Right ventricular systolic function and ventricular interaction during acute embolisation of the left anterior descending coronary artery in sheep

OBJECTIVE

Regional LV ischemia involving the septum affects LV systolic function and geometry. We investigated the effects of these changes on RV function and geometry.

METHODS

In six closed-chest sheep end-systolic pressure-volume relationships (ESPVRs) were constructed from ventricular volumes, measured with magnetic resonance imaging (MRI) and matching intraventricular pressures, before and after selective embolisation of the left anterior descending coronary artery (LAD). The extent of myocardial ischemia was assessed post-mortem by coronary perfusion with Evans-Blue. Alterations in septal geometry were studied by measuring the curvature, segmental length and thickness of the septum in two midventricular (short-axis) MRI slices before and during ischemia. From these data, changes in LV and RV free wall segmental lengths were calculated.

RESULTS

Selective embolisation of the LAD resulted in left ventricular ischemia (15 +/- 2.1% of the total LV) with 23% of the septum involved. Stroke volume did not change significantly, while LV systolic pressure decreased by 24 mmHg (p < 0.05). Although RV systolic function decreased to a significantly lesser extent than LV function (p < 0.01), systolic function of both ventricles diminished significantly as indicated by substantial rightward shifts of the ESPVRs: 121% for LV and 41% for RV (both p < 0.01). At mid-ventricular level and end-systole, the septum showed significant increases in its radius of curvature and segmental length (both p < 0.05), and a significant wall thinning (p < 0.01). Calculated end-systolic lengths of LV and RV free walls also increased, by 57 and 14% respectively.

CONCLUSIONS

LAD embolisation not only results in a significantly diminished LV systolic function but also causes RV systolic function to decline significantly. Regional dysfunction by necessity entails global dysfunction as well. Analysis of ventricular geometry reveals that both the septum and the RV free wall increase their length, which plays an important role in the pathophysiology of diminished RV systolic function concomitant with reduced LV function.

Differential response of the right and left ventricle to beta-adrenergic stimulation: an echo planar MR study in intact animals

PURPOSE

The purpose of this study was to compare the response in contractility of the right (RV) and left (LV) ventricle of the heart to beta-adrenergic stimulation using an echo planar MR technique.

METHOD

In six sheep, RV and LV pressure-volume (P-V) relationships were constructed simultaneously using intraventricular pressures and volumes measured with echo planar MRI at rest and during dobutamine stress. Contractility changes were quantified by assessment of the end-systolic P-V relationship (ESPVR) and the preload recruitable stroke work (PRSW).

RESULTS

Both the ESPVR the the PRSW showed a significant increase in contractility for both ventricles after dobutamine administration. The increase in contractility was significantly larger for the LV than for the RV, both measured wit the ESPVR (p < 0.0003) and the PRSW (p < 0.007).

CONCLUSION

This study shows the usefulness of echo planar MRI to assess myocardial contractility of both ventricles simultaneously. Furthermore, the study shows that beta-adrenergic stimulation has a significantly greater positive inotropic effect on LV contractility than on RV contractility.

Development of an MRI-compatible catheter for pacing the heart: initial in vitro and in vivo results

An MRI-compatible catheter was developed for pacing the heart during MRI imaging. The device was tested in vitro and in vivo in 10 animal experiments, using spin-echo, gradient-echo, and echo-planar MRI sequences. Images were of good quality in all sequences. Pacing was effective without induced arrhythmias. Therefore, pacing the heart during MRI is feasible and seems to be safe when using dedicated hardware.

Role of calcium-activated neutral protease (calpain) in cell death in cultured neonatal rat cardiomyocytes during metabolic inhibition

Calcium-activated neutral protease (CANP), also known as calpain, has been implicated in the development of cell death in ischemic hearts. CANP is thought to be activated by the calcium overload that develops during ischemia. We studied the involvement of CANP in cell death in cultured neonatal rat cardiomyocytes during metabolic inhibition (5 mmol/L NaCN + 10 mmol/L 2-deoxyglucose). First, we isolated CANP using ion exchange and affinity chromatography. Then the efficacy of the CANP inhibitors calpain I inhibitor, leupeptin, and E64 to inhibit isolated CANP activity was tested with the use of fluorescently labeled beta-casein as a substrate. The IC50 for the inhibitors was between 2.1 and 56 mumol/L. Uptake of the inhibitors by intact cells was assessed with the use of 99mTc-radiolabeled inhibitors. The calculated intracellular inhibitor concentrations were sufficiently high to yield substantial inhibition of intracellular CANP activity. Intracellular CANP activity was measured directly with the use of the cell-permeant fluorogenic CANP-specific substrate N-succinyl-Leu-Leu-Val-Tyr-7-amido-4-methyl-coumarin. During metabolic inhibition, intracellular CANP activity was increased compared with control incubation. The time course of CANP activation was compatible with that of the rise in [Ca2+]i, as measured by fura 2 and digital imaging fluorescence microscopy. Calpain I inhibitor and leupeptin inhibited intracellular CANP activity both during metabolic inhibition and control incubation, whereas E64 did not. Despite their substantial inhibition of intracellular CANP activity, calpain I inhibitor and leupeptin did not attenuate cell death during metabolic inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)