Definition of SVT Discrimination Identify which patient populations might benefit from these features Understand the 4 types of SVT discriminators used by St Jude Medical Be aware of programmable parameters that affect how SVT discriminators perform
are a set of algorithms used individually or together to assist the ICD in differentiating a rapid ventricular rate originating above the ventricles (Supraventricular) from ventricular tachycardia. ICD principle review To detect any tachycardia, the primary Detection Criteria must first be met Ventricular Rate Cutoff Number of interval After detection, a rhythm diagnosis is made VT-1, VT-2 and VF Then programmed therapy will be initiated ATP, Cardioversion or High Voltage Shock
But what if the detected tachycardia is a due to supraventricular tachycardia (SVT)? FACTS: Approx 14% of patients receive inappropriate therapies without SVT discriminators enabled Inappropriate shocks cause Patient discomfort and anxiety Increased follow up demands Decreased device longevity Increased cost burden for the healthcare system A patient s ICD detects: VT VT VT VT The rhythm is: AF or Aflutter Sinus Tach Junctional Tach with retrograde conduction VT or VF
Sensitivity refers to the Sensitivity for VT The ability to detect ventricular tachycardia Sensitivity = # of Diagnosed VT episodes # of Actual VT episodes Specificity refers to Specificity for SVT The ability to differentiate VT from SVT Specificity = # of Diagnosed SVT episodes # of Actual SVT episodes An ideally programmed device would provide detection and treatment for true VT (sensitivity) as well as discern supraventricular arrhythmias and inhibit inappropriate therapies (specificity).
may be programmed: Off Passive (Will tell you how the ICD would have classified the rhythm, but does not actually affect therapy. Provides diagnostic information) On These options are available in Tachycardia Configurations VT-1 and VT-2 Zones When are ON and indicate: VT- A rhythm diagnosis (D) is made and programmed therapy will be Delivered SVT- Programmed therapy will be Inhibited (I) unless the SVT discriminators override rate branch
Turn On for your patients with known: Rate overlap SVT rates overlap VT rates Sinus tachy or A-fib/flutter with rapid ventricular rates Monomorphic VT rates <200 bpm Only affects the initial diagnosis of an episode (not applicable in redetection after failed first therapy) Remember, SVT discriminators ONLY work in the VT zones.
How does a clinician interpret this rhythm? Single Chamber ICD s Sudden Onset Interval Stability Morphology Discrimination
Dual Chamber ICDs Rate Branch Morphology Discrimination Interval Stability Sudden Onset Rate Branch
Is this VT? Does the atrial egm help?
Rate branch uses the atrial rate to determine if this is a ventricular tachycardia versus supraventricular tachycardia.
Available in St Jude Medical Dual Chamber ICDs Once a tachycardia is detected (binned interval T-1 or T-2) Compares median Atrial rate to median Ventricular rate during the initial detection window. Atrial and Ventricular rates are compared and are classified into one of three branches V<A V=A V>A V<A A fib/a flutter The V < A branch is where atrial fibrillation and atrial flutter will be classified VT that occurs during atrial fib or flutter will also fall here Atrial Signal Ventricular Signal Median Atrial Rate Median Ventricular Rate V < A
V=A Sinus Tach The V = A branch is where sinus tachycardia or 1:1 SVTs will be classified VT that has 1:1 retrograde conduction will also fall here Atrial Signal Ventricular Signal Median Atrial Rate Median Ventricular Rate V = A V>A VT/VF Any rhythms classified in the VT/VF (V > A) rate branch must be considered VT and will receive therapy Atrial Signal Ventricular Signal Median Atrial Rate Median Ventricular Rate **No discriminators will be utilized V > A
Morphology Discrimination (MD) Interval Stability Sudden Onset Morphology Discrimination Available in St Jude Medical s dual and single chamber ICDs Current and Promote Atlas II Epic II Photon Contour Angstrom
Morphology Discrimination Sinus Origin of wavefronts Determines relationship of wave vector to sensing electrode Vector-Electrode relationship Determines morphology of the signal Tachy Compares Characteristics: Real-time EGM complexes with stored sinus template for more accurate SVT discrimination Utilizes the Ventricular complex s morphology including the number, sequence, polarity, amplitude and area of the waveform peaks. Assigns template score then assigned, based on similarity to stored template Morphology Discrimination Non Match = VT Indicated Therapy Delivered!! Match = SVT Indicated Therapy Inhibited
Morphology Discrimination As each beat is compared to a sinus rhythm template stored in the device a percent match and markers will indicate match vs. non match ( ) = Match ( X ) = Non Match Morphology Discrimination Scoring Starts: when the first Tach interval is binned AND/OR Anytime you are viewing real-time EGMs (if an active template has been acquired) Scoring Stops: when Diagnosis of VT occurs
Morphology Discrimination Acquire a Template Must be done when initially programming MD ON Programmable automatic update interval Off, 8 hours, 1, 3, 7, 14 or 30 Days Manual update Morphology Discrimination Automatic Template Acquisition When the timer expires the device evaluates the conditions for template update Automatic update will only occur when the current rhythm is representative of sinus rhythm Slow rate No shock delivered within previous 8 hours Device not in noise reversion Device based testing not ongoing If the conditions are not met the device will try again 8 hours later
Morphology Discrimination Morphology Discrimination
Morphology Discrimination If current conditions are acceptable: The active template is compared to the current complexes If the active template is still representative of the current rhythm 5 out of 8 complexes show 80% or greater match (programmable options) The current template is kept and the timer is reset Morphology Discrimination
Morphology Discrimination (MD) Interval Stability Sudden Onset VT or SVT?? Interval Stability
Interval Stability Looks at ventricular rhythm for regularity or irregularity Stable or changing interval measurements Available under the V<A Rate Branch The most common irregular ventricular rhythm is caused by Atrial Fibrillation (AF) VT is typically regular due to the reentry circuit and therefore stable in cycle length Assists in distinguishing between AF and VT Interval Stability Interval Stability is programmed as a Delta or the amount of variance in the rhythms cycle lengths or interval measurements Nominal: Interval Stability Delta of 80ms Delta >80 ms = rhythm is irregular = SVT Delta < 80 ms = regular ventricular rate = VT
Interval Stability Looks back over the past 12 intervals Compares 2nd shortest with 2nd longest interval and calculates a difference or DELTA Interval Stability
Interval Stability Interval Stability Example: Interval Stability = ON, Delta = 80ms 310 ms 312 ms 395ms 313ms 271ms 342ms 272ms 268ms 345ms 330ms 378 ms 334ms 331ms 2nd longest - 2nd shortest = 378-271 = 107ms 107 ms > 80ms Interval Stability Delta indicates SVT Diagnosis is inhibited and Therapy withheld The larger the delta is, the more likely VT will be diagnosed
Morphology Discrimination (MD) Interval Stability Sudden Onset Sudden Onset Used to help discriminate rhythms that start suddenly from rhythms that start gradually Sinus Tachycardia usually increases in rate gradually in response to physiologic demands VT typically starts suddenly
Sudden Onset Rate (bpm) 170 150 130 110 90 70 Sinus Rate Crossover Gradual Onset Sudden Onset Detect rate Pathologic Tachycardia Sinus Tachycardia Time Sudden Onset Sudden Onset is available in single and dual chamber devices How suddenly did the rate change?
Sudden Onset Compares to previous interval averages Uses the interval average when tachycardia is binned Sudden Onset
Sudden Onset The measure of the abruptness of a tachycardia s onset The current Tach interval average is compared to 4 of the previous 8 (every other) running interval averages If the measured difference is equal to or greater than the programmed Sudden Onset Delta then VT will be diagnosed Nominal: Sudden Onset Delta of 100ms Delta >100ms = sudden change in interval rate indicates VT Delta < 100ms = little change in interval rate indicates SVT SVT Discriminator Timeout A timer that allows the ICD to inhibit therapy delivery for a programmable length of time, when SVT discriminators indicate SVT Starts after initial detection Stops and resets When it expires and therapy is initiated When tachycardia(vt/vf) diagnosis occurs When sinus rhythm is detected
Has two parts: SVT Discriminator Timeout 1. Length of time therapy will be inhibited due to SVT discrimination 1. 20 seconds to 60 minutes, or OFF 2. Nominal: 30 seconds 2. Therapy that will be given when time expires 1. Tach Therapy or Fib Therapy 2. Nominal: Fib Therapy SVT Discriminator Timeout
When you program in a tachycardia zone, most parameters will come on automatically at nominal values: Rate Branch set to Dual Chamber Morphology on (*new since the II family) Sudden Onset set to On Interval Stability set to On with AVA off Using as many discriminators as possible (in Dual Chamber ICDs) leads to a highly reliable decision from the device Discriminators should NOT be used if there is some reason to believe they might provide confounding information -Patient with BBB at rapid sinus rates Even in the passive mode discriminators provide valuable information
St Jude Medicals ICDs offer easy to understand SVT discrimination Easy programming with a few simple steps Nominal parameters provide excellent performance for the average patient Adjusting of parameters is available and may be necessary for the unusual patient Remember any adjustment can impact detection and therapy! Thank you
Tachycardia Diagnostic Data Tachycardia Diagnostic Data Where Should I Start? The most beneficial information is in the episodal diagnostics and stored EGMs, but. Start with the fast path summary, as well as, the diagnostic summary to get an impression for the overall system performance