QRS alterations in body surface potential distributions during percutaneous transluminal coronary angioplasty in single-vessel disease

A Simple Numerical Body Surface Mapping Parameter Signifies Successful Percutaneous Coronary Artery Intervention

BACKGROUND

In coronary artery disease (CAD), body surface potential mapping (BSPM) may reveal minor electrical potential changes appearing in the depolarization phase even if pathological changes are absent on the conventional 12-lead ECG. We hypothesized that a simple BSPM parameter, Max/Min signifies successful percutaneous coronary intervention (PCI).

METHODS

Ninety-two adult Caucasian patients with stable CAD and positive exercise test underwent coronary angiography. Seventy patients (age, 59 ± 8; 46 males) were revascularized by PCI (left anterior descending [LAD] in 38, right [RCA] in 17 and left circumflex [LCX] coronary artery in 15). Control groups contained 22 patients (age, 60 ± 8; 14 males) without intervention and 35 healthy subjects (age, 58 ± 2; 15 males). Left ventricular ejection fraction (LVEF, transthoracic echocardiography) and Max/Min BSPM parameter (63-lead Montreal system) were evaluated before and 4-40 days following coronary angiography. Max/Min was defined by the ratio of the highest maximum to the deepest minimum potential of all leads recorded by BSPM.

RESULTS

Before PCI, Max/Min value of patients with LAD lesion (0.83 [0.74; 0.93]) was significantly lower while that with RCA lesion (1.63 [1.35; 1.99]) was significantly higher than that of healthy group (1.01 [0.970; 1.13]) (P < 0.05) and LVEF was significantly lower in LAD lesion (46.50% [43.00; 51.00]) than in the healthy group (55.00% [50.00; 58.75]) (P < 0.01). Max/Min value significantly increased from 0.83 [0.74; 0.93] to 0.92 [0.82; 0.99] (P < 0.01) following LAD PCI while significantly decreased from 1.63 [1.35; 1.98] to 1.35 [1.21; 1.43] (P < 0.01) post-RCA PCI. It did not vary significantly, however, either following LCX PCI or without intervention. LVEF significantly increased (from 46.50% [43.00; 51.00] to 49.00% [46.00; 51.00]) only after LAD PCI.

CONCLUSION

Max/Min parameter is suitable to follow patients after LAD and RCA PCI.

COMPUTER MODELS OF DEPOLARIZATION ALTERATIONS INDUCED BY MYOCARDIAL ISCHEMIA: THE EFFECT OF SUPERIMPOSED ISCHEMIC INHOMOGENEITIES ON PROPAGATION IN SPACE AND TIME-FREQUENCY DOMAINS

A two-dimensional modified Luo-Rudy model was created to represent a 40 mm by 40 mm slab of myocardial tissue. An inhomogeneity was introduced to simulate acute myocardial ischemia, with components of hyperkalemia, acidosis and anoxia. Simulations were carried out for various degrees of ischemia, to study both the interaction of the propagation front with the inhomogeneity, and the reconstructed signals. The simulations utilized a modified LR model, with a realistic anisotropy of myocardial tissue. Each cluster (.4 mm ×.4 mm) was given bulk electric properties, Rx and Ry (25Ω and 250Ω, respectively). The slab was stimulated and the 2D depolarization pattern was computed by numerical integration. To study ischemia, a circular inhomogeneity with concentric regions (ro=12.8 mm{border zone, BZ} , ri=11.2 mm{extreme zone, EZ} ) regions was introduced in the model. From the 2D simulations and the regional action potentials (AP), unipolar and bipolar lead potentials were reconstructed. Time-frequency decomposition was performed on the lead signals by wavelet analysis. Isochrone and (dV/dt) max maps were obtained to study depolarization. Our results indicate that spatial inhomogeneities yield dramatic spatial dispersion of the wavefront and are the origin of mid-frequency intra-QRS components in cardiac signals. Severe APD shortening and spatial distortion of the isochrone and upstroke maps are also observed.

Body surface potential mapping improves detection of ST segment alteration during percutaneous coronary intervention

BACKGROUND

The 12-lead electrocardiogram underestimates ST segment alteration in acute coronary syndromes compared with multi-lead body surface mapping. We assessed whether 80-lead mapping would improve detection of ST alteration during percutaneous coronary intervention.

METHODS

Simultaneous maps and 12-lead electrocardiograms were recorded pre-procedure, during balloon inflation and post-procedure from patients undergoing elective intervention to native coronary arteries. Recordings were obtained from 39 inflations (19 patients). All arteries were successfully stented.

RESULTS

Mean 'lead specific' ST alteration (the difference in ST elevation/depression between pre-procedure and inflation recordings in the lead showing maximal ST alteration) was greater on the map than on electrocardiogram, both for ST elevation (0.16+/-0.02 vs. 0.06+/-0.01 mV; p<0.001) and ST depression (0.11+/-0.017 vs. -0.03+/-0.006 mV; p<0.001). During first inflations (n=19), mean lead specific ST elevation and depression on map were greater than on electrocardiogram (0.20+/-0.034 vs. 0.07+/-0.015 mV; p<0.001 and 0.11+/-0.029 vs. 0.03+/-0.009 mV; p=0.001, respectively). Mapping detected greater summated ST elevation and depression during inflation than electrocardiogram (0.04+/-0.005 vs. 0.021+/-0.003 mV; p<0.001 and 0.026+/-0.004 vs. 0.011+/-0.002 mV; p<0.001, respectively). Qualitative analysis of maps and electrocardiograms showed that 21/39 (53.8%) maps recorded during inflation met criteria for myocardial ischaemia compared with 7/39 (17.9%) electrocardiograms (p<0.001).

CONCLUSION

Body surface mapping compared with the 12-lead electrocardiogram improves detection of myocardial ischaemia during intervention.

Quantitative assessment of myocardial ischemia by electrocardiographic and scintigraphic imaging

We calculated distributions of epicardial potentials from body-surface electrocardiograms (ECGs) recorded during controlled myocardial ischemia and compared them with scintigraphic estimates of ischemia's extent/severity. The study population consisted of patients suffering from single-vessel coronary artery disease, referred for elective percutaneous transluminal coronary angioplasty of either the left anterior descending (n=7), the right coronary (n=9), or the left circumflex (n=2) artery. After the target vessel had been dilated, a 1960s "study" inflation was performed with a non-perfusion-type balloon catheter; at its commencement, technetium-99m sestamibi was injected via a femoral-vein catheter, and ECGs were recorded throughout the inflation from 120 leads. Single photon emission computed tomographic imaging was performed one hour after the injection of radionuclide to obtain an "occlusion image", and again one hour after a repeat injection 24 hours later to obtain a "control image"; the latter image was subtracted from the former, to derive a scintigraphic difference map (Delta map). The ECGs were signal-averaged over a 10-s window at preinflation and peak-inflation states, the preinflation averaged complexes were subtracted from the peak-inflation ones to produce body-surface Delta maps, and the corresponding Delta maps of epicardial potentials were calculated by applying the electrocardiographic inverse solution; this procedure is referred to as electrocardiographic imaging. The ECG-derived epicardial Delta maps related spatially to the scintigraphic Delta maps in all patients. The percent areas and surface integrals of positive values in ECG-derived Delta maps were found to be very good single-variable predictors of the extent (r=0.73; p=0.0006) and severity (r=0.72; p=0.0008) of the scintigraphically-estimated perfusion defect; a regression equation using two ECG-derived predictors further improved the agreement with scintigraphic estimates (r=0.81; p=0.0004 for estimates of severity). These findings suggest that noninvasive electrocardiographic imaging might provide quantitative estimates of the extent/severity of myocardial ischemia that agree closely with those provided by scintigraphic techniques.

Wavelet analysis and time-frequency distributions of the body surface ECG before and after angioplasty

In a pilot study, electrocardiographic (ECG) recordings of patients with left and right coronary stenosis taken before and after angioplasty were analyzed using the continuous wavelet transform. Time-frequency distributions were obtained for different leads in order to examine the dynamics of the QRS-spectrum and establish features specific of ischemia in the time-frequency domain. We found relevant changes in the mid-frequency range, reflecting the ECG's response to percutaneous transluminal coronary angioplasty (PTCA). The changes appeared in ECG leads close to ischemic zones of the myocardium. Time-frequency distributions of the ECG during the QRS may thus become another electrocardiographic indicator of ischemia, alternative to ST-level in standard ECG or body surface mapping. The paper demonstrates the ability of the continuous wavelet transform to detect short lasting events of low amplitude superimposed on large signal deflections.

A computer heart model incorporating anisotropic propagation. IV. Simulation of regional myocardial ischemia

The main goal of this study was to simulate clinical body surface potential maps, recorded during percutaneous transluminal coronary angioplasty protocols, using a realistic geometry computer heart model. Other objectives were to address the question of reciprocal ST-segment changes observed in the 12-lead electrocardiogram during ischemia and to verify the hypothesis that the shortening of the QRS duration observed in left anterior descending (LAD) coronary artery occlusion may be explained by conduction delay in the septal His-Purkinje system. Simulation was achieved by first introducing into the heart model three transmural zones of mild, moderate, and severe ischemia for assumed occlusions in the LAD, left circumflex, and right coronary arteries. The heart model was then excited, in turn, with these three zones present for assumed occlusions in the LAD, left circumflex, and right coronary arteries. Myocardial conduction velocities in the regions of moderate and severe ischemia were assumed to be reduced to 75 and 50% of normal, respectively. Model action potentials in the mild, moderate, and severely ischemic zones were also altered to reflect known ischemic changes in these action potentials. Body surface potential maps and electrocardiograms were computed by placing the heart inside a numerical torso model. Simulated map patterns during both ST-segment and QRS were qualitatively similar to clinical maps. Reciprocal ST-segment depression was observed for all three occlusions in remote leads that did not overlie the ischemic zones. QRS shortening due to septal His-Purkinje conduction delay was verified. The simulation results attest to the model's ability to reproduce body surface potential distributions recorded following percutaneous transluminal coronary angioplasty protocols. The simulations also showed that reciprocal ST-segment changes occur as a natural consequence of the primary ischemic region and that there is no need to invoke a second region of ischemia. Finally, the model demonstrated that QRS shortening can occur in LAD occlusion despite a slowing of conduction down the septal His-Purkinje system.