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Functional importance of the long axis dynamics of the human left ventricle
C J Jones1, L Raposo, D G Gibson
1Cardiac Department, Brompton Hospital, London.
Insights
Disturbances in left ventricular wall motion, specifically the timing of long and short axis shortening, are early indicators of systolic dysfunction. These changes in heart muscle fiber dynamics precede traditional measures of heart function.
Area of Science:
- Cardiology
- Biomedical Engineering
- Physiology
Background:
- Left ventricular (LV) wall motion is crucial for effective cardiac output.
- Understanding the interplay between longitudinal and circumferential fibers is key to diagnosing systolic dysfunction.
- Traditional measures of cardiac function may not detect early signs of disease.
Purpose of the Study:
- To examine the role of longitudinally and circumferentially oriented fibers in LV wall motion.
- To identify early indicators of systolic ventricular disease by analyzing the timing of LV long and short axis motion.
- To compare these motion dynamics in healthy individuals versus patients with various cardiac conditions.
Main Methods:
- Digitizing echocardiograms to analyze mitral ring (long axis) and standard minor axis motion.
- Assessing time relations between long and short axis shortening in 36 healthy individuals and 114 patients.
- Comparing epicardial and endocardial excursion timing.
Main Results:
- In healthy individuals, long axis shortening significantly preceded minor axis shortening.
- All patient groups showed disturbed time relations between long and short axis motion.
- These disturbances, including delayed long axis shortening and synchronous epicardial/endocardial changes, were observed even when traditional measures were normal.
Conclusions:
- Characteristic time relations between LV long and short axis motion in healthy individuals are lost in systolic ventricular disease.
- Loss of these relations is an early index of systolic dysfunction, preceding changes in fractional shortening.
- Observed disturbances are consistent with ischemic injury and indicate systolic dysfunction in various cardiac pathologies.
Abstract:
The role of longitudinally and circumferentially oriented fibres in left ventricular wall motion was examined by digitising echocardiograms of the mitral ring (whose motion reflects long axis change) and of the standard minor axis in 36 healthy individuals, 36 patients with coronary artery disease, 16 with left ventricular hypertrophy, 44 with mitral valve disease (24 of whom had undergone mitral valve replacement). In the controls long axis shortening significantly preceded minor axis shortening (mean (1 SD) difference 25 (40) ms) so that the minor axis increased more during isovolumic contraction (0.25 v 0.09 cm), indicating that the left ventricle became more spherical. Changes in the long and short axes were synchronous at end ejection and in early diastole in the controls. Epicardial excursion preceded endocardial excursion by 50 (20) ms at its peak. These time relations were consistently disturbed in all patient groups, irrespective of the extent of fractional shortening of the minor axis. The onset of long axis shortening was delayed, and this was often associated with premature shortening of the minor axis, the normal spherical shape change during isovolumic contraction was lost, and peak epicardial and endocardial changes became more synchronous. In patients with coronary disease these changes are the expected consequence of ischaemic injury to longitudinally orientated subendocardial fibres. In left ventricular hypertrophy their presence consistently showed systolic dysfunction when orthodox measures were still normal. They were more pronounced after mitral valve replacement when the papillary muscles had been sectioned; long axis shortening was reduced during systole and prolonged into early diastole, while normal shortening of the minor axis was maintained only by abnormal epicardial excursion. Relations between long and short axis motion in healthy individuals are characteristic, and their loss is an early index of systolic ventricular disease. These disturbances precede changes in orthodox measures such as fractional shortening or peak velocity of circumferential fibre shortening.