Proarrhythmogenic Effect of the L532P and N588K KCNH2 Mutations in the Human Heart Using a 3D Electrophysiological Model

Aulia Khamas Heikhmakhtiar; Abebe Tekle Abrha; Da Un Jeong; Ki Moo Lim

doi:10.3346/jkms.2020.35.e238

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Heikhmakhtiar, Abrha, Jeong, and Lim: Proarrhythmogenic Effect of the L532P and N588K KCNH2 Mutations in the Human Heart Using a 3D Electrophysiological Model

Original Article

Biomedical Engineering

Journal of Korean Medical Science 2020; 35(29): e238.

Published online: 26 June 2020

DOI: https://doi.org/10.3346/jkms.2020.35.e238

Proarrhythmogenic Effect of the L532P and N588K KCNH2 Mutations in the Human Heart Using a 3D Electrophysiological Model

Aulia Khamas Heikhmakhtiar^1,²

, Abebe Tekle Abrha³

, Da Un Jeong³

, Ki Moo Lim³

¹School of Computing, Telkom University, Bandung, Jawa Barat, Indonesia.

²Research Center of Human Centric Engineering (HUMIC), Telkom University, Bandung, Jawa Barat, Indonesia.

³Department of IT Convergence Engineering, Kumoh National Institute of Technology, Gumi, Korea.

Address for Correspondence: Ki Moo Lim, PhD. Department of IT Convergence Engineering, Kumoh National Institute of Technology, 61 Daehak-ro, Gumi 39177, Republic of Korea. kmlim@kumoh.ac.kr

Received 2 January 2020 Accepted 1 June 2020

The Korean Academy of Medical Sciences

(open-access, https://creativecommons.org/licenses/by-nc/4.0/):

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Atrial arrhythmia is a cardiac disorder caused by abnormal electrical signaling and transmission, which can result in atrial fibrillation and eventual death. Genetic defects in ion channels can cause myocardial repolarization disorders. Arrhythmia-associated gene mutations, including KCNH2 gene mutations, which are one of the most common genetic disorders, have been reported. This mutation causes abnormal QT intervals by a gain of function in the rapid delayed rectifier potassium channel (I_Kr). In this study, we demonstrated that mutations in the KCNH2 gene cause atrial arrhythmia.

Methods

The N588K and L532P mutations were induced in the Courtemanche-Ramirez-Nattel (CRN) cell model, which was subjected to two-dimensional and three-dimensional simulations to compare the electrical conduction patterns of the wild-type and mutant-type genes.

Results

In contrast to the early self-termination of the wild-type conduction waveforms, the conduction waveform of the mutant-type retained the reentrant wave (N588K) and caused a spiral break-up, resulting in irregular wave generation (L532P).

Conclusion

The present study confirmed that the KCNH2 gene mutation increases the vulnerability of the atrial tissue for arrhythmia.

Graphical Abstract

Keywords: KCNH2 Gene Mutation, L532P Mutation, N588K Mutation, Three-dimensional Heart Modeling

INTRODUCTION

Heart failure has been a major cause of death worldwide for the past few decades. Arrhythmia, one of the causes of heart failure, is characterized by an abnormal rhythm of the heartbeat and is caused by dyssynchronous ion exchange or current in myocardial cells resulting from genetic mutations in protein channels.1 2 Prolonged persistence of arrhythmia can alter the excitation and contraction sequences to cause fibrillation3 and even death because blood cannot be ejected effectively.4 5 Short QT syndrome is one cause subject to arrhythmia due to genetic mutation in the ionic channel.

Short QT syndrome is described by the time interval of Q to T wave of the electrocardiogram (ECG) is less than 300 msec.6 The first identification of short QT syndrome was described by Gussak et al.7 The short QT syndrome increased arrhythmia generation because it shortened the refractory period, which prone to reentry resulting in chaotic electrical activity in the heart. Giustetto et al.8 stated that short QT syndrome is a rare condition because of a limited number of patients reported in published data, however, may play a role in sudden infant death. N588K KCNH2 is the first protein with a genetic mutation to be discovered in patients with short QT syndrome.6 9 In 2011, Zhang et al.10 performed an experimental study of L532P KCNH2 mutation which associates with short QT as the comparative subject with N588K mutation.

The KCNH2 mutation affects the alpha-subunit of the rapid delayed rectifier potassium channel (I_Kr) that plays a role in repolarization (Fig. 1A).6 11 12 This gene can regulate changes in voltage activation in the heart and nervous tissue and is known to fasten cardiac repolarization by a gain of function and associated with short QT syndrome. N588K and L532P—the genetic mutations of KCNH2—are known to induce atrial arrhythmia. N588K is a fibril-related gain-of-function mutation in which the negatively charged asparagine (N) of residue N588 at the outer entrance of the KCNH2 channel subunit (S5) is replaced with the positively charged lysine (K) (Fig. 1B).9 In the L532P mutation, the leucine (L) of residue L532 located in the voltage sensor (S4) of the KCNH2 channel is replaced with proline (P) (Fig. 1B).13 L532P mutation is located in a different segment from the N588K in the KCNH2 and exhibited Kinect difference due to complex temperature dependency. Changes in the KCNH2 ion channel due to these mutations cause sudden cardiac death, resulting in abnormal QT intervals on the ECG.14 Therefore, it is essential to understand their association with cardiac arrhythmia through experiments related to KCNH2 ion channels.

Fig. 1

CRN cell model diagram (A), N588K and L532P mutations in the S5 sub-unit of the I_Kr channel and in the S4 voltage sensor, respectively (B).

CRN = Courtemanche-Ramirez-Nattel.

The experimental measurement of KCNH2 ion channels is time-intensive and expensive. Hence, researchers have observed the effects of a few mutations on the action potential duration (APD) and the propagation signal in a simulation study using advanced cardiac electrophysiology in three-dimensional (3D) heart models. In 2012, Adeniran et al.15 performed a simulation to study the effect of the D172N mutation on the APD, ECG, and the electrical propagation signal in 3D ventricles. In 2014 and 2016, our group studied the relation of two mutations (V241F and G229D) with atrial arrhythmia using methods similar to those used by Adeniran et al.16 17 In previous studies, simulations of the KCNH2 mutations—N588K and L532P—have been limited to a single cell model and a two-dimensional (2D) tissue model. Thus, quantification of the electric conduction patterns in the 3D heart geometry is limited. Therefore, in this study, we enhanced the observation of atrial conduction patterns due to KCNH2 ion channel mutation by applying the L532P and N588K mutations to the 3D atrium model as well. We hypothesize that L532P mutation plays a role in atrial fibrillation (AF) generation due to the significant shortening of APD by the mutation.

To simulate the AF conditions, we used Courtemanche-Ramirez-Nattel (CRN) electrophysiological model to simulate the WT, L532P, and N588K mutation conditions. The experimental values for the I_Kr mutation measured in previous studies were applied to the CRN cell model, and N588K and L532P mutation. The proarrhythmic effect of the KCNH2 ion channel variation was analyzed by comparing the differences in the APD, current density of I_Kr, wavelength, electrical activation in 2D and 3D geometry, and a vulnerable window between the wildtype (WT) and mutated (MT) genes.

METHODS

To numerically simulate the electrical excitation of the cell, a model of cellular voltage change caused by the flux of ions (Na⁺, K⁺, Ca²⁺, Cl^-) in and out of the cell is required. Electrical equilibrium (Hodgkin and Huxley18) is used to describe the changes in intracellular voltage when the bio-electrons entering the cell are injected into or out of the cell.

(1)

C_{m} \frac{d V_{m}}{d t} = - (I_{i o n} + I_{s t i m})

In (1), C_m is cell membrane capacitance per unit cell and V_m is cell voltage. I_ion is the total bio-ion current flowing into the cell, and I_stim is the amount of perturbation current flowing in and out of the cell to induce excitation of the cell. I_ion varies slightly depending on the cell model and channel type.

In this study, we used the CRN (Fig. 1A) model for the human atrium cell model. Similar to the Hodgkin and Huxley model, the CRN modeled the cell membrane as a capacitor connected with variable resistances (ionic channels) and batteries (driving forces) in parallel.19 The ionic channels (I_ion) of the CRN model are as follows:

(2)

I_{ion, atrium} = I_Na + I_K1 + I_to + I_Kur + I_Kr + I_Ks + I_{Ca, L} + I_{p, Ca} + I_NaCa + I_{b, Na} + I_{b, Ca}

In (2), I_Na represents rapid inward Na⁺ current, I_K1 is inward rectifier K⁺ current, I_to is transient outward K⁺ current, I_Kur is ultra-rapid delayed rectifier K⁺ current, I_Kr is rapid delayed rectifier K⁺ current, I_Ks is slow delayed rectifier K⁺ current, I_{Ca, L} is L-type inward Ca²⁺ current, I_{p, Ca} is plateau current, I_NaCa is Na⁺/Ca²⁺ exchanger current, and I_{b, Na}, and I_{b, Ca} are background Na⁺ and Ca²⁺ currents, respectively. Details of this have been described in previous studies.19 We used the CRN model in this study because the mathematical equations of the L532P and N588K mutations were measured and calibrated to be fit with the CRN model. Moreover, it is a well-known electrophysiological model for human atrial cells.

Modified CRN cell model

We modified some ion currents to mimic closely related AF phenomena following Jacquemet et al.20 The modified model reduces the I_to, I_{Ca L}, and I_kur currents by 80%, 30%, and 90%, respectively, and increases the I_Kr by 50%, resulting in AF action potential similar to the actual clinical results. We compared the original parameter input of CRN with the modified parameter of that in Jacquemet et al.20 study at the single-cell level (Fig. 2). In the 2D tissue and 3D atrium, we presented the electrophysiological activation based on the modified parameters setting.

Fig. 2

I_Kr current profiles (A), Action potential (B).

Implementation of mutation

The I_Kr of the CRN model was modified to accommodate I_Kr changes due to gene mutation (Fig. 1B). For this, maximal I_Kr conductance, activation, and inactivation gate values, and α- and β-subunit values of the CRN model were substituted into the gene mutation experimental values measured in the previous studies.13 21 22 The L532P mutation was applied to Xenopus laevis oocytes using a double-electrode voltage-clamp assay (Hassel et al.13), and the N588K mutation was examined in Chinese hamster ovary cell counts measured at room temperature, 37°C (McPate et al.21). CRN models using N588K gene mutations in I_Kr have been described by Loewe et al.22 and assumes the following explanation:

(3)

I_Kr = P₁x_r1x_r2(V_m − E_K)

(4)

x_{r 2} = [1 + e x p (\frac{V_{m} + P_{2}}{P_{3}})]

(5)

\frac{d x_{r 1}}{d t} = \frac{x_{r 1 \infty} - x_{1}}{τ_{x_{r 1}}}

(6)

x_{r 1 \infty} = [1 + e x p (\frac{- (V_{m} + P_{4})}{P_{5}})]

(7)

α_{x_{r 1}} = P_{6} \frac{V_{m} + P_{7}}{1 - e x p (\frac{V_{m} + P_{7}}{P_{8}})}

(8)

β_{x_{r 1}} = 7.3898 \times 10^{- 5} \frac{V_{m} + P_{9}}{e x p (\frac{V_{m} + P_{9}}{P_{10}}) - 1}

(9)

τ_{x_r1} = [(α_{x_r1} + β_{x_r1})·P₁₁]⁻¹

In (3), I_Kr is rapid delayed outward rectifier K⁺ current, and xr1 in (4) and xr2 in (5) are the activation and inactivation gating variables, respectively. αxr1 in (7) and βxr1 in (8) are the forward and backward rate constants for the gating variable, and τxr1 in (9) is the time constant for gating variables. P1-11 are experimental values for WT, N588K, and L532P mutation conditions (the values of P1-11 are provided in Table 1).22

Table 1

Parameter values of the control and mutation condition

Variables		Control	N588K	L532P
g_Kr
	P₁, nS/pF	0.029412	0.029412	0.09172
Inactivation
	P₂, mV	15	−38.65	−15.54
	P₃, mV	22.4	19.46	24.37
Activation
	P₄, mV	14.1	16.49	−9.88
	P₅, mV	6.5	6.76	22.31
A
	P₆, 1/mVmsec	0.0003	0.0003	0.00025
	P₇, mV	14.1	14.1	−196.86
	P₈, mV	−5	−5	−131.36
B
	P₉, mV	−3.3328	−3.3328	−40
	P₁₀, mV	5.1237	5.1237	3.79 × 10⁻⁶
KQ10
	P₁₁, 1	1	2	1

The parameters were obtained based on the experimental data from the work of Loewe et al.22

Tissue model

In 2D models, the spatial resolution was 0.02 cm; this is comparable to the size of atrial cells and provides a stable numerical solution. The size of the 2D atrial sheet model was 10 × 10 cm². The number of nodes and elements was 250,000 and 249,001, respectively. The purpose of the 2D simulation is to present the electrophysiological activation pattern of both N588K & L532P mutations on a simplified and limited medium. The limited 2D medium can show the arrhythmogenic and the duration of the rotor. The pattern shown can provide some clues of what happens in the 3D heart which is more complex geometry. The mesh of the 3D atrium is shown in Fig. 3. The electrophysiological model of the cardiac tissue was based on the following equation:

Fig. 3

Mesh of the 3D atrial model.

(10)

\frac{\partial V_{m}}{\partial t} = \frac{1}{β C_{m}} \nabla \cdot D \nabla V_{m} - \frac{1}{C_{m}} (I_{i o n} (V_{m}, \vec{n}) - I_{e x t})

where V_m represents membrane voltage, t represents time, D is the diffusion coefficient of the tissue, C_m indicates membrane capacitance, I_ion is the sum of all transmembrane ionic currents,

\vec{n}

is the activation gate variable, and I_ext is the externally applied stimulus. The partial differential equation above represents electrical propagation in the cardiac tissue; it covers diffusion in the tissue, and reaction in cardiac channels. The parameter values of the above equations are shown in Table 2.

Table 2

Parameter values of the current model

Symbols	Description	Values	Unit
C_m	Total membrane capacitance	1	uF/cm²
D	Diffusion coefficient of tissue	0.0001	cm²/msec
F	Faraday constant	96.4867	C/mmol
R	Ideal gas constant	8.3143	J/K/mol
T	Absolute temperature	310	K
g_Na	Maximal I_Na conductance	7.8	nS/pF
g_K1	Maximal I_K1 conductance	0.09	nS/pF
g_to	Maximal I_to conductance	0.1652	nS/pF
g_Kr	Maximal I_Kr conductance	0.0294	nS/pF
g_Ks	Maximal I_Ks conductance	0.129	nS/pF
g_Ca,L	Maximal I_Ca,L conductance	0.1238	nS/pF
g_b,Ca	Maximal I_b,Ca conductance	0.00113	nS/pF
g_b,Na	Maximal I_b,Na conductance	0.000674	nS/pF
I_NaK,max	Maximal I_NaK	0.6	pA/pF
I_NaCa,max	Maximal I_NaCa	1,600	pA/pF
I_p,Ca,max	Maximal I_p,Ca	0.275	pA/pF
I_up,max	Maximal I_up	0.005	mmol/msec

Computational resource

The hardware that we used for the simulation is a super-computer which consists of 12 processor units divided into two sockets. Each socket has 16 Gb memory so the total memory is 32 Gb with 6 cores in each socket. The processor series is Intel(R) Xeon(R) CPU E5-26400. Each core handles 1 thread per run. The operating system of the computer is CentOS Linux distribution with kernel version 2.6.18-238.3l5. The code to run the simulation is based on the C++ with Portable, Extensible Toolkit for Scientific Computation (PETSc) library for parallel computing.

Simulation protocol

We conducted single-cell simulations of MT and WT conditions with original parameters of CRN and modified maximum conduction values (as mentioned in part A) before performing the 2D and 3D simulation. Single-cell action potential was computed by conditioning the cell models for 30 times, at a basic cycle length (BCL) of 1 seconds with supra-threshold stimuli of 1.5 nA/pF (duration of 2 msec). APD90 was defined as the duration between action potential upstroke and 90% repolarization (−71 mV for CRN model). Diastolic interval (DI) was defined as the time interval between 90% repolarization of the previous action potential and the upstroke of an action potential.

Single atrial cell models have then incorporated into a multicellular 2D sheet and 3D models using simplified homogenous electrophysiology of the human atria. Re-entrant waves in the 2D and 3D models were initiated using a standard S1-S2 protocol. S1-S2 protocol is a common protocol to artificially trigger reentry generation, hence arrhythmia.23 24 25 The reentry occurrence will lead to spiral wave generation (in 2D tissue) and scroll wave (in 3D geometry) depending on the wavelength, conduction velocity, medium, and the effective refractory period. In the 2D model, three S1 stimuli were applied in sequence every 400 msec to produce a planar wave-front propagating in one direction. After allowing four planar waves to pass, a premature stimulus was applied in the lower left quadrant of the patch. Fig. 4A describes the principle of the S1-S2 protocol used in the 2D model (Fig. 4A).

Fig. 4

Description of the S1-S2 protocol in the 2D (A) and 3D (B) models.

In the 3D model, three S1 stimuli were applied in the SA node (Fig. 4B). When the refractory tail of this wave reached the center of the medium, and S2 stimulus was applied, parallel with the S1 stimulus, but cover only three-quarters of the length of the medium. This produced a second wavefront with a curly tip, generating a spiral wave. Temporal time-lapse was recorded as 0.05 msec for both 2D and 3D simulations.

To reveal the vulnerable time window under MT and WT conditions, we conducted periodic stimulation for all cases by using 3D heart tissue. First, we applied 10-fold of stimuli at the apex to create planar waves from apex to the base with 600 msec cycle length. Then we applied the 11th stimulation periodically in ranged from 450 msec to 150 msec with 10 msec decrease. These methods reveal the vulnerable window which generates reentry, thus arrhythmia, under N588K, L532P, and WT conditions.

RESULTS

The comparison of the action potential and I_Kr current between original parameters of CRN and modified CRN with the WT and MT (N588K, L532P) genes is shown in Fig. 2. The maximum amplitude of I_Kr current was 1.003, 1.703, and 2.125 (pA/pF) for WT, N588K, and L532P, respectively, and MT showed a greater increase than WT. Also, the current peak time of I_Kr reached 163.4, 63.6, and 60 (msec) for WT, N588K, and L532P, respectively. For APD90, MT reached its peak value earlier than WT (214.4 msec for WT, 104.99 msec for N588K, 105.26 msec for L532P) with the APD50 of 160.6, 76.8, and 63.2 msec for WT, N588K, and L532P, respectively (Table 3).

Table 3

Comparison of action potential and I_Kr current results between the original and modified crn cell models (WT, N588K, L532P)

Variables	Original CRN cell model					Modified CRN cell model
	Action potential			I_Kr current		Action potential			I_Kr current
	Amplitude	APD₉₀	APD₅₀	I_Kr,max	t(I_Kr,max)	Amplitude	APD₉₀	APD₅₀	I_Kr,max	t(I_Kr,max)
WT	100.41	308.0	184.9	0.298	179.2	95.49	214.4	160.6	1.003	163.4
N588K	101.75	236.4	116.5	0.593	95.0	104.99	135.9	76.8	1.703	63.6
L532P	102.95	160.5	71.1	0.880	66.0	105.26	111.8	63.2	2.125	60.0

APD = action potential duration, CRN = Courtemanche-Ramirez-Nattel, I_Kr = rapid delayed rectifier potassium channel, t = time, WT = wildtype.

The re-entrant wave pattern of the WT and MT through 2D simulation is presented in Fig. 5. In contrast to self-termination without wave breakup after 2,000 msec from the start of the last S1 stimulus (Fig. 5A), MTs maintained non-termination during the simulation period. The N588K mutation maintained a stable reentrant wave for 10 seconds (Fig. 5B), whereas the L532P mutation had a wave breakup after 3,300 msec from the start of the last S1 stimulus and a fibrillation phenomenon where the waveform split into smaller fragments (Fig. 5C).

Fig. 5

Spiral wave activity and action potential shape observed in the 2D tissue model. WT (A), N588K mutation (B), and L532P mutation (C).

The results of the electrical conduction simulation of the WT and MT for the 3D atrial model are shown in Fig. 6. The wavelengths were in the order of WT ≥ N588K > L532P and the conduction velocities for all three were similar (19.7 cm/sec ± 0.2 cm/sec). As a result of the spiral wave characteristics, the WT was self-terminate at 2 seconds after the S2 stimulus with a rather unstable re-entrant wave (Fig. 6A). In the N588K, a stable re-entrant wave was maintained until the end of the simulation after the S2 stimulus (Fig. 6B). In the L532P, the re-entrant wave progressed and a wave breakup phenomenon occurred generating an irregular waveform (Fig. 6C).

Fig. 6

Spiral wave activity and action potential shape observed in the 3D atrial model. WT (A), N588K mutation (B), and L532P mutation (C).

The vulnerable window of the WT and MT according to the 10th stimuli and 11th stimuli interval in the 3D LA model is shown in Fig. 7. The interval of the 10th and 11th stimuli was between 150 msec to 450 msec with a 10 msec resolution. The red block with F indicates the failure to generate an electrical signal in the tissue by the 11th stimulus due to the effective refractory period. The yellow block with R indicates that re-entry occurs by the 11th stimulus within that time interval. The re-entry interval in WT ranged from 360 msec to 400 msec. The re-entry interval in N588K and L532P were 270 msec to 340 msec and 200 msec to 290 msec, respectively. Lastly, the blue block with the letter P indicates a normal planar wave propagation of an electrical signal by the 11th stimulus.

Fig. 7

“Vulnerability to re-entry” grid constructed by summarizing the outcomes at varying S10th and S11th intervals.

F = failure to initiate S11th stimulus, P = normal propagation of S2 beat, R = re-entry.

DISCUSSION

In this study, we simulated KCNH2 mutations using an electrophysiological 3D atrial model. To this end, we modified two aspects of the CRN cell model. First, we modified the ion currents presented in a previous study and applied them to our cell model.20 Second, the clinical data of N588K and L532P mutations derived from previous studies were assigned to our cell model.13 21 This modified cell model for the mutation described by Loewe et al.22 was then applied to the anatomical LA model provided by Yonsei Severance Hospital to observe the KCNH2 mutation phenomenon.

First, the effect of the modified CRN cell model was confirmed by measuring I_Kr current (Fig. 4A) and AP (Fig. 4B). The maximum amplitude of I_Kr current in MT conditions was higher than that in the original CRN model, and it was observed earlier than the original CRN model. This change in I_Kr due to MT conditions resulted in a shortening of the APD, which further resulted in APD50 and APD90 being shorter than that of the CRN model. This confirmed that the modified ion current shortens the APD of the CRN model (Table 3). Shortening of the APD is important to induce fibrillation by increasing the vulnerability of the 2D and 3D models, indicating that the modified CRN cell model can exhibit fibrillation condition realistically.

The application of KCNH2 mutation to the modified cell model confirmed that the N588K and L532P mutations advance the peak I_Kr current and maximize the amplitude (Table 3). This change in I_Kr causes early repolarization, shortens the plateau of the AP compared to the normal condition, and ultimately shortens the APD. This suggests a relationship between KCNH2 mutations and the short QT syndrome, and comprehensively explains the increase in tissue susceptibility that maintains and sustains re-entry.

In this study, we analyzed the 2D tissue and 3D LA models by applying the N588K and L532P mutations to the modified cell model and confirmed that vulnerability is increased by the mutation. For the WT, the spiral wave is self-terminated due to the long wavelength that results in the lack of sufficient space for activation in the tissue. However, the N588K and L532P mutations significantly shortened the wavelength, which allows the spiral wave to remain constant. Previous studies have shown that the N588K-hERG SQT1 mutation in 2D and 3D tissues can reduce the minimum substrate size to allow for re-entry.26 These results were confirmed by the N588K mutation effect in this study. In particular, the L532P mutation was found to cause a wave break-up phenomenon after a time-lapse, resulting in irregular conduction-sustaining fibrillation. This confirmed our hypothesis that due to the significant APD shortening by the L532P, the electrical pattern wave propagates in such a chaotic condition resulting in the spiral wave break up (AF condition). The impact of the KCNH2 mutation on the vulnerability of the atrium model is also confirmed by a vulnerability graph in Fig. 7. Re-entrant waves were generated within 40 msec for WT, whereas for the N588K and L532P mutations, they were generated within 80 and 100 msec, respectively. This suggests that the effect of MT increases the vulnerability of the atrium model and that KCNH2 mutation causes AF.

Researchers have reported pharmacological substances that blockade the I_Kr channel, hence prolonged the QT interval including Vesnarione,27 Macrolide Antibiotic,28 Ketoconazole,29 and Seldane.30 However, none of the studies specifically observed the effect of the I_Kr blocker on either N588K or L532P mutation conditions. In 2004, Brugada et al.6 attempted to apply Sotalol, I_Kr blocker, which is categorized as class III antiarrhythmic drugs on N588K-hERG mutation. They found that the N588K mutation decreased the effect of Sotalol on the hERG channel which is consistent with clinical findings. In addition, a proper drug for L532P was open for future pharmacological study.10

The limitations of this study are as follows; First, we used a homogeneous cell model as 2D and 3D heart models, however, in reality, the heart tissues are discrete. Second, we only provide the electrophysiological analysis of the two mutations without considering the mechanical behavior, which previously observed for D172N, G229D, S140G, and V241F mutations.25 31 32 33 Third, we were unable to compare our simulation results with experimental data due to the limited availability of patients with N588K or L532P mutations. Nonetheless, this computational study demonstrated the relationship between the L532P and N588K mutations with atrial arrhythmia and AF. This study provides further insights into the N588K and L532P mutations to pharmacologists. Patients with N588K or L532P mutations can benefit from drug therapy with appropriate substance and dosage.34

In summary, we confirmed that the vulnerability of the atria is increased due to KCNH2 gene mutations, and the re-entrant wave is constantly maintained throughout the 3D left atrial model. In particular, the CRN modified cell model confirmed that the L532P gene mutation can cause AF.

Notes

Funding: This research was partially supported by the NRF (National Research Foundation of Korea) under the basic engineering research project (2016R1D1A1B0101440) and the EDISON (NRF-2011-0020576) Programs and the MSIT(Ministry of Science and ICT), Korea, under the Grand Information Technology Research Center support program(IITP-2020-2020-0-01612) supervised by the IITP(Institute for Information & communications Technology Planning & Evaluation).

Disclosure: The authors have no potential conflicts of interest to disclose.

Author Contributions:

Conceptualization: Lim KM.
Data curation: Heikhmakhtiar AK, Jeong DU, Abrha AT.
Formal analysis: Heikhmakhtiar AK, Jeong DU, Abrha AT.
Investigation: Heikhmakhtiar AK, Jeong DU, Abrha AT.
Methodology: Lim KM.
Software: Lim KM.
Validation: Lim KM.
Writing - original draft: Heikhmakhtiar AK, Jeong DU, Abrha AT.
Writing - review & editing: Lim KM.

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Proarrhythmogenic Effect of the L532P and N588K KCNH2 Mutations in the Human Heart Using a 3D Electrophysiological Model

Abstract

Background

Methods

Results

Conclusion

Graphical Abstract

INTRODUCTION

Fig. 1

CRN cell model diagram (A), N588K and L532P mutations in the S5 sub-unit of the IKr channel and in the S4 voltage sensor, respectively (B).

METHODS

(1)

(2)

Modified CRN cell model

Fig. 2

IKr current profiles (A), Action potential (B).

Implementation of mutation

(3)

(4)

(5)

(6)

(7)

(8)

(9)

Table 1

Parameter values of the control and mutation condition

Tissue model

Fig. 3

Mesh of the 3D atrial model.

(10)

Table 2

Parameter values of the current model

Computational resource

Simulation protocol

Fig. 4

Description of the S1-S2 protocol in the 2D (A) and 3D (B) models.

RESULTS

Table 3

Comparison of action potential and IKr current results between the original and modified crn cell models (WT, N588K, L532P)

Fig. 5

Spiral wave activity and action potential shape observed in the 2D tissue model. WT (A), N588K mutation (B), and L532P mutation (C).

Fig. 6

Spiral wave activity and action potential shape observed in the 3D atrial model. WT (A), N588K mutation (B), and L532P mutation (C).

Fig. 7

“Vulnerability to re-entry” grid constructed by summarizing the outcomes at varying S10th and S11th intervals.

DISCUSSION

Notes

References

CRN cell model diagram (A), N588K and L532P mutations in the S5 sub-unit of the I_Kr channel and in the S4 voltage sensor, respectively (B).

I_Kr current profiles (A), Action potential (B).

Comparison of action potential and I_Kr current results between the original and modified crn cell models (WT, N588K, L532P)