Week 7 Flashcards
Which direction is Q wave deflection?
downwards
What does the Q wave represent?
septal depolarisation (left to right)
Which leads are septal Q waves seen in?
Leads looking at the left side of the heart (I, II, aVL, V5 and V6)
What are the 3 characteristics of pathological Q waves
More than 2mV amplitude or 0.04 seconds long
What should you consider if you see pathological Q waves?
(1) myocardial infarction, (2) LV hypertrophy, (3) bundle branch block (4) pulmonary embolism (if Q wave in lead III).
In many cases do pathological Q waves become permanent following MI?
90%
Can myocardial infarctions be asymptomatic?
yes - 20% are silent
What are the symptoms of a MI?
chest pain, pain in left arm and jaw, sweating, nausea
Is ST segment elevation an ECG characteristic of MI?
Yes
Explain how MI leads to pathological Q waves
MI causes necrosis of myocardium which can no longer conduct electrical activity. Leads ‘look through’ necrotic tissue and since electrical activity moves from the inside to the outside of the heart, a negative deflection is detected.
A MI that produces a pathological Q wave is what type of MI?
Transmural
Is a subendocardial or transmural MI more serious?
Transmural - damage to all layers of the heart
What 4 questions should you ask about QRS complex?
- are R/S wave too tall? 2. are QRS complex too small? 3. are QRS complex too wide? 4. are QRS abnormal shape?
The deepest R and S wave should exceed how many mm?
25mm (2.5 large squares)
The R wave increases in height between V1 and V6?
True
Is the R wave smaller than the S wave in V1 and V2
True
Is the R wave smaller than the S wave in V5 and V6?
False
What waves are high/deep in LVH?
Leads that look at the heart from the left (I, II, aVL, V5 and V6) have high R waves and the reciprocal (leads that look at the heart from the right) V1 and V2 have deep S waves
What criteria must be met for LVH?
V5/6 R wave > 25mm, V1/2 S wave > 25mm or V5/6 + V1/2 = > 35mm
Can young, thin people exceed LVH ECG criteria? Does it mean they have LVH?
Yes - doesn’t diagnose LVH - echocardiogram necessary
What might cause pathological LVH?
hypertension
In what ways is LVH detrimental?
Chamber narrows inwards as well as outwards and reduces chamber size - reducing CO
What has to be present for LVH/RVH to be associated with ‘strain’?
ST segment depression and T-wave inversion
What ECG change does RVH cause?
dominant R wave in V1
What is RVH associated with?
(1) right axis deviation, (2) RBBB
How is a dominate R wave in V1-V3 associated with WPW?
In a left-sided WPW you typically see right axis deviation and so a dominant R wave as electrical activity flows towards the right side of the heart
How is a dominant S wave in V1-V3 associated with WPW?
In right-sided WPW you typically see left axis deviation and so a dominant R wave as electrical activity flows away from the right side of the heart
Are dominant R waves seen in posterior wall MI?
Yes - reciprocal appearance in anterior chest leads of typical MI changes - so pathological Q wave is seen as R wave.
Reasons for small QRS?
Reduced electrical activity recording: (1) obesity, (2) emphysema, (3) pericardial effusion (excess fluid in pericardial cavity)
Minimum length of ventricular depolarisation?
0.12 seconds (3 small boxes)
What does a wide QRS typically mean?
Conduction through the ventricles was slower than normal
What are three causes of wide QRS?
(1) bundle branch block, (2) ventricular ectopic, (3) hyperkalaemia
Does a bundle branch block lead to indirect depolarisation by other bundle branches?
Yes
What is a hemi-block?
Block of the left anterior fascicle or left posterior fascicle
What happens during v. depolarisation with bundle branch block
Ventricles are depolarisation by myocyte-myocyte conduction
What leads are used to determine a LBBB or RBBB?
V1 and V6
What is the acronym used?
WILLIAM MORROW
What is seen in V1 in RBBB?
(1) positive septal R wave, (2) S wave (LV dep), (3) R prime (late RV dep).
What is seen in V6 in RBBB?
(1) negative septal Q wave, (2) R wave (LV dep), (3) wide S wave (late RV dep).
Is LBBB an EECG contra-indication?
Yes
What is LBBB an EECG a contra-indication?
The ECG beyond QRS complex cannot be read
What is PVC?
Ectopic beat originating outside the conduction system
What is bigemy?
PVC after every 2nd normal QRS
What is trigemy?
PVC after every 3rd normal QRS
What may cause PVC’s?
Anything that disrupts electrolyte balance
Why are PVC’s important?
(1) they can lead to more serious arrhythmias (2) they decrease CO (particularly if they frequent - reduced ventricular filling)
Which direction is the T-wave deflected in premature beat (PVC)?
opposite of QRS complex
Are P-wave present in PVC?
Usually absent but retrograde conduction may depolarise the atrial and distort the ST segment
Can you measure the PR and QT intervals on premature beat?
No
What is the R-on-T phenomena
When a PVC strikes on the downstroke of previous T wave and can trigger more serious rhythm disturbances
What is seen after a PVC?
Compensatory pause - time between two normal QRS is doubled
A PVC that is not followed by a compensatory pause is referred to as what?
Interpolated
Why is a compensatory pause seen?
the ventricular myocardium is in refractory and cannot be depolarised
PVC that look alike are what?
Uniform
If PVC’s are uniform they likely originate from the same ectopic focus? T/F?
True
What are two PVC’s in a row called?
Couplet
Why can two PVC’s in a row cause ventricular tachycardia?
Because they meet refractory tissue
What is multiform PVC
PVC that look different as they originate from different foci or same sight with different conduction
What are dangerous PVC’s?
(1) R-on-T PVC, (2) paired, (3) trigemy, (4) bigamy, (5) multiform
is the pulse after a PVC stronger or weaker?
Weaker
What should you consider if you see a slurred or notched QRS?
(1) WPW, (2) hemi-block (3) incomplete bundle branch block
LBBB V1 characteristics
(1) Q wave (septal depolarisation from right to left), (2) R-wave from normal RV dep (3) S wave from late LV dep
LBBB V6 characteristics
(1) R wave (septeal depolarisation from right to left) (2) S-wave from normal RV dep (3) R-wave from late LV dep