What is the cardiac axis?
The average direction of electrical activity within the heart during ventricular depolarisation
What leads are used to determine the heart’s axis?
6 frontal leads
Left axis deviation has an angle of what?
beyond -30 degrees
Causes of left axis deviation?
- right sided WPW
- left anterior hemi-block
- inferior myocardial infarction
- ventricular tachycardia
Can left ventricular hypertrophy cause LAD?
Yes, but not because of increased muscle mass but instead left anterior hemi-block due to fibrosis
Most common cause of left axis deviation?
left-anterior hemi block
Block of the RBB and left anterior hemi block is called what?
A bifascicular block
Why does inferior MI cause LAD?
Fibrotic tissue doesn’t conduct activity and so the cardiac axis becomes directed away from this
How does left ventricular tachycardia cause left axis deviation?
When an electrical impulse arises in the LV, the wave of depolarisation spreads through the rest of the myocardium from that point, resulting in LAD.
When is right axis deviation diagnosed?
+ 90 degrees
What is ventricular asystole?
Ventricular standstill - no electrical activity in the heart - no cardiac output
What does asystole look like on the ECG?
A flat line
What is the immediate treatment for asystole?
CPR
Should asystole be confirmed in more than one lead?
Yes
What is another name for asystole
Arrhythmia of death - client is in cardiopulmonary arrest
What is sinus bradycardia?
Sinus rhythm below 60bpm - originating in SA node
Heart rate must be below what to be a contraindication to EECG?
40 bpm unless they are extremely fit individuals
What group of people might get bradycardia?
Athletes - increase in vagal tone
By what mechanism does vagal done reduce HR?
Vagal done reduces the automaticity (speed of depolarisation) of pacemaker cells
What are the 3 characteristics of sinus bradycardia?
- P wave proceeds QRS complex
- P wave is upright in lead II and inverted aVR
- HR is less than 60bpm
Causes of bradycardia?
- Drugs (digoxin and beta-blockers)
- Hypothyroidism
- ischemic heart disease/MI - AV node/Purkinji fibre escape rhythms
4.
When is treatment for bradycardia significant?
when CO becomes reduced
What are the symptoms of reduced CO?
hypotension, syncope, dizziness,
Can bradycardia predispose individuals to more serious arrhythmias?
Yes, e.g. V.fib as irritable focus has an opportunity to fire
In acute inferior wall MI, is bradycardia a good or bad prognosis?
Good unless it’s associated with hypotension
What drugs can enhance HR?
Dopamine, atropine and adrenalin
What are 4 non-cardiac causes of sinus bradycardia?
(1) increased intracranial pressure (2) glaucoma (3) sleep (4) hypothermia
What is ventricular tachycardia?
3 or more successive beats of HR > 120bpm
Is ventricular tachycardia wide or narrow QRS complex?
Wide
What causes ventricular tachycardia?
Re-entry or increased automaticity of ventricular foci
A ventricular tachycardia episode is considered sustained if it’s longer than?
30 seconds
What are the two characteristics of ventricular tachycardia?
- broad QRS
2. Ventricular rate above 120 bpm
Sustained VT usually has a rate between what?
150-250bpm
How might VT be corrected?
- drugs
- DV cardioversion
- pacing
What is torsade de points?
A variant of polymophic ventricular tachycardia, associated with a prolonged QT interval
What does torsade de points carry the risk of?
Abrupt deterioration into v. fib
What is ventricular fibrillation?
A chaotic pattern of electrical activity within the ventricles originating from a number of foci
What is the mechanical consequence of V.fib?
No co-ordinated muscular contraction and therefore reduced CO
How does V.fib appear on the ECG?
Fibrillatory waves and no intervals can be determined
Are smaller or larger fibrillatory waves better prognosis and why?
Large - they are easier to converted back to sinus rhythm as there is more electrical activity within the heart.
Is an individual in V.fib in full cardiac arrest?
Yes, the ventricles are not delivery blood to the body, no pulse will be measurable
What can mimic v.fib?
Interference from electric razor and muscle movement
How do you treat v.fib?
Defibrillation
What is sick sinus syndrome?
Abnormalities in the generation and conduction of impulses from the SA node
What are 4 causes of v.fib?
(1) myocardial ischemia (2) electric shock (3) untreated ventricular tachycardia (4) myocardial infarction
what is another name for sick sinus syndrome?
Sinus nodal dysfunction
How does sick sinus syndrome usually present?
Bradycardia with episodes of sinus arrest interspersed with sudden atrial fib.
What does sick sinus syndrome arise?
Dysfunction of SA node’s ANS due to degeneration
Causes of SSS?
- fibrosis of SA node (age, atherosclerosis, hypertension)
- Trauma to SA node due to surgery/pericarditis
- drugs - digoxin, beta-blockers, calcium channel blockers
What is a bad prognosis in SSS?
When atrial fibrillation is present
Sinus tachycardia rate?
above 100bpm
In sinus tachycardia what should be reduced?
In take of stimulants
Symptoms of sinus tachycardia?
(1) anxiety (2) reduced CO (3) palpitations (4) chest pain
Is tachycardia considered good or bad following MI?
bad - signals massive heart damage - seen in around 30% of people
Causes of tachycardia
(1) hemorrage, hypovolemia
(2) heart failure, MI,
(3) compensatory mechanism in shock, anaemia, hyperthyroidism
