ECG and arrhythmias Flashcards
How many seconds is 1 small square, 1 large square and 5 large squares?
0.04 secs, 0.2 secs and 1 second respectively
A P wave is normally less than ? squares wide and less than ? squares tall
3 small and 2 small respectively
QT interval is meant to be ______ than RR interval
half or less
Leads for Inferior aspect of the heart
leads 2, 3, aVF
Leads for lateral aspect of the heart
Lead 1, avL and V5, V6
Leads for anterior aspect of heart?
V1, V2, V3
Leads for septal aspect of the heart?
V3, V4
To calculate the rate
look at Lead 2 on rhythm strip, count QRS and times by 6
Which leads are the transition leads? What is the significance of the transition wave moving to V5, V6?
Normally the transition wave is in leads V 3, 4. When the transition wave appears in V5, V6 it indicates right ventricle enlargement–> rotation in a clockwise direction. this is characteristic of Chronic Lung Disease
What does a Prolonged P-R interval indicate? What is normal for PR interval?
1st degree heart block. A normal PR interval is less than 5 small squares (so less than 0.2 seconds)
Where do the coronary arteries arise?
Aortic sinuses of Ascending Aorta. Right coronary artery from the right sinus, left from the left
What does the right coronary artery supply?
The right coronary artery supplies the right atrium and right ventricle, the sinu-atrial and atrioventricular nodes, the interatrial septum, a portion of the left atrium, the posteroinferior one third of the interventricular septum, and a portion of the posterior part of the left ventricle.
Usually SA node (but not always)
Right marginal branch–>
Posterior interventricular branch–>
What does the left coronary artery supply?
The distribution pattern of the left coronary artery enables it to supply most of the left atrium and left ventricle, and most of the interventricular septum, including the atrioventricular bundle and its branches.
Left anterior descending artery
left circumflex artery–> left marginal artery
What is the difference between Type 1 and Type 2 2nd degree heart block?
Type 1: Wenckebach= PR interval progressively gets longer and longer before there is a skipped QRS segment. Cycle starts again
Type 2: Mobitz= PR interval remains constant and sometimes the QRS segment is skipped.
2:1 and 3:1 is when there are 2 or 3 P waves per QRS segment consistently
What does global ST elevation indicate?
PERICARDITIS
QRS segments in ventricular problems?
WIDE QRS segment
Escape rhythms
Bradycardia–> 50bpm if SA node x; 30bpm if AV node x
slow and protective, if SA or AV node depolarisation is ineffective
Atrial flutter? What do we see on the ECG
Sawtooth waves lead 2 and 3. When p waves occur > 250/min
What does fibrillation mean? What does AF look like on an ECG? What about VF?
Fibrillation occurs when individual muscle fibres contract independently.
AF- no p waves, irregular lines. Some QRS segments. Small ‘f’ waves for fibrillation
VF- no QRS segments, disorganised ECG. patient falls unconsious. often fatal.
What does a peaked P wave indicate?
What do we see in LV hypertrophy?
Hypertrophy of right ventricle
QRS of greater than 25 mm in V5, V6 and inverted T waves in V5, V6, lead 2, lead avL
How can digoxin affect ECG?
Causes T wave inversion
Sequence of changes on ECG for STEMI/ myocardial infarction
Sites of infarction?
- raised ST segments
- Q waves appear
- normalised ST segments
- inverted T waves appear (irreversible)
Anterior- changes in V3, V4
Inferior- changes in 3 and aVF
Lateral- changes in V1, VL, V5, V6
What might we see in hyperkalemia?
Prolonged PR interval, peaked T waves, flat P waves
What are some causes of ST elevation?
Myocardial infarction, pericarditis, Prinzmetal angina (vasospasming of the coronary artery)
What might we see in hypokalemia?
peaked p waves, prolonged PR interval, ST depression, inverted T waves
what is the normal scaling for ECGs? what is the normal voltage scale?
25mm/sec; 10mm/mV
300/ what can give us the rhythm?
300/ no. of large squares
which leads do you see p waves the best
Lead 2 and V1
Normal QT interval?
440ms for men, 460ms for women
what are the 2 types of bradycardia?
sinus bradycardia or AV block (look for hidden p waves)
ectopic beats? what are its other names?
extra beats, premature beats
escape beat?
beat comes in late
How long is the PR interval normally?
<200 ms
What is the definition of sinus rhythm?
a p wave before every QRS segment, positive p waves in Leads 1,2,3 and inverted in AVF= sinus rhythm
What are Q waves? When do we think they are pathological on the ECG?
Q waves are negative deflections that can either be pathological or physiological.
Pathological Q waves are when the Q wave is more than 1/3 the height or depth of the following R wave.
When do we see wide QRS segments?
VT, RBBB (if +ve in V1); LBBB (if -ve in V1)
What can a depressed PR interval mean?
A depressed PR interval= pericarditiis
What does the c stand for in QTc interval?
C stands for corrected QT interval for the RR interval. During physical exertion the RR interval decreases and hence the QT interval must also decrease.
how many leads do we put on a person for a 12 lead ECG?
Note that lead 1 goes to the middle of both legs, and lead 3 also goes to the middle of both legs. Hence we need TEN leads all up to do an ECG. 4 leads- one on each limb; and 6 leads V1-V6 on chest wall
what does p mitrale indicate?
LA hypertrophy
Lead 2 Lead V6
what does p pulmonale indicate?
tall p wave= RA hypertrophy
what can cause far axis deviation?
VT
What do we see on the ECG for RBBB?
MARROW pattern. V1- M; V6- W
what do we see on ECG for LBBB?
WILLIAM pattern; V1= W; V6=M
what is bigeminy?
normal beat ectopic normal beat ectopic pattern.
what controls the rate in AF?
AV node refractory period
what drugs can slow down the AV node?
digoxin, beta blocker, verapamil, diltiazam, amiodarone, sotalol
What can cause a wide QRS?
Ventricular beat; bundle branch block; pacemaker, altered pathway
junctional nodal escape rhythm
dissociation between QRS and P waves
what happens in BBB?
normal conduction to the unblocked side then slow cel; to cell conduction to the blocked side.
The late wave represents the actvation of the ventricle going to the side of the blocked bundle
Where do you see the late waves in the RBBB and LBBB?
RBBB late wave is positive in V1 and negative in V6
LBBB late wave is negative in V1 and positive in V6
what does it mean when the AV node conduction slows?
increased refractory period of the AV node
what do you think when you see AF on the ECG and there is a regular rhythm of wide QRS segments?
AF with heart block. Wide QRS segments= ventricular escape rhythm
what leads do we see atrial flutter best?
Lead 2, 3, aVF
what causes Aflutter?
Re-entrant circuit around the tricuspid annulus. Intermittently hits the AV node and ventricular depolarisation occurs (irregular QRS). When the impulse goes up and down- this causes the sawtooth appearance on the ECG
AVR is normally…
negative
How can you tell RBBB?
lead 1 negative, lead 3 positive
How can you tell the LBBB?
Lead 1 positive, 2,3 negative
describe bifasicular bock
RBBB and left axis deviation. This can be due to a blocking of the left anterior or left posterior fasicle coming off the left bundle branch
how can you tell the difference between a defibrillator and a pacemaker in a Xray?
defibrillator coil/wire appears thicker than the pacemaker
what artery corresponds with the lateral leads?
left circumflex artery
Anterior-inferior leads represent which artery?
LAD
Sequence of events that show acute MI on ECG?
- ST elevation first few hrs
- pathological Q waves
- T wave inversion (24 hrs later)
what artery correspond to the inferior leads?
right coronary artery
what causes ST elevation on the ECG- describe what happens to the action potential
due to a change between the AP in epicardium and endocardium during ischaemia causes a current coming towards the lead leading to ST elevation
what causes a Q wave electrophysiologically?
Usually AP goes from endocardium to epicardium. When infarction occurs, there is an ‘electrical hole’ leading to a negative deflection Q wave
what is the main cause of infarction?
atherosclerotic plaque rupture, thrombosis and subsequent infarction. Not atheroemboli
why can’t we rely on a troponin rise from a blood test rather than the ST elevation on ECG for suspected MI?
It takes approx 6 hours for troponin levels to come back and by then it is too late. With and ECG- ST elevation is an acute change indicative of infarction. Patient is then immediately thrombolysed (rural setting no access to angioplasty) or brought to cath lab.
what do we give to a patient who comes in with SVT?
adenosine, then after it reverted do an ECG to look for WPW syndrome
what are the 3 conditions on ECG that indicate WPW?
Delta + wide QRS + short PR= WPW syndrome
how can WPW present on the ECG?
- Retrograde WPW–> SVT (narrow complex QRS)
- WPW can also cause a wide QRS tachycardia that looks like VT.
- Sometimes, when there is AF and WPW- it can present as narrow and wide QRS! This is one situation where you DON’T want to block the AV node as it reverts the impulse down the accessory bundle and cause VT.
what might you think if you saw a random strange QRS and T wave?
ventricular ectopic beat
what is a quick way of telling Left vs R axis deviation?
L axis deviation= negative in Lead 2
R axis deviation= negative in lead 1
what do you think if you see Q waves on the ECG?
previous infarct
what would see if you see crazy waves in only one lead?
muscle artifact
what is this? what condition do we see this in?
electrical alternans in pericardial effusion
