Changes in Q-T and Q-aT intervals at rest and during exercise with different modes of cardiac pacing.
The influence of heart rate variation on the Q-T and Q-aT intervals (measured from the onset of the QRS to the end or the apex, respectively, of the T-wave) was studied both at rest and during exercise using different modes of pacing. The studies were made on 21 patients with high-degree atrioventricular block. In seven patients with programmable ventricular inhibited (VVI) pacemakers, an increase in pacing rate during rest produced significant shortening of both Q-T and Q-aT. During observations made at rest and during exercise in 14 patients with fixed rate VVI, atrial rate matched asynchronous (VVIm) or atrial triggered (VAT) pacing. Significant shortening of Q-T and Q-aT intervals occurred during exercise in all pacing modes, but was greatest with VVIm and VAT. The Q-T and Q-aT changes were almost parallel in all situations. For measurements made by two independent observers the coefficient of variation was lower for Q-aT than for Q-T (2.2 versus 2.5) and the correlation coefficient was higher (0.96 versus 0.93), indicating easier identification of Q-aT than of Q-T. This study indicated that changes in Q-T and in Q-aT are influenced by intrinsic factors in addition to the ventricular rate. Atrioventricular synchronization did not seem to influence these changes.
A
A
Hedman
R
R
Nordlander
S K
SK
Pehrsson
D000328:Adult; D000368:Aged; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004562:Electrocardiography; D005080:Exercise Test; D005260:Female; D006327:Heart Block / Q000628:therapy; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged