The electrocardiogram during sinus rhythm and tachycardia in patients with Mahaim fibers: the importance of an "rS" pattern in lead III.
OBJECTIVE
The purpose of the study was to identify the electrocardiographic (ECG) characteristics of the Mahaim fiber.


BACKGROUND
Mahaim fibers are slowly conducting accessory pathways reaching into the right ventricle. They often play a role in tachycardias.


METHODS
We retrospectively analyzed 40 patients with Mahaim fibers. Five patients had associated Wolff-Parkinson-White syndrome and were excluded from the study. Two patients had a short atrioventricular decremental accessory pathway and were also excluded. The remaining 33 patients had a tachycardia with anterograde conduction over a Mahaim fiber. Twenty were female. Their mean age was 24 +/- 10 years.


RESULTS
The most common pattern of minimal preexcitation during sinus rhythm was an rS pattern in lead III. This was found in 20 patients. There was a match between the presence of rS in lead III during sinus rhythm and left axis deviation during tachycardia with anterograde conduction over the Mahaim fiber. After ablation, a different QRS pattern emerged in lead III, indicating the absence of conduction over the Mahaim fiber. To obtain information on the prevalence of an rS pattern in lead III in age-matched controls with palpitations and without structural heart disease, the 12-lead ECG of 200 young individuals were examined. An rS pattern in lead III was found in 6%.


CONCLUSIONS
A narrow QRS with an rS pattern in lead III during sinus rhythm in a patient with a history of palpitations should alert the physician to the possibility of a Mahaim fiber. During tachycardia, these patients typically show a left bundle branch block-like QRS complex with left axis deviation.
Biocor Instituto, rua Correias 281/301, Belo Horizonte, Minas Gerais, 30315-340 Brazil. eduardosternick@aol.com
Eduardo Back
EB
Sternick
Carl
C
Timmermans
Eduardo
E
Sosa
Fernando E S
FE
Cruz
Luz-Maria
LM
Rodriguez
M Arcio
MA
Fagundes
Luiz M
LM
Gerken
Hein J J
HJ
Wellens
D000293:Adolescent; D000328:Adult; D002036:Bundle of His / Q000503:physiopathology; D002037:Bundle-Branch Block / Q000151:congenital / Q000175:diagnosis / Q000503:physiopathology; D002648:Child; D003937:Diagnosis, Differential; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011227:Pre-Excitation, Mahaim-Type / Q000175:diagnosis* / Q000503:physiopathology; D011247:Pregnancy; D012016:Reference Values; D012189:Retrospective Studies; D012815:Signal Processing, Computer-Assisted; D013223:Statistics as Topic; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000151:congenital / Q000175:diagnosis / Q000503:physiopathology