Introduction to the ECG and cardiac conduction Flashcards
What is a syncytium and a functional syncytium
One large “cell” having many nuclei that are not separated by cell membrane e.g. skeletal muscle cells
the functional syncytium is many cells functioning as one e.g. heart
What are 3 types of cardiac myocyte cells
pacemaker cells- for setting the heart’s rhythm
conducting cells- for transmitting rhythm throughout the heart
contractile cells- for contracting to that rhythm
How are cardiomyocytes linked
linked via gap junctions at the intercalated discs, when an action potential depolarises one cell, initiating an action potential in the adjacent cell.
Outline the cardiac conduction system
the pacemaker cells in the SAN initiate the impulse which travels to the AV node through the bundle of his where it delays shortly before the impulse travels down the Purkinje fibres to stimulate the ventricles to contract.
How many leads are there in an ECG and what are the types
3 bipolar leads
3 augmented leads and 6 precordial leads
Outline what’s happening at each point in the P QRS T complex
p: depolarization of atria in response to SA- node triggering
PR segment- delay of AV node to allow filling of ventricles
QRS complex: depolarization of ventricles, triggers main pumping contractions.
ST-segment: the beginning of repolarization
T: ventricular repolarization
Outline problems with QRS complexes
if the QRS complex is wide then ventricular conduction is abnormal e.g. ectopic pacemaker
large Q waves are a sign of dead tissue (old MI)
What sinus tachycardia
It is tachycardia that is driven by the SA node
How many little boxes should the PR & QT and QRS interval be
3-5 little boxes and QT should be 9-11.5 little boxes long.
QRS should be 2-3 boxes long
What is the box scale
1 big box= 300bpm or 300/big boxes 2 boxes= 150 bpm 3 boxes= 100 bpm 4 boxes= 75 bpm 5 boxes= 60 bpm 6 boxes= 50 bpm 10 boxes= 30 bpm
What nerve controls the parasympathetic activity
cranial nerve 10: Vagus nerve, based on acetylcholine and muscarinic stim, always slowing down heart rate
atropine is used for parasympathetic withdrawal
sympathetic input= beta-agonists increase rate and beta-blockers decrease rate
outline heart block, their causes and symptoms
Heart block= a type of dysrhythmia, any type of impulse conduction block of the heart
AV heart block is a delay or failure of atrial signal stimulating ventricle
causes: ischaemia or inflammation of the AV node or AV bundle. compression of AV bundle by the scar of calcified tissue
symptoms: may be asymptomatic, palpitations, hypotension-like: dizziness, malaise, syncope and risk of sudden death.
what is first-degree heart block
when the PR interval is greater than 5 little boxes, almost always asymptomatic, delayed AV transmission and rarely treated.
What is second-degree heart block and what are the two types
2nd-degree heart block= some p waves are blocked and are not followed by QRS.
Mobitz type 1: when the PR interval gets longer until the QRS wave fails to follow p wave
Mobitz type 2: some p waves are blocked and are not followed by QRS, PR Interval remains the same, can progress to 3rd heart block.
treatment: implant pacemaker.
What is third-degree heart block
atrial signals consistently fail to arrive at the ventricles, PR interval varies radically
