ST-segment deviations during pacing-induced increased heart rate in patients without coronary artery disease.
BACKGROUND
In order to interpret ST-segment changes as an indicator of ischemia in patients with higher heart rates (HRs), the relation between ST-segment levels and HR needs to be well defined in subjects without coronary artery disease.


METHODS
Eighteen patients with normal ECGs in the catheterization laboratory, after radiofrequency ablation of AV nodal re-entry tachycardia or an accessory pathway were included. Computerized online vectorcardiography (VCG) was performed during step-wise atrial pacing-induced increases in HR up to 150 beats min(-1) (bpm). The ST-vector magnitude (ST-VM) and the relative ST change vector magnitude (STC-VM) were analysed at the J point, J + 20 and J + 60 ms.


RESULTS
There was no divergence in the course of ST-VM or STC-VM based on J point + 0, 20, or 60 ms during increasing HR. The STC-VM mean values increased progressively during increases in HR above 100 bpm, with an average increase in STC-VM of 15-20 microV per 10 bpm increases in HR. The ST-VM response during HR increases showed a heterogeneous and unpredictable pattern.


CONCLUSIONS
The STC-VM increases linearly with rising HRs above 100 bpm. The STC-VM can exceed widely recognized ischemic thresholds during higher HRs in the absence of ischemia. The choice of J point time to ST-VM measurements as tested here is not important for the STC-VM relation to HR at these HR levels. Further clinical testing is needed to improve the diagnostic specificity of STC-VM measurements during increased HRs.
Cardiothoracic Surgery, Heart Centre, University Hospital, Umeå, Sweden. soren.haggmark@vll.se
Sören
S
Häggmark
Michael F
MF
Haney
Steen M
SM
Jensen
Göran
G
Johansson
Ulf
U
Näslund
D000328:Adult; D001145:Arrhythmias, Cardiac / Q000175:diagnosis* / Q000503:physiopathology* / Q000628:therapy; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D003327:Coronary Disease / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D013223:Statistics as Topic; D014672:Vectorcardiography / Q000379:methods*