JNTU B.Tech IV MEDICAL INSTRUMENTATION Previous Question Paper (February/March - 2022 - R15)

An Electrocardiogram (ECG) is a diagnostic tool that records the electrical activity of the heart over a period of time using electrodes placed on the skin. It captures the depolarization and repolarization of the cardiac muscle, represented by the P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization).

Normal cardiac rhythm, known as Sinus Rhythm, originates from the sinoatrial (SA) node, typically occurring at a rate of 60–100 beats per minute with a consistent P-QRS-T sequence. Abnormal rhythms, or Arrhythmias, include:

1. Tachycardia: A resting heart rate exceeding 100 beats per minute.
2. Bradycardia: A resting heart rate below 60 beats per minute.
3. Atrial Fibrillation: Irregular and rapid electrical impulses in the atria, leading to an irregular ventricular response.
4. Ventricular Fibrillation: A life-threatening condition where the ventricles quiver ineffectively, causing a loss of cardiac output.

The electrical state of a cell is governed by the distribution of ions (primarily Na+, K+, and Cl-) across the cell membrane.

Resting State: In the resting state, the cell membrane is polarized. The interior of the cell is negatively charged relative to the exterior, typically maintaining a resting membrane potential of approximately -70 mV to -90 mV. This is maintained by the sodium-potassium pump, which actively transports three Na+ ions out of the cell for every two K+ ions brought in, while the membrane remains more permeable to K+ leakage.

Active State: When a stimulus exceeds the threshold, the cell enters the active state (depolarization). Voltage-gated sodium channels open, allowing a rapid influx of Na+ ions into the cell. This causes the membrane potential to shift from negative to positive (overshoot). Following this, sodium channels close and potassium channels open, allowing K+ to exit the cell, which restores the negative resting potential during the repolarization phase.