Ventricular Protection Against Atrial Arrhythmias in DDD Pacing Based on a Statistical Approach: Clinical Results

Atrial arrhythmias (AA) are commonly encountered in DDD paced patients. Newer dual chamber pacemakers (PM) possess mode switching functions that convert pacing to an asynchronous mode when AAs are detected. The lack of a reliable mode switch leading to rapid, irregular ventricular responses may result from AA undersensing. To avoid this, the DDDR PM Chorum 7234 Eta Medical AA diagnosis is based on a statistical approach: the PM constantly compares arrhythmic and sinus cycles and, based on "strong" and "weak" criteria, provides for rapid or slower mode switch. The aim of the study was to evaluate the efficiency and reliability of these two criteria. Thirty-one patients with a Chorum 7234 implanted for AV block (11), sinus dysfunction (10), both (5), or hypertrophic obstructive cardiomyopathy (5) were evaluated at 24 hours and 1 month using the internal memory (IM) of the PM, surface 24-hour Holter recordings, and exercise testing. Interrogation of the IM on the first day of study showed that 8 patients had mode switching episodes, based only on the strong criterion confirmed by the surface Holter recording. At I month, the IM revealed mode switching episodes in 12 patients, 6 of whom had used the weak criterion. No inappropriate mode switching episode was recorded during exercise testing at the 1-month follow-up. These results confirm the reliability and efficiency of this algorithm as well as the requirement for a specific algorithm to compensate for transient loss of sensing during AA.     

Prevention of Atrial Arrhythmias during DDD Pacing by Atrial Overdrive

We evaluated the effect of atrial overdrive on the incidence of atrial arrhythmias (AA) in 22 patients (67 ± 9 years. 7 women, 15 men) with Chorus 6234 DDD pacemakers. Atrial overdrive was defined as a programmed paced rate 10 ppm faster than the mean ventricular rate stored for the last 24-hour period in the pacemaker memory. The protocol consisted of three phases of 1 month each. Phase I: observation after discontinuation of antiarrhythmic therapy. Phase II: arrhythmia analysis using the pacemaker memory after programming the lower rate to 55 ppm. The fallback function and histogram data were used to document the number and maximal duration of AA episodes as well as the total AA time in a month. Phase III: atrial overdrive. The mean ventricular heart rate was 65 ± 4 beats/min before atrial overdrive versus 75 ± 5 with atrial overdrive (P = 0.02). At the end of phase II, all patients presented with AA episodes (mean number per patient: 42 ± 78 in one month). In phase III (with atrial overdrive), 14 (64.6%) patients had no recorded AA (group A). In the other eight patients with persistent AA episodes in phase III (group B), there was a significant reduction in the number of AA episodes (90 ± 106 in phase II vs 38 ± 87 in phase III; P = 0.01), their total duration (166 ± 115 in phase II vs 92 ± 134 hours in phase HI; P = 0.03) and their maximal duration (121 ± 103 in phase II vs 85 ± 89 min; P = 0.04). Our short-term data suggest tliat atrial overdrive prevents or reduces A A episodes and demonstrate the feasibility and need of long-term studies to determine whether this benefit is sustained.     

Rate Augmentation and Atrial Arrhythmias in DDDR Pacing

SPENCER, W.H., ET AL.: 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 124 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. (PACE, Vol. 13, December, Part 11, 1990)     

Pacing in Atrial Arrhythmias

SUTTON, R.: Pacing in Atrial Arrhythmias. The history of pacing to control the atrial arrhythmias of sinoatrial node disease (SND) is reviewed and is demonstrated to have become more physiological in recent years. The importance of atrial stimulation is emphasized especially in the context of the natural history of SND. The role of single and dual chamber rate responsive pacing for correction of chronotropic incompetence is outlined and guidelines are proposed for the management of the different types of SND presentation.     

Atrial Natriuretic Factor Release During Exercise in Patients Successively Paced in DDD and Rate Matched Ventricular Pacing

Dual chamber pacemakers were implanted in nine patients with permanent second or third degree AV block feight had complete retrograde block). Two identical exercise tests were performed after at least 1 month after implantation. During the first test (T₁) the pacemaker was programmed to the DDD mode and heart rates were recorded every 15 to 30 seconds during exercise and 30 minutes after exercise. Following 30 minutes of rest, the implanted pacemaker was programmed to the VVT mode and driven by an external pacemaker via a skin electrode. The second exercise test (T₂) was then performed and the rate of the external pacemaker was progressively changed to reproduce exactly the rate observed during T₁ at the same exercise stress. Atrial natriuretic factor (ANF) levels were determined at rest, at regular intervals during exercise, and 30 minutes after exercise. ANF levels and release were statistically higher during rate matched ventricular, than DDD pacing. It is concluded that preservation of AV synchrony reduces ANF release induced by heart rate acceleration during exercise.     

Programmability in DDD Pacing

Des pacemakers DDD fiables, non dangereux ayant de nom-breuses possibilités de programmation sont maintenant au point. Certains paramètres programmables tels que mode, voltage (courant), largeur d'impuision, sensitivité et périodes réfractaires, dans chaque chambre sont fondamentaux. La fréquence maximum limite de même que ies donnees lors des rythmes Ients et les intervalles AV sont également iniportants. Avec certains modèles, la possibilité de programmer Ja période de blanking s'est montrée très utile. La corrélation de toutes ces fonctions assure Je fonc-tionnement sans fautes de ces appareiJs.     

Failure to Sense P Waves During DDD Pacing

ECG tracings of three patients in whom AV universal (DDD) pacemakers were implanted intermittently demonstrated dropped P waves. In one patient, true atrial undersensing was present; in the others, sensing of the atrial electrode was appropriate, but sensing of sinus P waves was intermittently blocked by normal pacemaker operation. In this report we discuss the electrocardiographic diagnosis of atrial undersensing in order to avoid unnecessary reinterventions.     

Occurrence and Significance of Arrhythmias Associated with Atrial-Triggered Ventricular Pacing

A review of electrocardiograms from 85 patients with atrial-triggered ventricular pacing (VAT, VDD, DDD) showed that various disturbances of rhythm were relatively common, and that the effects of an arrhythmia could be aggravated by this type of pacing. In certain circumstances even potentially dangerous ventricular extrasystoles were induced by the pacemaker. Abnormal triggering, sometimes with regular sinus rhythm, could also induce tachycardia. Our observations provided indications for a pacemaker design that would avoid such disturbing effects. The best available pacer for atrial-triggered ventricular pacing is the programmable DDD type.     

Advances in DDD Pacing

Advances in DDD design are increasingly directed toward imitating actual cardiac physiology. Eventually, biosensors will command implanted dual chamber units' responses, affording the most physiologic of circumstances. Since these improved design features are quite complex, the care of the paced patient may well have to be performed in specialized centers. The responsibility thereby incurred mandates to those involved in cardiac pacing critical validation of the actual clinical relevance of newer DDD features.     

The Right Atrial Free Wall: An Alternative Pacing Site

A major advantage of active fixation permanent pacing leads is their ability to be actively attached in areas where conventional passive fixation leads cannot be. In a review of records of 134 consecutive patients requiring dual chamber pacing, all of whom received active fixation atrial leads, 56 had right atrial appendage (AA) pacing and 78 had right atrial free-wall (AFW) pacing. Acute electrical parameters including sensed P wave amplitude (AA - 5.6 ± 2.3 mV. AFW = 5.5 ± 2.3 mV), slew rate (AA = 1.21 ± 0.77 V/sec, AFW = 1.20 ± 0.74 V/sec), stimulation thresholds (voltage and current) including rheobase voltage (AA = 0.6 ± 0.2 V, AFW - 0.6 ± 0.2 V), and pacing impedance (AA = 516 ± 89 ohms, AFW = 504 ± 84 ohms) were similar in both groups. There were two dislodgements fatrial appendage group) and no episodes of clinically important perforation or diaphragmatic stimulation. The free wall of the right atrium appears to he an excellent alternative pacing site to the appendage.     

Stability of the DDD Pacing Mode in Patients 80 Years of Age and Older

We reviewed the records of 119 consecutive patients aged 80 years or older (mean age 84 ± 3.7 years) in whom a dual chamber pacemaker was implanted between 1984 and 1991. Follow-up data was available up to February 1993. Immediate postimplantation complications were rare. Nine patients were lost to follow-up, all within 6 months of implantation. An additional seven patients died within 6 months of implantation. Long-term follow up for at least 6 months from implantation was available for 103 of the 119 patients (87%). Of these 89 (66%) remained in functioning DDD mode for a mean of 22 ± 15 months from implantation. Nine patients were reprogrammed to VVI mode, six due to atrial fibrillation and three due to failure of atrial sensing or pacing. One patient was programmed DVI for failure of atrial sensing; 94 of 112 patients (84%) whose status was definitely known in February 1993 remained in functioning DDD mode until death or last follow-up. Cumulative survival in DDD mode was 78% at 30 months. We conclude that DDD pacing is stable in the great majority of patients in their nineth and tenth decades who present with rhythms amenable to dual chamber pacing and who have no history of sustained atrial fibrillation.     

Dual Chamber Pacing with a Single-Lead DDD Pacing System

The successful application of single-lead VDD pacing during the last few years has generated the idea of single-lead DDD pacing. Preliminary data from several single-lead VDD studies attempting to pace the atrium by a floating atrial dipole are unsatisfactory, causing an unacceptably high current drain of the device. We studied the feasibility as well as the short- and long-term stability of atrioventricular sequential pacing, using a new single-pass, tined DDD lead. In eight consecutive patients (age 73+/-16 years) with symptomatic higher degree AV block and intact sinus node function, this new single-pass DDD lead was implanted in combination with a DDDR pacemaker. Correct VDD and DDD function was studied at implantation; at discharge; and at 1, 3, and 6 months of follow-up. At implant, the atrial stimulation threshold was 0.6+/-0.1 V/0.5 ms. During follow-up, the atrial pacing thresholds in different every day positions averaged 2.1+/-0.5 V at discharge, 2.9+/-0.5 V at 1 month, 3.8+/-0.4 V at 3 months, and 3.4+/-0.4 V at 6 months (pulse width always 0.5 ms). The measured P wave amplitude at implantation was 4.5+/-2.2 mV; during follow-up the telemetered atrial sensitivity thresholds averaged 2.1+/-0.3 mV. Phrenic nerve stimulation at high output pacing (5.0 V/0.5 ms) was observed in three (38%) patients at discharge and in one (13%) patient during follow-up; an intermittent unmeasurable atrial lead impedance at 3 and 6 months follow-up was documented in one (13%) patient. This study confirms the possibility of short- and long-term DDD pacing using a single-pass DDD lead. Since atrial stimulation thresholds are still relatively high compared to conventional dual-lead DDD pacing, further improvements of the atrial electrodes are desirable, enabling lower pacing thresholds and optimizing energy requirements as well as minimizing the potential disadvantage of phrenic nerve stimulation.     

Single Lead DDD System: A Comparative Evaluation of Unipolar, Bipolar, and Overlapping Biphasic Stimulation and the Effects of Right Atrial Floating Electrode Location on Atrial Pacing and Sensing Thresholds

Single lead DDD pacing using unipolar or bipolar stimulation is limited by high atrial threshold. Overlapping biphasic (OLBI) waveform stimulation via atrial floating ring electrodes may preferentially enhance atrial pacing and avoid diaphragmatic pacing. Single lead DDD pacing with OLBI atrial pacing was studied in 12 patients (6 men and 6 women; mean age 74 ± 7 years) with complete heart block. At implantation, atrial bipolar rings (area 27 mm², separation 10 mm) were positioned at radiological defined high, mid, and low right atrial (RA) levels, and P wave amplitude and atrial and diaphragmatic pacing thresholds were determined in each position using unipolar, bipolar, and OLBI stimulation in random order. Although statistically insignificant, both the maximum and minimum sensed P wave amplitudes tended to be lower in the low RA position. Independent of the stimulation modes, minimum atrial pacing threshold occurred in the mid-RA. At mid-RA. the atrial pacing threshold was significantly lower with OLBI pacing compared with either unipolar or bipolar mode (3.9 ± 2.2 V vs 6.7 ± 3.5 V and 6.9 ± 3.5 V, P < 0.05). Although the diaphragmatic thresholds were similar, OLBI pacing modes in the mid-RA and final location significantly improved the Safety margin for avoidance of diaphragmatic pacing compared with unipolar mode. There was no correlation between atrial pacing and sensing threshold. At predischarge testing, all but one patient who developed atrial fibrillation had satisfactory atrial capture and a stable atrial pacing threshold (day 0: 2.6 ± 1.1 V vs day 2: 3.2 ± 1.3V, P = NS). However, diaphragmatic pacing occurred in four of 11 (36%) patients, especially in the upright position (sitting and standing). Our preliminary clinical results suggest that OLBI pacing via atrial floating ring electrodes can reduce the atrial pacing threshold. To optimize atrial pacing and sensing, the bipolar electrodes should be located at the mid-RA level first, although the high RA is an alternative. Despite significant improvements in the safety margin for diaphragmatic pacing with OLBI pacing, diaphragmatic stimulation remains a clinical problem.     

Atrial and Ventricular Stimulation Threshold Development: A Comparative Study in Patients with a DDD Pacemaker and Two Identical Carbon-Tip Leads

The atrial and ventricular pacing threshold development during the first postoperative year was studied in a group of patients receiving DDD pacemakers. Identical carbon-tip endocardial leads were implanted in atrium and ventricle. Atrial and ventricular voltage stimulation thresholds were measured at implantation, and noninvasively at 1 and 12 months thereafter. The atrial amplifier sensitivity required for adequate P wave sensing during follow-up was also determined. The possible influence of a number of factors upon atrial and ventricular threshold evolution was statistically assessed. The threshold data were complete in 57 patients (mean age +/- SD, 65.2 +/- 12.4 years). Thirteen patients had a diagnosis of sinus node disease, whereas 44 had not. Patient age and diagnosis did not significantly influence atrial or ventricular stimulation threshold development. Atrial sensing thresholds were not related to atrial stimulation thresholds during follow-up. Atrial pacing thresholds were higher than ventricular thresholds at pacemaker implantation (P less than 0.00005), but the postoperative threshold rise and thresholds at 1 and 12 months postoperatively did not differ significantly between the atrium and ventricle. The ratio of chronic to acute stimulation thresholds was higher on the ventricular than on the atrial level (0.001 greater than P greater than 0.0005). The chronic atrial threshold showed a logarithmic relation to the threshold at implantation (P = 0.0006); postoperative threshold rise was not a significant determinant of the chronic atrial threshold (P = NS). On the ventricular level, the reverse was seen: The chronic threshold was related to the postoperative threshold rise (P = 0.0015, logarithmic relation), but not to the implantation threshold (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamic Electrophysiology of Ventriculoatrial Conduction: Implications for DDD and DDDR Pacing

CAZEAU, S., ET AL.: Dynamic Electrophysiology of Ventriculoatrial Conduction: Implications for DDD and DDDR Pacing. The behavior of ventriculoatrial conduction (VAC) during exercise remains unknown. In order to determine its characteristics and the consequences it might have on dual chamber pacemaker technology and programming, 17 patients underwent an electrophysiological study (EPS) of atrioventricular conduction (AVC) and of VAC during a protocol including three steps: supine rest, upright position, and finally during cycloergometric exercise; the measurements were done at progressively increasing pacing rates. During a preimplantation EPS, Wenckebach points AVC-W and VAC-W and conduction times, AVCT and VACT (as a function of pacing rate), were measured in ten consecutive patients using temporary leads and an external device. In another study, AVCT, VACT, AVC-W, and VAC-W were measured by telemetric recordings under identical conditions in seven patients implanted earlier with a DDD pacemaker. A 1/1 VAC was observed in 7/17 patients (41%) at rest, and in 13/17 patients (76%) at the end of the protocol; VAC was never observed in 4/17 patients [23%], but occurred in six of the ten patients initially free, three standing at rest and three on exercise. For all patients, the VAC behavior remained of “nodal” type, indicated by a progressive increase in VACT as pacing rate rose up to the VAC-W point. Neither the existence of exercise-induced VAC nor the maximal VACT-W could be predicted from AVC or VAC data obtained at rest. However, at the same pacing rates, standing up and exercise induced a shortening effect on VACT, and improved the VAC-W by an average of 33%. These results suggest that the electrophysiological behavior of VAC does not obey any general rule and cannot be predicted individually. It would thus appear unwise to base pacemaker mediated tachycardia (PMT) protection solely on long postventricular atrial refractory period (PVARP) programming in DDD patients. This work also revealed the potential risks of a rate responsive auto-adaptive PVARP algorithm as proposed in certain new devices.     

New Developments for Upper Rate Response in DDD Pacing

Although widely accepted as an effective method of dealing with rapid atrial rates in a DDD pacemaker, Wenckebach-type and multiblock-type upper rate behaviors may exacerbate pacemaker-mediated tachycardia through AV dissociation. In addition, pathologic atrial rates (e.g., atrial fibrillation, atrial flutter, automatic atrial tachycardia, etc.) frequently result in ventricular pacing at inappropriately high rates. New, more sophisticated algorithms available in today's microprocessor-based DDD pacing systems provide the capability to discriminate successfully a normal atrial rate response to exercise from a pathologic atrial rate. These and other improved capabilities allow the clinician to provide safe rate-responsive pacing to patients in whom rate-responsive pacing was previously contraindicated.     

Complications in Dual Chamber Pacing: A Six-Year Experience

In a six-year period (1980–1985), 345 dual chamber pacing systems were implanted in our hospital. Intraoperative complications were rare (n = 5/345 = 1.4%). 25 patients (7%) have died, 11 (3%) were lost follow-up. A total of 39 patients (13%) showed minor problems, which could be overcome by reprogramming. Another 48 complications (15%) required reoperation. Nearly 70% of those reoperations (n = 31/48) were caused by a malfunction of the atrial lead. This high complication rate of 9% related to all implanted atrial leads could be reduced in the last three years to 2%. We could maintain a dual chamber stimulation mode (DDD, DDI, DVI, VDD) in 396 patients (99%). We conclude that improvements in lead design, pulse generator's programmability, and surgical experience have reduced complication rates to acceptable low values. Meanwhile, dual chamber pacing con be considered as safe as single chamber pacemaker therapy.     

Mode Switch Despite Undersensing of Atrial Fibrillation in ODD Pacing

Mode switching algorithms are commonly used to protect the ventricles against high rates induced by atrial tachycardia. In the case of atrial fibrillation (AF), the response of these algorithms depends on the quality of atrial sensing. The Chorum 7234 DDDR pacemaker uses a new mode switching algorithm, based on a statistical analysis of the atrial rhythm. It includes two criteria of diagnosis: "high" if more than 28 of 32 cycles are abnormally accelerated; and "low" if more than 36 of 64 cycles are abnormally accelerated. Methods: From a taped database of electrophysiological studies, episodes of AF lasting more than 2 minutes were selected. A tape recorder replayed the atrial signals into an external Chorum device. Each episode was replayed eight times with a programmed atrial sensitivity increasing from 0.4 –2.0 mV. For each criterion of diagnosis and each programmed sensitivity, the percentage of atrial sensing, the time to switching, and the mean ventricular rate were measured. Ten episodes of AF from 10 patients (9 men and 1 woman; ages 62 ± 16 years) were included: 1.95 ± 0.97 mV and 196 ± 64 ms. The sensitivity of the algorithm to diagnose atrial tachycardia reached 100%, for an atrial sensitivity set between 0.4 and 1.0 mV. The mean percentages of atrial sensed events were 74%± 18% and 46%± 9% for the "high" and "low" criteria, respectively. The mean diagnostic times were 28 ± 26 seconds and 68 ± 27 seconds, respectively. Sensing of < 23% of AF events resulted in failure to diagnose the arrhythmias by both algorithms. In the event of diagnostic failure, the mean ventricular pacing rate was 79 ± 9 ppm. Conclusion: Up to an atrial sensitivity of 1 mV, 100% of AF episodes were diagnosed. The Chorum mode switching algorithms are 100% reliable if > 45% of the AF waves are sensed. In the event of switching failure, the ventricle is protected by an average rate remaining below 80 ppm. (PACE 1996;     

Atrial Arrhythmias in Dual Chamber Pacing and Their Influence on Long-Term Mortality

A retrospective study of 252 patients who received a DDD pacemaker between October 1982 and December 1990 was performed. During a mean follow-up of 30 months, reprogramming to the VVI mode was necessary in 39 patients (15.5%). Technical problems causing downgrading occurred 15 times, of which 13 problems became permanent. A total number of 24 patients had sustained atrial arrhythmias, including 14 with atrial fibrillation and 10 with atrial flutter. In this group, conversion to sinus rhythm could be obtained in 38%. After 2 years, reliable DDD pacing was maintained in 86% of the surviving patients. The survival after 1 and 2 years was 94% and 89%, respectively, and was not influenced by arrhythmias or technical problems. We conclude that atrial arrhythmias including flutter are the most important reasons for reprogramming to the VVI mode, although in an important number of patients, predominantly those with flutter, restoration of AV synchrony can be obtained. The high number of patients with atrial flutter could imply some role for DDD devices offering the option of antitachycardia pacing. Reprogramming of the pacing mode did not influence mortality.