Problem 116 - Objective Biology for NEET

Question

Find out the incorrect statement from the following: (a) ECG is a graphical representation of the electrical activity of the heart during cardiac cycle. (b) For a detailed evaluation of the heart's function, multiple leads are attached to the chest region (chest leads). (c) \(\mathrm{P}, \mathrm{R}, \mathrm{T}\) are \(+\) ve wave whereas \(\mathrm{Q}\) and \(\mathrm{S}\) are -ve wave in standard \(\mathrm{ECG}\). (d) Starting of T-wave marks the end of systole of ventricles.

Step-by-Step Solution

Answer

The incorrect statement is (d) Starting of T-wave marks the end of systole of ventricles.

Step 1: Understanding and Evaluating Statement A

Statement (a) says 'ECG is a graphical representation of the electrical activity of the heart during cardiac cycle.' If we understand the basic concept, Electrocardiography (ECG) is indeed a representation of the electrical activity of the heart muscles during each heartbeat, that is a cardiac cycle. So, this statement is correct.

Step 2: Understanding and Evaluating Statement B

Statement (b) says 'For a detailed evaluation of the heart's function, multiple leads are attached to the chest region (chest leads).' Indeed for a 12 lead ECG, multiple electrodes are attached to limbs and chest for capturing the cardiac activity from multiple angles. So, this statement is also correct.

Step 3: Understanding and Evaluating Statement C

Statement (c) says '\(P, R, T\) are +ve wave whereas \(Q\) and \(S\) are -ve wave in standard ECG.' In a standard ECG, \(P, R, T\) waves represent the electric activities with a upward deflection hence are positive whereas \(Q\) and \(S\) waves represent the activities with a downward deflection and hence are negative. This statement is correct.

Step 4: Understanding and Evaluating Statement D

Statement (d) says 'Starting of T-wave marks the end of systole of ventricles.' Now, in a cardiac cycle the T-wave represents the repolarization of ventricles. But the ventricular systole (contraction phase) actually ends at the end of S-wave. So, this statement is indeed incorrect.

Key Concepts

ECG interpretation

Electrocardiogram (ECG) interpretation is a skill that involves understanding the patterns and rhythms that appear in the ECG strip. The ECG is a vital tool in diagnosing cardiac conditions because it provides visual representations of the heart's electrical activity. Each wave on an ECG has a specific meaning.

• The P-wave indicates atrial depolarization, which is the electrical impulse spreading through the atria.
• The QRS complex reflects ventricular depolarization, a key phase where the impulse travels through the ventricles causing contraction.
• The T-wave represents ventricular repolarization, a phase when the heart's ventricles reset electrically for the next cycle.

Understanding these waves helps medical professionals assess if the heart's electrical pathways are working properly. Each deviation from the normal predictive shapes might hint at underlying heart issues. Being able to accurately interpret these cues is crucial for diagnosis and treatment.

Cardiac cycle

The cardiac cycle is the sequence of events that happen from the starting of one heartbeat to the beginning of the next. During this cycle, the heart goes through different phases of contraction and relaxation, ensuring blood is effectively pumped throughout the body.

• Systole: This is the contraction phase of the heart, during which blood is pumped out of the chambers.
• Diastole: This is the relaxation phase, allowing the chambers to fill with blood again.

The ECG plays an essential role in visualizing these phases, providing insights into how the atria and ventricles function during each cycle. For instance, the end of the S-wave marks the end of ventricular systole, a critical timing within the cycle. Understanding the cardiac cycle is fundamental in recognizing abnormal heart functions.

Heart's electrical activity

The heart's electrical activity is what allows it to function rhythmically. This activity originates from the sinoatrial (SA) node, which is often referred to as the heart's natural pacemaker. The SA node generates electrical impulses that travel throughout the heart muscle, triggering contraction. These impulses spread first through the atria, causing them to contract, and then proceed to the ventricles. The transfer of these signals is visible on the ECG, with each wave indicating a specific step in this electrical journey. Any disruption in this orderly flow can result in arrhythmias or other cardiac conditions. The careful reading of these signals helps in diagnosing conditions like atrial fibrillation or ventricular tachycardia. By understanding these electrical patterns, one can get a deeper insight into heart health and potential issues.

Ventricular systole

Ventricular systole is a crucial part of the cardiac cycle where the ventricles contract to pump blood out to the lungs and the rest of the body. It ensures that oxygenated blood reaches every organ, supporting their function. During ventricular systole, which starts with the QRS complex and ends at the S-wave in an ECG, the pressure within the ventricles increases causing the ejection of blood. The proper functioning of this phase is critical for maintaining adequate circulation. Any issues during ventricular systole can lead to conditions like heart failure due to inadequate pumping. Observing ventricular systole's duration and effectiveness provides insight into cardiovascular health and can help detect potential problems early on. Understanding when this phase begins and ends, especially via ECG, is key in pinpointing issues in the heart's contraction process.