Lecture 7 - ECG, Electrical Events In The Heart Flashcards
P wave =
Atrial depolarisation
P-R (q) interval =
Internal between beginning of excitability of atria and ventricles (0-16s)
QRS complex =
Ventricular depolarisation, atrial repolarisation occurs but is obscured
Q-T interval
Contraction occurring (0.35s)
S-T segment =
All ventricle tissue depolarised, contraction occurring
T wave =
Ventricular repolarisation
In a healthy individual what is the normal P-R interval in seconds?
0.16 seconds
What is the P-R interval important for?
Identifies heart conditions if an individuals P-R interval is longer or shorter than 0.16seconds
Why can’t you see atrial repolarisation occurring in the QRS complex?
Can’t see on an ECG because it is obscured by ventricular depolarisation
Why is the ST segment a flat line on an ECG?
Because there is no change in the electrical currents
What is heart block?
Block of electrical signal between the atria and the ventricles usually in the AV node
What are the 3 types of AV heart block?
1st degree heart block, 2nd degree and 3rd degree heart block
What is 1st degree heart block?
P-R interval is longer at 0.28 seconds, can count how many squares the P-R interval is (40mmseconds per square)
What is second degree heart block?
Characterised by a dropped beat, not every p wave is followed by a QRS complex
What is an example of a condition which is classed as second degree heart block?
Atrial tachycardia (atrial flutter)
What is second degree heart block free one?
Where there is a QRS complex after every 3rd P wave!!
What is 3rd degree heart block?
Complete dissociation between the P wave and the QRS complex, complete block of the AV node
What is a condition that is classed as 3rd degree heart block?
Severe myocardial ischemia - need a pacemaker
What is the QRS complex like in third degree heart block?
It is fairly regular because the AV node set its own rhythm at 40 action potentials per minute, but this is not sufficient if you need to walk or stand up - you would need a pace maker to increase heart rate
What is cardiac arrhythmia?
An abnormal heart rate
What is bradycardia?
Heart rate slows (under 60 beats per minute)
What is tachycardia?
Heart rate is fast - over 100 beats per minute
What is ventricular tachycardia?
When the ventricles are beating abnormally at 100bpm
What are the two varieties that an abnormal heat beat can come In?
A regular abnormality or an irregular abnormality
What is a regular abnormality?
Atrial flutter
What is an irregular abnormality?
Atrial fibrillation
How do abnormalities arise?
In the ventricles or supraventricles e.g. the atria or in the AV node
Describe atrial fibrillation
Irregular a rhythm in the atria, chaotic ventricle activity in the atria - nothing is coordinated
What would you not see in atrial fibrillation?
A Pave - because the atria is not contracting it is chaotic
What are some symptoms of atrial fibrillation?
Breathlessness, tiredness and inability to exercise
Describe atrial flutter
Regular abnormality - one side of the atrium contracts while other relaxes, has a 2:1 or a 3:1 ECG rhythm
What are some treatments for atrial flutter?
Antiarrythmic drugs or cardioversion therapy (electrical shock)
Can you live with ventricular tachyacardia?
Yes it is not always life threatening
Describe ventricular arrhythmia
Abnormally fast heart rate arising at the AV node, additional pathway between the atrium and ventricle, the p wave is not obvious
What are the symptoms for ventricular arrhythmia?
Chest pain, feel weak, breathlessness or lightheaded, feel tired
What is the treatment for ventricular tachycardia?
Antiarrhythmic drugs or cardioversion therapy
Describe ventricular fibrillation
Chaotic ventricular activity, fatal in 1-3 minutes, uncoordinated ventricular contraction = can’t pump blood around the body.
Irregular ECG rhythm, no P wave, broad QRS complex
What is the treatment for ventricular fibrillation?
Implantable cardioverter defibrillator (ICD)
What does the implantable cardioverter fibrillator do?
If you heart stops it will defibriallate it and it sets a normal sinus rhythm at 72 beats per minute
What is an example of a class I antiarrhythmic drug?
Na+ channel blockers
What is an example of class II antiarryhtmic drugs?
Beta blockers (anti-sympathetic) - they block the beta 1 receptors
What do beta blockers affect?
The time between each action potential
What are class 3 antiarrythmic drugs?
K+ channel blockers, affect when there is repolarisation
What are class IV antiarryhtmic drugs?
Ca2+ channel blockers, affect of the plateau of the action potential, affect whether trigger ca2+ enters for CICR
What are class 5 antiarrythmic drugs?
Cardiac glycosides
How many types of class 1 are there?
3 - 1a, 1b, 1c
What are class Ia?
Moderate blockers, they moderately block the rate of depolarisation which results in an increase of action potentials - used for atrial fibrillation and atrial tachycardia
What is an example of class 1a?
Quinidine
What is class ib?
Weak blockers, hardly seen an affect, they shorten the action potentials and can be used for in the ventricles
What is an example of Ib?
Lidocaine
What is class Ic?
A strong blocker, only used for life threatening ventricular diseases as you risk blocking the transmission itself in the ventricles.
What is an example of class Ic?
Flecainide
What class is more favourable for treatment?
Class III - K+ blockers, as you slow down the rate of repolarisation so you don’t affect the rate of depolarisation so no risk of blocking transmission to the ventricles - you get a slower heart rate
What is an example of class III?
Amiodarone
