One of the inherent "beautiful aspects" of ECG interpretation is that so many rhythms can be equally applicable to the beginning, intermediate and advanced student. Adding to the challenge for many instructors is that the audience will often contain varying levels of ECG experience among those in attendance - so the instructor may need to speak on more than one level.

Dawn presented "the basics" of this rhythm strip - namely that there is marked sinus bradycardia and 1st degree AV block. If one's audience consisted primarily of less experienced interpreters - that might be as far as one goes (with notable ADDITION of the obvious variability in R-R interval that clearly satisfies a diagnosis of "sinus bradycardia and arrhythmia" ).

But IF more experienced providers were among your audience - there are number of additional important concepts that you might emphasize. These include:

• Sinus bradycardia VERY often will be at least somewhat irregular. The amount of R-R interval variation needing to satisfy the definition of "sinus arrhythmia" is at least 0.8-to-0.12 second - and the variability here is markedly more than this.
• Clinically - We NEED some history. I like to wait until my audience DEMANDS some history from me - since it is impossible to interpret this rhythm strip (and to know what to do clinically) without some history. Your audience ought to demand some history from you ... IF the patient is older than 60-70 (or so) - AND they are not on any rate-slowing medications (and no beta-blocking eye drops) - AND they are not hypothyroid and have not had recent infarction - then marked sinus bradycardia and arrhythmia like this is almost certain to indicate SSS (Sick Sinus Syndrome). We need to know if there has been "symptomatic bradycardia" - which is the accepted indication for permanent pacing for SSS.
• NOW - HOW MANY OF YOU noticed that the PR interval is NOT constant in this tracing? My caliper measurement suggests that the PR interval for beat #3 is a bit longer than the PR for other beats. Considering variation in PR interval that is not due to simple Wenckebach - AND marked sinus bradycardia and arrhythmia - I am suspicious that what we are seeing might be Vagotonic AV Block. Obviously there is not enough information to know for sure - but this entity should be considered IF: i) the clinical situation is consistent with increased vagal tone (ie, prolonged vomiting, bearing down, vasovagal syncope, invasive procedure, etc.); ii) there is marked bradycardia; iii) there is marked variation in the P-P interval and some variation in the PR interval from beat-to-beat; and iv) there is atypical AV block (which we don't truly see for sure here .... ). Full discussion of this fascinating entity is the subject of my ECG Blog #61.

Enough said!  There is a LOT of material on this tracing that one might explore depending on the interpretation experience of your audience.