Clinical Note on ECG

Chapter: Making Sense of the EKG : Why It Matters

~By Ronnie the Clinician,

The other day, one of the patient care technicians (PCTs) asked me a simple question:
“Why do we have to do an EKG every time there’s a rapid response?”

At first, I was shocked. But then it hit me that no one ever really explains anything in the hospital, especially to those who do not have a background in physiology or a clear understanding of why certain procedures are done.

Doctors often do not take the time to explain things to nurses. Nurses, overwhelmed and sometimes unsure themselves, rarely explain things to aides or technicians. And so, the cycle continues-people performing tasks every day without truly knowing why.

So, when that PCT asked me the question, I did my best to explain. But even as I spoke, I could sense that my answer did not fully bridge the gap in understanding. Later that night, I sat at home thinking about it, and that is when I decided to write this chapter-to share not just the what, but the why behind one of the most common and vital tools in medicine: the EKG.

What Is an EKG?

An EKG, short for electrocardiogram (ECG), is like a noninvasive camera that captures the heart’s electrical activity from twelve different angles, all without ever opening the chest.

It is an incredible tool because it gives us a real-time view of how the heart functions electrically. Every beat of the heart begins with an electrical impulse that triggers the muscle to contract. If that impulse is abnormal, delayed, or blocked, it will appear on the EKG-often before any clinical signs or symptoms become evident.

Why It Is So Important During a Rapid Response

When a patient’s condition deteriorates suddenly-whether they are short of breath, their heart rate spikes, or they lose consciousness-the heart’s electrical system is often the first place we look for answers.

The EKG helps us determine:

• If the heart rhythm is normal or life-threatening

• Whether the patient is having a heart attack (myocardial infarction)

• If there are electrolyte imbalances, such as potassium or calcium disturbances

• Or if the heart is simply under too much stress or strain

It is a noninvasive, fast, and accurate way to assess the heart’s status, and sometimes, it is the key to saving a life.

My Mission of Bridging the Knowledge Gap

That question from the PCT reminded me of something crucial: in healthcare, understanding why we do what we do is just as important as knowing how to do it. Each person on the care team-doctor, nurse, aide, technician- all play a role in patient survival. When one understands the reason behind an intervention, they perform it not out of habit, but with purpose.

Education should never stop at titles. If we took the time to teach each other, to share not just instructions but explanations-our hospitals would run with greater clarity, teamwork, and respect.

In short, the EKG is more than just a routine test. It is a window into the heart, a tool that allows us to see the unseen and to catch danger before it becomes disaster.

So, the next time someone asks, “Why do we do an EKG during a rapid response?”
the answer should be clear:
Because it lets us look directly into the heart when seconds matter most.

Details Note

1. ECG (Electrocardiogram) Overview

An ECG measures the electrical activity of the heart.
The heart is a muscle (myocardium) that contracts mechanically after electrical depolarization occurs.
ECGs allow us to visualize and interpret these electrical events to understand the mechanical function and detect abnormalities.

2. Basic Setup: Electrodes and Leads

• Electrodes = sticky dots placed on the skin

• Leads = electrical views or readouts obtained from these electrodes
  A 12-lead ECG uses 10 electrodes to produce 12 different views of the heart’s electrical activity.

3. Precordial (Chest) Leads — V1 to V6

These leads view the heart in the horizontal plane (anterior-posterior).

Lead	Position	Landmark
V1	4th intercostal space, right of sternum	Right side
V2	4th intercostal space, left of sternum	Left side
V3	Between V2 and V4	—
V4	5th intercostal space, midclavicular line	Over apex
V5	Same horizontal line as V4, anterior axillary line	—
V6	Same line as V4/V5, midaxillary line	—

4. Limb Leads

These view the heart in the vertical (frontal) plane.

Electrode	Placement	Function
RA	Right arm or wrist	Sensing
LA	Left arm or wrist	Sensing
LL	Left leg or ankle	Sensing
RL	Right leg or ankle	Ground (neutral)

5. Einthoven’s Triangle

Formed between RA, LA, and LL electrodes, providing three standard limb leads (bipolar):

• Lead I: RA → LA

• Lead II: RA → LL

• Lead III: LA → LL

Each lead represents a different vector or angle of electrical activity.

6. Augmented Limb Leads (Unipolar)

Created by combining information from limb electrodes:

• aVR: Augmented Vector Right

• aVL: Augmented Vector Left

• aVF: Augmented Vector Foot (inferior view)

Together with the six chest leads, these form the 12-lead ECG:

• 6 precordial (V1–V6)

• 3 standard limb (I, II, III)

• 3 augmented limb (aVR, aVL, aVF)

7. Electrical Conduction System of the Heart

Structure	Function	Intrinsic Rate (bpm)
SA Node (Sinoatrial Node)	Natural pacemaker; initiates depolarization	70–100
AV Node (Atrioventricular Node)	Slows conduction to allow ventricular filling	40–60
Bundle of His	Carries impulse from AV node to ventricles	—
Left & Right Bundle Branches	Conduct through septum to ventricles	—
Purkinje Fibers	Rapidly distribute impulse through ventricles	—

8. Ion Movements and Electrical Events

• Depolarization: Sodium and calcium enter cells, making the inside positive. This causes contraction.

• Repolarization: Potassium leaves cells, restoring the resting negative state so the heart can reset for the next beat.

9. ECG Wave Interpretations

Wave/Complex	Represents	Description
P wave	Atrial depolarization	SA node → atria
PR segment	AV nodal delay	Signal slows through AV node
QRS complex	Ventricular depolarization	Conduction via His-Purkinje fibers
T wave	Ventricular repolarization	Resetting phase
Isoelectric line	No net electrical activity	Flat baseline

(Atrial repolarization is hidden within the QRS complex.)

10. Direction of Deflections

• Depolarization toward a lead → upward (positive) deflection

• Depolarization away from a lead → downward (negative) deflection

• Repolarization away from a lead → upward deflection

• Repolarization toward a lead → downward deflection

• Perpendicular activity → flat (isoelectric) line

11. Example: Lead II

Lead II views the heart from the right arm to the left leg, roughly along the heart’s main electrical axis.

Typical waveforms:

• P wave: Upward (atrial depolarization)

• QRS: Sharp, tall upward deflection (ventricular depolarization)

• T wave: Upward (ventricular repolarization)

12. Opposite View Example: aVR

aVR views the heart from the right shoulder, opposite to Lead II.
Therefore, waveforms appear inverted compared to Lead II-a mirror image.

13. Clinical Insights

ECGs can reveal:

• Rhythm disturbances (bradycardia, tachycardia, arrhythmias)

• Conduction blocks (AV block, bundle branch block)

• Chamber enlargement

• Myocardial infarction (MI), including which coronary artery is affected

• Electrolyte or drug-induced changes

14. Summary Principles

An ECG is a record of the heart’s electrical signals through twelve different views.
Each wave corresponds to a specific cardiac event.
By comparing lead directions and waveforms, clinicians can:

• Diagnose cardiac arrhythmias

• Identify ischemic or infarcted areas

• Monitor electrolyte imbalances or drug effects

That was what I wish I could have had the time to convey to my PCT to help her understand ECGs. If most clinicians understood this, their attitude and approach to these clinical interventions would never be the same.

Thanks to her question, I now have something written to share with those who like to read.

Have a wonderful day.
Pal Ronnie