ECG part 2 Flashcards
What are the 3 categories of arrhthmias?
- Conduction abnormalities e.g. blocks
- Abnormal impulse initiation e.g. ectopics, VT
- Re-entry
How does an ECG look like when there is a sinus arrest?
-No P waves or any associated QRS-T during sinus pause
How does an ECG look like when there is a 1st degree AV block?
-PR interval is >0.2
How does an ECG look like when there is a 2nd degree AV block?
-P waves may not be followed by a QRS complex
How does an ECG look like when there is a 3rd degree AV block/complete AV block?
-P waves have constant P-P and R-R interval
-Lack of apparent relationship between the P waves and QRS complexes
-More P waves are present than QRS complexes
What happens in an ECG in left bundle branch blcok?
-QRS duration > 120ms
-Dominant S wave in V1
-Broad monophasic R wave in lateral leads(I, aVL. V5-6)
-Absence of Q waves in lateral leads
-Prolonged R wave peak time > 60ms in leads V5-6
What happens in an ECG in right bundle branch block?
-QRS duration > 120ms
-RSR’ pattern in V1-3(‘M-shaped’ QRS complex)
-Wide, slurred S wave in lateral leads(I, aVL, V5-6)
When does early afterdepolarization occur and what can this lead to?
occur during late phase 2 or 3 and can lead to a salvo of several rapid
action potentials or a prolonged series of action potentials e.g. VT.
When does delayed afterdepolarization occur?
occur in late phase 3 or early phase 4 when the action potential is
nearly or fully repolarised.
What happens to ECG in ventricular ecptopic?
-Premature wide QRS with no preceding P wave
-Following and encompassing the QRS is a compensatory pause
What is ventricular tachycardia?
Ventricular Tachycardia (VT) is a broad complex tachycardia originating in the ventricles
What may VT cause and what does this consequently result in?
Ventricular tachycardia (VT) may impair cardiac output, consequently hypotension, collapse, and acute cardiac failure.
What in ventricular fibrillation?
This rapid and irregular electrical activity renders the ventricles unable to contract in a synchronised manner,
resulting in immediate loss of cardiac output The heart is no longer an effective pump and is reduced to a quivering mess
What is the most common sustained arrhythmia?
Atrial fibrillation (AF) is the most common sustained arrhythmia
What is atrial fibrillation characterised by?
It is characterised by disorganised atrial
electrical activity and contraction.
What does the ECG look like for atrial fibrillation?
P wave – No distinct P waves - fibrillation waves (best seen in V1)
R-R – Varying
Fibrillatory waves may be present and can be either fine (amplitude < 0.5mm) or coarse (amplitude > 0.5mm)
What is atrial flutter?
Atrial flutter is a form of supraventricular tachycardia caused by a re-entry circuit within the right atrium.
What does atrial flutter look like on an ECG?
R-R – Irregular Ventricular rate depends on AV conduction ratio
What is ST depression on an ECG caused by?
ST depression caused by injury potential difference
What does myocardial ischaemia do to membrane potential in the heart?
Ischaemic myocytes have reduced
membrane potentials compared with
healthy myocytes.
The difference in potential between the
ischaemic region and healthy region
displaces the ST segment.
This is called the ‘injury current’ effect.
What happens to ECG from ischaemia?
manifests ECG with ST
depression +/- T wave inversion; result from
altered repolarisation.
What happens to ECG from injury?
ST segment elevation +/- loss
of R wave; ‘current of injury’
What happens to ECG from infarction?
deep Q waves (>0.06 sec /
> 25% R wave) resulting from absence of
depolarisation current from dead tissue
(transmural). Manifests receding currents
from opposite side of heart as an ‘electrical
window’ is formed.
What segments of an ECG indicate an injury in left circumflex artery?
- I
- V5
- V6
What segments of an ECG indicate an injury in right coronary artery?
- II
- III
- aVF
What segments of an ECG indicate an injury in left anterior descending artery?
- V2
- V3
- V4
