Inappropriate therapy from atrial fibrillation and sinus tachycardia in automated implantable cardioverter defibrillators

Electrophysiology

Inappropriate therapy from atrial fibrillation sinus tachycardia in automated implantable cardioverter defibrillators Kumar Nanthakumar, MD,” Miney Paquette, MSc,= Bruce Gunderson, MSC,~ Jim Gilkerson,

MSc,= David Newman, PhD,e Mary Greene,

Toronto,

St Paul,

Ontario,

Canada;

Background [ST])

Inappropriate

in patients

algorithms

with

from

all episodes

of inappropriate Therapy

electrograms,

history,

sensitivity

and

turer

receiver

and

Results available.

specificity

episodes

of ST from

facturers

at about

caused

and

for VT. We 19 patients. An onset

62

value

(atrial

Sunnyvale,

fibrillation

challenge.

We

therapy

delivered

because

tachycardia

and

(29%)

received

(VT),

inception.

tested

Calq

[AF] the

and

sinus

tachycardia

performance

of AF and

ST, or AF from By using

of onset

was

inappropriate for AF,

19 for

of VT from

in the clinically

of 80%

study percentage

therapy

83 episodes

Specificity,

and

of stability

an onset

algorithm

for

30

values

review

to 60

were

of stored

R-R intervals

calculated

for

intracardiac before

each

therapy,

manufac-

generated.

received

analyzed

Texas;

tachyarrhythmias

before

values

curves

1 patients

Angleton,

is a major

by ventricular R-R data

of stability

monitored, 2

MD,” D. Curtis Deno, MD, PhD,b Lisa Malden, MSC,~ Denis Heng, BSC,~ and Paul Dorian, MDa

by ST.

as caused

characteristic

patients,

40%.

of inappropriate

a family

Of the 2 17 patients therapy

for episodes

information,

operating

Of the 40

appropriate

for

supraventricular defibrillators

classified

clinical

from

Minn;

cardioverter therapy

was

and

therapy

implanted

3 manufacturers

Methods

rithm

Minneapolis

and

relevant

associated

with

therapy,

18 patients,

94

sensitivity

range

91%

sensitivity

and

1 patient

ST, and

episodes

had

for

noise;

complete

95%

was

R-R information

15 (38%)

of AF from

of 295%, and

40

comparable

specificity

also

1 patients,

2

received and

across

for the specific

56 manualgo-

tested.

Conclusions

Inappropriate

stability

used

algorithm

algorithms accurately

therapy

to differentiate

differentiates

is a common AF from

ST from

problem

VT was

VT. (Am

less than

Heart

Submitted August 16, 1999; accepted December 3, I999 Reprmt requests: Paul Dorion, MD, Division of Cardiology, St Mlchoel’s Hospital, 30 Bond St, Q-705 1, Toronto, Ontario, Canada, MSB I W8. E-mall. [email protected] co Copyright 0 2000 by Mosby, Inc. 0002.8703/2000/$ I2 00 + 0 4/l/104757 doi: IO. 1067/mh~.2000 104757

ideal,

though

cardiac comparable

defibrillators. across

The

performance

manufacturers.

of the The

onset

J 2000;139:797-803.)

It is estimated that more than 50,000 cardiac defibrillators (ICD) were implanted worldwide in 1997.’ Although ICDs are very accurate and effective in the diagnosis and treatment of ventricular tachycardia (VT) and ventricular fibrillation (VF), inappropriate therapy from supraventricular tachyarrhythmias is a major challenge and is reported to affect 20% to 30% of patients.z-9 Atria1 fibrillation and sinus tachycardia are the most common reasons for inappropriate delivery of therapy.” It is estimated that approximately 12% of all patients with an ICD will receive inappropriate therapy because of atria1 fibrillation,x~” and in those with a prior From 0St Mlchoel’s Hospifol, Toronto; bfnfermedrcs Inc. Angleton; cSl Jude/Venlritex Inc. Svnnyvole; dMedkonic Inc. Mmneopohs; and eGwdonf Inc. St Paul.

in implantable

history of atria1 fibrillation, twice as many will receive inappropriate therapy.‘O The consequences of inappropriate therapy include pain and its psychological sequelae (particularly anxiety), induction of ventricular arrhythmias, decreased battery longevity, and rarely, fatal outcomes. l l-l2 The primary detection criterion in all current ICDs is heart rate (R-R intervals). To decrease the frequency of inappropriate therapy, several detection criteria beyond R-R interval alone may be available in single-chambered tiered therapy (ICDs with antitachycardia pacing and low energy cardioversion capability) devices. These algorithms are based on R-R interval pattern or QRS morphologic criteria. Those relying on R-R intervals include sudden onset, stability, and sustained rate duration. The most commonly used algorithms rely on the expectation that atria1 fibrillation is more irregular than VT, with rate stability programmed to withhold therapy for rhythms that exceed the rate cutoff for tachycardia detection but exhibit R-R variability exceeding a pre-

Amerox

798

Nonthokumor

et al

specified value. Similarly, rhythms with a “Sudden onset” are thought to be likely caused by VT and those with more gradual onset by sinus tacliycardia5.‘3,1$ therapy can be withheld if onset is more gradual than the programmed value. These detection algorithms are, however, not programmable in the VF zone. However, clinicians have been hesitant to enable these functions because of the risk of withholding therapy for VT.‘5-17 Studies to date on the perfomiance of onset and stability algorithms have primarily been based on atrlal fibrillation induced at electrophysiology study and sinus tachycardia and atria1 fibrillation from Holter monitors.1j.14 There are few studies that prospectively evaluated the performance of single algorithms in a small number of inappropriate therapies.21*z3 The irregularity noted at the onset of spontaneous episodes of VT and the irregularity of polymorphic VT may result in overlap of stability values with atrial fibrillation with rapid ventricular response.5,17 Sinus tachycardia that leads into VT may have an overlap of onset values with VT. We therefore tested the hypothetical performance of stability algorithms from 3 different ICD manufacturers for episodes of inappropriately delivered therapy from atrlal fibrillation and performance of a particular onset algorithm for episodes of inappropriate therapy caused by sinus tachycardia and assessed their accuracy in detecting spontaneous VT ln the same group of patients.

Methods Patient population All patients who had ICDs with data-logging capability (II = 217) implanted between 1990 and 1998 at St Michael’s Hospital were included in the study. AI1 had single-chamber, third-generation tiered therapy devices with intracardiac electrocardiographic storage from 1 of the 4 major manufacturers (Guidant Inc, St Paul, Minn; Intermedics Inc. AngIeton. Texas; St Jude/Ventritex Inc, Sunnyvale, Calif; and Medtronic Inc, Minneapolis, Minn). AII tachycardia episodes leading to device therapy had been prospectively classified as appropriate or inappropriate by the 2 attending electrophysiologists and personnel in the ICD clinic. Inappropriate therapy was defined as therapy for other than VT or VF from a review of stored electrograms, R-R interval data, history, and clinical data for each episode. Ail patients who received any inappropriate therapy were included for analysis, whether or not they had received appropriate therapy for VT or VF episodes. Arrhythmia detection Arrhythmia detection was based on the evaluation of consecutive R-R intervals. The detection criterion is fulfilled in some devices if x/y (for example 8/ 12 or 12/ 16) R-R intervals (range 8 to 16) are shorter than the programmed value and in other devices if a certain number of consecutive beats have cycle length shorter than the programmed value. After this criterion has been met, some devices recont3-m the presence of arrhy-thmia while preparing for therapy, whereas others start therapy as soon as criteria have been met. None of the patients had additional discriminators programmed such as

Heart Journal May 2000

stability or onset. However, all patients had programmed sustained rate durdtion (when available). Sustained rate durdtion is a function of the ICD that triggers therapy after a certain period of progrdmn%IbIe time has elapsed during a tachycardia event independently of the classification of that rhythm. Study design We reviewed data logs of all our ICD patients and collected cIinicaI information and demographic data. Patients who had received inappropriate therapy were identified. Inappropriate therapies were classified as caused by atrial fibrillation, sinus tachycardia. or noise. The R-R intervals for all episodes leading to inappropriate therapy for atrial fibrillation or sinus tachycardia and R-R intervals of all episodes of true VT in these patients were retrieved from the data logs. Depending on the manufacturer, between 26 to 40 R-R intervals preceding device declaration of VT and 8 to 20 additional intervals before delivery of therapy were recorded. The data were stored in a Microsoft Excel database (Microsoft Inc. Redmond, Wash) and analyzed by a customized program designed to calculate a stability and onset value for each of the different algorithms. Stability criterion The performance of stability algorithms from 3 different manufacturers (Guidant, Intermedics, and St. Jude/Ventritex) in distinguishing between ventricular and supraventricular arrhythmias was tested with the stored R-R data from the episodes of detected tachycardia. The Guidant stability algorithm This algorithm measures differences between consecutive R-R intervals after the rate criterion has been satisfied. The stability of the rhythm is analyzed by the variance in cycle length. The weighted average variance (the recent R-R intervals contribute more than the remote R-R Intervals) is calculated after every newly detected R-R interval. This current weighted average difference in consecutive R-R intervals is compared with the programmed stability parameter. If the value is equal to or less than the programmed value, the rhythm is thought to be stable and therapy is delivered. However, if the calculated vziability value is greater than the programmed value, the rhythm is deemed unstable and therdpy is withheld. The Intermedics stability algorithm In this algorithm a ventricular rate criterion operates in parallel, although not independently because a single long R-R interval out of the tachycardia zone resets a stability counter. Each new R-R interval contributes to a running assessment of the longest R-R (R-Rmax) and shortest R-R (R-Rmin) vaIues over the beats since a reset. Evidence for stability is accumulated with each successive R-R interval that falls in the tachycardia zone and that does not result in the R-Rmax/R-Rmin difference exceeding a programmed stability parameter. When the stabilit) evidence counter exceeds the programmed value for a specific number of consecutive intervals, then the rhythm is judged both stable and fast enough for VT therapy to be delivered. The Ventritex stability algorithm The measured interval stability value is the difference between the second longest and second shortest intervals in

Amer,con Heart Journal Volume 139, Number 5

Figure

Nonthokumar

et al 799

1 Dlrtributlon

of Stability

Values

20

q VT slab n AF stab

16 16 f

'4

5 0 s

10

j

8

z'

6

12

4 2 0

J 25-30-35-40-45-60-5s-60.c70-75-60-&5. 30354045505560a70758-38590

Stability

Distribution

of stability

of 5 ms; y-axis, significant

overlap

number

values

for VT and

of episodes

in stability

values

atrial

of VT (open between

fibrillation bars) atrial

for and

fibrillation

a single

atrial

manufacturer.

fibrillation and

(solid

x-axis, barsj.

Stability

Histogram

values

in bins

demonstrates

VT.

a recent group of intervals defined by the programmable interval stability window. If the measured difference is greater than or equal to the programmed stability delta, the discriminator indicates SVT and therapy is withheld.

manufacturer and an ROC curve was generated. Sensitivity refers to the proportion of VT episodes correctly classified as VT, and specificity refers to the proportion of sinus tachycardia episodes correctly classified as sinus tachycardia.

The onset criterion We tested the performance of the onset criterion from one manufacturer (Medtronic). The onset criterion is a feature that inhibits the ICD from detecting episodes of sinus tachycardia when the ventricular rate undergoes a gradual increase and enters the VT zone. If an R-R interval is in the VT zone but the rhythm does not satlsIy the onset criterion, that cycle is marked as a normal sinus beat and the VT counter resets. After a sensed event the ICD compares the most recent 4 intervals to the 4 that preceded them. The criterion is fulfilled if the avenge of the most recent 4 intervals is less than the average of the 4 intervals that preceded them by a programmable percentage (sudden onset delta percentage).

Results

Data analysis The sensitivity and specificity for the detection of VT, as opposed to atria1 fibrillation, were retrospectively calculated for a wide range of different (programmable) stability values. Sensitivity refers to the proportion of VT episodes correctly classified as VT, and specificity refers to the proportion of atria1 fibrillation episodes correctly classified as atrial fibrillation. Rrceiver operating characteristic curves (ROC) were generated for stability values starting at 5 ms and every 5 ms increment thereafter. This analysis was performed separately for the 3 different algorithms from the 3 different manufacturers. Sensitivity and specificity in the detection of VT as opposed to sinus tachycardia were retrospectively calculated for a family of programmable percentage onset values for the single

Patient

characteristics

Of 2 17 patients, 62 (29%) received inappropriate therapy, of whom 40 patients had complete R-R information available for analysis. Of these 40 patients, 15 (38%) also received therapy for appropriate reasons for VT. Their mean age was 63 f 11 years, and 75% were male. The mean ejection fraction was 33% f 15%, and patients received a mean of 4.1 f 2.4 inappropriate therapies. In this population of 40 patients, 21 patients received therapy for atria1 fibrillation, 19 for sinus tachycardia, and 1 for noise (1 patient received therapy for both atrial fibrillation and for sinus tachycardia). We analyzed a total of 183 episodes of VT from 18 patients (15 patients who had also received inappropriate therapy and 3 patients who had only VT without other inappropriate therapy), 94 episodes of atrial fibrillation from 2 1 patients, and 56 episodes of sinus tachycardia from 19 patients. Stability We compared calculated stability values for the episodes of VT with stability values for atrial fibrillation. The mean stability value for all VT episodes was 17.9 f 15.0 ms, and the mean stability value for atria1 fibrillation was 29.7 f 19.6 ms (P c ,001) for 1 manufacturer (Guidant Inc). Figure 1 describes the distribution of sta-

800

Nonthakumor

American Heart jx~rnal May 2000

et 01

.

Figure 2

Elf:

Stability

1.0 0.6 E 5 0.6 E ee 0.4 cc

_ $Esurderlhewrve Man#l=0.70 Man#2=0.76 Man#3=0.73

0.2

0.0 0.0

0.2

0.4

0.6

0.8

1.0

l-speciicity Three

curves

depict

manufacturers.

ROC

y-axis,

clinically

relevant

ers have

similar

Guidant;

Man

of stability

Sensitivity;

range

of sensitivity

performance #2,

algorithm x-axis,

Intermedics;

(90%),

regarding

Man

for

In

all 3 manufoctur-

specificity. #3,

3 different

1 - specificity. Man

#I,

Venitrex.

bility values for VT and atrial fibrillation for this manufacturer. Table I describes the sensitivity and specificity values for the different stability values for this particular manufacturer. The stability value of 40 ms had a sensitivity of 88% and a specificity of 31%. If we had programmed stability at 40 ms we would have failed to treat 10 episodes of VT (12%) and would have inappropriately treated 65 episodes (69%) of atrial fibrillation in this select population for one particular manufacturer. The stability value 60 ms would have been associated with 98% sensitivity; however, 92% of episodes of atria1 fibrillation would have been treated inappropriately at this value. We then performed the same series of experiments for stability algorithms from 2 other manufacturers. Figure 2 depicts the ROC of the stability algorithm for the 3 different manufacturers with the same analysis. The specificity, in the clinically relevant sensitivity range of 95% and above, was comparable across manufacturers at about 40%. However, the absolute values of stability that apply for the particular algorithm for the different manufacturers were different. The stability values associated with 95% sensitivity were 50, 45, and 65 ms for Guidant, Intermedics, and Venitrex, respectively. Unstable VT at rhythm onset To assess if the VT would stabilize after its onset, we reanalyzed all episodes of VT with stability values greater than 40 ms. We recalculated stability values with R-R intervals recorded after detection, while the device was charging and reconfirming. Ten episodes of VT had stability values greater than 40 ms at onset of the rhythm, but when stability was recalculated includ-

1. Sensitivity

(ms)


and

specificity

Sensitivity 1.2% 4.8% 6.0% 9.5% 15.5% 36.9% 51.2% 67.9% 75.0% 83.3% 86.9% 88.1% 90.5% 91.7% 95.2% 97.6% 97.6% 97.6% 98.8% 98.8% 98.8% 98.8% 98.8% 98.8%

values

for different

stability

Specificity 98.9% 98.9% 96.8% 93.6% 93.6% 80.9% 70.2% 60.6% 55.3% 43.6% 35.1% 30.9% 23.4% 18.1% 13.8% 8.5% 4.3% 2.1% 2.1% 0.0% 0.0% 0.0% 0.0% 0.0%

ing the R-R intervals after detection until delivery of therapy, 8 of 10 episodes had stability values less than 40 ms (Guidant Inc). Onset Fii-six episodes of inappropriate therapy from ST in 19 patients, compared with 83 spontaneous episodes of VT in 18 patients, were analyzed. Table II describes the sensitivity and specificity values for different programmable onset values for a particular manufacturer. An onset of 75% would have been associated with a sensitivity of 91% and a specificity of 95%, and an onset of 85% would have been associated with a sensitivity of 99% and a specificity of 70%. Figure 3 describes a family of onset percentages and associated sensitivity and specificity values.

Discussion This study demonstrates that inappropriate therapy is a common problem in patients with ICDs. The performance of the stability algorithms used to differentiate AF from VT was less than ideal, though comparable across manufacturers. The study also demonstrates that the onset algorithm accurately differentiates sinus tachycardia from VT. Stability In patients with ICDs prone to atria1 fibrillation, the stability algorithm has poor specificity at acceptable

Amer,con

kteort Journal

Volume 139, Number 5

Table

II. Sensitivity percentage values

Onset percentage value

Nanthakumor

and

specificity

values

for different

onset

Figure

3

1.0

Sensitivity

\

Specificity

onSel=&i% *

0.6

30-35 35-40 40-45 45-50 50.55 55-60 60-65 65-70 70-75 75-80 80-85 85.90 90-95 95-100

1.2% 7.1% 21.4% 34.5% 53.6% 70.2% 73.8% 8 1 .O% 83.3% 90.5% 92.9% 98.8% 100.0% 100.0%

100.0% 100.0% 100.0% 98.2% 98.2% 98.2% 98.2% 96.4% 96.4% 94.6% 89.3% 69.6% 58.0% 0.0%

Srmcitidty=M%

jr onwt=75% sensis~91%. SpeciIicily=95%

-

t 0.2 .

of a stability

algorithm

from

other

Neuzner et als monitored 27 patients with ICDs with Ventak PR devices (CPI, St Paul, Minn) over a period of 11 months. In this series, there were 264 episodes detected; 201 were VT, 13 were supraventricular tachycardia, and 52 were atrial arrhythmias. Despite signi cant differences in the value of mean stability between VT and SVT, there was a broad zone of overlap. A programmed stability value of 35 ms resulted in a specificity of 46.2%. This finding is similar to our analysis, in which the specificity for 35 ms in our population was 35%. Swerdlow et ali3 demonstrated that a programmed stability of 40 ms for a particular algorithm (Medtronic) would result in decreased detection of induced, paroxysmal, and chronic atria1 fibrillation by 95%. However, these were only achieved by increasing the detection

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Depicts

ROC

approaching

levels of sensitivity for VT at the initiation of the arrhythmia episode. This is especially true of fast atrial fibrillation from the regularity of the R-R intervals. Most clinicians do not use stability for programming ICDs for the fear of underdetecting VT; this study suggests that this fear is well-founded. However, VT that would be initially underdetected because of the irregularity at the beginning of the episode may be detected appropriately with progression of the episode if VT becomes regular. Our data suggest that there is no universal cutoff that leaves adequate sensitivity for VT yet adequate specificity for atria1 Iibrillation at onset of arrhythmia episode. In addition, the actual stability values that give ideal performance are different for different manufacturers, and hence the programming cardiologist needs to be aware of the specific algorithm for each manufacturer.

.

,

.

,

*

, ’

*

0.0 Y

Sensitivity;

Performance studies

et al 801

0.2

of onset x-axis,

algorithm

1 - specificity.

ideal

0.6

o.&.spedficityo.6

for a single Curve

manufacturer.

describes

1.0

y-axis,

an algorithm

performance.

interval to 16 R-R intervals. In that same report, a programmed value of 50 ms and 8 R-R intervals would have resulted in 60% of the atrial fibrillations being detected inappropriately as VT. Barold et alzo prospectively evaluated the stability criteria in 17 patients with Medtronic 721X ICD. They induced atrial fibrillation at 3 and 6 months, and of the 33 inductions 4 resulted in inappropriate therapy. Brugada et al*3 prospectively monitored 82 patients with CPI-Guidant devices; in this series, stability programmed to 40 ms resulted in underdetection of 19 of 497 episodes of VT from stability being greater than 40 ms. The comparison of these studies to our data is limited by the differences in study design, differences in the rate detection algorithm, and the algorithm for stability used in the investigated devices. It is our belief that data from small investigational studies do not reflect the actual rate of inappropriate therapy in larger noninvestigational populations. Recently Rosenqvist et al*l published a prospective multicenter study of 778 patients with either Medtronic model 7219 C (392 patients) or model 7219 D (386 patients) ICDs with the primary intent of monitoring for adverse events. The average duration of follow-up was 4.0 * 4.6 months. Of 294 patients who received ICD therapy during the follow-up period, inappropriate detection and subsequent therapy delivery were observed 119 times in 102 patients. Stabilization

of unstable

VT after onset

of VT

Unstable VT in the ICD population may be caused by nonsustained VT with occasional capture beats or ventricular premature beats followed by a compensatory

American

802

Nanthakumar

Heart journal May 2000

et al

pause at the origin of VT, resulting in initial irregularity of R-R intervals.17 Several studies have reported variability in the cycle length of induced VT, particularly at the beginning of the episode.ls.19 Irregular VT may also be caused by polymorphic VT that has varying R-R intervals as a consequence of antiarrhythmic drug therapy.12 In our population, stability values decreased as the rhythm progressed in 8 of 10 episodes of VT. This finding suggests that the unstable VT seen in our population was caused in part by instability at the onset and not polymorphic VT. This finding is consistent with the series of Brugada et al’3 in which all 19 episodes of VT with stability greater than 40 ms dropped to below 40 ms within 2 * 1 seconds. Onset criterion Our study demonstrates that the enabling onset algorithm could result in considerable reduction in inappropriate therapy from sinus tachycardia. We did not evaluate the performance of the onset criterion in atria1 fibrillation because the onset of this arrhythmia is expected to be as sudden as VT. Performance of onset algorithm from other studies In a previous study of devices manufactured by Guidant Inc, onset programmed at 9% led to undertreatment of 27 (5.4%) of 497 episodes with 17 episodes of sinus tachycardia treated inappropriately. These 27 episodes of VT were ultimately treated after 72 f 34 seconds as the sustained rate duration monitor elapsed.

diagnostic data from dualchamber systems or QRS morphologic criteria may be needed to provide meaningful discrimination between atria1 fibrillation and VT in patients prone to atrial fibrillation. Our study does imply that onset should be programmed to the ICD for patients who are at risk to receive inappropriate therapy from sinus tachycardia. Limitations The main limitation of this cal and did not reflect actual However, device algorithms R-R events from patients for

We thank Guidant Inc, Intermedics, St Jude/Ventriter Inc, and Medtronic for their cooperation in participating in this project and Connie Yang for her assistance in the preparation of the manuscript.

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Clinical implications In patients prone to atrial fibrillation, and especially those with an expected rapid ventricular response, the specificity of diagnostic algorithms needs to be improved. Our results imply that the stability algorithm has limitations and may not be adequate for patients prone to atrial fibrillation if VT be appropriately detected 98% to 100% of the time. Other discrimination strategies such as atrial

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Dual-chamber devices and tachycardia discrimination Discriminating VT from ST or atria1 fibrillation may be difficult in singlechamber ICDs with existing tachycardia discriminators. 14 Dual-chamber ICDs have the advantage of monitoring atrial rate and its relation to the ventricular rate. The hypothesis that tachycardia discriminators in dual-chamber ICDs may be superior to singlechamber ICDs was tested in a recent trial.24 In this trial patients with dual-chamber devices were randomly assigned either to a strategy of enhanced detection with dual-chamber algorithms or to a rate based only on detection strategy. There was an absolute reduction of inappropriate therapy of 15% between the 2 strategies at 6 months. However, no trials have directly compared singlechamber devices with discrimination algorithms activated to dual-chamber devices.

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