Mechanism of right precordial ST-segment elevation in structural heart disease: Excitation failure by current-to-load mismatch

ECG recorded at initial presentation in 2004.

Sodium channel characteristics and action potential upstrokes of isolated left ventricular myocytes. Typical whole cell-current recordings (A) and corresponding current–voltage relations (mean ± SEM) (B) show a normal voltage dependency of the sodium current. C: Typical action potential upstrokes and dV/dt show significantly reduced upstroke velocities compared to myocytes of a previously reported control patient. Insets illustrate the voltage and stimulus protocols.

Pseudo-ECG of the isolated heart before (black) and after (red) sodium channel blockade (stimulation from right ventricular septum at basic cycle length = 800 ms). Note ST-segment elevation in pseudo-AVR after sodium channel blockade. Bars = 200 ms, 1 mV.

Activation and repolarization after sodium channel blockade (right ventricular septal stimulation at cycle length of 800 ms). Activation (A) and repolarization (B) times are depicted on the corresponding complex in pseudo-aVR and on a three-dimensional reconstruction of the heart. Anterior view of the heart is depicted on the left; posterior view is depicted on the right. The epicardium is viewed as transparent. No sign of activation or repolarization was found throughout the ST segment. Lines are 20-ms isochrones.

Regional ST-segment elevation in unipolar electrograms after sodium channel blockade. A: Pseudo-aVR (top row), unipolar electrogram (middle row), and calculated coaxial electrogram (bottom row) from the epicardial basal right ventricle (site indicated by asterisk in panel B) during stimulation from the right ventricular septum at increasing frequencies (cycle length indicated at top). ST-segment elevation in pseudo-aVR increased with higher stimulation frequencies and coincided with disappearance of the main activation signal followed by monophasic ST-segment elevation in the unipolar electrogram. The local origin of ST-segment elevation was confirmed using coaxial electrograms. B: Three-dimensional reconstruction of ST-segment amplitude on unipolar epicardial electrograms 100 ms after the J point in pseudo-aVR (moment indicated by arrows in panel A) at cycle length of 800 ms. ST-segment elevation was limited to the basal epicardial right ventricle. Right ventricular view is shown on the left; left ventricular view is shown on the right. Color scale is given in millivolts. LV = left ventricle; RV = right ventricle.

Subepicardial histologic sections and quantification of subepicardial fibrous and adipose tissue. A–C: Subepicardial sections from the right ventricular outflow tract (RVOT; A), basal right ventricular free wall (RVFW; B), and basal left ventricular free wall (LVFW, C). Low-magnification images show fatty infiltration (white) in the subepicardial myocardium of the RVOT and RVFW and interstitial-type fibrosis (red) at all locations. Picrosirius red staining; bar = 500 μm. Note that the epicardial rim of collagen seen in panel C was excluded from measurements. D, E: Morphometric analysis of fibrous (D) and adipose (E) tissue content as percent of total measured myocardial area in the heart of the patient (red dots) and in the hearts of controls (black dots). Analysis reveals that the heart of the patient contained more fibrous tissue at any location than did any of the control hearts, and that the adipose tissue content of the RVOT and RVFW was greater than in the LVFW. However, no difference in adipose tissue content was found between the patient and the control hearts. Bars in panel D indicate mean ± SD of controls.

Simulated subepicardial discontinuities and sodium channel dysfunction. A, B: ECGs of the heart without (A) and with structural discontinuities in the right ventricular subepicardium (B) at baseline (black) and after (red) reduction of sodium channel conductivity (G_Na) to 30% of normal_. Bars = 200 ms, 1 mV. C, D: Basal short-axis view of the heart with structural discontinuities at the right ventricular subepicardium before (C) and after (D) reduction of G_Na to 30% of normal. Colors indicate activation time; sites that failed to excite throughout the cardiac cycle are depicted in black. The current received from and given to surrounding elements and the corresponding action potentials at five neighboring sites are depicted in the left and right graphs, respectively. The locations of these elements were 0.2 mm (black) and 0.4 mm in (brown) and 0.2 mm (red), 0.4 mm (orange), and 1.0 mm (yellow) behind the gaps in the barriers. After reduction of G_Na, insufficient current was received by many elements behind the introduced structural discontinuities to reach threshold potential. This resulted in excitation failure and activation delay of the right ventricular subepicardium and in ST-segment elevation followed by a negative T wave in the right precordial leads. LV = left ventricle; RV = right ventricle.

Simulated ECGs in structurally abnormal heart during reduction of sodium conductance (A) or of simulated size of the gaps in introduced barriers by reduction of coupling in the gaps (B) and corresponding graphs relating excited elements with ST-segment elevation in the right precordial leads. Reduction of sodium channel conductance (G_Na) below 50% of normal resulted in a rapid reduction in excited elements and ST-segment elevation on the ECG. A reduction in the size of the gaps in the barriers at normal sodium conductance also resulted in a reduction in excited elements and ST-segment elevation on the ECG. However, the increased resistance between the excited and unexcited elements limited the ST-segment amplitude.