Heart 3 A Flashcards
Electrical conduction system of the heart composed
Sino atrial node Internodal conduction tracts and interact rial conduction tracts Atrioventricular junction Right bundle branch Left bundle branch Purkinje network
Cardiac cells
Myocardial cells
Pacemaker cells
Myocardial cells function
Primary function contraction and relaxation
Myocardium consist of
Interlacing bundles of cardiac muscles fibres arranged spirally around the circumference of the heart
Contractility
Myocardial cells shorten and return to their original length when stimulated by an electrical impulse
Conductivity
The ability for cardiac cells to conduct electrical impulses
Myocardial cells are
Working cells of the heart
Function of pcemaker cells
Generation and conduction of electrical impulses
Pacemaker cells
Cannot contract
Contain more gap junctions that allows them to conduct electrical impulses rapidly
Automacity
They are capable of generating impulses spontaneously
Autonomic nervous system
Heart is under the constant control
Regulation occurs
In medulla oblongata
Ecg
Is a graphic record of the changes in magnitude and direction of electrical activity of the heart
It records depolarisation and repolarisation of the atrial and ventricular myocardial cells
The ecg paper
Grid allows measurement of time in seconds ( along the horizontal axis) and voltage (amplitude) in mm along the vertical axis
Lead placement
12 lead ecg lead placement
Electrodes need to be placed in the correct position to ensure accurate ECG recording
Limb leads
L ( left)
R (right)
F (foot)
N (neutral)
Chest leads
V1, V2 V3 V4 V5 V6
P wave onset and end
Onset is first abrupt or gradual deviation from the baseline. The end is marked were the wave flattens out to return to the baseline
P wave direction
Upright in lead 11 (upright in most lead)
P wave duration
Between 0.08 and .10 seconds
P wave amplitude
Shape
P wave - qrs relationship
0.5 -2.5 mm
Smooth and rounded
1:1
Pr interval
Onset and end
Pr interval - qrs relationship
Begins with the onset of the p wave and ends with the onset of qrs complex
- 12 -.20 seconds
1: 1
Qrs complex Onset and end Components Direction Duration Amplitude Shape
At the point where the first wave of the complex just begins to deviate, abruptly or gradually from the baseline
Consist of one or more of the ff: upright deflection ( r wave) and inverted deflection (q, s waves)
May be predominantly upright, inverted or equiphasic
0.06-0.12 or 0.08 seconds
Vary from 1-15 mm in lead 11 for r and s wave. Q wave is less than 25% of the r wave
Narrow and sharply pointed
Qt interval
Onset and end
Duration
The point where the first wave of the qrs complex begins to deviate
