introduction to cardiac electrophysiology
TRANSCRIPT
ELECTROPHYSIOLOGY Electrophysiology is the study of the
electrical nature of tissues and cells. It involves the movement and measurement of
voltage and current coursing through the tissues through the ion channel proteins;
It also includes the movement and adverse effects of currents in whole organs such as the heart
In medicine, an Electrophysiology study (EP Test) is used to study abnormal heart rhythms (arrhythmia) and other related cardiophysiological functions that involves movement (tachycardia, bradycardia etc.)
ARRHYTHMIA Cardiac dysrhythmia or arrhythmia is the
abnormal rate or rhythm of the heart’s beat An irregular heartbeat must not be confused with an
irregular heart rate. Arrhythmias, irregular heart beating, may occur during regular and irregular heart rates
It can either cause the heart to beat faster, slower or irregularly
Though most arrhythmias are harmless, some could be serious and life-threatening; the heart may not be able to pump enough blood throughout the body, which can be fatal for vital organs that requires sufficient blood flow eg. brain, lungs, liver etc.
WHAT CAUSES AN ARRHYTHMIA? During a heartbeat, the electrical impulses travel in a specific and organized pathway.
When the impulses are interrupted this causes the heart to produce an irregular heartbeat Coronary artery diseases such as atherosclerosis (artery hardening), ischemia (blood-
supply restriction to tissues) and angina (chest pain due to restriction of blood-supply to muscles)
Blood electrolyte imbalance (lack of sodium and potassium in the diet, hyponatrimia etc.) Smoking, drinking and use of CNS-acting drugs such as cocaine, methamphetamine,
cannabis etc. Strong emotional stress such as anger, depression or even surprise Genetic or congenital heart defects The phrase “heart skipped a beat” refers to arrhythmia, which occurs when seeing or
experiencing something staggering. This is caused by the elevated hormone levels produced by the body, which in turn causes the heart to work profusely in an unexpected manner; this sudden surge of hormones may trigger an arrhythmia
DRUGS
SMOKING
SMOKING
STRONG EMOTIONAL STRESSSTRONG EMOTIONAL STRESS
STRONG EMOTIONAL STRESS
STRONG EMOTIONAL STRESS
DRINKING
ARRYTHMIA
ELECTROPHYSIOLOGICAL TEST (EP TEST)
An Intracardiac electrophysiological study (EPS) is a test to measure if the heart’s electrical signals are properly functioning
In the course of an average human lifespan, the possibility of having one or more abnormal heart functions is relatively high
An EPS is a minimally invasive procedure that helps physicians and specialists, such as cardiologist, determine heart rhythm problems and abnormal heart function
HOW IS THE TEST PERFORMED? Wire electrodes will be placed in the
heart. These electrodes measure the electrical activity in the heart
The groin or neck area will be cleansed and a topical anesthetic will be applied
• IV sheaths will then be inserted through the groin or the neck area
• The physician then uses a fluoroscope (moving x-ray images) to guide the catheter to the heart, placing the electrodes in the right places
• The electrodes pick up the heart’s electrical impulses for measurement
• The electrodes may produce controlled impulses to induce arrhythmia. This will help the physician understand the causes and location of the abnormalities lie.
THE SCIENCE BEHIND ELECTROPHYSIOLOGY
Living things are composed of electrical properties running through our cells and tissues. They are transferred and run across different parts of our bodies through the ion channels of the cells
The study of electrophysiology involves measuring these electrical charges to determine whether a part of the tissue, or even a whole organ is working and functioning properly
• Electrophysiology measures the bioelectricity of living things• In neuroscience, it includes the electrical properties of neurons
INTRACELLULAR RECORDING
Involves the measurement of voltage and current across the protective membrane of a cell
The tip of a fine microelectrode will be inserted into the cell so that the membrane potential can be measured
The tips have a diameter of less than 1 micrometer and a resistance of 7 megaohms
A typical membrane potential of a healthy cell is -60 to -80 mV and the action potential +40 mV
VOLTAGE CLAMP This technique allows the physiologist
to clamp, or hold onto a desired cell potential value
This allows easier measurement of how much ionic current crosses a cell’s membrane at a specific voltage
Many of the ion channels in the membrane of a neuron are voltage-gated ion channels, which only opens at a specific voltage range
This is made possible by the near-simultaneous currents that passes as the recording electrode are charged to alter the cell potential
CURRENT CLAMP This technique records the membrane potential by injecting a specifically
measured current through the electrode The electrode then records and transmits the current. Unlike voltage
clamp, the current clamp has the freedom in varying, and the amplifier records the voltage
This is used to study how a cell responds when current enters a cell, which is important in understanding how neurons respond to neurotransmitters
UNDERSTANDING THE HEART’S ELECTRICAL SYSTEM
As we know, the body requires electricity or “bioelectricity” in order to contract and expand muscles, which in turn results to movements
The heart’s electrical system controls the rate and rhythm of the heart In each and every heartbeat, an electrical signal spreads from the top part
of the heart and surges through the bottom. This causes the heart to contract and expand, hence, the pumping mechanism of our heart, also, the heartbeat
These electrical signal begins in the sinoatrial node and travels to and fro via the ion-channels, which is located in the right atrium
As the current travel from the right atrium to the left atrium, the atria contracts causing blood to be pumped into the ventricles
The current then moves downward the atrioventricular node, sited in between atria and ventricles. The signals here slows down a tad allowing the ventricles to be filled with blood
As the electrical signal leaves the AV node or “the bundle of His”, the signal causes a contraction action which allows the heart to pump blood into the lungs and the rest of the body
CARDIAC ELECTROPHYSIOLOGY Cardiac electrophysiology is the science in diagnosing and treatment of the
electrical activities of the heart It is usually done by using invasive catheters with electrodes to either
record and induce programmed electrical stimulation (PES)
STRUCTURE OF CARDIAC ELECTROPHYSIOLOGY
When the signals arise in the SA node and stimulates the atria to contract, which then travels to the AV node, stimulus is conducted through the bundle of His to the Purkinje fibers.
It travels towards the endocardium at the heart’s apex and finally rests at the ventricular epicardium
On a microscopic point of view, the wave depolarization propagates and travels through adjacent cells via the gap junctions
The heart, being a functional syncytium, freely allows propagation of electrical impulse in all direction, which results in a single contractile function
FUNCTION The cardiac muscles are similar to neurons and skeletal
muscles A myocardial cell has a negative membrane potential at rest,
the same as a neuron During a stimulation above the treshold value, the voltage-
gated ion channels open up and allows flooding of cations into the cell
The positively charged ions entering the cell causes depolarization of an action potential
Similar to skeletal muscles, depolarization causes the opening of calcium channels and release of Ca2+
This causes calcium-calcium induction release from the sarcoplasmic reticulum, hence, causes muscle contraction
Potassium channels then reopen, allowing potassium to flood out of the cells causing repolarization
DEPOLARIZATION AND THE ECG
Electrical activity is spontaneously generated by the SA node
The SA node is the physiological pacemaker, responsible for the hearts mechanism
Electrical impulses are propagated throughout the right atrium all the way to the left atrium, stimulating the myocardium of the atria to contract
The activity of the electrical impulse throughout the atria is visualize as the P wave in an ECG
Electrical charges spreads throughout the atria via intermodal tracts, from the SA node to the AV node
ECG AND PACEMAKERS
An electrocardiogram is used to examine the electrical conduction of the heart
A pacemaker is used to stabilize the heart’s rhythm. It is surgivally placed and inserted into the heart’s conduction system