Session 7-ECG Abnormalities Flashcards
Which rhythms are classified as supraventricular rhythms?
1) sinus node
2) atrial
3) AV node
Which system conducts supraventricular rhythms into and within the ventricles?
His-Purkinje system
True or false: supraventricular rhythms have a broad complex
FALSE - narrow complex, ventricular rhythms have broad complex
Where do ventricular rhythms arise from?
Focus/foci in ventricle
True or false: the conduction of ventricular rhythms is not via usual His-Purkinje systems
TRUE
Describe atrial fibrillation
Impulses have chaotic, random pathways in atria
What do atria do in atrial fibrillation rather than contract?
Quiver
True or false: ventricles depolarise and contract normally in atrial fibrillation
TRUE
Describe the characteristics of an atrial fibrillation ECG (2)
1) absent p waves - wavy baseline
2) narrow QRS complexes which are irregularly irregular
What is an AV conduction block or ‘heart block’?
Delay/failure of conduction of impulses from atria to ventricles via AV node and bundle of Hiss
What is the most common cause of an AV conduction block?
Acute myocardial infarction
What are the three types of heart block?
1) first degree heart block
2) second degree heart block (mobitz 1 and mobitz 2)
3) third degree heart block or complete heart block (CHB)
Describe the characteristics of first degree heart block
1) p wave normal
2) slow conduction in AV node and His bundle
3) PR interval prolonged > 5 small squares
4) QRS Norma
What is another name for Mobitz type 1 (2nd degree heart block)?
Wenkebach phenomenon
Describe the characteristics of Mobitz type 1, second degree heart block
progressive lengthening of PR interval until one P is not conducted (allowing time for AV node to recover)
Describe the characteristics of Mobitz type 2, second degree heart block
1) PR interval normal
2) sudden non-conduction of a beat (dropped QRS)
3) high risk of progression to complete heart block
Describe the characteristics of third degree heart block
1) normal atrial depolarisation but impulses not conducted to ventricle
2) ventricular pacemaker takes over (ventricular escape rhythm) and this rate is very slow (~30-40bpm)
3) usually wide QRS complexes
4) HR often too slow to maintain BP and perfusion
What is the relationship between P waves and QRS complexes in third degree heart block?
No relationship
What happens in ventricular ectopic beats?
1) Ectopic focus in ventricle muscle
2) Impulse not spread via fast His-Purkinje system therefore much slower depolarisation of ventricle and therefore wide QRS complex
What is ventricular tachycardia?
Run of 3 or more consecutive ventricular ectopics
What does someone with ventricular tachycardia have a high risk of?
Ventricular fibrillation
Describe the characteristics of ventricular fibrillation
1) abnormal, chaotic, fast ventricular depolarisation
2) impulses from numerous ectopic sites in ventricular muscle
3) no coordinated contraction so ventricles quiver
4) no cardiac output -> cardiac arrest
What does a patient with ventricular fibrillation require?
Immediate defibrillation to restore rhythm
What is the difference between atrial and ventricular fibrillation?
- VF has no coordinated ventricular contraction but AF does
- VF has no cardiac output but AF does
- VF has no pulse or heart beat but AF has irregularly irregular heart beat and pulse
Which ECG leads look at the lateral side of the heart?
Lead I
AVL
V5
V6
Which ECG leads look at the inferior side of the heart?
Lead II
Lead III
AVF
Which ECG leads look at the septal side of the heart?
V1
V2
Which ECG leads look at the anterior side of the heart?
V3
V4
Which part of the muscle is furthest away from surface and therefore most vulnerable to MI?
Sub endocardial muscle
What do ECG leads facing the affected sub endocardial region show in ischaemia/MI?
1) ST segment depression
2) T wave inversion
When can ischaemic ECG changes be seen?
During exercise
What is NSTEMI?
Non-ST elevation myocardial infarction
What is STEMI and what is it due to?
ST segment elevation myocardial infarction
Due to complete occlusion of lumen by thrombus
Where does muscle injury extend from and to in a STEMI?
Full thickness from endocardium to epicardium
What do ECG leads facing the area show in an epicardial injury?
ST segment elevation
What will happen in a STEMI if perfusion is not re-established?
Muscle necrosis follows
What dimensions are classed as pathological Q waves?
1) >1 small square wide
2) >2 small squares deep
3) depth more than 1/4 height of subsequent R wave
Describe the resting membrane potential in hyperkalaemia and how this affects conduction
Less negative -> inactivate some voltage gates Na+ channels -> heart becomes less excitable as hyperkalaemia worsens -> conduction problems
Describe the resting membrane potential in hypokalaemia
More negative
What does extreme hyperkalaemia lead to?
Ventricular fibrillation
Describe the ECG changes in hyperkalaemia
1) high T wave
2) prolonged PR interval
3) depressed ST segment
Describe the ECG changes in hypokalaemia
1) low T wave
2) high U wave
3) low ST segment
What is cardiac axis?
Average direction of spread of ventricular depolarisation
What is the normal cardiac axis?
-30 to +90 degrees (downward and to the left)
What is left axis deviation associated with?
- conduction block of anterior branch of left bundle
- inferior MI
- LV hypertrophy
What is right axis deviation associated with?
RV hypertrophy
Describe the QRS complex in left axis deviation
Upright QRS in lead I and inverted in aVF
Describe the QRS complex in right axis deviation
Inverted QRS in lead I and upright in lead III or aVF
