mode switching for atrial tachyarrhythmias

Mode Switching for AtrialTachyarrhythmias

Richard Sutton, DScMed, Zahra Stack, David Heaven, MBChB, and Ann Ingram

Mode switching for atrial tachyarrhythmias is a conceptthat originated from use of DDI mode and was intro-duced in the early 1990s to prevent dual-chamber pace-makers from ventricular tracking of rapid atrial rates.This article describes the currently available systems and

discusses the advantages and disadvantages of the tech-nique. The results of a preliminary randomized con-trolled trial of 1 algorithm and plans for a second studyare presented. Q1999 by Excerpta Medica, Inc.

Am J Cardiol 1999;83:202D–210D

Patients with intermittent atrial tachyarrhythmiaswho require DDD/DDDR pacing are limited by

the potential for rapid ventricular pacing due to track-ing of the atrial rhythm.1 As these patients requireatrioventricular synchrony during periods of sinusrhythm, a variety of mode-switch algorithms has beendeveloped to avoid the inappropriate tracking of atrialarrhythmias and to provide tracking of the sinus nodeat all other times.2 Usually, these algorithms enablethe pacemaker to change the mode of response toatrial sensed events from a tracking to a nontrackingmode, i.e., DDI/DDIR/VVI/VVIR/VDI/VDIR. Whenthe atrial rhythm exceeds a programmed detection ratefor a set number of intervals, the ventricle will bepaced at a predetermined rate in many cases modu-lated by a rate-adaptive sensor during the nontrackingmode.2 When sinus rhythm resumes, the pacemakerwill switch back to an atrial-tracking mode.

AIMSMode switching aims to achieve an appropriate

ventricular rate during periods of atrial arrhythmias bythe correct detection of premature atrial events andsmooth transitions between atrial-tracking and non-tracking pacing modes.

MODE-SWITCHING ALGORITHMSThe mode-switch algorithm differs from manufac-

turer to manufacturer and confusingly is given differ-ent names, e.g., automatic mode-switching (AMS), orAtrial Tachy Response (ATR). Telectronics (St. JudeMedical Center, Solna, Sweden) devised the first al-gorithm for mode switching in 1991 and called itAMS; it was the Meta DDDR 1250H that incorporatedthis algorithm.3 A description of each manufacturer’spresent device or devices follows.

SORIN–LIVING 1 DUAL-CHAMBER,DUAL-SENSOR ADAPTIVEPACEMAKER

This pacemaker (Sorin Biomedica, Saluggia, Italy)mode switches differently depending on whether it isoperating in the non-rate-responsive mode, DDD or

VDD (Figure 1), or a rate-responsive mode (DDDR orVDDR), and mode-switching behavior is known asAtrial Upper Rate (FAUR). When the pacemaker isoperating in the non-rate-responsive mode, it will rec-ognize an atrial tachycardia as being an intrinsic atrialrhythm that is faster than the Maximum Atrial Track-ing Rate (FMAT). Once the tachycardia is recognized,2 cycles occur at the maximum atrial-tracking rate andthen the mode is changed to VDI, with a reduction inthe ventricular pacing rate to the atrial upper ratewhere it paces for approximately 1,000 cycles. Theventricular pacing rate is then decremented in steps(fallback) down to a rate of 77 beats/min (this is anonprogrammable rate and therefore is recognizableas the mode-switching function). If 3 consecutiveatrial cycles are sensed at a rate lower than the max-imum atrial-tracking rate, then the pacemaker willrevert back to its actual programmed mode (DDD orVDD).

When the pacemaker is programmed to a rate-responsive mode (DDDR or VDDR), 2 different val-ues of upper rate can be programmed—FAUR andSensor Upper Rate (FSUR). If atrial upper rate isselected, then ventricular pacing will be limited whenthe atrial rate becomes too fast. If sensor upper rate isselected, the pacing rate can only increase to a levelcontrolled by the rate-responsive algorithm; the sensorupper rate has to be set at a higher rate than the atrialupper rate. Intrinsic atrial rhythm that is faster than theatrial upper rate will cause the pacemaker to functionin almost the same way as the non-rate-responsivemode if the rate calculated from the rate-responsivealgorithm remains lower than the atrial upper rate.This pacemaker has 2 sensors, a physical activitysensor (GVM) and a cardiac contractility sensor(PEA). If the physical activity sensor is activatedwhen a high intrinsic atrial rate is sensed, the pace-maker will switch to VDI for 250 cycles at atrial upperrate (Figure 2). The pacemaker then compares thecalculated rate of the rate-responsive algorithmagainst a predefined confirmation rate to checkwhether the high atrial rate is activity related. If thehigh rate is not activity related, the pacemakerchanges mode again to VDIR and the rate is allowedto fall back to the rest rate, which is calculated fromthe rate-responsive algorithm.

If the cardiac contractility sensor is activated (Fig-ure 3), it can detect whether the high atrial intrinsic

From the Department of Pacing and Electrophysiology, Royal Bromp-ton Hospital, London, United Kingdom.

Address for reprints: Richard Sutton, DScMed, Royal BromptonHospital Pacing and Electrophysiology Department, Sydney Street,London, United Kingdom.

202D ©1999 by Excerpta Medica, Inc. 0002-9149/99/$20.00All rights reserved. PII S002-9149(99)01024-8

rate is physiologic or not, allowing the pacemaker toswitch appropriately to VDIR and fall back as de-scribed above if the high atrial rate is due to an atrialtachyarrhythmia.

With this algorithm, the rate to which fallbackoccurs may not be high enough when rate response isprogrammed off.

ELA–CHORUS II DUAL-CHAMBERPACEMAKER

To detect atrial arrhythmias, this pacemaker (ELAMedical, France) uses a window of atrial rate accel-eration detection (WARAD) that starts after an atrialbeat and lasts for either 75% of the previous sinusinterval or, if the previous atrial interval is paced, 75%of the average 8 previous sinus intervals. A sensedatrial beat outside the absolute refractory period butinside the window of atrial rate acceleration detectionis defined as a premature atrial beat. If an atrial sensedbeat is then detected after the premature atrial beat butbefore the end of the atrial escape interval, the pace-maker enters an atrial arrhythmia suspicion phasewhere ventricular pacing is limited to 120 beats/min orthe programmed maximum rate if lower. If the atrialrate increases slowly until the maximum rate isreached, the pacemaker cannot enter the suspicionphase and a Wenckebach response will occur for2,000 ventricular cycles before fallback. During theatrial arrhythmia suspicion phase, the pacemakermaintains at least 2 : 1 association (Figure 4); once thecriteria for atrial arrhythmia have been observed for30 seconds (i.e., atrial events outside the absoluterefractory period but inside the window of atrial rateacceleration detection), the pacemaker will revert to afallback mode. In this mode, the pacemaker operatesin VDI and the ventricular escape interval is length-ened by 31 msec every 8 cycles until the ventricularrate decreases to 70 beats/min.

Once the intrinsic atrial rate decreases below theprogrammed maximum rate, the ventricular pacinginterval will be shortened by 63 msec every 8 cyclesuntil the ventricular rate equals the intrinsic atrial rate,thus re-establishing atrioventricular synchrony withDDD pacing. Mode switch with this device is slow butgentle. The final fallback rate may be too slow.

CHORUM RATE-RESPONSIVE DUAL-CHAMBER PACEMAKER

This pacemaker (ELA Medical, France) also usesthe window of atrial rate acceleration detection todifferentiate between sinus rhythm and atrial tachyar-rhythmias, but it functions slightly differently. In thiscase, the window of atrial rate acceleration detectionis a window that lasts for 62.5% of the sinus intervalwhen the sinus rate is,80 beats/min, and 75% of thesinus interval when the sinus rate is higher. Onceagain a suspected atrial arrhythmia phase is used andthe ventricular rate limited to 120 beats/min, or theprogrammed maximum rate depending on which is thelower (Figure 5). Every 32 cycles, the number of

FIGURE 1. Mode switching in a non-rate-responsive mode. Forexplanation see text. FAUR 5 atrial upper rate; FB 5 basic rate;FSA 5 spontaneous atrial rate.

FIGURE 2. Mode switching with the physical activity sensor(GVM). For explanation see text. FAUR 5 atrial upper rate;FB 5 basic rate; FRR 5 rest rate; FSUR 5 sensor upper rate.

FIGURE 3. Mode switching using the physical activity sensor(GVM) and the cardiac contractility sensor (PEA). For explanationsee text. FAUR 5 atrial upper rate. FB 5 basic rate; FRR 5 restrate; FSUR 5 sensor upper rate.

FIGURE 4. ELA Chorus II mode-switch algorithm. For explanationsee text. P 5 atrial rate; URL 5 upper rate limit; V 5 ventricularpaced rate.

A SYMPOSIUM: ELECTRICAL MANAGEMENT OF CARDIAC DISORDERS 203D

cycles in the suspected atrial arrhythmia phase arecounted; if$28 cycles have fallen into this phase or if$18 cycles in the last 2 groups of 32 cycles are in thephase, then the atrial arrhythmia is confirmed. Thepacemaker switches to VDI and falls back to the basicrate or the sensor-driven rate, but if the pacing rate is,83 beats/min, the pacemaker will pace in DDI mode.

When the atrial and ventricular rate decreases to,120 beats/min or the programmed maximum rate,the ventricular escape interval is shortened by 63 msecevery 12 cycles until the ventricular rate equals theintrinsic atrial rate and atrioventricular synchrony isrestored.

INTERMEDICS—MARATHON DUAL-CHAMBER RATE-RESPONSIVEPACEMAKER

This pacemaker (Intermedics, CPI Guidant, St.Paul, MN) has a “SmarTracking” algorithm (Figure 6)and a programmable mode-switching function (Figure7), a development of their earlier algorithm.4 Foreffective mode switching, these should be used inconjunction with each other. SmarTracking is a dy-namic ventricular tracking limit, which adjusts to thepatient’s level of activity.

The upper tracking limit is constantly adjusteddepending on the slope of the relation between the

FIGURE 6. SmarTracking. For explanation see text. BPM 5 beats/min.

FIGURE 7. Intermedics Marathon mode-switch algorithm. For explanation see text.

FIGURE 5. Mode-switch algorithm of the Chorum pacemaker. For explanation see text.

204D THE AMERICAN JOURNAL OF CARDIOLOGYT VOL. 83 (5B) MARCH 11, 1999

sensor-indicated rate and the upper tracking limit.Effective programming of the sensor will prevent in-appropriately high atrial rates from being tracked,because the sensor should indicate that the patient isinactive, an example of sensor corroboration. Themode-switching algorithm requires a detection rate tobe programmed that can vary from 10 beats/min abovethe maximum pacing rate (minimum 95 beats/min) upto 300 beats/min in 5-beat increments. The number ofdetection beats also needs to be programmed, and thiscan vary from 1 cycle up to 7 cycles. Every intrinsicatrial event that does not fall into the postventricularatrial blanking (PVAB) period of 100 msec will initi-ate a mode-switching interval. If an intrinsic atrialevent occurs within the mode-switching interval, anew interval starts and the counter increases by 1.When the programmed consecutive number of cycleshas been reached, the pacemaker reverts to VVIRmode (possibly in essence VDIR).

If no intrinsic atrial events are sensed within themode-switching interval, the pacemaker will revertback to the programmed mode. This is a sophisticatedmode-switch algorithm, but possibly a little slow.

VITATRON—DIAMOND II DDDR,RUBY II DDD, AND SAPHIR II VDDRPACEMAKERS

These pacemakers (Vitatron Medical B.V., KIDieren, the Netherlands) divide atrial events intophysiologic or pathologic events using a physiologicrate band.5 The physiologic rate is a “moving” averageof the intrinsic atrial rate or the sensor-indicated rate.This physiologic rate is limited between the pro-grammed lower rate and the maximum sensor ortracking rate (depending on which is higher). Thephysiologic band is an area 15 beats/min higher andlower than the physiologic rate if mode switching isselected as automatic (Figure 8). In this automaticmode switch, atrial tachyarrhythmias can be detectedabove and below the maximum tracking rate. If modeswitching is programmed to a fixed setting (Figure 9),the upper limit of the physiologic band will be equal tothe maximum tracking rate, and only atrial rates abovethe maximum tracking rate are not tracked.

Any atrial event outside this band is deemed patho-logic; if these rates are higher than the upper limit of

the band they will be assumed to be atrial tachyar-rhythmias. Once an atrial tachyarrhythmia has beensensed, the pacemakers will mode switch to a non-tracking mode, as shown in Table I.

Atrial rhythm is interpreted on a beat-to-beat basis,so a single premature atrial beat that occurs above thephysiologic band (a pathologic event) will not betracked, and the flywheel rate or the sensor rate de-termines the ventricular rate so that variations in theventricular rate are limited. Therefore, a prematureatrial beat will not result in a premature paced ven-tricular beat. When the second consecutive atrialsensed event falls inside the physiologic band, thepacemaker will revert back to the programmed modeand atrial tracking is restored. Fast mode switchingmay be achieved with this algorithm.

PACESETTER—TRILOGY DUAL-CHAMBER RATE-RESPONSIVEPACEMAKER

For mode switching to occur with this pacemaker(Pacesetter, St. Jude Medical Center, Solna, Sweden),6

an Atrial Tachycardia Detection Rate (ATDR) needsto be programmed. This atrial tachycardia detectionrate is programmable from 20 beats/min higher thanthe programmed maximum tracking rate or maximumsensor rate (whichever is the higher) up to a rate of300 beats/min in 10-beat increments. When the intrin-sic atrial rate increases above the atrial tachycardiadetection rate, a Filtered Atrial Rate Interval (FARI)automatically decreases by up to 38 msec and contin-ues to decrease until the filtered atrial rate reaches theprogrammed atrial tachycardia detection rate (Figure10). Mode switching will then occur (this can take upto 10 seconds for mode switching to be activated). Thefiltered atrial rate interval prevents a single prematureatrial contraction from triggering mode switching. Ifthe pacemaker is programmed DDDR, it will modeswitch to DDIR; if programmed DDD, it will modeswitch to DDI.

Once the averaged intrinsic atrial rate decreasesbelow the maximum tracking rate or maximum sensorrate, the pacemaker will revert to the programmedmode. This algorithm results in relatively slow modeswitching.

FIGURE 8. Automatic mode switching. For explanation see text. FIGURE 9. Fixed mode switching. For explanation see text.


BIOTRONIK—ACTROS DDDR/DDD/VDDR PACEMAKERS

The Actros family of pacemakers (BiotronikGmbH & Co., Berlin, Germany) uses the AutomaticMode Conversion (AMC) algorithm to deal with atrialtachyarrhythmias (Figure 11). The pacemaker mea-sures P-P intervals; if a P-P interval is shorter than theatrial refractory period, the pacemaker will modeswitch from DDDR/DDD to DVIR/DVI or fromVDDR/VDD to VVIR/VVI, preventing tracking ofthe intrinsic atrial events. An atrial sensed event thatoccurs during the atrial refractory period will restartthe atrial refractory period; any further sensed eventsthat occur in this new refractory period will extend itagain. This continues until either the lower rate limit isreached, so an atrial paced event occurs, or a sensedatrial beat occurs outside the refractory period, so itwill be tracked. Therefore, if an atrial tachyarrhythmiais present, the pacemaker will asynchronously pace inthe atrium at the basic rate or sensor rate if the rateresponse is programmed on (in VDDR/VDD modesonly the ventricle can be paced).

Once the P-P intervals lengthen (i.e., the atrialtachyarrhythmia has terminated) and become longerthan the atrial refractory period, the pacemaker willresume normal function in the programmed mode.

INOS2 CLOSED-LOOP STIMULATIONDUAL-CHAMBER PACEMAKER ANDRATE-ADAPTIVE DUAL-CHAMBERPACEMAKER WITH ANS CONTROL

To detect an atrial tachyarrhythmia, these pace-makers monitor the length of the preceding 8 atrialintervals; if 5 of 8 (or more) of these intervals areshorter than the programmed tachycardia interval orintervention rate, the pacemaker will mode switch to

VDI mode from the programmed mode (DDDR/DDDor VDD). The intervention rate can be programmedfrom 100 to 180 beats/min in 10-beat increments.When monitoring the atrial rate, atrial sensed eventsthat occur during the atrial refractory period arecounted. However, atrial events that have a couplinginterval,125 msec (.480 beats/min) are interpretedas interference and, therefore, will not initiate modeswitching. When mode switching occurs, the ventric-ular rate is decreased at a rate of 1 pulse per minute/interval until the programmed lower rate is reached. If8 consecutive atrial beats are sensed that have a ratelower than the intervention rate, or if no atrial eventsare sensed approximately 8 seconds after the last atrialsensed beat, the pacemaker will switch back to itsprogrammed mode. This algorithm results in ratherslow mode switching

CPI/GUIDANT—PULSAR DDD/VDD,DISCOVERY DDDR, AND MERIDIANDDD/DDDR

The algorithm for mode switching is called AtrialTachy Response (ATR) in the CPI family of pacemak-ers (CPI/Guidant, St. Paul, MN; Figure 12). For modeswitching to occur, an atrial tachy response triggerrate needs to be programmed, atrial events are con-stantly monitored (except during the atrial blankingperiod and noise interrogation intervals), and anyatrial events above the programmed trigger rate willincrease a detection counter. The trigger rate can beprogrammed from 100 to 200 beats/min in 5-beatintervals. When the atrial tachy response detectioncounter reaches 8 (this does not have to be 8 consec-utive high atrial rates, as atrial beats below the triggerrate will decrease the counter), atrial tachy responseduration starts. Atrial tachy response duration can beprogrammed as zero cycles or from 8 to 2,048 cycles;the number of cycles programmed determines howlong the atrial tachyarrhythmia will continue to bemonitored before mode switching can occur. Themode that the pacemaker switches to is programmablefor each pacemaker: the Pulsar can mode switch toVDI/VDIR or DDI, whereas the Discovery and Me-ridian switch to DDI/DDIR/VDI or VDIR. The ven-tricular paced rate will decrease or fall back to thelower rate limit (if a non-rate-responsive mode isprogrammed for mode switching) or the sensor-indi-cated rate (if a rate-responsive mode is programmed).This occurs over a period of time, which is dependenton the Fallback Time parameter and is programmable

FIGURE 10. Pacesetter trilogy mode-switch algorithm. For expla-nation see text. FARI 5 filtered atrial rate interval.

TABLE I Mode-Switching Behavior of Vitatron’s Collection II Pacemakers

Pacemaker Type Mode Switch Pacemaker Response

Diamond II DDDR/VDDRor DDD

DDIR/VDIR or DDI Sensor-driven ventricular pacing orlower-rate ventricular pacing

Ruby II DDD/VDD DDI/VDI Ventricular pacing at tachy fallback rate*Saphir II VDDR VDIR Sensor-driven ventricular pacing

*The tachy fallback rate is programmable between the lower rate and 100 beats per minute.


from 0 to 120 seconds in 5-second increments. Atrialevents that are slower than the trigger rate or absenceof atrial sensed events will cause the atrial tachyresponse counter to decrease; when this counterreaches zero, the pacemaker will revert back to theprogrammed pacing mode.

The Pulsar DDD pacemaker also has an AtrialFlutter Response (AFR) that provides instant fallbackfor atrial rates.230 beats/min (when this pacemakeris programmed to DDD or DDI). When the atrialflutter response is programmed to this rate, an atrialevent within the post-ventricular atrial refractory pe-

riod (PVARP), or a previously triggered atrial flutterresponse interval will start an atrial flutter responsewindow of 260 msec (230 beats/min). Atrial eventssensed within the atrial flutter response will not betracked, and paced atrial events will be delayed untilthe atrial flutter response window has expired; if#50msec remains before a ventricular paced event isscheduled, then the atrial paced event will be inhibitedfor the cycle. If the atrial rate remains.230 beats/min, constant retriggering of the atrial flutter responsewindow occurs and the pacemaker effectively worksin VDI mode. In summary, this ATR algorithm results

FIGURE 11. Automatic mode conversion with Biotronik Actros. For explanation see text.Ap 5 atrial pace event; AS 5 atrial sense event.

FIGURE 12. CPI atrial tachy algorithm. For explanation see text. ATR 5 atrial tachy response.


in a variety of programmability but may tend to evokevery slow mode switching, especially when long ATRdurations are programmed. However, when used incombination with the AFR algorithm, the responsebecomes immediate.

MEDTRONIC—THERA DDD/DDDR/VDD AND KAPPA 400 SERIESPACEMAKERS

When mode switching is programmed on, thesepacemakers (Medtronic Inc., Minneapolis, MN) con-tinuously monitor the atrial rate (Figure 13), whichresults in the pacemaker calculating a Mean AtrialRate (MAR).7 A detection rate also needs to be pro-grammed for mode switching to occur, and this isprogrammable from 120 to 190 beats/min in 5-beatincrements. When the mean atrial rate becomes fasterthan the detection rate, the pacemaker will modeswitch from DDDR/DDD to DDIR or from VDD toVVIR, and the ventricular pacing rate is decreased byadding 40 msec each cycle until the sensor-indicatedrate is reached. When the mean atrial rate decreases tobelow the upper tracking rate or 5 consecutive atrialpaced beats occur, the pacemaker presumes that theatrial tachyarrhythmia has terminated. If the pace-maker is programmed to DDDR or DDD, it will revertback to the programmed mode and the ventricular rateis gradually increased by decreasing each cycle lengthby 40 msec until the intrinsic atrial rate or the lowerrate is met. If the pacemaker is programmed to VDD,it will decrease the ventricular rate until atrial trackingoccurs. This algorithm results in slow mode switching.

KAPPA 600 AND 700 SERIESPACEMAKERS

The mode switching algorithm for these pacemak-ers works differently than for the earlier models, but aprogrammed rate detection is still required and it canbe programmed from 120 to 200 beats/min in 5-beatintervals (Figure 14). A detection duration is now

required and can be programmed from “no delay” upto 60 seconds’ delay. A-A intervals are constantlymonitored when the intrinsic atrial rate is the same orfaster than the detection rate for 4 of 7 consecutiveatrial events and occurs for the whole of the detectionduration; the pacemaker will mode switch fromDDDR/DDD to DDIR and from VDD to VDIR.

The ventricular rate is gradually decreased until itreaches the sensor-indicated rate. If Blanked FlutterSearch (BFS) (Figure 15) is programmed on, the pace-maker will decide whether a faster atrial rate is hiddenwithin the Total Atrial Blanking (TAB) period.

If 8 consecutive A-A intervals are less than twicethe total atrial blanking period and less than twice thedetection rate, the pacemaker will extend the PVARPfor 1 beat to determine whether a blanked atrial eventis present; if it is, mode switching will occur. When 7consecutive A-A intervals are slower than the UpperTracking Rate, or if 5 consecutive atrial paced beatsoccur, then the termination criteria have been reachedand the pacemaker will switch back to the pro-grammed mode. This newer approach permits fastermode switching. The Blanked Flutter Search appearssophisticated.

ADVANTAGES OF MODESWITCHING

Patients with paroxysmal atrial tachycardias canbecome extremely symptomatic due to tracking of thearrhythmia, which causes inappropriate rapid ventric-ular rates. If these patients were programmed to apermanent atrial nontracking mode, they would notexperience rapid ventricular rates but would not haveatrioventricular synchrony during the periods of sinusrhythm and, therefore, be compromised. Mode switch-ing has enabled this group of patients to benefit fromphysiologic pacing during periods of normal atrialactivity and avoidance of symptoms when an atrial

FIGURE 13. Calculation of the mean atrial rate (MAR). For explanation see text. MAR 5 meanatrial rate.


tachycardia is present and the pacemaker modeswitches.8,9

DISADVANTAGES/PROBLEMS OFMODE SWITCHING

All of the above-mentioned algorithms have draw-backs. The main problems associated with modeswitching include the actual detection of atrial ar-rhythmias. The sensing amplifier of the pacemakerneeds to be of a high enough sensitivity to ensure thatatrial arrhythmias are detected, particularly becausethe atrial electrogram typically decreases during atrialarrhythmias. Bipolar sensing should be used so thatmyopotentials, far-field R waves, and other interfer-ence will not be sensed. Sinus tachycardia can causeinappropriate mode switching, so the criteria need tobe stringent enough to prevent this from happening.Stringent criteria will also prevent too many modechanges occurring, which can be unpleasant for thepatient.10,11 However, if the criteria are too stringent,the patient can experience prolonged rapid ventricularrates before mode switching occurs. Considerationneeds to be given when programming a mode-switch-ing algorithm to obtain the most accurate use of thealgorithm. A high level of atrial sensitivity is required,along with a short postventricular atrial blanking pe-riod and atrioventricular delay, to enhance the chancesof an atrial arrhythmia being sensed correctly, butlong enough to ensure that far-field sensing does notoccur.

MODE-SWITCHING EXPERIENCEWITH THE CPI VIGOR PACEMAKER—MOSATR 1

Initially, a study group was formed to conduct a3-month prospective randomization/crossover studyinvestigating the benefits to patients with sick sinussyndrome if the mode-switching algorithm, AtrialTachy Response (ATR) in the Vigor pacemaker wasprogrammed on, compared with ATR being pro-grammed off. This study was known as MOSATR 1.12

During the course of the study, it was noted that therewere vast problems with the atrial sensing, leading tofailure of the atrial tachy response algorithm. Theextent of this problem led to the initial objective of thestudy being suspended and the data that had beencollected up to that time being carefully analyzed forappropriate atrial sensing. The study was set up as amulticenter prospective study with the primary goal ofassessing symptomatic benefit of atrial tachy responseon, compared with atrial tachy response off. The studyperiod was 3 months, the first month being a random-ized run-in period, followed by a second randomizedperiod and a crossover period during the last month. A24-hour Holter monitor was fitted at the end of eachperiod, coincident with clearance of the histograms.Upon return the following day, the histograms wereagain reset and the atrial tachy response repro-grammed according to randomization. Quality-of-lifequestionnaires were performed at the end of each

FIGURE 14. Medtronic Kappa 600/700 series mode switch algorithm. For explanation seetext.

FIGURE 15. Blanked flutter search. For explanation see text.


month to evaluate effectiveness of the atrial tachyresponse algorithm.

A total of 74 patients were recruited into 3 studygroups: those with sick sinus syndrome and intactatrioventricular conduction (group A), those with sicksinus syndrome without atrioventricular conduction(group B), and those patients who have undergoneatrioventricular node ablation (group C). ChronotropicAssessment Exercise Protocol (CAEP) exercise tests,24-hour Holter monitor, and quality-of-life question-naires were performed before implant. All patientswere then implanted with either CPI Vigor DDD 950or DDDR 1230. The atrial tachy response algorithmwas randomized to on or off, 1 day after implant. Thelower rate limit of the pacemaker was set to 70 beats/min and the upper rate could be programmed between130 and 150 beats/min, although these limits could bechanged during the first 28 days of the study. Initially,atrial sensitivity was programmed to 0.25 mV. How-ever, approximately 1 year into recruitment, problemswith atrial sensing were noted on the 24-hour Holtertapes. This was due to saturation of the amplifiers, andatrial sensitivity was recommended to be repro-grammed to 0.75 mV. Of the 74 patients entered intothe study up to then, completed data were provided on63; 27 of these showed some evidence of atrial un-dersensing on Holter monitors. Analysis of these datashowed that all 3 study groups were significantlyimproved by DDD pacing (p,0.01) irrespective ofwhether mode switching was programmed on or off,but there was no statistically significant benefit ofmode switching on or mode switching off. Becausethe mode-switching algorithm has now been rede-signed and the atrial amplifier improved, it seemedvalid to reattempt this study with a modified protocolMOSATR 2.

MOSATR 2The initial objective of the study, to evaluate

whether Atrial Tachy Response offers symptomaticbenefit to patients with sick sinus syndrome, will nowbe performed in this study; recruitment for this is justbeginning. MOSATR 2 has some differences com-pared with MOSATR 1, the main difference being thatCPI has replaced the Vigor pacemaker with a newfamily of pacemakers, and it is the Pulsar or Discov-

ery pacemakers that will be used. Days 2–28 of thestudy are now a run-in period where the lower ratelimit is set to 70 beats/min and the upper rate is set to90 beats/min (120 beats/min for group C patients)with atrial tachy response programmed off. The atrialsensitivity will be programmed to 0.5 mV unless clin-ically inappropriate. On day 29, patients are random-ized to atrial tachy response on or off, and on day 58,this randomization is crossed over. Again, 24-hourHolter tapes are recorded, but enhanced pacemakerdiagnostic data are now available, so analysis of atrialevents will be easier and more complete. Patients willreceive the same quality-of-life questionnaires as inMOSATR 1. It is these questionnaires that will test thehypothesis of MOSATR 2 in proving whether theAtrial Tachy Response algorithm gives symptomaticbenefit.

1. Castallanet M, Florio J, Messenger J. DDI: a new mode for cardiac pacing.Clin Prog Pacing Electrophysiol1984;2:255–260.2. Mond HG, Barold SS. Dual chamber, rate adaptive pacing in patients withparoxysmal supraventricular tachyarrhythmias: protective measures for rate con-trol. PACE Pacing Clin Electrophysiol1993;16:2168–2185.3. Lau CP, Tai YU, Fong PC. Atrial arrhythmia management with sensorcontrolled atrial refractory period and automatic mode switching in patients withminute ventilation sensing dual chamber rate adaptive pacemakers.PACE PacingClin Electrophysiol1992;15:1504–1514.4. Lee MT, Adkins A, Woodson D, Vandegriff J. A new feature for control ofinappropriate high rate tracking in DDDR pacemakers.PACE Pacing ClinElectrophysiol1990;13:1852–1855.5. den Dulk K, Dijkman B, Pieterse M. Initial experience with mode switching ina dual sensor, dual chamber pacemaker in patients with paroxysmal atrial tachy-arrhythmias.PACE Pacing Clin Electrophysiol1994;17:1900–1907.6. Levine PA, Bornzin GA, Barlow J, Florio J, Sholder J, Tyler J, Mann B. A newautomode switch algorithm for supraventricular tachycardias.PACE Pacing ClinElectrophysiol1994;17:1895–1899.7. Ovsyshcher IE, Katz A, Bondy C. Initial experience with a new algorithm forautomatic mode switching from DDDR to DDIR mode.PACE Pacing ClinElectrophysiol1994;17:1908–1912.8. Sutton R. Mode switching in DDDR pacing. In: Aubert AE, Ector H, Stroo-bandt R, eds.Cardiac Pacing and Electrophysiology: A Bridge to the 21stCentury. Dordrecht, The Netherlands: Kluwer Academic Publishers, 1994:363–370.9. Kay GN, Bubien RS. Algorithms for management of atrial fibrillation inpatients with dual chamber pacing systems. In: Rosenqvist M, ed.CardiacPacing: New Advances. London: WB Saunders, 1997:61–82.10. Pitney MR, May CD, Davis MJ. Undesirable mode switching with a dual-chamber rate-responsive pacemaker.PACE Pacing Clin Electrophysiol1993;16:729–737.11. Wagshal AB, Dansereau LJ, Mittleman RS, Stephen Huang SK. Undesirablemode switching with a Telectronics 1250 META DDDR pacemaker. (Letter,Comment.)PACE Pacing Clin Electrophysiol1993;16:2212–2213.12. Sutton R. Evaluation of DDD pacing with and without atrial tachy responsein patients with sick sinus syndrome.Eur J Cardiac Pacing Electrophysiol1995;5:49–53.


mode switching for atrial tachyarrhythmias

Documents