ECG and Heart Conductivity

What does an abnormally sized wave indicate, whether too tall or too short?

- Abnormally tall indicates hypertrophy of whichever structure the wave represents: -Tall P wave indicates atrial hypertrophy -Tall QRS complex indicates ventricular hypertrophy -Short P wave indicates decreased atrial cells (atrial ischemia and cell death) -Short QRS complex indicates decreased ventricular cells (ventricular ischemia and cell death) -Short waves can also indicate damage to the nerves of the structure, meaning some cells are not receiving the current due to damaged nerves and are not discharging (less likely case)

What does an abnormal P wave indicate?

-sinoatrial node firing abnormally OR -atria contracting abnormally

How long in seconds is a normal QRS complex?

0.06 to 0.10 seconds

How long in seconds is a normal P-R Interval?

0.12 to 0.20 seconds.

When reading an ECG, how do you determine which waves go with which heartbeat? For example, with atrial fibrillation there will be many P waves, but how do we know when the former heartbeat ends and the next one begins?

1. Find the QRS waves first on the ECG. 2. The FIRST wave after the QRS complex is the T wave. 3. The SECOND wave after the QRS complex is the P wave of the next heartbeat. 4. Thus any waves between the second wave and the next QRS complex count as atrial firings.

What is indicated if the PR Interval is too long?

A PR interval longer than normal, greater than 2 milliseconds, indicates a problem with the AV node, as the electric current isn't traveling quickly enough from the SA node to the ventricles to allow them to fire on time.

What does an abnormal QRS wave indicate?

Abnormal contraction (depolarization) of the ventricle muscles.

What does the P wave represent?

Atrial contraction - P wave represents atrial contraction as the action potential travels from the sino-atrial node through the atria of the heart.

Why is the normal heart conduction called normal SINUS rhythm?

Because it is the rhythm initiated by the sino-atrial node, thus it is a sinus rhythm.

What does an abnormal P-Q Interval indicate?

Conduction problem with the atrioventricular node or bundle of hiss.

What does the flat period of an ECG between the P Wave and the Q of the QRS wave represent?

During this period, the action potential is traveling through the AV node, bundle of Hiss, and bundle branches. This electrical conduction is too weak for ECG to pick up, so it is flat on the ECG.

What second time interval is the ECG strip set at?

Each little box on the ECG strip represents 0.04 seconds.

Why does the number of leads used for a ECG matter?

Each pair of leads provides a different perspective for the way electric current travels through the heart. We can create a more three dimensional and accurate image of this process by using more leads. The most we can use is 6 perspectives or 12 leads total.

What if an ECG strip doesn't have written what lead it was reading for the printing?

Either write it down yourself if you saw which lead it was using during the recording. Otherwise, the strip is useless if there is no lead recorded.

What does an ECG Strip represent?

It is a graph of voltage changes over time. Voltage on the Y axis, time in milliseconds on the X axis.

What is Lead II (lead 2)?

Lead two is the pair of leads whose placement best match the travel of current through the heart, from upper right to lower left. Lead two includes 1 lead on the upper right chest or arm, and one on the lower left abdomen or left leg. Most ECG strips are printed using the readings from lead 2 as it most accurately matches the heart's conductive pathway.

How long is a normal Q-T Interval?

Less than 0.44 seconds

How long in seconds is a normal P wave?

Normal P Wave: 0.08 to 0.10 seconds. The entire P wave should fit within two horizontal boxes on the ECG strip grid.

Name the 3 Heart ECG Waves:

P Wave, QRS Wave, T Wave

What does a peaked T wave indicate? (pointed instead of rounded ^ vs. ~)

Peaked T wave indicates hyperkalemia or high potassium

If the T wave represents ventricle cells repolarizing, why is there no wave indicating when the atrial cells repolarize?

The atria cells repolarize at the same time the ventricle cells depolarize - both show up as the QRS wave.

What exactly does an ECG measure?

The electrocardiogram measures the voltage output of the heart in millivolts.

What do the height of the waves on the ECG indicate?

The height is proportional to the amount of cells recharging and discharging current. This is why the QRS wave is so much larger than the P wave - there are way more ventricle cells than atrial cells.

What does the QT Interval measure exactly?

The time from ventricular depolarization to ventricular repolarization (V discharge to V recharge)

What does the PR Interval measure exactly?

The time it takes for the impulse to travel from the SA Node to the Ventricles at the bottom of the heart.

What does the P-R Interval represent?

The time period from P to R represents the time it takes for the repolarized ventricle to fire off.

What is the T wave representing?

The ventricle cells are repolarizing (recharging).

Why is the QRS wave larger than the P or T waves?

The wave is larger because there are more ventricular cells depolarizing than there are cells in the atria, so the electrical current measured is larger.

What does a prolonged PR Interval, greater than 0.2 seconds, indicate?

Usually indicates a problem with the AV Node, as it is taking too long for the impulse to travel from the SA Node to the ventricles. Usually indicates that cardiac muscle ischemia has damaged the AV Node.

What does an abnormal T wave indicate?

Ventricles not repolarizing correctly.

What does an absent or flat T wave indicate?

Ventricular ischemia as the ventricles aren't recharging

What does an inverted T wave indicate?

Ventricular myocardial infarction. dead myocardial tissue in the ventricles which don't repolarize normally

What does it indicate on the ECG when the line dips below baseline; for example in the QRS complex?

Whether the wave goes upward or downward relates to the directionality of the electrical current in relation to the leads placed on the body. - A current that travels from a negative measuring lead to a positive lead will read as an elevated wave. - A current that travels from a positive lead to a negative lead will read as a depressed wave.