Cardiology Flashcards
Function of a ECG
representation of the electrical events of the cardiac cycle
Function of the SA node?
dominant pacemaker with an intrinsic rate of 60-100 bpm
Function of the AV node?
backup pacemaker with an intrinsic rate of 40-60 bpm
Another pacemaker besides the two nodes?
ventricular cells - intrinsic rate of 20-45 bpm
Impulse conduction pathway of the heart with ECG phase
Sinoatrial node - AV node (flat between P&Q)- bundle of His - bundle branches - Purkinje fibres (all QRS)
Standard calibration & how to determine pos / neg of wave?
- 25 mm/s or 0.1 mV/mm calibration
- impulses that travel towards the node causes an upright positive deflection, goes away causes a negative deflection
To determine heart rate from ECG graph
300 / # large sq between 2 R waves
If heart rate is irregular
count # QRS complex on the strip, usually a strip is 10 seconds long so multiply number of complexes by 6
What does the P wave represent in the heart cycle?
atrial depolarisation, electrical summation within the atrium
features of the P wave in ECG
normally
<120 ms wide, <0.3 mV tall
<3 s. sq wide, <2.5-3 small sq tall
always positive in lead I, II
always negative in lead aVR
How would atrial enlargement show up on the ECG?
Right AE - tall P wave (P pulmonale)
Left AE - bifid, broad notched P wave (P Mitrale)
What does the PR interval represent in the heart cycle?
= start of P to start of QRS
sinoatrial depol, atrial depol, conduction of AV junction so from A to V (node & bundle of His) (in which there is a delay)
Pathological principles of PR interval
if shorter .. if longer ..
Longer: disorders of the AV node and specialised conduction tissues
Shorter: in younger patients and preexcitation
One cause of short PR interval
Wolff Parkinson White Syndrome - extra conduction pathway causing rapid heartbeat with short PR and slurred QRS
One cause of long PR interval
first degree heart block
What does the QRS complex represent in the heart cycle
= start of Q to end of S
- ventricular depolarisation (& purkinje and bundle branches)
- also when atrial repolarisation occurs
Features of the QRS complex in ECG
normal <120ms
size of complex relates to myocardial mass
predominantly neg S wave in V1, transition to positive R by V6
Pathological principles of QRS complex
if broader .. if smaller .. if taller …
Broad QRS = ventricular conduction delay or bundle branch block
Smaller = obese patient, pericardial effusion, infiltrative cardiac disease
Taller QRS = thin patient, LV hypertrophy (S wave in V1 and R wave in V5/V6 > 35mm)
Features of hypertrophies of the ventricles
- deeper waves (best seen in 1 and 6!)
- S wave in V1 and R wave in V5/V6 > 35mm or R wave is 11-13
- due to hypertension or valvular disease
- diagnose using sokolow & lyon criteria
What does the ST segment represent in the heart cycle
interval between ventricular depolarization and repolarization
Features of a ST segment
flat = isoelectric
so elevated or depressed = pathology but 1mm or more is normal in V1 and V2
Diseases in which ST segment is elevated
Early repolarisation, myocardial ischaemia, inflammation, pericarditis or myocarditis
What does the T wave represent in the heart cycle
ventricular repolarisation
Features of a T wave
normal = asymmetrical, first half having a gradual slope than second
12.5% - 66% of amplitude of R but < 10mm