ECGs and Conduction Flashcards
What are the main generalised symptoms of heart block ?
SOB
Palpitations (caused by irregular heart beat)
Fainting
Can result in bradycardia
What is heart block?
A type of arrhythmia (a problem with rate or rhythm) whereby the electrical signals from the SA node to the AV node are disrupted / slowed
What is 1st degree heart block?
A split second delay in time taken for electrical impulse to pass from SA node to AV node
What is 2nd degree heart block?
Intermittent complete failure of excitation passing through the AV node or bundle of His (2/3 types of 2nd degree heart block)
What is Mobitz Type 2 heart block?
Most beats conducted with a constant PR interval but occasionally a P wave (atrial depolarisation/contraction) is not flowed by a QRS wave (ventricular depolarisation/contraction)
What happens in Mobitz Type 1 “Wenkebach” heart block?
Progressive lengthening of PR interval (delay between atrial and ventricular contraction) until failure of conduction (P wave NOT followed by QRS) then a conducted beat with short PR interval
What is 2:1 type 2nd degree heart block?
Where you get alternate conducted followed by non-conducted atrial beats. Twice as many P waves as there are QRS (some P waves will present hidden within T waves, showing as distorted T wave on ECG)
What can both Mobitz Type 2 and 2:1 lead to if not treated?
Complete (3rd degree) heart block
What is 3rd degree heart block?
Where atrial contraction is normal but NO beats are conducted to the ventricles
How do the ventricles contract with 3rd degree heart block?
Via a slow “escape mechanism”
What is the “escape mechanism” which occurs in 3rd degree (complete) heart block?
Where other sites in the heart (further down the conduction pathway) initiate depolarisation where SA node fails to or where there is a blockage in the depolarisation pathway.
What average depolarisation frequencies do foci in the atrial muscle or around the region of the AV node have (atrial / AV escape rhythm)?
50 per minute (resulting in bradycardia)
What average depolarisation frequency does a ventricular focus (ventricular escape rhythm) have and when would this focus take over?
30 per minute (very bradycardic).
Occurs when there is a failure of conduction through Bundle of His
Give an example of when acute complete heart block might be experienced.
During a myocardial infarction (MI)
Give an example of why chronic complete heart block might be experienced.
Due to fibrosis around the Bundle of His
Widening of the QRS complex is indicative of what?
A Bundle Branch Block
In what direction does the intraventricular septum normally depolarise?
Left to right
The left ventricle has a greater muscle mass and so exerts more influence on the ECG
An UPWARD deflection on an ECG signifies what?
That the electrical impulse / excitation is spreading TOWARDs that particular lead
A DOWNWARD deflection on an ECG signifies what?
Excitation / electrical impulse moving AWAY from that particular lead
What is a normal PR interval?
0.12 - 0.2 seconds (3-5 small squares on ECG paper)
What is the PR interval?
Time taken for excitation to spread from SA node, through AV node, down Bundle of His and through ventricles
What does the QRS complex illustrate?
How long excitation takes to spread through the ventricles
What is a normal QRS duration?
0.12 seconds (3 small squares)
What is the correct calibration of an ECG?
1mV; should move stylus 1cm (2 large squares) vertically
What length of time does one large square denote?
200 milliseconds / 0.2 seconds
What length of time does one small square denote?
40 milliseconds
What length of time do 3 small squares denote?
0.12 seconds
When calibrated properly what does a tall P wave indicate?
Atrial hypertrophy
When calibrated properly what does a tall R wave indicate in left ventricular leads?
Ventricular hypertrophy
What do 5 large squares represent?
1 second
Why ECG changes are typical of pericarditis?
Widespread ST elevation (throughout limb and precordial leads)
(May also get a Troponin rise)
What are the treatment options for a patient in AF?
Cardioversion (Direct Current synchronised shock)
Pharmacological (Flecainide, Amiodarone - rhythm control; Beta-Blockers, calcium channel blockers or digoxin - rate control)
What major ECG change is seen in AF?
No defined P waves as no synchronised contraction
What is the characteristic change seen on an ECG in Atrial Flutter?
‘Saw-toothed’ appearance
Usually due to re-entry circuit in the right atrium
What ECG changes are typical of Left Atrial Hypertrophy?
Bifid P waves
Give some causes of LAH
HTN, aortic stenosis, mitral regurgitation
Though mitral stenosis in association with LVH is prob more common
What ECG features are seen with a Junctional Escape Rhythm?
Narrow complex QRS
SA node rate 60-100bpm
AV node rate 40-60bpm
Ventricular rate 20-40bpm
What ECG changes are typical of Wolff-Parkinson-White syndrome?
Very short PR interval
Broad complex QRS with “Delta wave” (slurred upstroke to QRS)
(Accessory pathway)
What ECG changes are typical is RBBB?
“MaRRoW” or “MaRRooN” (latter perhaps more accurate)
V1 - “M” (rSR)
V6 - “W” or “N” (qRs)
Wide QRS complexes
What ECG changes are typical is LBBB?
"WiLLiaM" or "ViLLhelM" (latter better) V1 - "V" (rS - dominant S wave) V6 - "M" (double peaked R) Absence of Q waves in lateral leads Wide QRS complexes
What ECG changes are typical of LVH?
Increased S wave in V1-V3 (downward deflection)
Increased R wave in V4-V6 (upward deflection)
Left axis deviation
(Causes aortic stenosis, HTN, mitral or aortic regurgitation)
What ECG changes are typical of hyperkalaemia?
Peaked T waves
Prolonged PR though P waves may be absent
Bizarre QRS complexes which merge with P and T waves each side
Which leads do you compare to assess for left or right axis deviation?
Leads I and II
Leads aVL and aVF
Give two causes for left axis deviation and three causes for right axis deviation?
Left - LVH and LBBB
Right- RVH, PE and COPD
Which two arrest rhythms are shockable and which are not?
Shockable - VF and pulseless VT
Non-Shockable - PEA and Asystole (IV adrenaline every 3-5mins)
List 3 things a Long QT rhythm can lead to
Palpitations
Fainting
Sudden Death due to VF
(Implantable cardioverter used to treat)
