Electrocardiogram (ECG) PhillipN, (2007) Display device of a medical monitor as used in anesthesia [photograph]. Retrieved from

Summary Clinical Use Specifications History Principles of Operation Block Diagram Commercial Examples Preventive Maintenance Common Problems Test Procedures

Typical Heart Rate Normal heart rate – 60 to 80 beats/min (5 liters/min) During Exercise – 120 to 160 beats/min (15 to 25 liters/min) Tachycardia - heart rate more than 100 beats/min (resting). Bradycardia - heart rate less than 60 beats/min (resting). Maximum Heart Rate = 220 – Age Athletes - Max HR = 160 to 220

Circulation Two separate pumps: Right Side moves deoxygenated blood to the lungs for oxygenation Left Side moves oxygenated blood to the body Which leads to two distinct circulatory systems: Pulmonary vessels to and from the lungs Systemic vessels to and from the rest of the body Vessels that move blood away from the heart are called arteries and vessels that return blood to the heart are called veins. Blausen Medical Communications, Inc. (2013), Cardiovascular System [image]. Retrieved fromhttps://en.wikipedia.org/wiki/Talk:Circulatory_system#/medi a/File:Blausen_0168_CardiovascularSystem.png

The Nernst Equation E K =  log (K i /K o ) Animation: As we discussed, the inside of the cell is slightly negatively charged (resting membrane potential of -70 to -80 mV).cell A disturbance (mechanical, electrical, or sometimes chemical) causes a few sodium channels in a small portion of the membrane to open.electrical Sodium ions enter the cell through the open sodium channels. The positive charge that they carry makes the inside of the cell slightly less negative (depolarizes the cell). When the depolarization reaches a certain threshold value, many more sodium channels in that area open. More sodium flows in and triggers an action potential. The inflow of sodium ions reverses the membrane potential in that area (making it positive inside and negative outside -- the electrical potential goes to about +40 mV inside) When the electrical potential reaches +40 mV inside (about 1 millisecond later), the sodium channels shut down and let no more sodium ions inside (sodium inactivation). The developing positive membrane potential causes potassium channels to open. Potassium ions leave the cell through the open potassium channels. The outward movement of positive potassium ions makes the inside of the membrane more negative and returns the membrane toward the resting membrane potential (repolarizes the cell). When the membrane potential returns to the resting value, the potassium channels shut down and potassium ions can no longer leave the cell. The membrane potential slightly overshoots the resting potential, which is corrected by the sodium-potassium pump, which restores the normal ion balance across the membrane and returns the membrane potential to its resting level. Now, this sequence of events occurs in a local area of the membrane. But these changes get passed on to the next area of membrane, then to the next area, and so on down the entire length of the axon. Thus, the action potential (nerve impulse or nerve signal) gets transmitted (propagated) down the nerve cell.­ Membrane potential depends of ions concentration: Na +, K +, Cl - Ionic Current

Cell Depolarization Villetakanen (Own work), Nerve Cell Depolarization [CC BY-SA 4.0 ( via Wikimedia Commons

Cell Depolarization The cardiac pacemaker cell action potential: Silvia3 (2010), Pacemaker Action Potential [image]. Retrieved fromhttps://en.wikipedia.org/wiki/Cardiac _action_potential#/media/File:Pacemaker _potential_annotated.gif

Heart’s Anatomy Wikipedia. “Heart.” Wikipedia, p Retrieved from:

Four-chambered muscular vessel: Two Atria (left and right) Two Ventricles (left and right) Atrium: Filling chamber Pushes blood into ventricle Ventricle: Pressurization chamber Ejects blood into circulation Chambers separated by heart valves: One-way flow valves Four in total (tricuspid, pulmonary, mitral, aortic) Heart’s Anatomy Wikipedia. “Heart.” Wikipedia, p Retrieved from: Blood Flow in Heart:

Circulatory Pressures Yaddah (2006), View from the front [image]. Retrieved from

Clinical Use Measures –Rate and regularity of heartbeats –Size and position of the chambers –Presence of any damage to the heart –Effects of drugs

Specifications Input: Voltage (biopotential) Output : –Electronically (display) –Paper

Einthoven’s triangle Principles of Operation Kychot (2009), Einthoven Triangle [image]. Rwtrieved from

ECG Signal ECGpedia.org, “Basics.” Wikipedia. Retrieved from:

ECG Signal Openstax College. “The Cardiac Cycle, Fig ” From the publication: Biology. Rice University: 2013, pgs

ECG Signal P – atrial depolarization QRS complex – ventricular depolarization T – ventricular repolarization Anthony Atkelski (2007), Schematic diagram of a normal sinus rhythm [image]. Retrieved from

Signal of Heart Diseases Atrial Fibrillation Ventricular Fibrillation Michael Rosengarten BEng, MD.McGill [CC BY-SA 3.0 ( via Wikimedia Commons Jer5150 (Own work) [GFDL ( or CC BY-SA 3.0 ( via Wikimedia Commons

Sensor Disposable Ag/AgCl surface electrode Electrodes Malkin, Robert. Medical Instrumentation in the Developing World. Engineering World Health, 2006.

Electrodes Gel is important for a good contact with skin! TYPES: Disposable: $.05 to $.11 each Reusable Plate electrode

Diagnostic ECG Cooper, Justin and Alex Dahinten for EWH. “Electrocardiogram (ECG) Preventative Maintenance.” From the publication: Medical Equipment Troubleshooting Flowchart Handbook. Durham, NC: Engineering World Health, ECGpedia.org,.“ECG.Reference.Card.”.Wikipedia..Retrieved.from:.

Wave Forms Npatchett (2015), Derivation of the limb leads [image]. Retrieved from

Wave Forms Malkin, Robert. Medical Instrumentation in the Developing World. Engineering World Health, 2006.

Block Diagram for an analog ECG

Amplifier V OUT = (V 1 – V 2 )R 2 /R 1 Amplifies a difference. V OUT = A C (V 1 + V 2 ) + A D (V 1 – V 2 ) A D :differential (signal) gain, A C :common mode (noise) gain. The ratio A D /A C (Common Mode Rejection Ratio – CMRR) is a very important parameter. Ideally CMRR →∞

ECG amplifier (instrumentation amplifier) Input impedance >100 MΩ Range: 0.05–150 Hz Differential amplifiers with high gains (1000) CMMRs: 80 – 120 dB Amplifier

Differential Amplifier Arthur Ogawa (2014), Differential Amplifier with non-ideal on amp [image]. Retrieved from

Sampling The heartbeat rate itself is typically in the 60 to 200 beats per minute (1 Hz to 3.3 Hz) Range: 0.05–150 Hz 512 Hz sampling (2 ms) 10 samples at the QRS complex 12 bit resolution in analog-to-digital conversion ECGpedia.org,.“ECG.Reference.Card.”.Wikipedia..Retrieved.fro m:.

Sources of Interference AC interference: Cooper, Justin and Alex Dahinten for EWH. “Electrocardiogram (ECG) Preventative Maintenance.” From the publication: Medical Equipment Troubleshooting Flowchart Handbook. Durham, NC: Engineering World Health, Muscular interference

Commercial Examples PhillipN, (2007) Display device of a medical monitor as used in anesthesia [photograph]. Retrieved from (medical).jpg DiverDave (2010), Bispectral index monitor indicating a nearly isoelectric pattern of electroencephalographic activity [photograph]. Retrieved from _Monitor-Burst_Suppression.JPG

Commercial Examples Defibrillators also have a wave II ECG signal Pollo (2010), Biphasic defibrillator [photograph]. Retrieved from

Patient’s Safety Leak currents –Sometimes ECG may be used in direct contact with the heart –Even a small current running through the lead wires can cause death (ventricular fibrillation) Defibrillators display ECG leads I, II & III

Preventive Maintenance Calibration Clean reusable electrodes with alcohol and cloth physical checks-lead wires, Welch cups (if used), case damage, connectors, keypad/switches operation-paper speed, calibration pulse, trace/printout quality, front panel buttons and lights, battery life (if applicable) cleaning electrical patient safety

Weak or poor signal: –User error (may be no manual) –User error in position of electrodes –Loose wire –Dry disposable electrode –AC inference –Interference from other machines Common Problems

No signal: –No contact at Electrode (fallen off, no gel, broken wire) –Saturated Amp (gain too high) –Problem with cable connection –Damaged amplifier due to defibrillator Common Problems

User error –Manual lack or disregard –Complex user interface –Older models may require to adjust the gain for proper rate reading –Stylus position if applicable Common Problems

User error –Other electrode devices (ESU, bioimpedance) may interfere with each other –Wrong brightness settings – no display trace Common Problems

User error –Wrong electrodes positioning Symptom: Signal is saturated or distorted by power line noise Rules, electrodes should not be placed : 1 - On scar tissue 2 - Over a lot of body hair 3 - Closer than 2 inches from each other may Common Problems

Lead wires and main cord damage Lead interference Common Problems

AC interference –50 Hz/60 Hz: Check for a filter switch Common Problems

AC interference Line fluctuation Procedure: Test the machine in another room Connect the equipment to a voltage regulator Common Problems ligia diniz [CC BY 2.0 ( via Wikimedia Commons

Movement Artifact –Check to see if the patient is cold or nervous (muscle tremors interfere) –Patient or nurse touching any metal or wall Common Problems

Lack of disposable electrodes and gel –One can make cheap electrodes with sewing snaps and tape –Gel can be replaced by an ion free solution (Ex: salt water) or hand cream, shampoo, etc… Common Problems By Grkauls (Own work) [Public domain], via Wikimedia Commons

Paper feed problems No trace in the printer –Newer devices: clean the print head with alcohol gently with a fine soft clean cloth or Q-tip –Older devices (use alcohol to clean clotting in the ink tube) Common Problems

Test on yourself Check the heart rate alarms: –Lower than your own heart rate (upper rate alarm) –Higher than your own heart rate (lower rate alarm). Check battery (if present) charging circuit Test Procedures

Electrode lead leakage. (connect 1 KΩ resistor from electrode wire to ground, measure voltage (< 50 mV) in resistor and compute current (should be < 50 µA) Test Procedures 1 KΩ < 50 mV < 50 µA ECG Lead PhillipN, (2007) Display device of a medical monitor as used in anesthesia [photograph]. Retrieved from e:Monitor_(medical).jpg By Thiagoalmeidasa (Own work) [Public domain], via Wikimedia Commons David R. (Own work) [CC BY-SA 3.0 ( or GFDL ( via Wikimedia Commons

Troubleshooting Cooper, Justin and Alex Dahinten for EWH. “Electrocardiogram (ECG) Troubleshooting Flowchart.” From the publication: Medical Equipment Troubleshooting Flowchart Handbook. Durham, NC: Engineering World Health, 2013.