Attenuation of stretch-induced arrhythmias following chemical ablation of Purkinje fibres, in isolated rabbit hearts

Figures

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  FIGURE 1. Stretch-induced ectopics are attenuated by Lugol. Records from 2 Langendorff perfused rabbit hearts in sinus rhythm (A,B). Schematic of change in balloon volume (upper traces) and pseudo-ECG (lower traces). The red arrows indicates the start of a left ventricular (LV) indwelling balloon inflation from 0.2 mL to 0.9 mL to dilate/stretch the LV. Records prior to Lugol treatment (left, Tyrode) and following LV lumen irrigation with 0.5 mL Lugol, over a 10 s period, followed by Tyrode irrigation (right, Lugol). In both hearts, prior to Lugol, dilation provoked mechanically-activated ectopics; following Lugol these ectopics were abolished.

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  FIGURE 2. Lugol decreases the number and duration of stretch-induced ectopics. Number of ectopics (A) and duration of ectopics (B) for paired stretches before (Tyrode) and after (Lugol) exposure to Lugol. After exposure to Lugol, a significant reduction in the number and duration of mechanically-activated ectopics was recorded (red bar). Data from 20 paired stretches from 7 hearts, Wilcoxon signed ranks test for ectopic number and paired Student’s t-test for duration. With either n = 20 stretches or n = 7 hearts (Tyrode vs. Lugol, p < 0.05), symbols may represent more than 1 pair of data. Frequency histograms for ectopic number (C) and duration (D), a leftwards shift in both parameters is visible after exposure to Lugol, 24 stretches from 8 hearts in Tyrode and 20 stretches from 7 hearts for Lugol.

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  FIGURE 3. Location of necrotic tissue on the left ventricular endocardial surface following exposure to Lugol. The left ventricular (LV) lumen of isolated Langendorff perfused rabbit hearts were exposed to 0.5 mL Lugol (120 mM KI, 38.6 mM I2) solution for 10 s, followed by a Tyrode wash. Hearts were stained with TTC and fixed in 10% formalin prior to imaging. (A) LV, with incision through the free wall. The Purkinje fibre network stains as a white meshwork indicating necrosis. The endocardial surface shows a thin layer of necrosis that is not universal, while the LV bulk myocardium is unaffected (green asterick). Prominent, ablated Purkinje fibres are visible (yellow asterick). (B) Absence of necrotic tissue on the untreated RV endocardial surface from the same heart, with Purkinje fibres staining as healthy tissue (blue asterick). (C,D) Magnified view of the area indicated by dashed box in (A,B) respectively. Individual Purkinje fibres are necrotic after exposure to Lugol (C; yellow asterick), but intact within the RV (D; blue asterick) in the absence of Lugol. Scale bars, (A–D): 2 mm.

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  FIGURE 4. Epicardial activation from sinus stimulation spreads faster than from endomyocardial stimulation. Optical mapping of left ventricular (LV) epicardial activation in response to (A) sinus stimulation or (B) focal endomyocardial stimulation near the LV base. Images show colour coded 4 ms contours. Images are 80 × 80 pixels in 26 mm squares. In response to sinus stimulation, which involves conduction through the Purkinje network, early activation occurs at the base and apex and there is a rapid spread of activation. In contrast focal endomyocardial stimulation results in a small basal area of initial activation that spreads slowly to the apex. Thus, the activation pattern gives information about the stimulation source. Lower traces show sections from the pseudo-ECG; P wave and QRS in sinus and stimulus artefact (Stim) and QRS in endomyocardial stimulation. Consistent with the slower epicardial activation, QRS is longer following endomyocardial stimulation.

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  FIGURE 5. Stretch-induced ectopic activation mimics sinus and focal stimulation. Pseudo-ECG (upper trace), optically measured action potentials (middle trace) and epicardial activation maps, as described in Figure 4 (lower images), in the left ventricle (LV) of 2 Langendorff perfused rabbit hearts (A, B). (A) at the red arrow the LV is dilated from 0.2 mL to 0.9 mL by inflation of an indwelling balloon over a 2 s period, triggering ectopics. Activation maps from selected points 1–5 show sinus stimulations at 1, 2 and 5 with broad basal and apical early activation and typical rapid activation spread. Excitations 3 and 4 are ectopic. Activation 3 falls upon the t-wave of the preceding sinus beat but this does not trigger sustained arrhythmias, the activation pattern closely resembles that of sinus stimulation. There is some slowing of lateral conduction, possibly explained by the short preceding diastolic period. Excitation 4 has 2 focal-like early activation sites, in the base and laterally, and conduction is slower than the other 4 excitations. (B) at the red arrow the LV is dilated from 0.2 mL to 0.9 mL by inflation of an indwelling balloon over a 2 s period, triggering ectopics. A…

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  FIGURE 6. In silico simulation of epicardial activation in response to ectopic foci. Hearts are orientated with apex to the top to match experimental images. Epicardial activation is colour-coded as in the optical studies (Figures 4, 5). (A) Left, closest match to sinus stimulation (deep foci, PF origin 40% to base). Centre, match to basal endomyocardial stimulation (superficial foci, myocardial origin, 80% to base). Right, basal myocardial stimulation from a ‘PF-free’ region (deep foci, myocardial origin, 80% to base). There is close similarity between the characteristics of the activation patterns predicted by sinus and endomyocardial stimulation and those optically recorded (see Figure 5). Sinus stimulation leads to broader initial breakthrough and a faster spread of activation. Note that endomyocardial stimulation that does not include PF propagation results in activation slower than that seen in Figure 4B. (B–D) Epicardial activation in response to ectopic foci (arising, for example from mechanical stimulation) in the LV anterior (Ant), posterior (Post) and free wall (Free) at 40% and 60% distance to the LV base. (B) foci with an endocardial PF origin, (C) Foci with an endomyocardial…

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  FIGURE 7. In silico simulation of the spread of activation in the myocardium and Purkinje fibre network. (A–D) 1 ms sequential frames representing an area of myocardium and associated Purkinje network (dark blue strands in A). (A) Myocardium, only, within a 2 mm cubic region is activated (pink/red) and the depolarisation spreads outwards through (B) to (D). (B, C) Some Purkinje fibres within the depolarised region become activated retrogradely and conduction through these fibres propagates. (D) Faster conduction in the Purkinje fibres results in Purkinje-mediated propagation outpacing that from the myocardium. See Supplementary Figure S3 for a video of this effect in the full model.