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Cardiac EP Lab : Amplifiers, Filters, Digital Recording System

EP Procedure in Progress

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1. Patient

2. Catheter & Connectors

3. Junction Box

4. Fluro Display

5. EP Recording System

The Components

EP Equipment

◦ Recording System

◦ Amplifier

◦ Stimulator

◦ Catheters

Diagnostic

Ablation

◦ RF Ablator

Fluoroscopy & Radiographic table

Other Essential Equipment: Hemodynamic monitor, Pulse

Oximetry, Infusion pumps, External Defibrillator, Essential Drugs,

Temporary Pacemaker & Resuscitation equipment

The Patient Handbook of Cardiac Electrophysiology: A Practical Guide to Invasive EP Studies and Catheter Ablation. F. D Murgatroyd, et al.

Diagnostic Catheters ◦ 4 – 7Fr, Hollow sealed tubes made of Polyurethane (steel braided core) or

Dacron fiber (woven core) material with platinum or steel electrodes at the

distal end.

◦ Conducting wires used are steel (polyurethane) or Silver (Dacron)

◦ Electrical signals are recorded from the endocardium by specialized

catheters with embedded platinum electrodes

◦ Commonly, there are either 4 (Quad), 8 (Octa), 10 (Deca: CS) or

20 (Duo Deca: RA, PV) electrodes

◦ These electrodes can also be configured to pace, that is, apply electrical

stimulation to the heart

Boston Scientific Image Library.

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Alden

Redel

Easy-Mate

Josephson

Ablation Catheter

7Fr Polyurethane hollow sealed tubes

Temperature sensor

◦ Thermistor

◦ Thermocouple

Tip Size

◦ 4 / 8 mm large dome - most commonly used tip dome

◦ 5 mm large dome

Irrigated (Thermocouple)

◦ 3.5 – 4 mm dome

◦ Also available 8 mm

◦ 6 – 12 perfusion holes

Diagnostic Catheter Placements

HRA High Right Atrium RA-SVC

junction

◦ Records Sinus node

HIS above TV

◦ Marker for the AV node

CS in CS and advanced in the

AV groove

◦ Records left atrial and ventricular

activity

RVA apex of right ventricle

◦ Records RV from bottom most area

Radiofrequency Ablation of Cardiac Arrhythmias; Lawrence S. Klein and William M. Miles; Scientific American Science and Medicine; May/June 1994. Permission of authors.

Unipolar Signals

Derived from the potential

difference between a point

source using an exploring

electrode in direct contact

with the heart (positive input

- anode) and a zero reference

(negative input - cathode)

The Wilson Central Terminal

or a remote electrode (e.g. in

the IVC) as the other

electrode

Bipolar Signal

Record signals using two

electrodes close to one another

Sharper local signals

Much smaller far field signals

Preferred recording method in

most EP labs

(Signal 1 + Noise) – (Signal 2 + Noise) = Signal 1 – Signal 2

Signal 1

Signal 2

Junction Box

JB or CIM receive IC signals

from the catheters and

provide an interface into the

physiologic recorded

◦ 20, 40, 54, 80, 102 upto 320

inputs

Multiple switches within

the JB are designated to

a recording and

stimulation channel

which is predefined by

the recording system.

Handbook of Cardiac Electrophysiology. Organization of the arrhythmia lab. Andrea Natale et al. 3:17-24. 2007.

Cardiac Amplifier

Consists of

◦ ECG Interface

◦ Hemodynamic Interface

◦ Intracardiac Interface (Jbox)

◦ Stimulation Interface

◦ Input Aux Ports

◦ Output Aux Ports

Functions

◦ Amplifies Input Analog Signals

◦ Apply filtering to input analog

signals

◦ Convert Analog data to digital

◦ Direct Stim impulse to

appropriate channel

Conducts POST (Power On Self Test)

1. Board Integrity

2. Working Environment

Signal Processing

Signal Amplification Physiologic signals acquired from surface and IC electrodes are typically

◦ 25 μV (as measured in infracted regions during ventricular tachycardia mapping)

◦ 5mV (from a surface ECG lead)

◦ Upto 20 mV in healthy myocardium

Considerable amplification is required before the signals are digitized,

displayed and stored.

Amplifiers have different techniques of amplifying the input signals.

◦ Hardwired gain

◦ Gain value -> In mV,

percentage or factor

◦ Software gain

Venkatachalam K et al. Circ Arrhythm Electrophysiol 2011;4:965-973

Signal Amplification

Low gain - Surface ECG, Unipolar IC signals

Moderate gain - RV, RA,CS signals

High gain

◦ His signals (100-μV*)

◦ Mapping catheter signals

◦ Pulmonary vein catheter signals

Issues include gaining up noise, saturation of current causing amplifier

to blank out (typically flat line) and display no signals


Low Gain

Very High Gain

Appropriate Gain Settings

High Pass Filter

Allows frequencies higher than the cut off or

corner” frequency to pass

Anything lower than the corner frequency is

removed

Surface ECG and unipolar intracardiac signals

50Hz

Bipolar intracardiac signals 10-30Hz

Helps to remove baseline sway due to

breathing or movement

The selections available are Disable, 0.01Hz,

0.05Hz, 0.1Hz, 0.5Hz, 1.0Hz, 10Hz, 30Hz, and

100Hz.

System default is 30 Hz

High Pass at 100Hz

High Pass Off

With Nominal Settings

For ECG –HP = 1 Hz For IEGM – HP : 30 Hz

Low Pass Filter Allows frequencies lower than the cut off or

“corner” frequency to pass

Anything higher than the corner frequency is

removed

Surface ECG 100Hz

Intracardiac ECG 500Hz

Helps to remove high frequency electrical

noise from the lab surroundings

The selections available are 10 Hz, 25 Hz, 50

Hz, 100 Hz, 250 Hz, 500 Hz, 1000 Hz, and 2000

Hz. System default is 250 Hz

Amplitude change with different low-pass filter

settings on His1 (150 Hz vs 1000 Hz).


Copyright © American Heart Association, Inc. All rights reserved.

Amplitude change with different low-pass filter

settings (10 Hz vs 300 Hz).

10 Hz 300 Hz

Application of Filters

Signal Type High Pass Filter Low Pass Filter

Surface ECG 0.5Hz 100Hz

Intracardiac Bipolar 30Hz 300Hz

Intracardiac Unipolar 1-2Hz 300Hz

Unfiltered Unipolar 0.1Hz

(or no high pass) 300Hz

Low Pass Filter

High Pass Filter 0.05 Hz

300 Hz

Band Pass Filter

Is a combination of low and high pass filters

Allows a specific frequency range to pass

Diagnostic-quality ECG signals typically require a processing

bandwidth of 0.05–100 Hz, whereas monitor-quality ECGs may be

limited to 0.5–40 Hz

E.g. 10-500Hz is the band pass for intracardiac bipolar signals

E.g. 0.05-100Hz is the band pass for ECG

Notch Filter

Removes a specific frequency

In India mains frequency is 50Hz and cause electrical

interference in poorly grounded labs

A notch filter helps to remove this

It is better to remove the noisy piece of equipment as

clinically important signals occur at 50Hz

Notch Filter : OFF Notch Filter : ON

Pulmonary vein potentials on Lasso catheter with and without 50/60 Hz notch.



In (A) significant reduction in signal amplitude with “smearing” of the signals, mimicking far-field

signals, when the notch filter is active. In (B), fractionated potentials on ABLd lose a lot of the

fractionation slowly as the notch filter is turned on

Issues of Notch Filtering

Notch Filtering causes

“Ringing” Effect when

applied to high

amplitude signals

Understanding A/D Conversion 16-bit A/D converter-

The analog to digital converter (A/D) is responsible for transforming the electrical voltage detected by the amplifier into digital waveforms

Resolution

The ADC resolution is defined as the smallest incremental voltage that can be recognized and hence it causes a change in the digital output. It is usually expressed as the number of bits output by the ADC.

2 mV 16 bit = 216 = 65536 steps Resolution16 0.0305 microVolt per step RTI

12 bit = 212 = 4096 steps Resolution12 0.488 microVolt per step RTI

More bits means finer dots to accurately describe the waveform

2 mV

•16-bit resolution

produces finer dots

•With 1kHz

sampling, achieve

~1000 steps of

resolution for a 30

microvolt AF signal

Choosing the Right Amplifier Technology requires High Speed and High Resolution

How many bits do we need

12/16/24/32- what do we need?

Calculating steps -> 2n

Displaying a 2 mV signal -> 2 / Steps

◦ 12 bit -> 4096 steps -> 0.488 microVolts

◦ 16 bit -> 65,536 steps -> 0.0305 microVolts

◦ 24 bit -> 16,777,216 steps -> 0.0001 microvolts

◦ 32 bit -> 4.3 million steps -> ????????

2 mV 16 bit = 216 = 65536 steps Resolution16 0.0305 microVolt per step RTI*

* Resolution Relative To Input Signal

Sampling Rate

A/D converter is usually multiplexed (shared) by many channels

Data sampling and data storage devices capable of dealing with the aggregate rate of all channels

◦ Using a sampling rate of 1000 Hz (1 KHz) for 80 channel, the sampling rate achieved is 80,000 Hz. *

Look for amplifiers which maintain the total IC channels available at higher sampling rates.

◦ Some amps will give a #IC/Sampling rate

◦ i.e. at 2 KHz if total IC channels at 1 KHz is 180, you would get 90 IC recordable at 2 KHz and 45 IC channels at 4 KHz.

* R C Barr and M S Spach. Sampling rates required for digital recording of intracellular and extracellular

cardiac. Circulation. 1977;55:40-48

Sampling Rate & Sweep Speed

1 KHz - Sweep speed max 200 mm/sec



50mm/sec 200mm/sec

Noise Affecting Signals

EP laboratory is an extraordinarily noisy environment.

◦ ECG Machine, Pulse Oximeter, External Defib, EAM System,

Catheters.

◦ Patient acts are a huge antennae picking up environmental noise like

fluorescent lamps, wireless monitors etc

Leakage current of upto 10 μA acceptable per equipment

which most patients can tolerate without significant risk of

inducing ventricular fibrillation.

Leakage current can interfere substantially with our ability

to process extracardiac and intracardiac signals with

minimal artifact.


Noise & Source

Effect of Noise

The main sources of noise in ECG are

◦ Low Frequency noise (Baseline Wander)

Muscle Tremor

Respiration

◦ 50/60 Hz supply line noise

◦ High Frequency noise

Other interference (i.e., radio frequency noise from other equipment)

Fluorescent lamps / bulbs

Any A/C Motor based equipment (pumps, Air Conditioners etc)

ECG SIGNAL Artifacts (disturbances) can have many causes.

Common causes are:

Movement

Environmental Noise

Sudden movement

From a nearby electrical appliance. A typical example is a 100 Hz background distortion from fluorescent lights. To be confused with atrial fibrillation.

http://en.ecgpedia.org/wiki/Atrial_Fibrillation



Noisy Signals

Intracardiac Signals affected by RF noise.

Noise During RF Delivery

Grounding?

Connecting cable

IEGM cable

Faulty Catheter

Back patch with inadequate Gel

Pacing enabled

Noise on the ABLd electrode during radiofrequency ablation with (A) and without (B) the

pacing function enabled on ABLd. The noise goes down substantially when the pacing

function is disabled, eliminating the imbalance on the ABLd electrodes and improving

noise rejection.



Grounding

Dedicated isolated ground

◦ Pipe

◦ Plate

◦ Water Pipe

◦ Steel encased in Concrete

◦ Ground Ring

Plate / Pole at a minimum depth of 8-10 ft

Must have a plate / ground resistance of < 5 ohms

Add second Plate / Pole if resistance > 5 ohms

The process of making a planned, continuous, connection between NON-

CURRENT CARRYING parts of the electrical wiring installation and the earth

and some other conducting body

Note : Grounding & Earthing are two different systems designed

for two entirely different purposes

The Perfect Scenario

EP Recording System

Consists of

◦ High End Intel based

workstation

◦ Special Interface cards

◦ 2, 3 or 4 HD monitors

◦ High End Graphics Card

◦ Dedicated Mirrored Storage

Space

◦ High Speed Laser Printer

EP Recording System

Function

◦ Interface to configure the

amplifier for signal acquisition

◦ Record and Display data

Real-time Monitor

Review Monitor

◦ Review historical data

◦ Provide for additional tools

Template matching

Auto measurements etc..

◦ Tools for archiving & backup

◦ Reporting tool

◦ Advance systems interface

with other imaging systems

Real-Time Monitor

Real-Time Waveform Display and Status Area

Review Monitor

Tools Provided

Calipers

Event Log

Holter Mode

Stim Sensed Review

Trigger Mode

Sweep Speed

Archive

Restore

Backup

Additional Tools

Template Matching

T-Wave Subtraction

Image Acquisition

Dominant Frequency Analysis

CFAE / FFT

Reporting App.

Template Matching

Your review screen will update like this. Yellow is %

match Lead to Lead.

Overall match is displayed in two areas ( ).

T-Wave Subtraction

Subtract a T-Wave template from an overlapped PT waveform to recover an obscured P wave

Saves time localizing atrial arrhythmias

Original

Revealed P-Wave

T-Wave Template

• Automated real-time waveform analysis for detection of P-wave morphology using trigger detection

The T-Wave Subtraction feature automatically removes the T-wave from an overlapped patient waveform to recover an obscured P-wave.

T-Wave Substraction

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Typical Workstation Specifications

Sr

#

Specification

1 Operating System Windows XP / 2000 Server

2 Computing Power Intel® Core™2 DUO E8400 3.0 GHz - 6 MB L2 cache, with 1333 MHz Front Side Bus

3 Memory (RAM) 4 GB DDDR RAM

4 Graphics nVIDIA GeFORCE GTS 450 PCIe (Dual Port). 1GB VRAM Dedicated

5 Monitors 24” or 27” EIZO monitors

6 Hard Disk HDD1 : 250 GB (7200 rpm) HDD2 : 300 GB (10K rpm)

7 Data Protection OS drive & Data drive should be separate, hence if OS drive gets corrupt, data drive still intact.

8 DVD/CD Archiving TEAC CD/DVD ±R±RW/DVD-RAM Speed : DVD+R 24x, DVD±RW 8x

9 Power Source Through dedicated isolation box

10 Printing Option to use own specs or HP

11 Work Table Anthro Cart

12 Image Capture Image Capture Kit for High Res Fluro Image Capture

All The Best