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Published on: May 12, 2017
Full ventricular capture indicated by the QT interval function
C Gottfridsson1, I Wallentin, L Dernevik
1Department of Cardiology, University Hospital, Goäteborg, Sweden.
Insights
The study found that the bending point in QT interval measurements accurately predicts full ventricular capture and fusion in dual chamber pacing for hypertrophic obstructive cardiomyopathy patients. This suggests QT interval analysis may enable automatic capture detection.
Area of Science:
- Cardiology
- Electrophysiology
- Biomedical Engineering
Background:
- The atrioventricular (AV) interval is crucial in dual chamber (DDD) pacing for hypertrophic obstructive cardiomyopathy (HOCM) patients.
- Optimizing the AV interval ensures full ventricular capture (FVC), reduces left ventricular (LV) outflow gradients, and improves LV diastolic filling.
Purpose of the Study:
- To investigate the relationship between AV interval, QT interval, FVC, and fusion in DDD pacing.
- To determine if QT interval measurements can reliably identify optimal pacing parameters in HOCM.
Main Methods:
- 11 patients with cardiac conditions and stable AV conduction received DDD pacemakers with QT sensing capabilities.
- The AV interval was systematically shortened from 400 ms to 90 ms, and then lengthened at a faster pacing rate, while measuring QT intervals.
- Full ventricular capture (FVC) and fusion were assessed using surface ECG.
Main Results:
- Shortening the AV interval initially shortened the QT interval, then prolonged it until it stabilized at the FVC point.
- The "bending point" in the QT interval versus AV interval plot correlated well with FVC.
- Similar correlations were observed for fusion when lengthening the AV interval at an increased pacing rate.
Conclusions:
- The bending point in QT interval plots reliably indicates FVC and fusion during DDD pacing.
- QT interval measurement presents a feasible method for automatic discrimination between fusion and full capture in pacing.
Unlabelled:
The atrioventricular (AV) interval is critical in dual chamber (DDD) pacing in patients with hypertrophic obstructive cardiomyopathy (HOCM) to obtain full ventricular capture (FVC) with maximal reduction of the left ventricular (LV) outflow gradient and optimal LV diastolic filling. We studied the relationship of FVC, fusion, spontaneous AV conduction, and the QT interval.
Methods:
11 patients with various cardiac diseases and stable AV conduction received a QT sensing Diamond, Vitatron, DDD pacemaker. Software was downloaded into the pacemaker. In the DDD pacing mode, with the QT interval measured from the ventricular pacing stimulus to the end of the T wave, the AV interval was shortened from 400 ms, in 20-ms steps, to 90 ms. At 90 ms the stimulation rate was increased by 30 beats/min and the AV interval was increased stepwise. FVC and fusion was examined on the surface ECG.
Results:
At 400 ms interval, spontaneous AV conduction inhibited the pacemaker. Shortening the AV interval resulted in pacing with a short QT interval. Further reduction of the AV interval resulted in a longer QT interval up to a point where the QT interval became stable. This point, the bending point in the plot of measured QT interval versus shortened AV intervals, coincided with the point of FVC. The relation of the QT-AV interval plot and the point of fusion was comparable when lengthening the AV interval at a 30 beats/min faster stimulation rate.
Conclusion:
The bending point in the QT interval versus AV interval plots showed a good correlation with the FVC and fusion points observed on ECG. The results suggest that automatic discrimination between fusion and full capture using QT interval measurements may be feasible.
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