ECG Basic Concepts Flashcards
The resting membrane potential of a myocardial cell is ?
~-90 mV
Threshold potential of cardiomyocytes is ?
- 40 mV
When the cardiomyocytes reach threshold potential what channels open to incur depolarization?
Voltage gated Na+ channels
The AP plateau of cardiomyocytes is caused by ?
The net efflux of K+ is balanced by the net influx of Ca+ through the calcium channels.
What is Cardiac syncytium?
It is a network of cardiomyocytes connected by intercalated discs that enable rapid transmission of cardiac impulses.
Depolarization of SA and AV nodes depends on what irons ?
Calcium
The time AV node takes to conduct electricity to ventricles is ?
100 Ms
The physiological reason for slow AV nodal conduction?
It is to allow atrial myocadrium to relax and empty the blood to ventricles
The causes of AV nodal delay of electrical conduction?
The arrangement of AV nodal cells which are thin at right angles to the conduction pathway.
The number of Gap junctions are less in AV node as compared to the Hiss-Purkinje system.
The AV nodal conduction depends on slow calcium channels. Whereas, in purkinje system it depends on fast sodium channels
Resting membrane potential of AV nodal cells?
-90 mV
Resting membrane potential of Purkinje system cells?
-60 mV
Septal myocardium is stimulated by ?
Left BB
Q wave represents?
Septal depolarization by left BB.
The S wave is negative in ECG. Why ?
The S wave represents depolarization of the base of the ventricles. The vector is moving rightward. Consequently, the wave form is negative.
The electrophysiological cause of ST segment formation is ?
Due to the complete depolarization of ventricles there is no net movement of electrical charges occurring on the ventricular syncytium. Consequently the event is recorded by the ECG as isoelctric line.
