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Left ventricular parallel conductance during cardiac cycle in children with congenital heart disease
P A White1, R R Chaturvedi, D Shore
1Department of Paediatric Cardiology, Royal Brompton Hospital, London, United Kingdom.
Insights
The conductance catheter technique accurately measures left ventricular volume in congenital heart disease. Parallel conductance (Vc) changes during the cardiac cycle are minimal and do not impact accuracy, even with shunts.
Area of Science:
- Cardiovascular Physiology
- Medical Imaging and Instrumentation
Background:
- The conductance catheter technique is crucial for assessing left ventricular volume.
- Accurate parallel conductance (Vc) measurement is vital for reliable volume calculations.
- Existing methods for Vc determination do not account for cardiac cycle variations.
Purpose of the Study:
- To evaluate the accuracy of the conductance catheter technique by analyzing parallel conductance (Vc) changes during the cardiac cycle in the human left ventricle.
- To assess the impact of left-to-right shunts (atrial septal defect and interventricular communication) on Vc measurements.
- To compare pre- and postoperative Vc data in patients with interventricular communication.
Main Methods:
- Assessed two patient groups: one with an open atrial septal defect and another with interventricular communication.
- Measured Vc changes over four cardiac cycles, dividing them into six isochrones based on left ventricular pressure derivatives (dP/dtmax and dP/dtmin).
- Regressed apparent ventricular volume against stroke volume to determine Vc at each time interval [Vc(t)].
Main Results:
- In patients with atrial septal defects, Vc(t) variations during systole were small (mean maximal variation of 2.60 ml), not significantly different from Vc at dP/dtmax or dP/dtmin.
- In patients with interventricular communication, mean Vc did not significantly change after defect closure.
- Cyclical Vc(t) variations and Vc as a percentage of end-diastolic volume were similar between groups and did not preclude accurate volume measurement.
Conclusions:
- The conductance catheter technique provides accurate left ventricular volume measurements in congenital heart disease, even with left-to-right shunts.
- Temporal changes in parallel conductance during ventricular ejection are small and insignificant.
- The magnitude of cyclical Vc changes does not compromise the reliability of the conductance catheter technique for volume assessment in this patient population.
Abstract:
This study examines the accuracy of the conductance catheter technique and, in particular, parallel conductance [expressed as offset volume (Vc)] changes during the cardiac cycle in the human left ventricle. Two groups of patients were assessed: group 1, with an open atrial septal defect, and group 2, with an interventricular communication. In a subgroup, pre- and postoperative data were compared to assess the possible impact of shunting or anatomic considerations on our measurements. Vc is normally obtained by a saline-dilution technique previously described by Baan et al. [Vc(Baan); J. Baan, E. T. Van der velde, H. G. Debruin, G. J. Smeenk, J. Koops, A. D. Van Dijk, D. Temmerman, P. J. Senden, and B. Buis. Circulation 70: 812-823, 1984]. This does not take into account potential changes during the cardiac cycle. Four cardiac cycles were taken from the hypertonic saline washin and were divided into six equal isochrones between the maximum and minimum first derivatives of left ventricular pressure (dP/dtmax and dP/dtmin, respectively). The apparent ventricular volume was regressed against stroke volume for the corresponding cardiac cycle. The volume at the gamma-intercept corresponds to the Vc at each time interval [Vc(t)]. In group 1, there was a variation in Vc(t) during systole, but the temporal changes were quite small, on the order of 4.28% (SD = 5.18%) of total corrected end-diastolic volume (mean maximal variation of 2.60 ml). Furthermore, the value of Vc obtained at dP/dtmax was not significantly different from that obtained at dP/dtmin. For group 2 as a whole, mean Vc(Baan) did not change significantly with ventricular septal defect closure (preoperative, 8.85 +/- 11.1 ml; postoperative, 9.82 +/- 11.84 ml). Group 2 children also exhibited a systolic cyclical variation in Vc(t) similar to group 1. Finally, Vc(t) as a percentage of end-diastolic volume was no different when group 1 and group 2 were compared. We conclude that in the left ventricle, even in the presence of a left-to-right shunt, there is a small but insignificant difference in parallel conductance during ventricular ejection. The magnitude of this cyclical change does not preclude ventricular volume measurement in congenital heart disease by the conductance catheter technique.