Cardiac electrophysiology fellow with an interest in the familial, words, and the history of electrophysiology.
Some more ECGs of the patient mentioned in the previous post. Do they help give us the diagnosis?
Thanks to Jason Roediger for sending this one in – I think it is fascinating.
What is the cause of long and short PR intervals in this tracing?
Leading to a low amplitude signal in lead II. One to burn into the neurones...
But the diagnosis is certain...
Update: To Dr Sharma, correct. This is VT with clear AV dissociation in V1. It is not a typical pattern of RBBB, and therefore is unlikely to be fascicular (idiopathic) VT.
We've talked before about localising accessory pathways by the characteristics of the delta wave. The question for today: can a concealed accessory pathway be localized using the surface ECG?
Here are two ECGs, one during sinus rhythm, the other during tachycardia. The differential diagnosis for the SVT is not broad. I can think of two possibilities. However, I know from an EPS study that this is a SVT using a concealed bypass tract.
What is the other possibility?
If this is an SVT using a concealed bypass tract, where is the bypass tract located?
Update: So, as mcg points out (comments) this tracing is suggestive of a left lateral accessory pathway. The differential diagnosis is atrial tachycardia, and the two cannot be differentiated on the surface ECG unless there is wobble in the tachycardia cycle length, which there is not in this case.
It is presumably concealed, but left lateral pathways with some antegrade conduction can have minimal preexcitation on the surface ECG due to delayed conduction to the atrial insertion. In this case we paced the CS catheter close to the atrial insertion without demonstrating preexcitation.
Unfortunately the tachycardia could not be induced in the laboratory. Here are the baseline recordings – 12 lead ECG, and His bundle electrogram.
The diagnosis was made however with pacing manoeuvres in sinus rhythm.
Considering the differential diagnosis mentioned in the comments on the post previous, what pacing manoeuvres could be used in sinus rhythm to make a diagnosis?
22 yo Male with a history of palpitations for 2 years.
What abnormalities do you note on the baseline ECG?
What is the differential diagnosis of the tachycardia?
EGMs will follow.
Thanks to Eraldo de Moraes for contributing this case! (If any other readers have a case I'm more than happy to put it up – it only needs to be interesting).
And for the bonus question: what treatment has this patient received?
From the boss:
"When you're searching for a needle in 12 haysticks, where do you look first? The smallest haystack."
The best advice is obvious – especially when you are practiced in ignoring the obvious.
The most common form of limb lead reversal is a switch of right arm electrode with left arm electrode. This form is quickly identified by inspection of aVR where the usual pattern of negativity (p, qrs, and t wave) is replaced by positivity. But how to quickly identify limb lead reversal where left leg and left arm are reversed? The right arm electrode is in its usual place, therefore aVR reads negative; aVL and aVF remain positive.
The trick lies in inspecting the p wave throughout the limb leads. Concordant p waves are the rule; rarely with ectopic atrial foci or tachycardia this may not be the case, but let's put that aside for the moment. In sinus rhythm the p waves should be positive in all limb leads. If one or two of the leads have a negative p wave then something is wrong with the electrode placement. (With right arm, left arm switch, lead I will have a negative p wave; with left arm, left leg switch, lead III will have a negative p wave).
So which form of limb lead reversal is present in the ECG below? (Thanks to Chris Nickson at lifeinthefastlane.com for the ECG).
1. Limb Lead Reversal
2. Limb lead Reversal Reversed!
Of course, all is not lost when the patient has departed and the ECG is already taken. When you are certain which electrodes are switched, the ECG can be reconstructed (see picture 2) by an understanding of Einthoven's triangle – nice explanation of this at Christopher Watford's blog. Now that makes more sense!
When p waves are not visible, it becomes more difficult to spot limb lead reversal e.g. WCT. My method is to look at leads which are close by and see if they are recording roughly similar complexes. For example, aVF should not be so different from lead II or III. In this case however, this method may mislead as aVF and III do look similiar as there is lateral TWI present. The p wave in III is also biphasic, but predominantly negative where it is definitely positive everywhere else; and that is the vital clue.
First question: how do you explain the pattern of AV block in this atrial flutter?
Hint: 5:2 AV block. See picture 2 for the answer.
