Week 9 Advanced CIED Follow-Up

VVI Pacing Interval

• Determined by LRL (60000/rate = interval)

• Begins after every paced or sensed beat

• Device paces when interval times out

• Sensing will lead to inhibition and reset the pacing interval

Automatic and Escape Interval

• Automatic interval triggered by paced beat

• Escape interval triggered by sensed beat

• Can be programmed separately with rate hysteresis

Rate Response

• Sensor-indicated rate (SIR): rate controlled by rate response sensor

• Max sensor rate (MSR): highest rate device will pace

Refractory Period

• Prevents sensing of T waves and non-physiologic signals

• Divided into absolute and relative refractory periods

• End of refractory period triggers alert period

• Fixed or dynamic

DDD Pacemakers

• More physiologic than VVI

• Leads pace each chamber separately and communicate with each other to maintain AV synchrony

• Sinus rate slows: pace atrium

• AV conduction slows: pace ventricles

Ventricular-Based Timing

• Atrial pacing driven by VA interval (AKA atrial escape interval)

• VA interval = pacing interval - AV delay

• Device adjusts other intervals to keep VA interval constant

Atrial-Based Timing

• Atrial pacing driven by A-A interval

• Device adjusts other intervals to keep A-A interval constant

• VA interval can be calculated, but is not used

A Paced, V Paced

Ventricle-based vs Atrial-based AP/VP diagram

A Paced, V Sensed

Ventricle-based vs Atrial-based AP/VS diagram

A Paced, V Paced to A Paced, V Sensed

Ventricle-based vs Atrial-based AP/VP to AP/VS diagram

A Paced, V Sensed to A Paced, V Paced

Ventricle-based vs Atrial-based AP/VS to AP/VP diagram

Importance of Timing Quirks

• Changes in rate as patient transitions in and out of block

• Telemetry unit: variations in rate can alarm nurses

• Understand timing quirks, answer concerns

• Know basic rules:

  • Ventricular-based: VA interval constant

  • Atrial-based: A-A interval constant

PVC Response

• PVC defined by the device:

  • Two consecutive ventricular events

  • No intervening atrial events

  • Second event is VS

PVC Response: Ventricular-Based Timing

• PVC defined by the device:

  • Two consecutive ventricular events

  • No intervening atrial events

  • Second event is VS

• Ventricular-based timing: PVC triggers new VA interval

PVC Response: Atrial-Based Timing

• PVC defined by the device:

  • Two consecutive ventricular events

  • No intervening atrial events

  • Second event is VS

• Atrial-based timing: PVC triggers new A-A interval

Modified Atrial-Based Timing

• Normal beats: operates like atrial-based

• PVCs: triggers VA interval instead of A-A interval

Impact of Atrial Fibrillation

• Loss of atrial kick: 10-30% CO

• Loss of AV synchrony: reduced ventricular filling, preload, CO

• Rapid, irregular ventricular response: reduced diastole, reduced ventricular filling, reduced coronary perfusion, palpitations, decreased exercise capacity

• Remodeling: worsening AF, tachycardia-induced cardiomyopathy

CIED Algorithms

How can CIEDs minimize these negative effects?

• Prevent AF

• Minimize frequency/duration

• Manage/reduce symptoms

• Terminate AF

• Prevent recurrence

Type of Algorithms

• Preemptive algorithms

  • Prevent/minimize AF

  • Pre-mode switch

• Responsive algorithms

  • Manage/reduce symptoms

  • Terminate AF

  • Inside mode switch

• Reactive algorithms

  • Reduce recurrence of AF

  • Post-mode switch

Pre-Mode Switch: Pace Conditioning

• Adjusts atrial pacing rate above intrinsic rhythm

• Pace ~95% of time

• Keep atria refractory to suppress AF triggers

• Sinus beats detected (usually 2+): raise pacing rate

• Programmable maximum rate (seperate from MSR)

• Rate slowly decreases towards base rate

Pre-Mode Switch: PAC Response

• PACs can trigger atrial tachyarrhythmias

• PAC response activated by single rapid beat

• Triggers atrial pacing at fast rate

• Gradually decrements to base rate

• Pace quickly to eliminate pause after PAC and prevent arrhythmias

Pre-Mode Switch: NCAP

Non-competitive atrial pacing

• Pacing in atrial vulnerable period can trigger atrial
  tachyarrhythmia

• NCAP delays time to next paced atrial event after PAC

• Defines PAC as atrial signal inside PVARP

• Extends NCAP window

• Next AV interval shortened

Functional Undersensing of Atrial Flutter

• Atrial rate of 300 bpm

• Every other beat in PVAB: no mode

Blanked Flutter Search

• Similar to PMT termination

• Detects A sensed V paced beats at consistent, fast rate

• Extends PVARP: next atrial beat will be refractory

• Previously blanked flutter beat sensed: triggers mode switch

Atrial Flutter Response

• Separately programmable atrial flutter response rate

• Triggers flutter response window: atrial refractory period

• Atrial event within window triggers new window

• Continues until mode switch criteria met or rate slows

Pre-Mode Switch: Rate Smoothing

• Reduces symptoms from rate changes

• Beat-to-beat basis: maximum percentage change in interval

• AT/AF starts: gradually increases ventricular rate

• AT/AF stops: gradually decreases ventricular rate

• Many mode switch algorithms have rate smoothing built in

Inside Mode Switch: Regularization

• Regularize rate of ventricular response to AF

• Pace between intrinsic beats to prevent large variations in rate

• Uses rolling window

• Pace slightly faster than average rate

• Increases % RV pacing: no longer used in non-CRT devices

Inside Mode Switch: Termination

• ATP in the atrium

• Works best for regular, monomorphic, reentrant

• Unlikely to work for AF

• Risks: trigger VT, transient AV block, increase patient symptoms

• More aggressive than normal burst

  • Ramp

  • Burst+

  • Reactive ATP

PMOP

Post-mode switch overdrive pacing

• Pacing at elevated rate after termination of mode switch

• Keeps atria refractory

• Prevents early recurrence of atrial fibrillation (ERAF)

Minimizing RV Pacing

• Increase AV delay

• AAl mode

• Algorithms that promote intrinsic conduction

  • AV search hysteresis

  • Algorithms that change modes

• Alternative pacing site

• Upgrade to CRT

Rate Smoothing

• Prevent large fluctuations in rate

• Used in either chamber

• Separate percentages for increase/decrease

• Useful scenarios:

  • AF, SVTs

  • Frequent PACs/PVCs

  • Brady-tachy syndrome

  • Sinus pauses

  • LQTS: Torsades initiated by long-short-long interval pattern

• Turned off during certain algorithms

  • PMT termination

  • Search hysteresis

  • Programmed increase in LRL

  • Intrinsic rate > MTR

  • Mode switch with regularization algorithm

• Increases RV pacing %

Pacemaker Mediated Tachycardia

• Requirements for initiation:

  • Dual chamber tracking mode

  • Ability to conduct retrograde

  • Longer VA conduction time than PVARP

  • Triggering event causing loss of AV synchrony

• VA conduction:

  • 80% of patients with SSS

  • 35% of patients with AV block

• 20% of patients with VA conduction have experienced PMT

PMT Triggers

• PACS

• PVCs

• Loss of atrial capture

• Atrial undersensing

• Atrial oversensing

• Long AV delays

• AV search hysteresis

• Magnet removal

PMT Termination

• Self-termination: fatigue of conduction system, PAC/PVC

• Active termination:

  • Vagal maneuvers (carotid sinus massage)

  • Medications (verapamil, beta blockers)

  • Magnet application: switch to asynchronous

  • PMT termination algorithms

PMT Termination Algorithms

• Look for specific number of P waves tracked at MTR

• Extend PVARP for one interval

• Alternative: deliver atrial paced beat

• VA stability: alternative for PTM below MTR

Inappropriate PMT Termination

• Sinus tachycardia: program MTR higher

• Atrial flutter: blanked flutter search

PMT Prevention

• Run VA conduction test, set PVARP 50 ms longer than RVAC

  • Not possible in all patients

  • RVAC varies over time

• PVC response: extend PVARP or atrial pace in response to PVC

• Correct underlying cause

RNRVAS

Repetitive non-reentrant ventriculoatrial synchrony

• Dual chamber pacemaker

• Retrograde conduction

• VA conduction time shorter than PVARP

• Atrial pacing occurs within intrinsic atrial refractory period

• Triggering event

RNRVAS: FUNC & FUS Part 1

• Triggering event allows retrograde conduction

• Retrograde beat lands within PVARP: functional undersensing

RNRVAS: FUNC & FUS Part 2

• Fast atrial pacing rate causes atrial paced beat to land within intrinsic refractory period: functional non-capture

  • Sensor-indicated rate

  • High base rate

  • Atrial overdrive pacing

RNRVAS: FUNC & FUS Part 3

• No intrinsic conduction: AV delay times out

• V pacing causes retrograde conduction again: FUS

RNRVAS Pattern

• Atrium paced again: FUNC

• Pattern continues:

  • Loss of optimal AV delay

  • Unnecessary RV pacing

  • Possible triggering of arrhythmias/algorithms

RNRVAS Prevention

• Extend PVARP after PVC: delays atrial pacing

• Shorten PVARP

• Dynamic PVARP

• Shorten AV delay

• Dynamic AV delay

Neurocardiogenic Syncope (NCS)

• Vasovagal syncope, neurally-mediated syncope, carotid sinus syndrome, carotid sinus hypersensitivity

• Inappropriate physiologic response to stress causing sudden drop in HR & BP

• Decreased blood flow to brain: LOC

• Many presyncopal symptoms: sit down to avoid falling

NCS Diagnosis

Rule out other possible causes:

• Temperature: fever

• Heart rate: tachyarrhythmia, ACS

• Blood pressure: orthostatic hypotension

• Blood tests

• 12 lead

• Echocardiogram

• Stress test

• Tilt table test

NCS Treatment

• Treatment often unnecessary

• Avoid triggers:

  • Lifestyle changes

  • Increase salt in diet

  • Drink fluids

  • Avoid prolonged standing

• Medications for hypotension

• Sometimes goes away with age

• Pacemaker as last resort

NCS Indications

NCS classes indication

Rate Drop Response

Patient indicated for syncope turn this feature on

Unique Properties of the Cardiac Cell

• Automaticity is the ability of cardiac cells to generate their own impulses spontaneously

• Excitability is the ability of cardiac cells to respond to an electrical stimulus

• Conductivity is the ability of cardiac cells to transfer or propagate an electrical stimulus

• Contractility is the ability of cardiac cells to shorten and cause myocardial contraction in response to an electrical stimulus

Stimulation Threshold

Minimum output of electrical stimulation needed to consistently produce cardiac depolarization

• Voltage @ pulse width

• Map thresholds using strength-duration

Rheobase and Chronaxie

• Rheobase: minimum voltage that captures at any pulse width

• Chronaxie: shortest pulse width that captures at 2x rheobase voltage

Threshold Testing

• Hold pulse width constant, decrement voltage

• Threshold: voltage just before capture is lost

• Set output 2x threshold voltage

Battery Longevity

• Battery technology

• Impedance (higher = longer)

• Pacing outputs (lower = longer)

  • J = V^2xT/R

  • Raising voltage has greater effect on battery life

Battery Longevity: Cell Voltage

Lithium-iodide cell voltage: typically 2.8-3 V

• Higher output requires voltage multiplier

• Consider changing pulse width:

  • Decrement voltage at higher fixed pulse width

  • Decrement pulse width (3:1 safety margin)

  • Pulse width no higher than 1.0 ms

Battery Longevity: Other Factors

• Percentage pacing (lower = longer)

• Activity sensor

• Remote monitoring

• Interrogations: make sure you end the session

Threshold Changes

• Safety margins set to accommodate threshold fluctuations

• Loss of capture in 1-5% of patients

  • Dangerous for pacemaker-dependent patients

  • Renders device useless

Threshold Changes: Lead Complications

• Long term impacts on threshold

• Lead fracture

• Lead insulation break

• Helix crystallization

• Lead encapsulation

Threshold Changes: Autonomic Tone

Activity	Effect on autonomic tone	Effect on capture threshold
Sleeping	Stimulates parasympathetic	Increased threshold
Eating	Stimulates parasympathetic	Increased threshold
Exercise	Stimulates sympathetic	Decreased threshold

Threshold Changes: Other Abnormalities

• Electrolyte imbalances (hyperkalemia)

• Hyperglycemia

• pH imbalance

  • Acidic (low pH)

  • Alkalotic (high pH)

  • Affected by many factors

Threshold Changes: Medications

• Antiarrhythmics can raise thresholds

  • Spironolactone

  • Quinidine

  • Flecainide

  • Sotalol

• Stimulants can lower thresholds

  • Epinephrine

  • Ephedrine

• Steroids can lower thresholds

  • Glucocorticoids

  • Isoproterenol

Autocapture

Automatically tests thresholds and resets outputs

• Pulse response (PR)

  • Traditional sensing amplifier

  • Used to sense intrinsic R waves

• Evoked response (ER)

  • New sensing amplifier for autocapture

  • Electric potential recorded following pacing stimulus

  • Morphology changes when capture is lost

Polarization

Residual charge (concentration of ions) that remains near electrode after pacing pulse

• Consistent with or without capture

• Autocapture will not function if polarization dominates ER
  morphology

• Must be minimized

Minimizing Polarization

• Smaller electrode size increases polarization

  • Increased current density at tip

  • Small electrode leads designed to increase impedance

  • Maximize surface area: fractal surface, coatings

• Larger pulse width increases polarization

  • Autocapture uses 0.4 ms

• Second order bandpass filter to distort polarization artifact

• ER blanking period to block filtered polarization signal

Autocapture Sensing Test

• Determine if:

  • Evoked response is large enough

  • Polarization is small enough

  • Large enough safety margin between sensitivity and ER

  • Large enough safety margin between ER and polarization

• 5-7% have inadequate signals

Automatic Threshold Test

• Run periodically by device

• Gradually decrements outputs to look for loss of capture

• No 2:1 safety margin

• Paces to override intrinsic activity

• Delays test for high intrinsic rate, algorithms

• Backup pulse at elevated outputs when capture is lost

Automatic Threshold Test in Clinic

• Can run an automatic test using programmer

• Compare device's assessment with you own

• Always use to test autocapture

• Watch for loss of capture: device may get it wrong!

Capture Verification

• Device constantly monitors evoked response

• Beat to beat or rolling window

• Capture lost: high output backup pulse

• Runs another threshold test after certain # of beats

Atrial Autocapture

• Atrial signals too small for ER

• Algorithms test threshold periodically

  • Pace faster than intrinsic rate

  • Intrinsic or retrograde signals indicate loss of capture

• No capture verification

Autocapture Benefits

• Smaller safety margin: reduced battery consumption

• Maintains capture during threshold fluctuations

• Backup safety pacing

• Sends alerts when thresholds rise

• Runs threshold tests automatically: included in RM

Autocapture Drawbacks

• Algorithms not initially reliable

• Backup pacing can be proarrhythmic

• AF: fusion beats confuse algorithm

• Questionable benefits in certain populations

  • Low pacing %

  • Low thresholds

• Monitor mode if physician unsure

Heart Failure

• Progressive disease

• 50% of HF patients die within 5 years of diagnosis

• Begins with injury/stress to myocardium:

  • CAD

  • HTN

  • Diabetes

  • Obesity

• Heart remodels: causes dyssynchrony

Electrical Dyssynchrony

• Seen on ECG

• Damaged myocardium alters electrophysiologic properties

• Impairs velocity/direction of propagation

• Abnormal ventricular depolarization: wide QRS

• Systolic dysfunction

Mechanical Dyssynchrony

• Interstitial fibrosis

• Rearrangement of extracellular matrix and myocytes

• More diffuse wavefront

• Disorganized contraction

• Causes further fibrosis/remodeling

Areas of Dyssynchrony

1 & 2: AV dyssynchrony:

• Between RA and RV

• Between LA and LV

• Loss of atrial kick

• Reduced cardiac output

• Regurgitation

3: interventricular dyssynchrony:

• Between RV and LV

• Measured using doppler echo

• Aortic vs. pulmonic outflow

• Delay > 40 ms abnormal

4: intraventricular dyssynchrony:

• Between walls of LV

• Important abnormality in progression of heart failure

Apical Rocking

End diastole

Isovolumetric contraction

Ejection

Cardiac Resynchronization Therapy

• Biventricular device resynchronizes heart

  • Electrical depolarizations

  • Mechanical contractions

• Goal of CRT: BIV pace 100% of the time in order to reverse remodel the heart

• Reduce dyssynchrony

• Improve CO/EF

• Decrease EDV/ESV

• Improve QOL

Categories of CRT Responses

1. Clinical measures assessment

2. LV reverse remodeling assessment

3. Outcome measures assessment

Clinical Measures

• NYHA Class

  • Class I: asymptomatic with reduced EF

  • Class II: mildly symptomatic during ordinary exertion

  • Class III: moderately symptomatic during less than ordinary exertion

  • Class IV: symptomatic at rest

• 6 minute walk test

• Exercise duration

• Cardiopulmonary stress test

LV Reverse Remodeling

• Acute measures:

  • Increased CO

  • Increased LV dp/dt max: maximum rate of rise in LV pressure in early systole

• Chronic measures:

  • Increased LVEF

  • Decrease in ESV/EDV

  • Reduced MR

Outcome Measures

• Heart failure hospitalizations

• Morbidity

• All cause mortality

CRT Non-Responders

• HF gets worse after they receive device

• Increased remodeling, no improvement in functional class after 6 months

• Initial improvement then worsening symptoms

• Contributing factors:

  • Poor patient selection

  • Suboptimal LV lead positioning

  • Inappropriate device programming

CRT Class I Indication

CRT is recommended for patients with:

• Sinus rhythm

• LVEF <= 35%

• LBBB

• QRS >= 150 ms

• NYHA Class II, III, ambulatory IV

• On GDMT

Class IIa Indication for AF Patients

CRT is reasonable for patients with:

• Atrial fibrillation

• LVEF <= 35%

• Symtoms on GDMT

• If the patient requires ventricular pacing or otherwise meets CRT criteria

• If AV nodal ablation or pharmacological rate control will allow near 100% BIV pacing

CRT Patient Selection: ECG

• Best results with LBBB

• Results improved with wider QRS

• Longer LV activation time

  • Time difference between first notch after 40 ms of QRS and end of QRS

Factors in CRT Response

• ~30% of patients with reduced LV systolic function and narrow QRS have mechanical dysfunction

• Research into patients with wide QRS, no mechanical dyssynchrony

• Data suggests patients with both electrical and mechanical dyssynchrony respond best

• Other factors:

  • Female sex

  • Non-ischemic cardiomyopathy

  • Genetic factors

Other HF Management Strategies

• Pharmacological therapy

• Surgical procedure

• Heart transplant

• Other devices:

  • Mechanical circulatory support to pump blood

  • ICD to prevent SCD

  • Barostimulation to address compensatory mechanisms

During CRT Implant

• Achieve optimal stimulation configuration

  • LV lead position

  • Pacing vector

• Choose optimal device settings

• Reprogram post-implant if needed

• May need lead revision

After the Implant

• Patient education and continued care

• Remote monitoring

• Continue OPT

• Communication between EP and HF specialist

• Manage underlying disorders

  • Anemia

  • Myocardial ischemia

  • Mitral regurgitation

• Treat arrhythmias

  • Antiarrhythmics

  • Ablation

Physiologic Pacing

More physiologic as it goes down

• Asynchronous

• VVI mode

• RV apical pacing

• Demand

• DDD mode

• Rate response

• Dynamic intervals

• His bundle pacing

• Biventricular pacing

Resynchronization

• AV dyssynchrony

  • AV sequential pacing

  • Atrial tracking

• Interventricular dyssynchrony

  • Pacing RV and LV in unison

  • Pacing with calculated delay between RV and LV

• Intraventricular dyssynchrony

  • Pacing lateral wall of LV early

AV Synchrony

• Maximizes ventricular preload

  • Increases contractility

  • Increases stroke volume

• Allows AV valves time to close

  • Prevents regurgitation

• Maintains low atrial pressures

  • Easier venous return

  • Prevents congestion

• Regulates autonomic & neurohormonal reflexes

Dual Chamber CIED

Degree of Heart Block	Appropriate Algorithm
None	Fixed extended AV delay, intrinsic promotion algorithm
1st Degree	Fixed extended AV delay, intrinsic promotion algorithm
Intermittent 2nd Degree	Intrinsic promotion algorithm, AV search hysteresis
Consistent 2nd Degree	AV search hysteresis
3rd Degree	Fixed or dynamic AV delay

CRT-P or CRT-D

• 100% BIV pacing required

• Program AV delay shorter than intrinsic conduction while keeping it as physiologic as possible

• Suboptimal AV timing: #1 reason for poor CRT response

Mitral Velocity Doppler Echo

• Flow of blood through mitral valve

• Assess mechanical dyssynchrony between atria and ventricles

• E (early) wave: passive ventricular filling

• A (atrial) wave: atrial systole

E Waves & A Waves Part 1

• AV delay optimal:

  • E wave begins after isovolumetric relaxation

  • A wave begins at end of E wave

  • Isovolumetric contraction begins at end of A wave

E Waves & A Waves Part 2

• AV delay too short:

  • Ventricular contraction begins during atrial systole

  • A wave is truncated by closing of mitral valve

  • Less time for filling

  • Systolic MR

E Waves & A Waves Part 3

• AV delay too long:

  • Ventricular contraction delayed

  • Ventricular relaxation delayed: late E wave

  • Fused E/A wave: A wave begins part way through E wave

  • Diastolic MR

Optimizing AV Delays

Goal: ventricular contraction directly after A wave

• Too early: A wave truncation

• Too late: E/A wave fusion

• Check percentage A paced

  • 0% A Paced: SAV optimization only

  • Permanent AF: no AV optimization

  • Otherwise: SAV and PAV optimization

Ritter Method

1. Program SAV/PAV to 75% intrinsic PR interval

2. Shorten delay in 20 ms increments while recording on echo

3. Continue to shorten until A wave first begins to truncate

4. Lengthen delay in 10 ms increments until truncation disappears

5. Program this delay as the permanent SAV/PAV

V-V Optimization

• LBBB: LV depolarized before RV

• Most have mechanical interventricular dyssynchrony as well

• BIV pacing:

  • Pace both ventricles at same time

  • Offset pace LV before RV

  • Offset pace RV before LV