An Approach to ECG Analysis

This will be an extensive section covering an approach to the analysis of ECGs. Compared to the previous sections, which covered an overview of various ECG conditions in an instructional manner, this section apply knowledge from those sections to develop an algorithmic approach aimed at helping students better interpret ECGs.

Firstly, we will go over fundamentals on how to approach ECGs, such as: measuring intervals, comparing findings with old ECGs, determining the rate and axis, and so on.

Then, the approach will be split into two major sections: an approach to the analysis of rhythm and conduction abnormalities on an ECG, followed by an approach to the analysis of structural and metabolic disorders on an ECG.

The logic behind the rhythm analysis section is as follows:

1. Students will learn how to identify the atrial rhythm. They will learn practical tips on how to find atrial waves (whether they be p waves, flutter waves, or fibrillatory waves) in a wide assortment of ECGs, including cases in which the p waves may be relatively hidden (i.e. SVTs or VTs, prolonged PR interval). They will then learn to identify the origin and examine the regularity of the atrial waves to get a sense of the atrial rhythm. They will also learn what to do in the case of no easily identifiable atrial rhythm.

2. Students will then learn how to identify atrioventricular conduction. This will include identifying the direction (i.e. anterograde versus retrograde) of the conduction, any degree of conduction delay or block, and evidence of other uncommon phenomena (such as accessory tracts, dual AV nodal physiology). They will also learn how to identify special cases where the AV junction is the origin of the heart's rhythm, such as in junctional escape rhythms or AVNRT.

3. Students will then learn how to identify the ventricular rhythm. This will involve examining the QRS and trying to identify whether ventricular activation occurs via a supraventricular source or a ventricular source. We will have a dedicated section on how to differentiate between SVT with aberrancy and VT, and what the pitfalls of this method are.

4. Students will then consolidate the information they gained from the above steps, and come up with a differential diagnosis of conditions that may cohesively explain the ECG rhythm, and identify the most likely cause. If needed, students will also learn how to use more complicated diagnostic manoeuvres (such as examining the initiation and termination of the rhythm, or by administering tests or medications that may elucidate the rhythm further, or by getting repeat ECGs) to try to clarify a diagnosis.

5. During this, students will also be exposed to common differential diagnoses pertaining to rhythm disorders, such as: an approach to irregular rhythms, an approach to tachycardia, and an approach to bradycardia.

The logic behind the structural and metabolic disorder analysis is as follows:

1. Examine the p wave (if present) to try and identify atrial enlargement or conduction defects, and practical manoeuvres (such as changing the gain and paper speed settings on an ECG machine) to further elucidate the p wave.

2. Examine the PR interval (if present) to try to identify evidence of atrial injury (i.e. pericarditis or infarction) or AV nodal injury (i.e. block).

3. Examine the QRS interval to understand whether there are changes to the structure or function of the ventricles by examining the height, width, axis, and morphology of the Q waves.

4. Examine the ST segment, first for evidence of pronounced J waves and then for ST deviation. The student is exposed to practical tips on how to thoroughly examine the ST interval to better understand the problem in the case of ST deviation. The student will also have an approach to lengthened or shortened ST segment (such as in the case of hypocalcemia or benign early repolarization, respectively).

5. Examine the T and U waves to try and identify any dynamic changes concerning for acute ischemia, or any changes consistent with other emergency conditions (such as peaked T waves with hyperkalemia).

6. Examine the QT interval to determine if there is any QT prolongation, and if so, the significance of this. 

7. Finally, students will consolidate the information from the previous steps to reach a cohesive diagnosis, with a list of differential diagnoses.

8. Students will understand that many of the findings are specific but not sensitivity for various diagnoses.

9. Additionally, during this, students will be exposed to common differential diagnoses pertaining to structural disorders, such as an approach to tall R waves in the early precordial leads or an approach to ST elevation.