Blockade of sodium‑calcium exchanger via ORM-10962 attenuates cardiac alternans

Figures

• 

  Fig. 1. Alternans attenuation via ORM-10962. A) Example of APD alternans at two levels (APD25 and APD80) in control condition and following ORM-10962 exposure in muscle preparations. B) APD25 alternans at a range of pacing rates (n = 13). C) APD80 alternans at a range of pacing rates (n = 13). In B,C, paired t-test was used to compute the p-values. D) Example of reduction in CaT alternans in isolated cells via ORM-10962. E) Quantitative summary of CaT alternans (expressed as the ratio between the amplitude of the larger versus smaller CaT) without (n = 6) and with (n = 6) ORM-10962. Unpaired rank-sum test was used in E given different variance between control and ORM-10962.

• 

  Fig. 2. Distinct patterns of alternans at two repolarization levels. A-C) Examples of '++', '+−', and '+0' types of alternans respectively (i.e., shortening plateau corresponds to prolonged, shortened, or unchanged APD at 80% level of repolarization). The three recordings shown were obtained at bcls of 250, 190, and 190 ms respectively. D) Correlation of the difference in consecutive APDs at repolarization levels of 25% and 80%; all tested bcls were pooled together in this plot. E) Composition of the three alternans types in the control condition and following ORM-10962 treatment. The lower total number of entries following ORM-10962 stems from alternans attenuation by the compound: a recording has to manifest alternans of at least 3 ms at the APD25 level in order to be classified as one of the three types. F) A transition matrix encoding the change in alternans type upon ORM-10962 application. Each matrix element colour-codes the number of preparations manifesting a given type of alternans in the control condition (y-axis) that transitioned into a given type of alternans after ORM-10962 application (x-axis).

• 

  Fig. 3. ORM-10962 and restitution properties. A) Restitution curves measured before and after application of ORM-10962 to canine tissue samples (n = 8). Thick lines give the median S2 APD (computed where at least 3 data points are available for the given diastolic interval). B) Paired measurements of maximum slope of the restitution curve before and after ORM-10962; the overlay gives mean ± SD. C) Longest diastolic interval before which the slope of restitution curve is greater than 1; the overlay gives mean ± SD.

• 

  Fig. 4. Simulations of alternans and ORM-10962. A) The longest basic cycle length at which was alternans detected in control condition and several combinations of NCX and ICaL availability representing simulated ORM-10962 (NA = not available = no alternans). See Appendix C for a full frequency-alternans relationship at all the studied conditions. B) Calcium transient at 1000 ms bcl pacing. C) Calcium concentration in the network SR at 1000 ms bcl pacing. D) Calcium concentration in the junctional SR at 280 ms bcl pacing. E) A breakdown of the effect of five treatments simulating ORM-10962 (50% NCX availability and the five listed availabilities of ICaL) compared to the baseline model using a population of models approach. For each of 684 tested models in the population and for each treatment, a simulation was classified as ‘alternans attenuated’ if the treatment shifted alternans onset to shorter basic cycle length, ‘alternans promoted’ if alternans onset was shifted to longer basic cycle lengths, and ‘alternans maintained’ if alternans first appeared at the same basic cycle length. See Appendix D for a breakdown of how much was alternans promoted or attenuated in each condition.

• 

  Fig. 5. Simulations of heart failure remodelling and alternans. A) Action potential in control and heart failure (HF) condition at 1 Hz pacing, showing APD prolongation and loss of notch following the peak in HF. B) Calcium transient in control and HF, showing its prolongation, prolonged time to peak, and reduced amplitude. The calcium transient was normalised between 0 and 1 to facilitate comparison: first, the minimum was subtracted from both calcium transients; second, both calcium transients were divided by the maximum of the control trace, preserving the ratio of amplitude between control and HF. C) Calcium concentration in the network SR showing reduced SR loading in HF. D) Simulation of the effect of heart failure (HF) remodelling and HF + ORM-10962 treatment (50% NCX + 65% ICaL) on alternans development. For each model, the minimum and maximum APD90 achieved over two subsequent beats at the given basic cycle length is given, with bifurcations indicating alternans. Small-amplitude alternans in the HF condition developed already at bcl of 330 ms.

• 

  Fig. 6. ORM-10962 extends PRR. A) Experimental data from papillary muscle preparations of the shortest DI which led to formation of an action potential in the S1-S2 protocol (n = 6). B) Simulations of S1-S2 protocol under NCX block and ICaL reduction. The leftmost point on each curve determines the PRR in the given condition. C) Simulations of S1-S2 protocol where the S1 phase was carried out using control model without any perturbation of NCX and ICaL, with the ICaL reduction being introduced only for the S2 beat.