Cardiovascular: Session 7 Flashcards
What are the causes of abnormal rhythms?
-Abnormal Impulse formation
Abnormal conduction
What are supraventricular rhythms?
Rhythms that arise from
- Sinus node
- Atrium
- AV node
Where do ventricular rhythms arise from?
Ventricle
What is different about ventricular rhythms compared to supraventricular rhythms ?
- From a focus/foci in ventricle
- Conduction not via usual His-purkinje system
- Depolarisation takes longer
- Wide (>3 small boxes) and bizarre QRS complexes
What are the characteristic features of an atrial fibrillation ECG?
- No p waves
- Just a wavy baseline
- Narrow QRS complexes
What causes atrial fibrillation?
- Atrial depolarisation chaotic. The atria quiver rather than contract
- Impulses arrive at the AV node at rapid irregular rate so only some conducted to ventricle when AV node is not refractory.
Pulse and heart rate is irregularly irregular in atrial fibrillation. True/False
True.
What happens to ventricles in Atrial fibrillation?
Ventricles depolarise and contract normally.
What is a conduction block?
Delay/Failure of conduction of impulses from atrium to ventricles via AV node and bundle of His
What are the causes of Heart block?
- Acute myocardial infarction
- Degenerative Changes
What does an ECG from first degree heart block appear as?
- P wave normal
- Slow conduction in AV node and his His bundle. P-R interval prolonged. (>5 small squares)
- QRS normal
What does an ECG from Mobitz type 1 (2nd Degree heart block) look like?
- Progressive lengthening of P-R interval until one P is not conducted
- Allows time for the AVN to recover and condition begins again
- Cycle begins again
What does an ECG from Mobitz type 2 (2nd Degree heart block) look like?
- PR interval normal
- Sudden non-conduction of a beat. Dropped QRS
Which type of 2nd Degree heart block has a high risk of progression to complete heart block?
Mobitz type 2
What is the mechanism of 3rd degree heart block?
Atrial depolarisation is normal but the impulses are not conducted to ventricle. Ventricular pacemaker takes over so ventricular escape rhythm.
What does an ECG of 3rd Degree heart block appear as?
- Slow heart rate
- Usually wide QRS complexes
- No relationship between P and QRS complexes
What are the effect of the slow heart rate in 3rd degree heart block? What is the treatment?
Heart rate is often too slow to maintain blood pressure and perfusion.
Urgent pacemaker insertion is required
What are ventricular ectopic beats?
Ectopic focus in ventricle muscle. The impulse is nots read via the fast His-prukinje system therefore much slower depolarisation of the ventricle.
What are the features of an ECG of a ventricular ectopic beat?
- Wide QRS complex
- Different in shape to usual QRS
What is ventricular tachycardia?
Run of more than or equal to 3 consecutive ventricular ectopics is defined as ventricular tachycardia.
Why does persistent ventricular tachycardia require urgent treatment?
It is a dangerous rhythm and has a high risk of ventricular fibrillation.
What is ventricular fibrillation?
Abnormal, chaotic, fast, ventricular depolarisation. Impulses from numerous ectopic sites in ventricular muscle. This results in no coordination in contraction and the ventricles quiver. The consequence of this is no cardiac output and cardiac arrest.
What are the features of an ECG of a patient with ventricular fibrillation?
No discernible PQRS complex.
What is the procedure of treatment for patients in ventricular fibrillation?
Require CPR and immediate defibrillation to restore the rhythm.
What can cause ischaemia of the heart and myocardial infarction?
Reduced myocardial perfusion due to coronary atherosclerosis.
Which region of the heart is most vulnerable to ischaemia and why?
The sub endocardial region is most vulnerable due to being further away from major coronary arteries that lie on the epicardial surface
What do leads facing an area of ischaemia in the heart show?
- ST segment depression
- T wave inversion
When can most ischaemic ECG changes be seen?
During exercise. If severe there can ischaemic changes at rests well.
What is a STEMI?
ST segment elevation Myocardial Infarction
What causes a STEMI?
It is due to complete occlusion of lumen by thrombus. The muscle injury extends ‘full thickness’ from the endocardium to epicardium.
What does an ECG of leads facing an area of myocardial infarction show?
ST segment elevation due to abnormal current during repolarisation.
What occurs if perfusion isn’t returned to the heart tissue?
Muscle necrosis
How much time does it take for a Q wave to begin in a STEMI?
HOURS
What does a serum potassium of 7, 8, 9, 10 mEQ/L in hyperkalaemia?
At 10 (severe), ventricular fibrillation At 9, atrial standstill and intraventricular block At 8, Prolonged PR interval, Depressed ST segment, High T wave At 7, High T wave
What are the evolving changes in a ST segment elevation MI?
Acute - ST elevation
Hours - ST elevation, Decreased R wave and Q wave begins
Day 1-2 - T wave inversion, Deeper Q wave
Days later - ST normalises, T wave inverted
Weeks later - ST & T normal, Q wave persists
What happens in heart in hyperkalaemia?
In hyperkalaemia the resting membrane potential is less negative. This inactivates some voltage gated Na+ channels. Heart becomes less excitable as hyperkalaemia worsens. There are conduction problems.
What are the ECG changes in hyperkalemia?
At
7 mEq/L - high T wave
8 mEq/L - Prolonged PR interval, depressed ST segment, high T wave
9 mEq/L - P wave absent (Atrial standstill, intraventricular block)
10 mEq/L - Ventricular fibrillation
What is the cardiac axis?
The average direction of spread of the ventricular depolarisation. Usually toward and to the left. between -30 to 90 degrees.
What is left axis deviation?
When the overall direction ventricular depolarisation is upwards and to the left so less than -30 degrees.
What is left axis devation associated with?
- Conduction block of the anterior branch of the left bundle
- Inferior MI
- Left ventricular hypertrophy
What is right axis deviation?
-When overall direction ventricular depolarisation is downwards and to the right (more than 90 degrees)
What is associated with right axis deviation?
-Right ventricular hypertrophy
What does an upright QRS in lead 1 and an inverted QRS in AVF?
Left Axis deviation
What does an inverted QRS in lead 1 and an upright QRS in lead 3 show?
Right axis deviation
