The inward rectifier current inhibitor PA‐6 terminates atrial fibrillation and does not cause ventricular arrhythmias in goat and dog models

Figures

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  Figure 1. AF termination during PA‐6 administration in goats with rapid pacing induced AF (n = 6). (A) Left atrial electrogram (a) and unipolar ventricular electrogram (v) recordings of goat #1 demonstrating AF and irregular ventricular rhythm (baseline), decrease in AF complexity (first minute of maintenance) and finally cardioversion resulting in SR (cardioversion). AFCL and fractionation index for each stage are indicated. (B) The end of each bar represents the moment of cardioversion. Baseline: 60 min of stabilization period after turning off the pacemaker and preceding the start of the PA‐6 infusion; Bolus: administration of 2.5 mg·kg−1 PA‐6 over 10 min; Maintenance: administration of 0.04 mg·kg−1·min−1 PA‐6 over the next 50 min; Washout: washout period after the end of PA‐6 infusion.

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  Figure 2. PA‐6 lengthens the AFCL. (A, B) Time course for AFCL in both atria during PA‐6 infusion until the moment of cardioversion to SR in two goats. CV, cardioversion to SR. (C) AFCL for the LA and RA, (D) relative change in AFCL, (E) p5 of the AFCL and (F) relative change of p5 of the AFCL. All parameters were calculated for the baseline, the first minute of maintenance period (maint. start) and the last minute preceding cardioversion. Data for n = 5 goats displaying cardioversion are shown. * P < 0.05, significantly different as indicated; #P<0.05, significantly different from corresponding value in LA.

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  Figure 3. PA‐6 decreases the complexity of atrial fibrillation for LA and RA. (A) Fibrillation patterns. Wave maps of three consecutive AF beats at baseline, at the first minute of maintenance and at the last minute preceding cardioversion (left panel) reconstructed based on the mapping data acquired with LA spoon electrode (Ø 4 cm, 247 electrodes, interelectrode distance 2.4 mm). Wave maps depict the total number of waves, origin of the waves (peripheral and breakthrough), wave size and wave order. The right panel depicts the calculation method of the unipolar fractionation indexes at one electrode for three different time points according to dominant activations. The fractionation index is calculated as the ratio between the number of dominant (green) and subsidiary (red) deflections. (B) Total number of waves per cycle, (C) number of epicardial breakthrough waves per cycle, (D) wave size expressed as mean number of electrodes assigned to one wave, (E) fractionation index (mean values of ratios of remote to local deflections per electrode) and (F) mean conduction velocity for each electrode. Data for n = 5 goats displaying cardioversion are depicted in panel B–F. * P < 0.05,…

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  Figure 4. Absence of pro‐arrhythmia upon PA‐6 application in cAVB dogs. (A) IK1 current–voltage relationships from isolated ventricular cAVB cardiomyocytes (n = 8) for control (closed circles) and 200 nM PA‐6 (open squares) treatment. Inset: enlargements of currents from −90 to −10 mV. (B) Electrocardiogram (leads II and AVR) displaying normal paced cAVB rhythm following PA‐6 (2.5 mg·kg−1·10 min−1) application. (C) Electrocardiogram (leads II and AVR) from the same animal as in panel A, showing TdP arrhythmia episode following dofetilide (25 μg·kg−1·5 min−1) application. (D) Quantification of TdP arrhythmias in nine cAVB animals tested serially with dofetilide and PA‐6 (in random order). Non‐filled: normal cAVB rhythm; checkered pattern: TdP arrhythmia inducible (three or more TdP arrhythmias). *P < 0.05, * P < 0.05, significantly different from PA‐6.

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  Figure 5. PA‐6 plasma concentrations in AF goats and cAVB dogs. (A) PA‐6 plasma concentrations (nM) in cardioverted AF goats (n = 5) following PA‐6 infusion (0–10 min bolus (2.5 mg·kg−1·10 min−1, dark grey bar), 10–60 min maintenance (0.04 mg·kg−1·min−1, light grey bar), 60–90 min (washout)). (B) PA‐6 plasma concentrations in SR (n = 2) and cAVB dogs (n = 2) following a low dose [0–10 min (0.5 mg·kg−1·10 min−1, light grey bar)] and a high dose (30–40 min 2.5 mg·kg−1·10 min−1, dark grey bar) bolus. Washout between 10–30 and 40–60 min respectively.

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  Figure 6. Absence of chronic QTc interval prolongation in cAVB dogs (n = 9) upon 16 days post‐infusion. ECG recordings were taken in awake animals during idioventricular rhythm (IVR) or right ventricular apex pacing at 1 Hz (RVA VVI60).

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  Figure 7. Effect of PA‐6 (200 nM) on inward rectifier K+ currents in human atrial cardiomyocytes. (A) Original recording of basal current with response to 2 μM carbachol (CCh; upper panel; IK,ACh was defined as CCh‐sensitive current) and response to 200 nM PA‐6 (lower panel). (B) Time course of IK1 and IK,ACh during two successive CCh applications (S1, S2, 4 min apart). During activation the initial increase (‘Peak’) of IK,ACh faded (‘rapid desensitization’) to a quasi‐steady‐state level (‘QSS’). PA‐6 (200 nM) was applied 1 min after the first CCh application (right panel) and compared with application of bath solution only (left panel; time‐matched controls, TMC). (C) Basal current and CCh‐activated IK,ACh at ‘Peak’ and ‘QSS’. (D, E) Effects of PA‐6 (200 nM) on basal current and on the S2/S1 ratio of IK,ACh at ‘Peak’ and ‘QSS’. Data are expressed as mean ± SEM. *P < 0.05, * P < 0.05, significantly different from time‐matched controls (TMC). Numbers indicate cardiomyocytes/patients.