Tachycardia Detection (SVT discrimination)

Jaemin Shim, MD

Arrhythmia Center,

Korea University Anam Hospital, Seoul, Korea

Tachycardia Detection

Detection of a ventricular arrhythmia is based mainly on two rhythm characteristics ‒ Heart Rate (HR) or Cycle length (CL) ‒ Duration

A sustained ventricular HR >250 bpm or a CL

<250 ms is very specific for fast VT or VF

Tachycardia Detection: Heart Rate

Heart Rate

Sensing

Sinus Rhythm VT / SVT VT VF

50 bpm 100 150 200 250 300

Tachycardia Detection: Duration

Number of Interval Detection (NID), x out of y

Tachycardia Detection: Duration

If NID=12

If NID=18

Gunderson Gunderson et al PACE 2007

Cascade of Events Leading to ICD Shock

Circulation. 2013;128:659-672

Hardware Independent

Hardware dependent

Tachycardia Detection: Rate & Duration

Up to 3 programmable zones − Defined by heart rate (VF/FVT/VT) − Independently programmable rates, durations,

and therapies (ATP, shock)

VT zone: cumulative or consecutive counting VF zone: a percentage of intervals shorter than the rate cutoff, shorter detection duration

Tachycardia Detection: 1o Prevention

Primary prevention patients experience faster VTs with rates less likely to overlap SVT than secondary prevention

Programming of faster VT rate cutoffs with prolonged detection time is recommended (PREPARE, RELEVANT, MADIT-RIT trials)

Tachycardia Detection: 1o Prevention

Zone Rate Duration Therapy

Therapy zone 200 bpm 5-9 seconds ATP during charge, Max. Energy shock

Monitor-only zone 170-199 bpm 9-60 seconds None

ICD Programming for Primary Prevention

Tachycardia Detection: Heart Rate

Circulation. 2013;128:659-672

Primary Prevention

Secondary Prevention

VT

VT

SVT

SVT

Heart rate

Heart rate

Overlap Zone: Detection enhancement needed

SVT-VT discrimination

Single chamber discriminators − Onset − Stability − Morphology

Dual chamber discriminators

SVT-VT discrimination-Single Chamber

Onset

Stability

Morphology

Onset

Abrupt onset of VT

Slow warm up of sinus tachycardia

Onset

Onset misclassification ‒ The development of VT during sinus tachycardia ‒ The presence of ectopy immediately preceding

VT onset ‒ AF that begins abruptly

The onset algorithm makes its determination

only once, so that initial errors cannot be corrected.

Stability

Irregular RR intervals in AF

Stable RR intervals in VT

Stability

Variability in beat-to-beat RR intervals ‒ AF: variable, unstable intervals ‒ VT: regular/stable intervals

Applied during ongoing arrhythmia, so that a VT that begins with interval variability and stabilizes will be classified correctly

Stability misclassification ‒ Rapidly conducted AF (approximately >175 bpm) ‒ Regular SVTs such as atrial flutter ‒ Irregular VT (as may occur in the presence of

class 1C AAD) and polymorphic VT

Stability

Morphology

VT: morphology does not match template

SVT: morphology matches template

Morphology

The only non–interval-based single-chamber SVT-VT discriminator

Comparison of electrograms during tachycardia with a template acquired during normally conducted rhythm

The approach for aligning and comparing a tachycardia electrogram with a baseline template varies by manufacturer, but all have similar efficacy and failure modes

Most accurate of the single chamber algorithms (sensitivity: 92-99%, specificity: 90-97%)

Morphology

ICD leads and electrograms (EGMs)

Morphology

Not match Not match

• Parameter setting: 5/8, EGM > 60% match (St. Jude Medical) • In this case, 6 matches from 8 the algorithm votes for SVT (75%).

Morphology

JCE 2006;17:1310-19.

Sensitivity & specificity according to match threshold

Match Threshold (Medtronic Wavelet™)

Morphology

Misclassification ‒ SVT with rate-related aberrancy ‒ Errors in electrogram alignment ‒ Electrogram truncation (ie, signal clipping

caused by improper amplifier setting) ‒ Electrogram distortion caused by myopotentials ‒ Changes in morphology over time caused by

lead maturation or BBB ‒ Electrogram distortion in the minutes

immediately after shock delivery

Morphology

Morphology Error: Truncation

Not clipped

Clipped

Morphology

Morphology algorithms use either EGM only or a combination of EGM and a can to coil lead

Rhythm ID™ (Boston) discrimination algorithm based on an internal ECG electrode from can to RV and SVC coil.

SVT-VT discrimination-Dual Chamber

Significant addition is the comparison of atrial (A) and ventricular (V) frequency.

In case of V>A, VT therapy is initiated directly. For cases with V=A or V<A further

discrimination algorithms are used to differentiate between SVT and VT.

SVT-VT discrimination-Dual Chamber

RV tip to ring

Can to coil

Atrial EGM

SVT-VT discrimination-Dual Chamber

SVT-VT discrimination-Dual Chamber

Achilles’ heel of dual-chamber algorithms: Atrial sensing

Undersensing ‒ Low-amplitude electrograms (esp. during AF) ‒ Lead dislodgement ‒ Atrial blanking that occurs during and

immediately after ventricular sensed or paced events

Oversensing ‒ Large Far-field R-waves

SVT-VT discrimination-Dual Chamber

Far-field R-wave Oversensing in Dual Chamber ICD

SVT-VT discrimination-Dual Chamber

Medtronic (PR Logic)

Medtroni

c

SVT-VT discrimination-Dual Chamber

St. Jude Medical (Rate branch algorithm)

St. Jude Medical

SVT-VT discrimination-Dual Chamber

Boston Scientific (Rhythm ID)

SVT and VT Discrimination Criteria

Criteria ECG Single Dual CL or HR + + + Sudden onset + (Holter) + + Stability + + + Morphology + + + AV rate branch - - + QRS axis* + +* +* AVA interval - - + Sinus interval history ** - +** - Capture beats*** + - +*** RBBB & LBBB criteria + - -

*: Rhythm IDTM Boston; **: St.Jude Medical; ***: PR LogicTM Medtronic

Key Points

Prolonged or high rate detection 을 통해 SVT-VT discriminator 의 오류를 줄일 수 있다.

SVT/VT 가 overlap 되는 heart rate 영역에서 detection enhancement 가 필요하다.

Single chamber ICD의 SVT-VT discriminator 는 onset, stability, morphology가 있으며 이 중 morphology가 가장 유용하다.

Dual chamber discriminators 는 A lead의 function이 매우 중요하다.

고려대학교의료원 소개 2012. 00.

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Thank you for your attention.

Tachycardia Detection: Rate & Duration

Rate and duration triggering tachycardia detection is similar across all devices and is therefore hardware independent.

After tachycardia detection, algorithms may be applied to distinguish SVT from VT.

These algorithms are hardware dependent and differ markedly between single-chamber, dual chamber, and subcutaneous ICD.

Tachycardia Detection: 1o Prevention