Basic interpretation of ECG

Here's some ECG paper. It's comprised of, in Dr Flynn's terms, "big squares" and "little squares". Each big square is 5x5 little squares. For one LITTLE square, select the correct size in mm, the correct voltage its height represents in mV of current, and the correct time period its width represents in seconds.

Here is a textbook-perfect segment of an ECG. What's the flat line, without any deflections, called?

What is the first upward wave called?

Sometimes there is a downward deflection at this point. What is it called?

What is the combination called of a downward deflection, followed by an upward deflection, followed by another download inflection?

In the six steps to interpreting ECGs, the first is to determine the rate. The heart rate is determined by the number of squares or mm between two R waves. What are the TWO easiest ways to determine the rate?

What is the second step to interpreting the ECG?

The third step is interpreting the p wave, which indicates depolarisation of the atria. When considering the p wave, first determine if it is present. If it is present, what should a normal p wave look like?

The PR interval should be 3-5mm. What does it represent?

The fourth step is interpreting the QRS complex (representing depolarisation of the ventricles), which has several sub-steps. First, consider the cardiac axis. The wave of depolarisation spreads in multiple directions through the ventricles. The differing magnitudes and directions of the various depolarisation currents can be “summed” to form a resulting electrical vector, which is known as the cardiac axis. If we consider the heart in the coronal plane (using the limb leads), an abnormal axis is outside -30 to +90 degrees. What are the steps to determining the cardiac axis?

What should q waves look like?

Considering QRS complexes from from V1 to V6, two trends are apparent: the R-wave becomes progressively larger, and the S-wave becomes progressively smaller. This is called R wave progression. What is a lack of R wave progression usually an indication of?

The QRS complex duration should be less than 2.5mm. When considering amplitude, we need to consider whether there is indication of left ventricular hypertrophy or right ventricular hypertrophy. Is the following criteria to determine LVH or RVH? a. Sokolow-Lyon criteria: S-wave in lead V1 + R-wave in either lead V5 or V6 > 35 mm. b. Cornell criteria: Males: S-wave in lead V3 + R-wave in lead aVL > 28 mm. Females: S-wave in lead V3 + R-wave in lead aVL > 20 mm.

For the fifth step, consider the ST segment. ST segments can be elevated or depressed from the iso-electric line. The ST-segment is said to be depressed if it slopes down 1mm or more from the J-point, or is depressed 1mm or more horizontally. ST-segment elevation of up to 3 mm in the right-sided chest leads, and up to 1 mm in the limb leads may be normal, and is referred to as early repolarisation. What conditions do these phenomena indicate?

For the sixth and final step, we need to consider the t wave. What should the amplitude of the t wave be?