植入性心臟電子儀器地基本原理與設定

林口長庚 巫龍昇醫師

Voltage, Current, and Impedance Recap

• Voltage: The force moving the current (V)

– In pacemakers it is a function of the battery chemistry

• Current: The actual continuing volume of flow of electricity (I)

– This flow of electrons causes the myocardial cells to depolarize (to “beat”)

• Impedance: The sum of all resistance to current flow (R or W or sometimes Z)

– Impedance is a function of the characteristics of the conductor (wire), the electrode (tip), and the myocardium

2

Voltage and Current Flow Electrical Analogies

Spigot (voltage) turned up, lots of water flows (high current drain)

Spigot (voltage) turned low, little flow (low current drain)

Water pressure in system is analogous to voltage –

providing the force to move the current

Resistance and Current Flow Electrical Analogies

• Normal resistance – friction caused by the hose and nozzle

More water discharges, but is all of it going to the nozzle?

• High resistance – a knot results in low total current flow

• Low resistance – leaks in the hose reduce the resistance

Ohm’s Law • Describes the relationship

between voltage, current,

and resistance

• V = I X R

• I = V / R

• R = V / I

V

I R

V

R

I

V

R

I

R

V

I =

=

=

X

Other terms

• Cathode陰極: – For example, the electrode on the tip of

a pacing lead

• Anode陽極: – Examples:

• The “ring” electrode on a

bipolar lead

• The IPG case on a unipolar

system

6

Anode

Cathode

PACING MODES

Pacing Modes

I II III IV

Chamber(s)

Paced

Chamber(s)

Sensed

Response

to Sensing

Rate

Modulation

O = None

A = Atrium

V = Ventricle

D = Dual (A + V)

S = Single (A or V)

O = None

A = Atrium

V = Ventricle

D = Dual (A + V)

S = Single (A or V)

O = None

T = Triggered

I = Inhibited

D = Dual (T + I)

O = None

R = Rate

modulation

Pacemaker modes most often seen:

DDDR/VDD

VVIR AAIR->DDDR (MVP)

What mode would you use for 3rd Degree Block?

What mode would you use for SSS?

What mode would you use for permanent AF?

Knowledge Checkpoint

What is the rhythm? What type of device does this patient need?

VVI Mode

I II III

Chamber(s)

Paced

Chamber(s)

Sensed

Response to

Sensing

O = None

A = Atrium

V = Ventricle

D = Dual (A + V)

S = Single (A or V)

O = None

A = Atrium

V = Ventricle

D = Dual (A + V)

S = Single (A or V)

O = None

T = Triggered

I = Inhibited

D = Dual (I + T)

VVI Example

• Chamber paced: Ventricle

• Chamber sensed: Ventricle

• Response to sensing: Inhibition

–VVI 60 = Lower Rate timer of 1000 ms

• Pacing every 1 second if not inhibited

V

P V

P

V

P

Lower Rate Timer 1000 ms Lower Rate Timer 1000 ms Lower Rate Timer ….

VVI Example (60 bpm)

V

P

V

S

V

P V

P

Lower rate timer 1000 ms

x

Lower rate timer 1000 ms

•Paces and Senses in the ventricle

•Timed from each QRS

•If it sees a sensed event, it will inhibit the next pace

VOO Mode – Asynchronous Pacing

Chamber paced: Ventricle

Chamber sensed: None

Response to sensing: None

The intrinsic ventricular event

cannot be sensed, and thus, does

not interrupt the pacing interval.

1000 ms 1000 ms 1000 ms

V

P

V

P

V

P

V

P

VOO results in fixed-rate pacing in

the ventricle.

Knowledge Checkpoint

What is the rhythm? What type of device does this patient need?

AAI Mode

I II III

Chamber(s)

Paced

Chamber(s)

Sensed

Response to

Sensing

O = None

A = Atrium

V = Ventricle

D = Dual (A + V)

S = Single (A or V)

O = None

A = Atrium

V = Ventricle

D = Dual (A + V)

S = Single (A or V)

O = None

T = Triggered

I = Inhibited

D = Dual (I + T)

AAI

• Paces in the atrium

• Timed from last P wave

Pacing Interval

A P

A P

Lower Rate Timer 1000 ms

Knowledge Checkpoint

What is the rhythm? What type of device does this patient need?

DDD Mode

I II III

Chamber(s)

Paced

Chamber(s)

Sensed

Response to

Sensing

O = None

A = Atrium

V = Ventricle

D = Dual (A + V)

S = Single (A or V)

O = None

A = Atrium

V = Ventricle

D = Dual (A + V)

S = Single (A or V)

O = None

T = Triggered

I = Inhibited

D = Dual (I + T)

DDD

A S V

P

A S V

P

A P V

S

A P V

S

• Senses and paces in both chambers when needed

Knowledge Checkpoint

A

B

C

D

Label each EKG with the faces of pacing (AS-VS, AP-VS, AP-VP,

AS-VP).

Magnet Application for devices

• Magnet application temporarily changes pacing mode to DOO/VOO

Magnet Applied

1 2 3

1

0

0

1

0

0

1

0

0

The 4th letter: “R”

• Question: what does your heart rate do when you exercise?

• “R” means “Rate response”

• Pacemaker will increase pacing rate in response to exercise – if patient does not increase his own rate

General guidelines for programming common pacemaker parameter

parameter situation Chronic setting comments

Lower rate limit General : minimal pacing desired;

50-70bpm 40-60bpm

Use rate hysteresis

Upper rate limit General Child/athletes CAD/angina

85% maximal predicted HR 0.85*(220-age) (220-age) bpm 110-120bpm

Based on average levels of activity May require programing short refractory periods Approximates peak HR on maximal beta blocker

Rate hysteresis

General guidelines for programming common pacemaker parameter

parameter situation Chronic setting comments

Pacing output Fixed voltage Fixed pulse width

3-4 X pulse width threshold 2-3X voltage threshold

Minimizing voltage output more efficient Use autothreshold function

sensitivity Atrium ventricle

25-50% threshold 25-50 % threshold

Need <1mV setting for mode switching Evaluate oversensing in unipolar system

General guidelines for programming common pacemaker parameter

parameter situation Chronic setting comments

AV delay AV block Intrinsic conduction (no HF) Intrinsic conduction (CHF)

150-180msec paced AV delay, sensed AV delay 25-50msec <paced AV delay Up to 220msec Often set even longer AV delay

Turn on rate adaptive AV delay in active patients Longer AV delay may compromise hemodynamics, use AV hysteresis to promote intrinsic conduction Paced induced dyssynchrony of very long AV delay Optimize by doppler,

AV hysteresis

Programmer

Programmer - PAV, SAV

Programmer - Mode Switch

ICD Function

What is the function of an ICD?

• Sense cardiac rhythms

• Detect arrhythmias

• Deliver therapy

• Pace when necessary

Typical Transvenous Lead

Transvenous Leads Placement

Single Coil Dual Coil

ICD Therapies

• Tachyarrhythmia Therapy

–Cardioversion (CV)Sychronized ro R

–Anti-Tachycardia Pacing (ATP)

–Defibrillation Shock

Low Power

oBradyarrhythmia Therapy –Pacing Modes

Low Power

High Power

High Power

Bradyarrhythmia Therapy

• Most ICDs offer:

–Single Chamber Pacing • AAI(R), VVI(R) and VOO

–Dual Chamber Pacing • DDD(R), DDI(R), DOO and ODO

• Mode Switch

–Separate post-shock pacing programming • Ensures capture

ICD common setting

• VT zone 160-200bpm

• VF zone >200bpm

• The rate usually set 10bpm slower than the documented ventricular arrhythmia rate to reliable detection

• Ventricular sensitivity must allow for the detection of very low amplitude ventricular fibrillation signals and typically set to 0.3 mV

ICD basic parameters parameter function programming comment

VF zone Detection rate for fastest VF zone: rate of VF zone must be on

VF zone; Hemodynamically unstable VT

Must be on at all times, only shock Rx available

VT zone Detection rate for slower VTs in multizone programming

On or off; Usually 10bpm < spontaneous VT

ATP and cardioversion Rx available

Initial detection No. of intervals

VF zone : 75% intervals > VF rate VT zone: number of consecutive intervals > rate limit

VF typically 12/16, or 18/24 beats > VF rate VT typically 8-20 beats >VT rate

ICD basic parameters

parameter function programming comment

Ventricular sensitivity

Usually 0.18-0.3mV High sensitivity needed to detect small EGM in VF

ATP Painless pace termination of VT

On or off Often initial RX for VTs <200bpm

Type of sequence (burst or ramp)

Burst: all paced intervals the same Ramp: decrements between paced intervals in sequence

Burst or ramp Ramp therapy considered more aggressive but equal efficacy for spontaneous

ICD basic parameters

parameter function programming comment

Cardioversion/defibrillation

Shock therapy Always on in all zones

Only RX in VF, or single zone; initial RX or follows ATP in VT zones

Energy Magnitude of shock in joules

VF: DFT =5-10 J VT: at or above smallest successful energy

VT often terminated with 2-10 J

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• 13% - 38% of ICD patients experience significant levels of psychological stress related to the fear of receiving a shock.6

• Patients receiving shocks reported feeling less healthy, had

lower levels of psychological well-being, and reduced physical and emotional function.7

• Shock therapy is inversely correlated with quality-of-life.8,9

• Patients receiving ATP first showed a significant increase in

QOL over those receiving shock first.10

Shock Therapy is Related to a Decrease in QOL

6. Hammil SC, et al. J Cardiovasc Electrophysiol, 2000.

7. Namerow PB, et al. PACE, 1999.

8. Carroll DL, et al. Heart Lung, 2005.

9. Irvine J, et al. Am Heart J, 2002.

10. Wathen MS, et al. Circulation, 2004.

Shock Reduction

• Anti-tachycardia pacing

• 延長VT/VF偵測

• 藥物

Anti-Tachycardia Pacing

Re-entry initiated ATP delivered at a rate faster than tachyarrhythmia.

Wavefronts collide.

Subsequent Pulse: Wavefronts collide closer to re-entry circuit

Subsequent Pulses: Wavefronts collide even closer to re-entry circuit

Arrhythmia terminated

Anti-tachycardia pacing (ATP)

ATP的風險

Anti-tachycardia pacing（ＡＴＰ） Burst v.s Ramp

Programmed Values:

Number of S1 Pulses = 4

Number of Sequences = 4

R- S1% = 91% (less agrassive)

Decrement* = 10 ms

* Decrement between sequences

Programmed Values:

Number of S1 Pulses = 4

Number of Sequences = 4

R-S1% = 91% (less aggrassive)

Decrement* = 10 ms

* Decrement between pulses

* Adds a pulse per sequence

PITAGORA ICD study: Bust is significantly more efficacious than ramp in terminating FVT episodes

Sensing

• Sensing is:

–The process of identifying cardiac depolarizations from an intracardiac electrogram

Measured Peak-to-Peak

>5 mV for optimal sensing

Detection

• Measured in:

–Beat-to-beat intervals (milliseconds), or

–Beats-per-minute (BPM)

Detection Rate

•Classifies rhythm by detection zone:

–VT = Ventricular Tachycardia +/- FVT

–VF = Ventricular Fibrillation

•Programmable in ranges of rates

Example:VT = 162 bpm – 188 bpm

VF = 188 bpm and faster

Detection Zone Classifications

ＩＣＤexample

Detection

• Measured in: – Number of intervals to detect (NID), or

– Length of time to detect

•Programmable by:

– Beat or interval counters

• Consecutive ex: 16 beats within the detect zone

• Probabilistic (percentage or fraction) ex: 12 out of 16 beats within the detect zone

– Time in seconds

Detect Duration

Detection

Used for detection of VT

Consecutive Counter

Detection

NID = 12/16

Probabilistic Counter

• Can you identify the detect zones?

• Name the rate & duration for each

Detection Detect Zones

Cardioversion

• Delivers shock on an R-wave

• Aborts if synchronization cannot be obtained due to arrhythmia termination

Cardioversion

Defibrillation Programming

*Medtronic Programming Screen

Major Challenges Faced

• Inappropriate therapies

• Unnecessary shocks

• Repetitive shocks

58

59

• 13% - 38% of ICD patients experience significant levels of psychological stress related to the fear of receiving a shock.6

• Patients receiving shocks reported feeling less healthy, had

lower levels of psychological well-being, and reduced physical and emotional function.7

• Shock therapy is inversely correlated with quality-of-life.8,9

• Patients receiving ATP first showed a significant increase in

QOL over those receiving shock first.10

Shock Therapy is Related to a Decrease in QOL

6. Hammil SC, et al. J Cardiovasc Electrophysiol, 2000.

7. Namerow PB, et al. PACE, 1999.

8. Carroll DL, et al. Heart Lung, 2005.

9. Irvine J, et al. Am Heart J, 2002.

10. Wathen MS, et al. Circulation, 2004.

辛苦了 謝謝聆聽

Differentiation of SVT from VT parameter What It does Potentially

useful For Potential problem

stability Suppressed therapy for tachyarrhythmia with variable ventricular rate

Atrial fibrillation

Underdetection of VT with irregular rate; failure to suppress therapy for SVTs with regular ventricular response

onset Suppressed therapy for tachyarrhythmia that slowly accelerate

Sinus tachycardia

Underdetection of gradually accelerating VT or VT onset during sinus tachycardia; failure to suppress therapy for sudden onset SVT

Ventricular electrogram width

Suppress therapy for tachyarrhythmia with narrow ventricular EGM correlated to narrow QRS complex

Differentiation of narrow complex SVT from VT

Limited specificity with BBB; may prevent therapy for narrow complex VT

Differentiation of SVT from VT

parameter What It does Potentially useful For

Potential problem

Ventricular electrogram morphology

Suppressed therapy for tachyarrhythmia with ventricular EGM morphology similar to that in sinus rhythm

D/D SVT from VT

Limited specificity with BBB

Atrial to ventricular ratio

Compare atrial to ventricular rate

Atrial fibrillation

Atrial undersensing can result in false diagnosis of VT

SVT Discriminators

• Distinguishes SVTs by analyzing P and R-wave:

–Rate

–Regularity

–AV Association

PR Logic™

– Pattern

SVT Discriminators

• Based on the premise that AF conducts irregularly to the ventricles

(and VT is a stable, regular rhythm)

• Discriminates regular from irregular intervals within a detect zone

Stability

SVT Discriminators

Unstable Varies >50 ms from previous 3

Stability = 50 ms Stability

* in Medtronic devices

SVT Discriminators

• Based on the premise that most VTs are characterized by a sudden onset

•Evaluates the acceleration of the ventricular rate

•Discriminates between:

–Gradual rate increase

–Abrupt rate increase

•Determines VT present if rate

increase is abrupt

Onset

SVT Discriminators

• Onset Percentage = 81%

530ms X 81% =

430ms

430ms 460ms = Onset Not Met

Onset

* in Medtronic devices

SVT Discriminators

• Measures and stores the QRS characteristics of a normal sinus beat

• Identifies SVT vs. VT based on the QRS changes that occur in most VTs

SINUS RHYTHM VT

Waveform Morphology

SVT Discriminators

• Identifies start and end points of a sensed QRS complex

• Uses 2 parameters to measures QRS: –Slew Width

–Slew Threshold

EGM Width

SVT Discriminators EGM Width

SVT Discriminators

• Records and stores a template of a normal QRS wave

•Compares stored template with a QRS

occurring within the detection zone

•Withholds detection if 3 of last 8 QRS

complexes match the stored template

– Detects VT/FVT/VF if 6 out of 8 do not match

•Applies to initial detection only

Wavelet

SVT Discriminators

• Template

% difference compared against:

Match Threshold Value

Wavelet

Refractory and Blanking Periods

• Pacemaker sensing occurs when a signal

is large enough to cross the sensing

threshold

1.25 mV Sensitivity

Time

5.0 mV

2.5 mV

1.25 mV

Sensing does not tells us

anything about the origin or

morphology of the sensed

event, only its “size.”

In DDD & VDD modes the

pacemaker will “track” the atrium

AS

VP

Tracking = Pacing the ventricle after an atrial intrinsic event

Maintains AV Synchrony

Want to limit how fast we pace

Upper Tracking Rate

DDDR 60 / 120 A-A = 500 ms

Upper Activity Rate Limit

Lower Rate Limit

Upper Sensor Rate

• Sensor rate drives the atrial rate up

• In rate responsive, dual chamber modes, the Upper Activity (Sensor) Rate

provides the limit for sensor-driven atrial pacing

PAV PAV

1000 ms

500 ms

Post Shock Pacing