26 - ECG

Question 1

what is ECG

Answer 1

electrocardiography

Question 2

how is cardiac muscle unlike skeletal muscle?

Answer 2

cardiac muscle contracts on its own.

Question 3

where is the hearts audtorhythmicity generated?

Answer 3

generated primarily at sinoatrial (SA) node. (the hearts natural pacemaker)

the SA node initiates electrical impulses that ultimately cause cardiac muscle to contract.

Question 4

how are cardiac cells connected?

Answer 4

electrically

contraction through electrical stimulation allows blood to be pumped through the body.

Question 5

what is a ECG?

Answer 5

a recording of the electrical activity of the heart from the skin.

Question 6

when was the first ECG published?

Answer 6

1887 by Augustus Waller

Question 7

how much is the ECG used per year?

Answer 7

about 75 million ECG procedures in the US per year, and 300 million worldwide.

Question 8

why might an ECG be used?

Answer 8

it is first line investigation for patients with chest pain, palpitations or blackouts.

it also allows early recognition of conditions such as acute myocardial infraction (heart attack)

Question 9

what information can an ECG provide?

Answer 9

can determine the cause of chest pain

evaluates other heart-related signs and symptoms. e.g. fatigue, shortness of breath, dizziness or fainting.

to identify irregular heartbeats.

it can determine the status of the heart, prior to procedures such as surgery.

status of the heart after treatment for conditions such as:
- heart attack
- endocarditis (disease of the heart valves)
- after procedures such as heart surgery or cardiac catheterisation.

to assess the function of an implanted pacemaker.

to determine the effectiveness of certain heart medications.

Question 10

what do P waved represent?

Answer 10

arterial depolarisation - electrical signals from the SA node cause depolarisation, which in turn causes the atria to contract.

in healthy individuals, there should be a P wave preceding each QRS complex.

Question 11

what is the PR interval?

Answer 11

The PR interval begins at start of the P wave and ends at beginning of the Q wave.

It represents the time taken for electrical activity to move between the atria and the
ventricles – the time between atrial and ventricular activity.

Question 12

what is the QRS complex?

Answer 12

The QRS complex represents depolarisation of the ventricles.

It appears as three closely related waves on the ECG (the Q, R and S wave).

Question 13

what is the ST segment?

Answer 13

The ST segment starts at the end of the S wave and ends at the beginning of the T wave. The ST segment is an isoelectric line that represents the time between contraction and relaxation of the ventricles.

Question 14

what is the T wave?

Answer 14

The T wave represents ventricular repolarisation and initiates relaxation.

It appears as a small wave after the QRS complex.

Question 15

what is depolarisation of the heart?

Answer 15

Depolarisation of the heart is the orderly passage of electrical current sequentially through the heart muscle.

The cells change, from the negative resting polarised state to a more positive depolarised state, which induces muscular contraction

Question 16

how is heart rate an indicator of baseline health?

Answer 16

generally, a lower heart rate at rest implies more efficient heart function and better cardiovascular fitness.

for example, a well-trained athlete might have a normal resting heart rate closer to 40 beats per minute.

Question 17

what is normal resting heart rate?

Answer 17

60-100 bpm

Question 18

what might it mean if someones heart rate is below 60?

Answer 18

a normal response to sleep or in well-conditioned athlete.

Question 19

why might someones heart rate be above 100?

Answer 19

stress, exercise, pain, fever.

drugs - caffeine & nicotine (increases adrenaline in blood, increases PB and HR).

Question 20

what does low heart rate variability mean?

Answer 20

• “fight or flight”
• easily exhausted
• low adaptability
• decreased cognition

Question 21

what does high heart rate variability mean?

Answer 21

• “rest & digest”
• improved performance
• high adaptability
• improved cognition

Question 22

what is arterial fibrillation?

Answer 22

most common, affects up to 800,000 people in the UK.

electrical signals fire off rapidly in several different parts of the atria, overriding the SA node.

Question 23

what is ventricular fibrillation?

Answer 23

uncoordinated contraction of ventricular muscle fibres making them flutter rather than contract properly to pump blood to the arteries.

can be rapidly fatal - it is the leading cause of cardiac arrest.

Question 24

what are the treatments of atrial fibrillation and ventricular fibrillation?

Answer 24

anti-arrhythmic drugs - which work by blocking certain ion channels in cardiac muscle cells.

pacemaker - to control the natural rhythm of the heart.

defibrillation - delivers a therapeutic electrical shock to the heart and allows the heart beat to restart from the SA node.

Question 25

what does the ECG of arterial fibrillation look like?

Answer 25

P waves: no identifiable P waves, erratic, wavy baseline. - atrial "quivers" - Ineffective in allowing for an effective atrial kick/contraction and therefore does not result in a heart beat. - Blood may pool or stagnate in the atria and the patient is at risk for clot formation. - May be due to: ischaemia, MI, previous heart surgery

Question 26

explain ventricular fibrillation?

Answer 26

irregular quivering of the ventricular muscle - ineffective at pumping blood. Lack of blood circulation leads to almost immediate loss of consciousness and death within minutes. This is a shockable rhythm – V-Fib may be stopped with an external defibrillator. Can be the result of heart muscle disease, injury to the heart such as electrocution, or the use of drugs such as cocaine or methamphetamine

Question 27

explain cardiac arrest?

Answer 27

if the heart fails to contract at all this leads to a sudden stop of blood supply to the body known as cardiac arrest. results in death if not immediately treated. CPR chest compressions necessary in cardiac arrest to stimulate pressure for blood to flow.

Question 28

what is flatline?

Answer 28

flatline, this is a state of no electrical activity from the heart and therefore no blood flow. It results in cardiac arrest This is usually associated with prolonged circulatory insufficiency and cardiogenic shock (the heart suddenly can't pump enough blood to meet your body's needs) Asystole is synonymous with Ventricular Standstill and death. Requires urgent emergency life support (it is not a shockable rhythm) – CPR, oxygen, epinephrine

Question 29

what is STEMI?

Answer 29

ST-elevation Myocardial Infarction (STEMI). A STEMI is the most serious type of heart attack where there is a long interruption to the blood supply. This is caused by a total blockage of the coronary artery, which can cause extensive damage to a large area of the heart. Can be diagnosed by an ECG that displays ST elevation

Question 30

what is a NSTEMI?

Answer 30

A non-ST-elevation myocardial infarction (NSTEMI) is a type of heart attack that happens when a part of your heart is not getting enough oxygen. This is indicative of a partial block of the coronary artery. People with an NSTEMI present with heart attack symptoms but do not have ST-elevation – it tends to be lower than baseline. Both are time-sensitive and need urgent intervention – PCI etc….

Question 31

what is wolff-parkinson-white-syndrome?

Answer 31

An accessory pathway conducts an electrical current between the atria and the ventricles, thus bypassing the atrioventricular node. About 60% of people with the electrical problem developed symptoms, which may include an abnormally fast heartbeat, palpitations, shortness of breath, lightheadedness, or syncope. Rarely, cardiac arrest may occur. Treatment – often cardiac ablation

Question 32

what is a pacemaker?

Answer 32

A pacemaker is a small device placed in the chest/abdomen to control abnormal heart rhythms. Uses low-energy electrical pulses to prompt the heart to beat at a normal rate.

Question 33

what are implantable cardioverter defibrillators (ICDs) ?

Answer 33

An implantable cardioverter defibrillator (ICD) is a device similar to a pacemaker. It sends a larger electrical shock to the heart that essentially "reboots" it to get it pumping again. Some devices contain both a pacemaker and an ICD. ICDs are often used as a preventative treatment for people thought to be at risk of cardiac arrest at some point in the future. If the ICD senses the heart is beating at a potentially dangerous abnormal rate, it'll deliver an electrical shock to the heart. This often helps return the heart to a normal rhythm