Leads I, II and III
Leads aVR, aVL and aVF
Leads V1, V2 and V3
Leads V3, V4, V6
Features suggestive of WPW syndrome: Short PR interval and delta waves. In lead I delta wave is almost isoelectric and pre-excitation can be missed. Delta waves and QRS complexes are negative in aVR and aVL, while it is positive in all other leads. Since there is left atrial enlargement in this ECG belonging to a novagenarian, there is every chance of development of atrial fibrillation.
Pathway localisation: Left lateral pathway as there is a negative delta in aVL and V1-V6 positive (courtesy Dr. KKN Namboodiri).
Update: Repeat ECG after three days showing disappearance of pre-excitation
No pre-excitation is seen in this repeat ECG, meaning that there is no conduction through the accessory pathway. Initial deflection in Lead 1/aVL are positive, R/S in V1 is less than 1. (Two most sensitive indicators of anterograde conduction through left lateral pathway).
With all other factors constant, this can happen due to three things: (1) Block at accessory pathway, (2) Interatrial conduction delay (notched P in lead 1), or (3) Accelerated conductiion through AV node; akin to the disappearance of accessory pathway conduction with stress test. The last one is not applicable here.
The initial two cannot be differentiated in surface ECG. Of course some soft pointers may give some clue: 1. APC from left atrium results in pre-excitation – second factor is negated. 2. Evidence of notched P has been suggested as an evidence of interatrial conduction delay / delay at Bachman Bundle / spike and dome P wave classically described with left upper pulmonary vein (LUPV) focus (till last decade it was put as left atrial (LA) rhythm- but this pattern is seen only when the rhythm is from lateral LA and RA activation).
Two more points of relevance: Left lateral pathways are well known to have no pre-exciation on surface ECG due to some of these reasons and may manifest with atrial pacing only (Latent pre-excitation).
(courtesy Dr. KKN Namboodiri)