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For Cardiology Fellows

Electrical Management of Cardiac Rhythm Disorders

December 5-8Austin, Texas

The Nuts and Bolts of ICD Therapy

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Action Potential – Localized Differences in Conduction

• 0.2 meters/second in the AV node• 0.4 meters/second in ventricular muscle• 1 meter/second in atrial muscle• 4 meters/second in the Purkinje fibers

Conduction velocity within cardiac tissue varies from slowest to fastest as follows:

TachycardiaMechanism

Reentry80 -90%

Non-reentryTorsade de pointes

Acute ischemia

Mechanisms

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Normal Heart Scarring Due to Myocardial Infarction

Ischemic Re-entry

Mechanisms

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Mechanisms

Gray areas represent scar

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Mechanisms

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THE BIG FOUR

• Sensing• Detection• Diagnosis• Therapy

SenseAbility™

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Ideal Sensing Circuit

• Ideal sensing circuit:

– Senses R-waves– Senses varying amplitudes of arrhythmias from sinus rhythm to

low amplitude ventricular fibrillation– Does not over sense P-waves, T-waves, myopotentials or EMI– Filters the signal to achieve a clean, noise-free waveform

suitable for detection

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Sensing Challenges

• Sensing challenges

– Combine the functions of an ICD with a dual chamber rate responsive pacemaker

– Add the ability to use atrial sensing as an SVT discriminator– Accurate sensing in both the atrium and ventricle is critical for

appropriate therapy delivery

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Sensing Options Pacemakers

• Fixed sensitivity

NSR

VT/VF

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Programmable Sensing Features

• Programmable sensing features – Threshold start– Decay delay– Maximum sensitivity– Refractory periods

• All parameters can be adjusted or “fine tuned” in the presence of sensing problems

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Sensed Refractory

• Sensed Refractory :• Ventricular: 125 (nominal) or 157 ms • Atrial: 93 (nominal), 125 or 157 ms

Maximum Amplitude

R-Wave or P-Wave Sensed

Sensed Refractory

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Threshold Start

• Definition: percentage of maximum peak amplitude sensed during the sensed refractory period used to begin the linear decay– Ventricular threshold start

• 50%, 62.5% (nominal), 75% or 100%– Atrial threshold start

• 50% (nominal) , 62.5%, 75% or 100%

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Threshold Start

• Nominally 62.5% of measured R– (Max start value 3.75 mV if R waves are >6mV))

• Nominally 50% of measured P– (Max start value 1.5 mV if P-waves are >3mV))

• Fixed rate of decay– Atrium 0.5 mV per 312 ms– Ventricle 1.0 mV per 312 ms

50%

62.5%

R-Wave T-Wave

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Rules to SenseAbilityTM Threshold Start

• Ventricular: Threshold start will not start higher than 6.0 mV or lower than 1.0 mV

• Atrium: Threshold start will not start higher than 3.0 mV or lower than 0.3 mV

• I.E. If R-waves are 10 mV and threshold start is 62.5%, it will begin at 3.75 mV

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Decay Delay

• Holds threshold at starting value for a period of time• May be increased if oversensing

– T-wave oversensing on RV channel– Far field R-waves on RA channel

0 ms

60 ms

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Decay Delay Programming

• Ventricular – Post sensed: 0, 30, 60 ms (nominal), 95, 125, 160, 195 and 220

ms– Post paced: Auto, and the options above

• Atrium– Post sensed: 0 (nominal), 30, 60, 95, 125, 160, 195 & 220 ms– Post paced: Same as post sensed

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Maximum Sensitivity (The “Floor”)

• Definition: The most sensitive level to which the device can decay – Anything below the maximum sensitivity is not seen by the

device– Separately programmable (ICD and pacemaker)

• Nominals:– Ventricular 0.3 mV – Atrial 0.2 mV

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Maximum Sensitivity

• Decays until reaches max sensitivity or another signal is sensed

V- Max Sensitivity = 0.3 mVA- Max Sensitivity= 0.2 mV

0.3 mV

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Post Paced

• There is a separate algorithm used when the device is pacing

• There is no P- or R-wave to measure• The threshold start and decay delay are based upon the

pacing rate

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Post Paced

• As the rate increases, the threshold start will decrease• This allows the device to become more sensitive at fast

rates

VRPVRP VRP VRP

Automatic Post Pace Threshold Start

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Atrial SensingAutomatic or Fixed

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Pacemaker and defib max sensitivity can be different

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Can Change for Double Counting Due to Wide QRS

DETECTION

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Detection – Ideal Design Considerations and Challenges

• High sensitivity for detecting VT and VF

• Diagnose tachyarrhythmias in a timely manner

• Make appropriate diagnosis decisions– Avoid diagnosing SVT as VT and treating inappropriately

• Classify hemodynamically stable vs. unstable VT with rate cut offs

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Detection

• Proper rhythm detection is dependent upon:

– Accurate sensing: • Undersensing (signal dropout) • Oversensing (double-counting or T-wave sensing)

• This will result in incorrect interval measurement and classification

• The ICD makes detection decisions based upon the programmed rate cut-off only– It is not a "clinical" diagnosis

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Detection

• The ICD uses the bipole IEGM• Detection decisions are based upon the programmed

ventricular rate cut-off, but rate is not enough

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Detection

• The recognition by the device of a minimum number of intervals that satisfy the programmed rate criteria for

– Fibrillation– Tachycardia– Sinus rhythm

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Detection - Terminology

• Interval– Current interval– Interval average

• Binning– Fibrillation detection– Tachycardia detection– Sinus redetection

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Detection

• Current interval– Measures the time in milliseconds between any two sensed

events, paced events or combination

• Interval average– The current interval, in milliseconds, plus the 3 prior intervals

divided by 4– This helps to provide a “smoothing effect” on detection– Thus, 1 or 2 beat variations don’t have a large effect on

detection

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Detection Zones

• 1 Zone– VF only

• 2 Zone – VF and VT

• 3 Zone– VF zone and VT-1 and VT-2

• OFF– Defibrillator OFF

• Bradycardia pacing is available in any Detection Zone configuration

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Detection

• 3 zone– VF with VT-1 and VT-2– Tiered therapy with 2 tach zones and VF – Arrhythmias in tach zones receive:

• ATP and low energy cardioversion– Used in patients with 2 different VTs

• Fast VT• Slow VT

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3 Zone

• Must have 30 ms between pacing upper rate, VT-1, VT-2 and VF Zone

Normal Bradycardia Rhythm VT 1 Zone VT 2 Zone VF Zone

140 bpm 160 200 bpm

Rhythm:VVI(R) or DDD(R)

Pacing

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Detection

• OFF– Provides bradycardia pacing only and needs to be programmed

ON – Used if patient is experiencing inappropriate shocks– When patient is undergoing surgery involving electrocautery

• Shocks during delicate surgery could be disastrous

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Disable/ Enable Tachy Therapy

• Disable/ Enable Tachy Therapy– A red line will cross over the VT/ VF parameters on the FastPath

Summary page

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Monitor Zone

• Will monitor, store EGM and not treat tachy arrhythmias• Multiple uses: palpitations, additional tachy arrhythmias

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Detection – Binning Rules

• When the interval and interval average are the same, the interval is binned in that zone

• When the interval and interval average are not the same classification, but are tach/ fib the interval is binned in the faster zone

• Always errors on the safe side!• The interval is not binned if the interval or interval

average is sinus and the other is VT/VF• Prevents 1 beat variations from impacting detection!

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Detection – Binning Rules

Interval Interval Average Binned

Sinus Sinus SinusVT/VF Sinus Not BinnedSinus VT/VF Not BinnedVT-1 VF VFVT-2 VT-1 VT-2VF VT-2 VFVF VF VF

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Interval Average Calculation

• Programmed Parameters– VT Detection: 140 bpm (430 msec)

• Current Interval = 418 – Interval Average = 418 + 422 + 422 + 430 = 1692/ 4 = 423

Episode Detection at 142 bpm (420 ms)

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Diagnosis

• Diagnosis– The point at which a rhythm meets all the programmed criteria

once diagnosis is made therapy will be given– But in order for a diagnosis, the device needs to know how many

intervals must be binned to qualify

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Diagnosis

• Tach Detection: T-1/140 bpm,12 Intervals

• T-2/ 160 bpm, 12 Intervals• F- 182, 12 Intervals

CI IA422 + 422 + 430 + 434 = 427 ms418 + 422 + 422 + 430 = 423 ms422 + 422 + 418 + 422 = 421 ms

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Sinus Redetection

• For the device to consider the episode over after a tachyarrhythmia has been detected:– The appropriate number of sinus intervals must be binned– Brady pacing counts– Intervals must be consistent (non-tach/ fib) but not consecutive

• Programmable • Nominal = 5• Slow = 7• Fast = 3

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Sinus Redetection

• Brady pacing counts as sinus

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Redetection After Therapy

• After therapy has been delivered a certain number of intervals must be binned before the next therapy can be initiated

• This insures the arrhythmia is still present

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Redetection After Therapy

• Fib redetection – Fixed at 6 intervals

• Tach 1 & 2 redetections are separately programmable – 6 to 20– Nominal = 6

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Tach - Redetection

• Tach detection = 400 ms/ 12 Intervals• Fib detection = 300 ms/ 12 Intervals• Tach redetect – 6 Intervals

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Redetection After Therapy

• An arrhythmia may continue at a slower rate after therapy

• If the rate is slower than the programmed initial detection rate, the device must be able to recognize and continue to treat the arrhythmia

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What happens if my patient has PVCs in a bigeminal pattern?

• Tach / sinus ratio counterAKA bigeminal avoidance

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Tach/ Sinus Ratio Counter

• AKA bigeminal avoidance– Tach/sinus ratio counter protects against inadvertently treating

ventricular bigeminy• This is NOT a lethal arrhythmia and should not be treated• Patients are usually not symptomatic

– Must protect against detecting a bigeminal rhythm as a tachycardia (do not want to treat)!

– Also could happen with T-wave oversensing

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Tach/ Sinus Ratio CounterVT = 400Number of Intervals = 12

T/S counter = 0

2.5 2.5 2.5 2.5200 200 200 200 200 200 200 200 200 200 200200

500 500 500 500 500 500 500 500 500 500 500200

500200

500

Tach/Sinus CounterFor Each Sinus – 1For Each 2.0 Seconds – 1For Each non Sinus + 1If T/S Counter ≥ 3 = TachIf T/S Counter < 3 = Bigeminy

Will Tell You if Bigeminal Avoidance in Diagnostics

Reason Store = “Bigeminal Avoidance”

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Discrimination/Diagnosis

• Covered by Tom Kenny

High Voltage Therapy

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High Voltage Therapy

• Purpose of high voltage therapy– To terminate:

• Ventricular tachycardia• Ventricular fibrillation

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Shock Therapy

• Shock therapy can be successful no matter what phase the cell is in as long as we capture the cell

• The trick is capturing the cell

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The Challenge of Stopping VF

• The more muscle mass you can place between the shocking electrodes, the more likely you are to be successful with the shock

Shocking Coils

Can Electrode

Left Ventricle

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Battery

• Lithium silver vanadium oxide• 3.2 volt battery• Gradual decline in voltage

gives good end of service indicator

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Capacitors

• The battery alone can’t deliver energy rapidly enough and doesn’t have enough voltage– Capacitors use to be the largest component

in the defibrillator– High-voltage capacitors are used to store

the charge and then deliver the shock

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High Voltage Therapy Delivery – Detection During Charging

Charge

**

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**

22

**

33 44 55 66

Interval and Interval Average must be Non Sinus

SHOCK

After beginning to charge, the device must reconfirm the presence of the tachyarrhythmia by binning 6 non-

sinus intervals before delivering the shock

TT TT TT

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High Voltage Therapy – Aborted Therapy

* ******* * *

1

*

2

*

3

*

4

*

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Sinus Redetect

Stop Charging

If device redetects “sinus rhythm” during charging, the shock is aborted and not delivered to the patient

F FF FF FF F F VS VS VS VS VS*

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What Is a High DFT?

• When the amount of energy being delivered is not enough to safely defibrillate the patient on a regular basis, the patient has a high DFT

• Many physicians believe that there must be at least a 10 J safety margin between your patient’s DFT and the maximum programmable energy of the device

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Who Will Have Hight DFTs?

• Almost impossible to predict• Common indicators

– Low LV ejection fraction– Higher NYHA class– Previous history of bypass surgery– Amiodarone use within the past six weeks– History of prior VF

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How Were Your Physicians Trained to Deal with High DFTs?

• Reverse polarity (non-invasive)• Reposition the lead (invasive)• Start adding hardware (invasive)

– Manually add an SVC coil if you started with a single-coil lead– Manually remove the SVC coil from the header if you started

with a dual-coil lead– Add an SVC coil in the coronary sinus– Add an array

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Each of the Traditional Options Require

• Additional shocks• More hardware

– More incisions– If an array is implanted, the patient can be left with chronic back

pain

• More time

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An Overview of St. Jude Medical’s Portfolio of Advanced Options

• Programmable polarity

• Programmable tilt

• Programmable fixed pulse widths

• Programmable shocking vectors

• Unsurpassed delivered energy (36 J)

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Programmable Shocking Vectors

• In a 2 coil lead system, program SVC Coil ON or OFF• Allows change in the location of current flow• Eliminates the need to invasively change lead-header

configuration, preventing additional surgical procedures

Nominal: RV to SVC/Can

Nominal: RV to Can

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Waveform Programmability

• What do we mean by waveform programmability?

– We mean that the waveforms have programmable “fixed tilts”and “fixed pulse widths”

– St. Jude branded ICD waveforms (both monophasic and biphasic) can be programmed to either fixed tilt or fixed pulse width

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Waveform Programmability – Fixed Tilt

• Definition: Tilt represents the percentage fall in voltage on the capacitor from the beginning to the end of each phase over the course of the entire pulse

• For example, a 200 V shock with 65% tilt would deliver 130 V in the first phase then shift its polarity– (200V X .65 = 130); (200 – 130 = 70 V left over)

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Cellular Time Constant• The example below shows a shock being delivered and the cell's response. The cell

ends its response at about 4 ms, but notice the shock continues. The energy is wasted, but worse than that, it is counter-productive to the cell. It reduces the cell’s final response.

-20

0

20

40

60

80

100

0 2 4 6 8 10milliseconds

shock voltage

membraneresponse

Wastedenergy

Optimal PW

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Waveform Programmability – Fixed Tilt (Biphasic)

• Pulse width will adjust based on programmed shock impedance

• Fixed tilt - shock therapy will be in joules (a voltage reference is provided)

Tilt = 50%Charge to 400 V (aprox 10 J)

Biphasic

InitialVoltage

Phase 1Width

Phase 2Width

TILT

TILT

400 V

200 V

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Waveform Programmability – Fixed Tilt

• One might think that a higher tilt which would deliver more energy would be best (more is better)– Studies have shown that tilts between 40% and 65% are better

than other tilts

• A fixed tilt device (or a device programmed to a fixed tilt) delivers a constant energy by varying the pulse width as a function of the patient’s defibrillation lead impedance

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Waveform Programmability – Pulse Width (Model Specifics)

• Each pulse width phase is programmable in volts (joules provided as reference)– St. Jude branded devices

• 1st phase: 3.0 to 10.0 ms in 0.5 ms increments – Nominal: 5.5 ms

• 2nd phase: 1.2 or 1.5 - 10 ms in 0.5 ms increments– Nominal: 5.5 ms

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Waveform Programmability – Burping Theory Cont.

• Recommended pulse widths are derived• Optimal pulse widths are a function of

– High voltage lead impedance– Device capacitance– Cell membrane time constant

• Shortening of the second phase pulse width lowers DFTs in patients on class III anti-arrhythmics

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Pulse Width Optimization Table

Device Family

Resistance

Block Number

ATP Therapy

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Antitachycardia Pacing (ATP)

• Advantages– When this therapy is utilized the patient usually has minimal

symptoms– No charge time, so it is a quick therapy– Pain free

• Disadvantages– Requires time to deliver multiple bursts– ATP may accelerate the VT– Prolongs time to shock therapy

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Antitachycardia Pacing

• Works best with reentrant ventricular tachycardias

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EP “Talk”

• Burst pacing– Delivery of multiple fast stimuli

• Burst or train– A single series of paced stimuli

• Ramp pacing– The paced rate is progressively

increased within a burst

• Scanning– An automatic change in cycle length

from burst to burst attempt

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Burst Cycle Length (BCL)

• Fixed or adaptive– Nominal: adaptive 85%

• Adaptive - % of average tach interval at the time of diagnosis

• Example:– Adaptive ON @ 75%– Tach interval 400 ms– BCL = 300 ms

Burst Cycle Length Fixed

X Milliseconds

X

Burst Cycle Length Adaptive

X % of Tach Detect Rate

X

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ATP Burst Therapy

• Simple burst therapy– BCL = 80% (adaptive)– Tach cycle length = 400 ms– 400 ms X 80% = 320 ms

Tach CL 400 ms

Burst CL 320 ms 320 ms 320 ms 320 ms

BCL: 80% No. of Stimuli = 4 No. of Bursts: 4

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ATP Parameters

• Ramp – Successively decreases the intervals between pulses within a

burst which will pace faster• ON / OFF (nominal)

– Ramp step• Intra burst step size• Nominal 8 ms when ON

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ATP Parameters

• Ramp pacing • Ramp pacing can be combined with readaptive to adapt

the first cycle of each burst to the VT cycle length can be combined with readaptive to adapt the first cycle of each burst to the VT cycle length

Ramp: On Ramp Step: 20 ms BCL: 90% No. of Stimuli = 4 No. of Bursts: 4

Tachy CL 400 ms

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Scanning

• A scanning burst sequence consists of multiple bursts where the rate is faster (cycle length shorter) between bursts– ON (decremental) or OFF, nominal ON (dec)– Scan step (nominal 12 ms)

Scanning: On Scan Step: 10ms BCL: 90% No. of Stimuli = 4 No. of Bursts: 4

VT CL 400 ms

Burst Cycle Length 360 ms 350 ms 340 ms 330 ms

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ATP Parameters

• Ramp with scanning

BCL = 90 % Scanning Step 10 msRamp Step = 25 ms400

360 335 310

400

350 325 300400

340 315 290

285

275

265

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ATP Parameters

• Minimum BCL – Shortest possible cycle length delivered during any ATP scheme– Will not pace faster than the min BCL– Nominal 200 ms

• ATP therapy is based on the initial detected tachycardia rate and will not change if the tachycardia cycle length is altered, unless readaptive is ON

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ATP Parameters

• ATP may need more energy than traditional brady pacing– Amplitude choices of 7.5 V (nominal) or 10.0 V (max)– Pulse width choices of 1.0 ms (nominal) or 1.9 ms (max)

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ATP Delivery

• When tach bin is full, the first ATP pulse is delivered synchronous with the next tach event (QRS)– The surface ECG typically shows the stimulus 40 to 80 ms after

the onset of the QRS– The remaining stimuli will be delivered as VOO

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Questions?