Find the incorrect statement

Options

A. The enlarged Q and R waves in ECG are the indication of myocardial infarction
B. Lubb sound appears during ventricular systole
C. There is no effect on heart beat by increasing extracellular `Ca^(+2)`
D. In Stokes-Adams syndrome, the atrial impulse fails to be transmitted to the ventricle, so artificial pacemaker is required

Answer

To find the incorrect statement among the provided options, we will analyze each statement step by step.

### Step 1: Analyze the first statement
**Statement:** Enlarged Q and R waves in ECG are the indication of myocardial infarction.

**Analysis:** Myocardial infarction, commonly known as a heart attack, is characterized by changes in the ECG, particularly the enlargement of the Q wave. This statement is correct as enlarged Q waves are indeed indicative of myocardial infarction.

### Step 2: Analyze the second statement
**Statement:** Lub sound appears during ventricular systole.

**Analysis:** The "Lub" sound, or the first heart sound (S1), occurs when the mitral and tricuspid valves close during ventricular systole (the contraction phase of the ventricles). This statement is also correct.

### Step 3: Analyze the third statement
**Statement:** There is no effect on heartbeat by increasing extracellular calcium.

**Analysis:** This statement is incorrect. Calcium plays a crucial role in muscle contraction, including cardiac muscle. An increase in extracellular calcium can enhance the force of contraction and affect the heart's rhythm. Therefore, this statement is indeed incorrect.

### Step 4: Analyze the fourth statement
**Statement:** In Stokes-Adams syndrome, the actual impulse fails to be transmitted to the ventricle, so an artificial pacemaker is required.

**Analysis:** Stokes-Adams syndrome is characterized by intermittent heart block, where the electrical impulses do not reach the ventricles. This can lead to fainting spells due to insufficient blood flow to the brain. An artificial pacemaker is often required to restore normal heart rhythm. This statement is correct.

### Conclusion
After analyzing all the statements, the incorrect statement is:
**"There is no effect on heartbeat by increasing extracellular calcium."**