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Effects of incoordination on left ventricular force-velocity relation in aortic stenosis
X Y Jin1, J R Pepper, D G Gibson
1Cardiac Department, Royal Brompton Hospital, London.
Objective:
Tension development is often incoordinate in the hypertrophic left ventricle (LV). The present study aimed to elucidate the possible effects of incoordination on standard LV force-velocity relations in patients with aortic stenosis (AS).
Design:
Prospective study during aortic valve replacement with transoesophageal cross sectionally guided M mode echocardiogram, combined with high-fidelity LV pressure recorded by pressure transducer tip catheter, and thermodilution cardiac output.
Setting:
Tertiary cardiac referral centre.
Patients:
37 patients (mean (SD) age 63 (12)) years were studied before and 20 hours after aortic valve replacement.
Main Outcome Measures:
LV function was assessed regionally by peak velocity of circumferential fibre shortening (peak Vcf), mean systolic wall stress, and peak myocardial power; and globally by LV stroke work index. LV coordination was quantified as cycle efficiency, derived from LV pressure-dimension loop (lower normal limit > or = 76%).
Results:
22 patients with a coordinate LV had significantly higher peak Vcf (1.85 (0.47) v 1.46 (0.64) s-1) peak myocardial power (20.8 (8.5) v 12.0 (6.1) mW.cm-3) and global stroke work index (440 (155) v 325 (150) mJ.m-2) than those of 15 patients with an incoordinate ventricle, all P < 0.05; though there was no significant difference in LV end diastolic dimension, mean systolic wall stress, LV mass index, or the incidence of coronary artery disease (P > 0.05, respectively). Furthermore, when contraction was coordinate, mean systolic circumferential wall stress correlated inversely with peak Vcf (r = - 0.71) and positively with peak myocardial power (r = 0.83), both P < 0.01. When contraction was incoordinate, these correlations did not apply; instead peak Vcf (r = 0.65) and peak myocardial power (r = 0.73) both correlated positively with cycle efficiency (P < 0.02 and 0.01, respectively). By 20 hours after surgery, values of cycle efficiency, peak Vcf, and myocardial power were indistinguishable in the previously coordinate and incoordinate groups.
Conclusions:
In aortic stenosis, incoordination causes a fall in LV peak Vcf proportional to the increase in systolic wall stress, and thus modifies the standard LV force-velocity relation to mimic depressed contractility. However, incoordination and subsequent ventricular dysfunction were largely reversible once the aortic stenosis had been relieved.