Cardiovascular Physiolgy 3 Flashcards
What are the components of ECG?
2 components of ECG- waves and segments
Waves- deflections above or below baseline
Segments- are in between waves
Intervals include waves and segments
What does the P wave indicate?
The initial stimulus is generated by the SA node and depolarizes both atria. This ongoing depolarization is represented by the P wave. After completion of the depolarization the ECG shows a baseline again. The atrial muscle is contracting
What does the PQ segment indicate?
Both atria are still ddpolarized and contracting
What occurs at the QRS complex?
The stimulus has arrived in the ventricle. First the septum gets depolarized (Q wave), then the left and right ventricle (R wave). The depolarization of the left ventricle takes longer than of the right ventricle (thicker ventricle wall). This generates the S wave
Where does the ventricle contract?
Within the S-T segment
What happens in the S-T segment ?
As the depolarization of the ventricles is completed, there is no electrical change anymore and consequently the ECG shows a baseline. The ventricle is in full contraction
What happens during the T wave?
The ventricle is repolarizing and- with some delay- relaxing
Where does atrial repolarization occur?
Atrial repolarization is extremely small and is also hidden in the QRS interval
Differentiate ECG and ventricular action potential
- The electrocardiogram represents the summed electrical activity of all cells recorded from the surface of the body
- The ventricular action potential is recorded from a single cell using an intracellular electrode. Notice that the voltage change is much greater when recorded intracellularly
What are the causes of the QRS and T wave?
They are the net result of the individual action potentials within the ventricular myocytes and the direction that the currents are spreading throughout the ventricles
Explain the correlation of electrical events of the cardiac cycle
- P wave: atrial contraction begins with atrial depolarization
- PQ or PW segment: conduction through AV node and A-V bundle, atrial contraction
- bundle of His gets current from AV node- Q wave forms
- Beginning of R wave is when current goes towards apex/electrode(depolarization)
- downward r wave when current moves up(downward deflection)
- then S wave follows when ventricles are starting become depolarized
- in the ST segment, ventricles contract
- T wave begins when ventricles begin to repolarize
- ventricles repolarize from top to bottom(same direction as current) bringing an end to the T wave
Ventricle pressure then falls below atrial pressure and then AV valves open and ventricles start filling passively
How do we increase speed and conduction velocity in change, without changing the PQRS complex?
Between T wave and next p wave is diastole
Decrease the diastolic phase. When heart rate increases, diastolic phase/ filling phase shortens, reduces the chances of changes to PQRS complex
What are the questions of analyzing ECG tracing?
- What is the rate? Is it within the normal range of 60-100 beats per minute?
- Is the rhythm regular?
- Are all normal waves present in recognizable form?
- Is there one QRS complex for each P wave? If yes, is the P-R segment constant in length?
- If there is not one QRS complex for each P wave, count the heart rate using the P waves, then count it according to the R waves. Are the rates the same? Which wave would agree with the pulse felt at the wrist ?
What can heart block cause?
Widened QRS complexes
What do second and third degree block?
AV node take over , QRS and P waves no longer associated
