Why the P and T waves are low-frequency signals whereas
the QRS complex is a high-frequency signal. Include diagrams of action potentials and an ECG waveform in your reasoning.
ECG waveform reflects depolarization and repolarization of the heart. Conduction velocity in the His-Purkinje system is the fastest, 2-4 m/sec. Propagation of activation through the His-Purkinje system and ventricular myocardium forms a fast-moving QRS complex on an electrocardiogram (ECG) and by a QRS loop on a vectorcardiogram (VCG). Conduction velocity in atria is slower (0.5-1 m/sec) than in the His-Purkinje system. Propagation of activation through atria forms P-wave on ECG (P-loop on VCG). Repolarization spreads very slowly and forms slow-deflecting T-wave (T-loop).
Differences in the speed of wavefront propagation through the cardiac cycle are reflected by different frequencies content of ECG waves. The content of T wave lays mostly within a range from zero (DC) to 10 Hz. The content of P wave is characterized by 5-30 Hz frequencies. The content of QRS usually contains within 8-50 Hz frequencies while abnormal ventricular conduction is characterized by high frequencies (above 70Hz), forming notches on the QRS. However, the full spectrum of frequencies producing the QRS complex has not been adequately explored. In this manuscript we review the history of QRS frequencies content investigations and discuss our novel method of non-invasive assessment of ventricular conduction.
P wave indicates depolariztion of atria and qrs represents depolariztion of the ventricles. The ventricular walls are much more thiker than atrial walls.
The amplitude of the waves in depends upun the chamber dimensions and the wall thickness. So the qrs waves are more prominent as it reflects ventricular activity. So propagation velocity is not sole determinant of frequency or amplitude of the waves in the ECG.
P wave denote Atrial Depolarisation , QRS wave denote Ventricular Depolarisation or contraction and T wave denotes Ventricular Depolarisation PR interval usually 0.12-0.2 sec, QRS interval less than 0.2 sec , ST interval is 0.3 sec and QT interval 0.4 sec .
Are you asking in general or in response to a specific ECG? Depending on the amplitude of the waves - obesity can cause low frequency readings, as well as cardiomyopathy.
Arrythmia happen due to either increased or decreased interval of all ECG wave eg PR , QT ,ST , or QRS interval . Basic cause of all the arrythmia are either Automatically or Reentry or Triggered phenomenon.
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