eLFH - Cardiovascular Physiology Part 2 Flashcards
12 Lead ECG electrode placement
ECG lead categorisation
Limb leads (Bipolar)
Augmented limb leads (Unipolar)
Chest leads (unipolar)
Limb leads
Read potential difference between 2 active electrodes
Form borders of Einthoven’s triangle
Augmented limb leads
Record potential difference between one active limb electrode and a composite reference electrode formed by the average of signals from the other limb leads
Readings have lower amplitude so are augmented
Chest leads
Aka precordial leads
Record electrical activity perpendicular to limb leads in ‘horizontal plane’
Standard ECG recording speed
25 mm/s
Standard ECG calibration
1 mV/cm
Normal cardiac axis
- 30 degrees to + 90 degrees
Time represented by one small ECG square
0.04 s
ECG changes associated with Posterior STEMI
ST depression V1-4
Upright T waves in V1-2
R>S wave in V1-2
ECG electrode position to pick up posterior STEMI
V7-9 continue posteriorly along same horizontal plane from V6
CM5 electrode position
Red over Manubrium
Yellow in V5 position
Green is neutral and can go anywhere, but often placed on left clavicle
Hence name CM5:
Clavicle
Manubrium
V5
CM5 use
Good view of left ventricle and very sensitive at detecting left ventricular ischaemia (>80%)
Most common Atrial flutter ventricular rate
150 bpm
2:1 conduction ratio most common with atrial rate of 300
Ways in which valvular lesions result in increased work for the heart
Volume
Pressure
Volume changes leading to increased work for the heart in valvular lesions
Regurgitant lesions allow backflow
Increase volume load in the heart chamber preceding the valve
Leads to distension and dilatation
Pressure changes leading to increased work for the heart in valvular lesions
Stenotic pathology reduces cross sectional area of valve
Therefore higher resistance against flow and pressure load
Chamber preceding the valve develops higher pressure to eject blood past the narrowed valve
Leads to hypertrophy
Two most common valvular pathologies
Aortic stenosis
Mitral regurgitation
Most common causes of acute mitral regurgitation
Ruptured chordae tendinae
Post MI
Trauma
Most common causes of chronic mitral regurgitation
Mitral valve prolapse
Rheumatic fever
Connective tissue diseases
Dilated cardiomyopathy
Effects of chronic mitral regurgitation on cardiac function
LA volume increases due to backflow during systole
Can lead to AF
Progressive dilatation of left heart as LAEDV increases so greater volume delivered to LV
If muscle fails and stroke volume falls, LA and LV pressure increases as LVESV and LVEDV increase
Clinical features of chronic MR
Initially asymptomatic
As left heart failure develops then get symptoms of SOB, orthopnoea, etc
Palpitations if AF develops
Cardiac auscultation with MR
Pansystolic murmur
Maximal at apex
Radiation to axilla
3rd heart sound
ECG changes with MR
P mitrale due to LA enlargement
AF
LVF