(A) Pedigree of the family. Phenotypic traits are designated within pedigree symbols. (B) Electrocardiograms (ECGs) obtained from the proband, IV-3, before (left panel, atrial fibrillation [AF]) and after (right panel, sinus rhythm) he underwent radiofrequency catheter ablation. (C) At rest and post-exercise ECGs recorded from the proband (IV-3) and his uncle (III-1). Exercise-induced AF for the proband and atrial tachycardia for the uncle can be observed. (D) Electrocardiograms recorded from other affected individuals. Arrows indicate P waves of premature atrial contractions (PACs) in II-3, III-1, and IV-1. III-3 and IV-4 demonstrated AF.

The first (A to C) and the second (D and E) ablation sessions on the proband. (A) Repetitive atrial tachycardias (ATs) from multiple origins. Shown are intracardiac recordings from the coronary sinus (CS), the His bundle (His), and a catheter placed along the posterior septum (PS) in the right atrium. Note that atrial activation sequences in CS during ATs were consistently proximal to distal, suggesting right atrial origins. Asterisks indicate the successfully ablated AT originating from the lower-right atrial septum. (B) Fluoroscopic images of the electrodes in the left anterior oblique (LAO) and right anterior oblique (RAO) views. Position of the ablation catheter (ABL; indicated by arrows); successful ablation site of the AT. (C) Three-dimensional electroanatomic map of the AT in the right posterior oblique view. The AT focus in the lower-right atrial septum was successfully ablated in the first session. (D) Noncontact mapping of PACs in the right lateral view. Two PAC foci in the middle of the crista terminalis (upper panel) and the high posterolateral wall (lower panel) ablated successfully in the second session are shown. (E) Numerous electrical firings () from the contact site during radiofrequency energy delivery in generating tricuspid valve isthmus block. Continuous pacing was performed from proximal CS. Stim = stimulator; TV = tricuspid valve annulus; other abbreviations as in Figure 1.

(A) The denaturing high-performance liquid chromatography elution profiles for an SCN5A mutation, M1875T, detected in the affected family members. (B) Deoxyribonucleic acid sequencing electropherograms demonstrate heterozygosity for a SCN5A mutation. (C) Topology of the -subunit of voltage-gated cardiac sodium (Na⁺) channel. The location of the detected mutation is shown. (D) Amino acid sequence alignments of SCN5A with related Na⁺ channels. The SCN5A indicates human heart; SCN1A, human brain type I; SCN2A, human brain type II; SCN3A, human brain type III; SCN4A, human skeletal muscle. The sequences of other species represent the cardiac isoforms of Na⁺ channels.

(A) Representative whole-cell current traces of wild-type (WT) and M1875T sodium (Na⁺) channels. Cells were transfected with human β1-subunit (protocol shown as an inset). (B) Voltage dependence of inactivation time constants. The time course of inactivation was fit with a 2 exponential equation: I/I_max = A_f x exp(–t/_f) + A_s x exp(–t/_s). Lower and upper bundles of symbols indicate fast (_f) and slow (_s) time constant values, respectively. Statistically significant differences are indicated (*p < 0.05, **p < 0.01). (C) Average current-voltage relationship for WT and M1875T channels. The current is normalized to cell capacitance to give a measure of Na⁺ current density. Asterisks indicate the voltages at which the current density was statistically different (*p < 0.05). (D) Average peak Na⁺ current density of WT and M1875T channels. The peak current density was significantly larger in M1875T (WT at –20 mV, 326.2 ± 28.2 pA/pF, n = 23; M1875T at –30 mV, 484.6 ± 49.6 pA/pF, n = 31, p < 0.05). (E) Representative Na⁺ current traces recorded in the absence or presence of 30 µmol/l tetrodotoxin. Tetrodotoxin-sensitive persistent currents were calculated by digital subtraction. M1875T channels showed no persistent inward Na⁺ currents.

Detailed parameters are given in Table 2. (A) Voltage dependence of relative sodium (Na⁺) conductance activation and steady-state inactivation were determined by means of the voltage protocols, as shown in the inset. Curves were fit with the Boltzmann equation, I/I_max = (1 + exp[V–V_1/2]/k)^–1 to determine the membrane potential for half-maximal inactivation or activation (V_1/2) and the slope factor k. Note that M1875T channels showed a pronounced depolarized shift (+16.4 mV) in the V_1/2 of steady-state inactivation compared with wild-type (WT). (B) Time course of recovery from inactivation was elicited with a double pulse protocol. Data were fit with a 2 exponential equation: I/I_max = A_f x (1 – exp[–t/_f]) + A_s x (1 – exp[–t/_s]), where A_f and A_s are fractions of fast and slow inactivation components, and _f and _s are the time constants of fast and slow inactivation components, respectively. (C) Onset of slow inactivation. Time course of entry into the slow inactivation state was obtained by a double pulse protocol. Curves were fit with a single exponential equation: I/I_max = y0 + A x exp(–t/). (D) Closed-state inactivation. The transfer rate of Na⁺ channels from closed-state to inactivated closed-state without an intervening opening state was measured by a double pulse protocol. Time course for development of closed-state inactivation was fit with a single exponential equation: I/I_max = y0 + A x exp(–t/). The extent of closed-state inactivation was significantly less and the time constant larger in M1875T channels in comparison with WT.