Electric activity of the heart. Flashcards
What spreads throught the tissues during depolirization and repolarization?
Electrical currents generated by the cardiac muscle.
Electrical currents are conducted through?
The body fluids.
How is the electrical activity measured?
A small portion reaches the body surface, detected by electrodes.
What is the name of the record produced, when measuring theese electrical currents?
Electrocardiogram / ECG
What is the method of ECG called?
Electrocardiography
Various components of the ECG record can be correlated to?
Specific cardiac events.
Bipolar limb leads?
I - RF to LF
II- RF to LH
III- LF to LH
Unipolar limb leads?
aVR - RF
aVL- LF
aVF - LH
What are chest leads?
They measure the cardiac electric potential at six different locations surrounding the heart (V1-V6)
What are the aims for the electric activity of the heart exercise?
Application of leads
ECG- quiescent cond.
ECG- after exercise
Evaluation
What is Einthoven’s triangle?
Einthoven’s triangle is an imaginary formation of three limb leads in a triangle used in electrocardiography, formed by the two shoulders and the pubis.
Why and how is ECG an important tool?
The heart must sustain a regular cycle of relaxation and contraction if it is to fulfill its objective. This regularity is predicated on a series of complex electrophysiological events within the cardiac tissues that can be monitored using a electrocardiogram.
Experimental design - 2 ways of measuring ECG?
Mains-independent system
Conventional ECG measurement
3 basic distinct waveforms in ECG?
P wave - atrial depolarisation (systola, started by SA- node)
QRS complex - ventricular depolarization (systola by AV-node) and repolarization & diastola of atria.
T wave - ventricular repolarization (diastola)
Y axis of ECG?
Voltage, electric potential (mV)
X axis of ECG?
Time (s)
Formula for frequency of heart activity?
T= R1-R2 [s]
R1-R2 = 45mm –> set point = 25 mm/s
45mm/25 mm/s = 1,8 s
Which three electrode locations form the Einthoven’s triangle?
right arm, left arm, left foot
What lies in centre of Einthovens triangle?
Heart
Which leads can the vector be calculated from?
Any two limb leeds
What does the third lead correspond to?
The vector
What does the recording of the vector movement during cardiac cycle form?
Three loops –> vectocardiogram
What is cardiac vector?
The vector at the maximal deflexion of QRS complex –> electrical axis of the heart
What does ECG represent?
a record of the electrical activity conducted in the body fluids from the cardiac impulses that reaches the body surface (not direct heart activity)
What does the ECG display?
The sum of all electrical activity in all the cardiac muscle cells.
Why are the results expressed as voltage in mV?
Because it does not represent the actual potential, but comparison at two different points on body surface.
1 mV =
10-3 V = 0.001 V
What is masked by the QRS complex?
Atrial repolarization, occurs simultaneously with ventricular depolarization.
Why is the P wave smaller than the QRS complex?
atria have smaller muscle mass then the ventricles and generate less electrical activity.
AV- nodal delay?
current is flowing throughthe AV node but magnitude is too small to be detected by ECG , RP segment
Plateu phase
Ventricles are completely depolarized and the cardiac cells undergo plateau (refractory period), ST segment
Rest and filling phase?
heart muscle is completely at rest and ventricular filling is taking place. TP interval
If no current is detected and the ECG remains at baseline indicates the following?
RP segment
ST segment
TP interval
Inotropic effects?
change the strength of the contraction of the heart muscle
Chronothropic effect?
change the heart rate
Dromotropic effect?
change amount of time it takes for the heart to complete one beat
Bathmotropic effect?
influence the excitability of the cardiac muscle.
Sympathetic influence on the heart?
Innervation of both atrii and ventriculi
Positive chronotrophy in atrium
Positive inotrophy in ventricles
Noradrenaline, activation of adrenergic receptors
Parasympathetic influence on the heart?
SA -node, negative chronotrophy
AV-nodes, negative dromotrophy
Acetylcholine –> activation of K+ channels
Humoral stimulation of the heart?
Noradrenaline - sympathetic effects
Acetylcholine - parasympathetic effects
Glucagon - positive inotropic and chronotropic effects
Prostaglandin E2 - positive inotropic effect
Insulin - positive dromotropic and bathmotropic effect
Progesterone - negative ino, chrono and bathmotropic effects.
