +/- 20 bpm to maximal bradycardia or (multiple) asystolic pauses which lasted a median of 19 s (10-30). The recovery phase lasted 22 s (7-52). The total duration of the cardioinhibitory reflex was 85 s (47-116). We then calculated the potential increase in benefit that an optimally programmed drop rate detection could provide compared with a reference Lower Rate detection. Compared with Lower Rate detection (defined as two consecutive beats at 40 bpm), drop rate detection (assumed to be drop size = 20 bpm, detection window = 1 min, and drop rate = 50 bpm) would have been able to introduce intervention pacing, a median of 5.7 s (interquartile range -5.1- -10.4) earlier in 28 cases (58%). CONCLUSION: Cardioinhibitory neurally-mediated reflex varies widely from a few seconds to some minutes. In our data the total duration was <2 min. Optimal RDR programming, being potentially able to anticipate the detection of the cardioinhibitory reflex by a few seconds, could provide an increase in benefit for cardiac pacing therapy in prevention of syncope.

Influence of autothreshold sensing and sinus rate on mode switching algorithm behavior.

Mode switching is beneficial to pacemaker patients with paroxysmal atrial tachyarrhythmias. However, the optimal mode switching algorithm is still in evolution. Mode switching algorithms and atrial sensing circuitry can influence mode switching behavior. This study compared the mode switching behavior of four Medtronic, Inc. implantable devices: Thera DR model 7960 pacemaker, Kappa 700 model KDR701 pacemaker, Gem DR model 7271 dual chamber pacing defibrillator, and Jewel AF model 7250 dual chamber pacemaker atrial and ventricular defibrillator. The Thera and Gem DR use the same mean atrial rate mode switch algorithm. The Kappa and Jewel AF use four of seven short atrial intervals and an atrial fibrillation evidence counter algorithm, respectively. The Thera and Kappa devices use fixed gain sensing and the Gem DR and Jewel AF use autothreshold atrial sensing. Digitally recorded atrial electrograms from 52 episodes of human atrial fibrillation were fed into each device with differing simulated sinus rates before and after the atrial fibrillation. The percent of appropriate mode switching was highest for the Kappa 700 (94%) and lowest for the Thera (85%) (P = 0.046). The time to mode switching was significantly longer for the Thera and Gem DR compared to the Kappa 700 or Jewel AF (all P < 0.05). The time to mode switching was shorter for the Gem DR (9.0 +/- 1.6 s) using autothreshold atrial sensing than for the fixed gain Thera (11.1 +/- 2.1 s, P < 0.05). The mean atrial electrogram amplitude and cycle length were not correlated with the time to mode switching for any device. Faster sinus rates shortened the time to mode switching and prolonged the time to resynchronization in the two devices using the mean atrial interval algorithm. In conclusion, (1) mode switching function among these devices is influenced by algorithms and sensing circuitry, (2) the time to mode switching among these devices is influenced by the algorithm and use of autothreshold atrial sensing, and (3) the sinus rate before and after episodes of atrial fibrillation greatly influences the times to mode switching and resynchronization in devices using the mean atrial interval algorithm.

Clinical experience of a new rate drop response algorithm in the treatment of vasovagal and carotid sinus syncope.

Dual chamber pacing has proven beneficial in patients with sudden drops in heart rate as seen in vasovagal syncope and carotid sinus syndrome. Newer algorithms for faster detection of an insidious drop in heart rate and short lasting intervention pacing at a high rate, as in the rate drop response algorithm in the Medtronic Kappa series of pacemakers, might improve the effect of pacing. Two case reports, that demonstrate the use of these rate drop response algorithms, are presented. A 24-year-old woman with recurrent episodes of syncope and repeated tilt-table tests with vasovagal cardioinhibitory outcomes had a Medtronic Kappa 400 pacemaker implanted. Syncope was abolished during repeat tilt-table testing following pacemaker implantation and proper functioning of the rate drop response algorithm. The patient has been free of syncope during follow-up apart from a single episode that occurred due to neglect of vasovagal warning symptoms. A 52-year-old man with coronary artery disease developed recurrent blackouts. Carotid sinus massage resulted in 5.5 s of asystole and presyncope. A Medtronic Kappa 700 pacemaker with a rate drop response algorithm was implanted and the patient became asymptomatic. The rate drop response algorithm is discussed in detail based upon the case reports, and recommendations are given for the use of this algorithm in patients with vasovagal syncope and carotid sinus syndrome.

"Rate-drop response" cardiac pacing for vasovagal syncope. Rate-Drop Response Investigators Group.

Recent reports suggest that cardiac pacing incorporating a rate-drop response algorithm is associated with a reduction in the frequency of syncopal episodes in patients with apparent cardioinhibitory vasovagal syncope. The detection portion of the algorithm employs a programmable heart rate change-time duration "window" to both identify abrupt cardiac slowing suggestive of an imminent vasovagal event and trigger "high rate" pacing. The purpose of this study was to develop recommendations for programming the rate-drop response algorithm. Pacemaker programming, symptom status, and drug therapy were assessed retrospectively in 24 patients with recurrent vasovagal syncope of sufficient severity to warrant consideration of pacemaker treatment. In the 53 +/- 19 months prior to pacing, patients had experienced an approximate syncope burden of 1.2 events/month. During follow-up of 192 +/- 160 days, syncope recurred in 4 patients (approximate syncope burden, 0.3 events/month, p < 0.05 vs. pre-pacing), and pre-syncope in 5 patients. In these patients, rate-drop response parameters were initially set based on electrocardiographic and/or tilt-table recordings, and were re-programmed at least once in 14 (58%) individuals. A 20 beat/min window height (top rate minus bottom rate), a window width of 10 beats (61% of patients), and 2 or 3 confirmation beats (79% of patients) appeared to be appropriate in most patients. Treatment intervention rate was set to > 100 beats/min in 89% of patients, with a duration of 1 to 2 min in 79%. In conclusion, a narrow range of rate-drop response parameter settings appeared to be effective for most individuals in this group of highly symptomatic patients.

An algorithm for automatic measurement of stimulation thresholds: clinical performance and preliminary results.

We have developed an algorithmic method for automatic determination of stimulation thresholds in both cardiac chambers in patients with intact atrioventricular (AV) conduction. The algorithm utilizes ventricular sensing, may be used with any type of pacing leads, and may be downloaded via telemetry links into already implanted dual-chamber Thera pacemakers. Thresholds are determined with 0.5 V amplitude and 0.06 ms pulse-width resolution in unipolar, bipolar, or both lead configurations, with a programmable sampling interval from 2 minutes to 48 hours. Measured values are stored in the pacemaker memory for later retrieval and do not influence permanent output settings. The algorithm was intended to gather information on continuous behavior of stimulation thresholds, which is important in the formation of strategies for programming pacemaker outputs. Clinical performance of the algorithm was evaluated in eight patients who received bipolar tined steroid-eluting leads and were observed for a mean of 5.1 months. Patient safety was not compromised by the algorithm, except for the possibility of pacing during the physiologic refractory period. Methods for discrimination of incorrect data points were developed and incorrect values were discarded. Fine resolution threshold measurements collected during this study indicated that: (1) there were great differences in magnitude of threshold peaking in different patients; (2) the initial intensive threshold peaking was usually followed by another less intensive but longer-lasting wave of threshold peaking; (3) the pattern of tissue reaction in the atrium appeared different from that in the ventricle; and (4) threshold peaking in the bipolar lead configuration was greater than in the unipolar configuration. The algorithm proved to be useful in studying ambulatory thresholds.

Atrial septal pacing: a method for pacing both atria simultaneously.

By pacing both atria simultaneously, one could reliably predict and optimize left-sided AV timing without concern for IACT. With synchronous depolarization of the atria, reentrant arrhythmias might be suppressed. We studied four male patients (73 +/- 3 years) with paroxysmal atrial fibrillation and symptomatic bradyarrhythmias using TEE and fluoroscopy as guides; a standard active fixation screw-in lead (Medtronic model #4058) was attached to the interatrial septum and a standard tined lead was placed in the ventricle. The generators were Medtronic model 7960. The baseline ECG was compared to the paced ECG and the conduction time were measured to the high right atrium, distal coronary sinus and atrial septum in normal sinus rhythm, atrial septal pacing, and AAT pacing. On the surface ECG, no acceleration or delay in AV conduction was noted during AAI pacing from the interatrial septum as compared with normal sinus rhythm. The mean interatrial conduction time for all 4 patients was 106 +/- 2 ms; the interatrial conduction time measured during AAT pacing utilizing the atrial septal pacing lead was 97 +/- 4 ms (P = NS). During atrial septal pacing, the mean conduction time to the high right atrium was 53 +/- 2 ms. The mean conduction time to the lateral left atrium during atrial septal pacing, was likewise 53 +/- 2 ms. We conclude that it is possible to pace both atria simultaneously from a single site using a standard active fixation lead guided by TEE and fluoroscopy. Such a pacing system allows accurate timing of the left-sided AV delay.

Clinical experience with Thera DR rate-drop response pacing algorithm in carotid sinus syndrome and vasovagal syncope. The International Rate-Drop Investigators Group.

This study examined the effectiveness of cardiac pacing using the Thera DR rate-drop response algorithm for prevention of recurrent symptoms in patients with carotid sinus syndrome (CSS) or vasovagal syncope. The algorithm comprises both diagnostic and treatment elements. The diagnostic element consists of a programmable "window" used to identify heart rate changes compatible with an evolving neurally mediated syncopal episode. The treatment arm consists of pacing at a selectable rate and for a programmable duration. Forty-three patients (mean age 53 +/- 20.4 years) with CSS alone (n = 8), CSS in conjunction with vasovagal syncope (n = 4), or vasovagal syncope alone (n = 31) were included. Thirty-nine had recurrent syncope, while the remaining four reported multiple presyncopal events. Prior to pacing, 40 +/- 152 syncopal episodes (range from 1 to approximately 1,000 syncopal events) over the preceding 56 +/- 84.5 months. Postpacing follow-up duration was 204 +/- 172 days. Three patients have been lost to follow-up and in one patient the algorithm was disabled. Among the remaining 39 individuals, 31 (80%) indicated absence or diminished frequency of symptoms, or less severe symptoms. Twenty-three patients (23/29, or 59%) were asymptomatic with respect to syncope or presyncope. Sixteen patients had symptom recurrences. Of these, seven experienced syncope (7/39, or 18%) and 9 (29%) had presyncope: the majority of patients with recurrences (6/7 syncope and 7/9 presyncope) were individuals with a history of vasovagal syncope. Consequently, although symptoms were observed during postpacing follow-up, they appeared to be of reduced frequency and severity. Thus, our findings suggest that a transient period of high rate pacing triggered by the Thera DR rate-drop response algorithm was beneficial in a large proportion of highly symptomatic patients with CSS or vasovagal syncope.

Rate augmentation and atrial arrhythmias in DDDR pacing.

Dual chamber, rate-modulated pacemakers provide the capability of augmenting the heart rate of patients with chronotropic incompetence but also may cause atrial arrhythmias because of high rate, competitive atrial pacing. We studied ten patients with two consecutive 24-hour Holter monitors during which they were alternately programmed to either DDD or DDDR pacing in random order. Maximum heart rates (max HR) were measured at every 15-minute interval during each 24-hour period. DDDR pacing showed rate augmentation, 80 +/- 7 average max HR when compared with DDD pacing, average max HR 76 +/- 5. These results were even more striking when waking hours (7 am to 10 pm) were compared: average max HR 86 +/- 7 DDDR versus 78 +/- 4 average max HR DDD. Several patients showed marked rate augmentation. Seven of ten patients preferred DDDR pacing over DDD pacing. In the entire population, DDDR pacing did not result in an increased number of atrial arrhythmias (1.25 atrial events/24 hour) when compared to DDD pacing (1.75 atrial events/24 hour). We conclude that DDDR pacing provides heart rate augmentation during daily life in a clinical population while not resulting in a significant increase in atrial arrhythmias.

An office-based exercise protocol for predicting chronotropic response of activity-triggered, rate-variable pacemakers.

Activity-triggered, rate-variable pacing systems offer a wide range of pacemaker patients the benefits of an appropriate paced chronotropic response. However, optimizing settings for these devices often entails treadmill exercise testing. To assess simpler procedures for predicting appropriate settings, pacing rates of "strapped-on" and implanted Activitrax pacemakers were evaluated during arm exercise, walk-in-place exercise and treadmill exercise (0% slope at 1.5, 2.0 and 3.0 mph). For exercise of similar duration, steady-state pacing rates of implanted devices during arm and walk-in-place exercise were lower than those achieved during treadmill exercise. Linear regression analysis resulted in the slope of these relations most closely approaching 1.0 for arm exercise at "low" activity threshold, while walk-in-place tended to result in slopes approaching 1.0 at all activity thresholds. Similarly, although strapped-on devices underestimated rates obtained with implanted devices, differences fell within a narrow range (-6 to -14%). Thus, in patients with implanted or strapped-on Activitrax pacemakers, relatively simple exercise procedures suitable for office or clinic environment may be useful to provide an estimate of pacing rates during physical activity, and may thereby facilitate selection of appropriate programmable settings.

Timing markers showing pacemaker behavior to aid in the follow-up of a physiological pacemaker.

In the present study a multiprogrammable, atrial synchronous, ventricular inhibited pacemaker (Enertrax) was used in six patients. This pacer makes it possible to evaluate pacemaker performance non-invasively and facilitates the correct interpretation of the difficult ECGs produced by these complex pacemakers.