CARDIAC SESSION
QRS: it's NOT complex !
Part 3
ECG Strips Analysis
by Dr. Dan Ohad
The following 3 strips (A through C) were recorded
from a large, 9 year old mixed breed male dog with a
chronic organic heart disease, with resultant progressive
atrial enlargement. Strip B was recorded 3 months
following Strip A, and Strip C was recorded 2 years later.
All 3 strips were recorded in Lead II at 25mm/sec
(10mm=1mV).
What is your diagnosis for each strip?
Also, we encourage you to send us any cardiac cases with which
you need consultation: ECGs, radiographs, echograms,
historical and physical examination findings are welcome.
Cases of teaching value will be publicly discussed in this web
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About the Author
Dr. Dan Ohad
DVM - Koret School,
Hebrew University.
PhD - Hebrew
University in applied
cardiac
electrophysiology
Diplomate ACVIM
Specialty of
Cardiology
Hints
Hint for Strip B:
There is an Atrial Premature Complex (APC) (labeled as "1"), seen as a seemingly "non-conducted" P w
after the 5th QRS complex from the left. It is followed by another (seemingly "conducted") APC tha
labeled as "2". In fact, the first P-wave ("1") is the one that is responsible for the following QRS complex
contrast, the second premature P-wave ("2") found the AV-node still totally refractory, and therefore co
not result in the following QRS. There is then a normal sinus beat ("3"), another APC ("4") that is follow
by a normal sinus beat ("5"), and finally a run of "Paroxysmal Atrial Tachycardia". It is defined
"paroxysmal" because its onset is sudden (right after the sinus beat labeled "5"), rather than gradual. Thi
atypical of rhythms originating in the SA-node (such as sinus tachycardia), and is very typical of an ecto
rhythm such as would originate in an atrial focus, away from the SA-node.
This atrial ectopic activity prompted a therapeutic decision of using a Digitalis glycoside.
Hint for Strip C:
Note the absence of P-waves and the presence of flutter waves on the baseline (labeled as "f" waves). Th
are regularly spaced (as opposed to fibrillation waves that would have been highly irregular, appearin
unpredictable and chaotic and usually much shorter time-intervals). Although the ventricular (Q
complexes seem irregular and unpredictable, as one would expect in atrial fibrillation, the R-to-R interva
actually always an exact multiplication (in this case between 2 to 9 times) of the basic f-to-f interval.
overall heart rate is within normal limits (rather than a typically fast ventricular rate during untreated a
fibrillation or flutter) due to the chronic therapeutic control through Digitalis.
Diagnoses

Arrhythmia.
Strip A: Normal Respiratory Sinus