The Nuts and Bolts of ICD Therapy

Electrical Management of Cardiac Rhythm Disorders For Cardiology Fellows December 5-8 Austin, Texas The Nuts and Bolts of ICD Therapy 1 2

Action Potential Localized Differences in Conduction Conduction velocity within cardiac tissue varies from slowest to fastest as follows: 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 3 Mechanisms Tachycardia Mechanism Reentry 80-90% Non-reentry Torsade de pointes Acute ischemia

Mechanisms Ischemic Re-entry Normal Heart Scarring Due to Myocardial Infarction 5 Mechanisms Gray areas represent scar 6

Mechanisms 7 THE BIG FOUR Sensing Detection Diagnosis Therapy 8

SenseAbility 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 10

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 11 Sensing Options Pacemakers Fixed sensitivity NSR VT/VF 12

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 13 Sensed Refractory : Ventricular: 125 (nominal) or 157 ms Atrial: 93 (nominal), 125 or 157 ms Sensed Refractory R-Wave or P-Wave Sensed Maximum Amplitude Sensed Refractory 14

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% 15 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 62.5% 50% Threshold Start R-Wave T-Wave 16

Rules to SenseAbility TM 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 17 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 60 ms 0 ms 18

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 19 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 20

Maximum Sensitivity Decays until reaches max sensitivity or another signal is sensed 0.3 mv V- Max Sensitivity = 0.3 mv A- Max Sensitivity= 0.2 mv 21 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 22

Post Paced As the rate increases, the threshold start will decrease This allows the device to become more sensitive at fast rates Automatic Post Pace Threshold Start VRP VRP VRP VRP 23 Atrial Sensing Automatic or Fixed 24

Pacemaker and defib max sensitivity can be different 25 Can Change for Double Counting Due to Wide QRS 26

DETECTION 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 28

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 29 The ICD uses the bipole IEGM Detection decisions are based upon the programmed ventricular rate cut-off, but rate is not enough Detection 30

Detection The recognition by the device of a minimum number of intervals that satisfy the programmed rate criteria for Fibrillation Tachycardia Sinus rhythm 31 Interval Current interval Interval average Binning Fibrillation detection Tachycardia detection Sinus redetection Detection - Terminology 32

Current interval Measures the time in milliseconds between any two sensed events, paced events or combination Detection 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 33 1 Zone VF only 2 Zone VF and VT 3 Zone VF zone and VT-1 and VT-2 OFF Defibrillator OFF Detection Zones Bradycardia pacing is available in any Detection Zone configuration 34

35 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 36

Must have 30 ms between pacing upper rate, VT-1, VT- 2 and VF Zone 3 Zone Rhythm: Normal Bradycardia Rhythm VT 1 Zone VT 2 Zone VF Zone VVI(R) or DDD(R) Pacing 140 bpm 160 200 bpm 37 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 38

Disable/ Enable Tachy Therapy Disable/ Enable Tachy Therapy A red line will cross over the VT/ VF parameters on the FastPath Summary page 39 Monitor Zone Will monitor, store EGM and not treat tachy arrhythmias Multiple uses: palpitations, additional tachy arrhythmias 40

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! 41 Detection Binning Rules Interval Interval Average Binned Sinus Sinus Sinus VT/VF Sinus Not Binned Sinus VT/VF Not Binned VT-1 VF VF VT-2 VT-1 VT-2 VF VT-2 VF VF VF VF 42

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) 43 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 44

Diagnosis Tach Detection: T-1/140 bpm, 12 Intervals T-2/ 160 bpm, 12 Intervals F- 182, 12 Intervals CI IA 422 + 422 + 430 + 434 = 427 ms 418 + 422 + 422 + 430 = 423 ms 422 + 422 + 418 + 422 = 421 ms 45 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 46

Sinus Redetection Brady pacing counts as sinus 47 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 48

Redetection After Therapy Fib redetection Fixed at 6 intervals Tach 1 & 2 redetections are separately programmable 6 to 20 Nominal = 6 49 Tach detection = 400 ms/ 12 Intervals Fib detection = 300 ms/ 12 Intervals Tach redetect 6 Intervals Tach - Redetection 50

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 51 Tach / sinus ratio counter AKA bigeminal avoidance What happens if my patient has PVCs in a bigeminal pattern? 52

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 53 VT = 400 Number of Intervals = 12 Tach/ Sinus Ratio Counter 2.5 2.5 2.5 2.5 200 200 200 200 200 200 200 200 200 200 200 200 200 200 500 500 500 500 500 500 500 500 500 500 500 500 500 T/S counter = 0 Tach/Sinus Counter For Each Sinus 1 For Each 2.0 Seconds 1 For Each non Sinus + 1 If T/S Counter 3 = Tach If T/S Counter < 3 = Bigeminy Will Tell You if Bigeminal Avoidance in Diagnostics Reason Store = Bigeminal Avoidance 54

Discrimination/Diagnosis Covered by Tom Kenny 55 High Voltage Therapy

High Voltage Therapy Purpose of high voltage therapy To terminate: Ventricular tachycardia Ventricular fibrillation 57 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 58

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 Can Electrode Left Ventricle Shocking Coils 59 Lithium silver vanadium oxide 3.2 volt battery Gradual decline in voltage gives good end of service indicator Battery 60

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 61 High Voltage Therapy Delivery Detection During Charging After beginning to charge, the device must reconfirm the presence of the tachyarrhythmia by binning 6 nonsinus intervals before delivering the shock 1 2 3 4 5 6 SHOCK * * * T T T Charge Interval and Interval Average must be Non Sinus 62

High Voltage Therapy Aborted Therapy If device redetects sinus rhythm during charging, the shock is aborted and not delivered to the patient Sinus Redetect 1 2 3 4 5 * * * * * * * * * * * * * * * F F F F F F F F F VS VS VS VS VS Stop Charging 63

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 65 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 Who Will Have Hight DFTs? 66

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 67 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 68

Programmable polarity An Overview of St. Jude Medical s Portfolio of Advanced Options Programmable tilt Programmable fixed pulse widths Programmable shocking vectors Unsurpassed delivered energy (36 J) 69 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 70

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 71 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) 72

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. 100 80 60 shock voltage membrane response Optimal PW 40 20 0-20 0 2 4 6 8 10 milliseconds Wasted energy 73 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 Initial Voltage 400 V Phase 2 Width 200 V Biphasic Tilt = 50% Charge to 400 V (aprox 10 J) Phase 1 Width TILT 74

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 75 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 76

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 77 Pulse Width Optimization Table Device Family Block Number Resistance 78

ATP Therapy 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 80

Antitachycardia Pacing Works best with reentrant ventricular tachycardias 81 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 EP Talk 82

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 83 ATP Burst Therapy Simple burst therapy BCL = 80% (adaptive) Tach cycle length = 400 ms 400 ms X 80% = 320 ms BCL: 80% No. of Stimuli = 4 No. of Bursts: 4 Tach CL 400 ms Burst CL 320 ms 320 ms 320 ms 320 ms 84

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 85 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 86

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 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 87 Ramp with scanning ATP Parameters BCL = 90 % 400 Ramp Step = 25 ms Scanning Step 10 ms 360 335 310 285 400 400 350 325 300 275 340 315 290 265 88

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 89 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) ATP Parameters 90

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 91 Questions? 92