Contractile function assessment by intraventricular balloon alters the ability of regional ischaemia to evoke ventricular fibrillation

Abstract

Background and purpose: In drug research using the rat Langendorff heart preparation, it is possible to study left ventricular (LV) contractility using an intraventricular balloon (IVB), and arrhythmogenesis during coronary ligation-induced regional ischaemia. Assessing both concurrently would halve animal requirements. We aimed to test the validity of this approach.

Experimental approach: The electrocardiogram (ECG) and LV function (IVB) were recorded during regional ischaemia of different extents in a randomized and blinded study.

Key results: IVB-induced proarrhythmia was anticipated, but in hearts with an ischaemic zone (IZ) made deliberately small, an inflated IVB reduced ischaemia-induced ventricular fibrillation (VF) incidence as a trend. Repeating studies in hearts with large IZs revealed the effect to be significant. There were no changes in QT interval or other variables that might explain the effect. Insertion of an IVB that was minimally inflated had no effect on any variable compared with 'no IVB' controls. The antiarrhythmic effect of verapamil (a positive control drug) was unaffected by IVB inflation. Removal of an inflated (but not a non-inflated) IVB caused a release of lactate commensurate with reperfusion of an endocardial/subendocardial layer of IVB-induced ischaemia. This was confirmed by intracellular (31) phosphorus ((31) P) nuclear magnetic resonance (NMR) spectroscopy.

Conclusions and implications: IVB inflation does not inhibit VF suppression by a standard drug, but it has profound antiarrhythmic effects of its own, likely to be due to inflation-induced localized ischaemia. This means rhythm and contractility cannot be assessed concurrently by this approach, with implications for drug discovery and safety assessment.

Figure 1

One of the IVBs used in the present study shown uninflated (for insertion into the left ventricle), minimally inflated (0.01 mL), and inflated (0.12 mL) according to the definitions provided in the text.

Figure 2

Part A shows IZ sizes from the separate studies. Data expressed as mean ± SEM of group mean % values. There were no significant differences within each separate trio of values. Part B shows LV developed pressure at baseline (pre‐drug values). Data expressed as mean ± SEM. All groups are n = 12 hearts, except the two ‘Large IZ (Lactate Analysis)’ groups, which are both n = 5, *P < 0.05.

Figure 3

Occurrence (% incidence per group) of increasingly severe ventricular arrhythmias (VPB to VF) and five‐point summary arrhythmia score (mean ± SEM) during 120 min ischaemia in hearts with small IZs. There were n = 12 hearts in each group. *P < 0.05.

Figure 4

Occurrence (% incidence per group) of increasingly severe ventricular arrhythmias (VPB to VF) and five‐point summary arrhythmia score (mean ± SEM) during 120 min ischaemia in hearts with large IZs. There were n = 12 hearts in each group. *P < 0.05.

Figure 5

Occurrence (% incidence per group) of increasingly severe ventricular arrhythmias (VPB to VF) (part A) and five‐point summary arrhythmia score (mean ± SEM) (part B) during the first 10 min of ischaemia in hearts with small IZs. There were n = 12 hearts in each group. *P <0.05 (A); *P <0.05 versus No IVB (B).

Figure 6

Occurrence (% incidence per group) of increasingly severe ventricular arrhythmias (VPB to VF) and five‐point summary arrhythmia score (mean ± SEM) during 120 min ischaemia in hearts with large IZs + verapamil. There were n = 12 hearts in each group. *P < 0.05.

Figure 7

Heart rate (part A), coronary flow (part B), PR (part C) and QT₉₀ intervals (part D) (mean ± SEM) in hearts with small IZs. There were n = 12 hearts in each group. *P < 0.05 versus No IVB; †P < 0.05 versus IVB inflated.

Figure 8

Heart rate (part A), coronary flow (part B), PR (part C) and QT₉₀ intervals (part D) (mean ± SEM) in hearts with large IZs. There were n = 12 hearts in each group. *P < 0.05 versus No IVB ; †P < 0.05 versus IVB inflated.

Figure 9

Diastolic and developed LV pressures (mean ± SEM) from hearts with small (A–B) and large (C–D) IZs. There were n = 12 hearts in each group. *P < 0.05 versus IVB.

Figure 10

Changes in lactate release (mean ± SEM) in sequential 15 s coronary effluent samples taken at the intervals shown before (−1), during and after 30 min of ischaemia. There were n = 5 hearts per group. Only seven hearts (n = 2 or 3 per group) had measurements taken for +5 min owing to a temporary design oversight. *P < 0.05.

Figure 11

An example of ³¹P NMR spectra from an IVB inflated heart at baseline before ischaemia (A, top part) and after 25 min ischaemia (A, bottom part) showing the development of the split P_i peak. Group data (mean ± SEM), all n = 5 per group, show PCr to total P_i ratio (part B), β‐ATP (part C), intracellular pH (part D) P_i in the IZ (part E) and P_i in the UZ (part F). †P <0.05 for each IZ value versus each time‐matched UZ value; *P <0.05 versus No IVB.