Ralph J. Damiano

The Effects of Distant Cardiac Electrical Events on Local Activation in Unipolar Epicardial Electrograms

The effect of potentials generated during depolarization of the left ventricle on epicardial unipolar electrograms recorded from the right ventricle was studied using the right ventricular isolation procedure. This surgical technique disrupts electrical conduction and prevents activation wavefronts from propagating between the ventricles. Following the procedure, the ventricles were paced asynchronously with the left ventricle paced 100 ms before the right ventricle to geparate the electrogram into its local (due to depolarization of the right ventricle) and distant (due to depolarization of the left ventricle) components or with an interval of 20 ms or less between pacing the ventricles to mimic electrograms resulting from normal (synchronous) activration. Electrical activity in the left ventricle significantly affected the magnitude of the slope of the most rapid deflection and the timing of the maximum and minimum potentials of right ventricular unipolar electrograms. However, distant activity did not significantly alter the timing of the fastest 1 ms downstroke. No electrograms of distant components had negative slopes with magnitudes greater than 1.3 mV/ms, nor did any slopes of electrograms containing only local components have magnitudes less than 1.5 mV/ms. Simulated electrograms, calculated from the local and distant components, correlated well (r = 0.83 to 1.00, N = 48) with electrograms recorded during synchronous pacing.

Effects of distant potentials on unipolar electrograms in an animal model utilizing the right ventricular isolation procedure.

The effects of distant potentials on local epicardial unipolar electrograms were examined utilizing a model that enabled both ventricles to be paced independently in five dogs. The right ventricular isolation procedure electrically isolates the right from the left ventricle. Right ventricular electrograms were separated into their local (right ventricular) and distant (left ventricular) components by altering the left-right ventricular pacing interval. Waveform configuration, peak to peak amplitude, magnitude of the slope and timing of the fastest downstroke were carefully evaluated at each electrode site, both with and without the presence of distant left ventricular potentials. Except for the timing of the fastest downstroke, all of these variables were significantly altered by distant potentials. Although the slope of the fastest downstroke was significantly affected by distant potentials, it remained a sensitive indicator of local versus distant activation. All electrograms of local right ventricular activation had a slope magnitude greater than 2.5 mV/2 ms whereas none of the right ventricular electrograms containing only distant left ventricular activity had a magnitude greater than 2.5 mV/2 ms. Computer-generated electrograms were calculated by digitally summing the recorded local right and distant left ventricular components. The simulated electrograms correlated well with the recorded electrograms during synchronous ventricular pacing. Thus, the configuration, amplitude and slope of unipolar electrodes were profoundly influenced by distant potentials. The timing of the fastest downstroke is largely independent of the effect of distant potentials and most closely represents local activation. The magnitude of the slope of the recorded electrogram accurately distinguishes local from distant activation.

Four digital algorithms for activation detection from unipolar epicardial electrograms

The reproducibility of activation detection by each of four algorithms used to calculate maximum derivatives was tested on two sequential paced beats of right ventricular unipolar epicardial electrograms, which represented either local activation of the right ventricle alone or synchronous activation of both ventricles. The methods were evaluated by comparing the shape of the two beats aligned on their selected activation times, i.e. the time at which the maximum negative deflection occurred, the differences in activation intervals for the two beats, and the effect on the activation time of superimposing distant events on local activation. The 17-point second-order data fit algorithm performed slightly better than the first-order difference, three-point Lagrange derivative, and five-point second-order data fit algorithms except that activation time selection by the 17-point technique was slightly, but significantly, delayed by the superposition of distant potentials. The 17-point second-order data fit technique is therefore recommended for use in detecting activation unless computation time is a major consideration.<<ETX>>

Interpolating Unipolar Epicardial Potentials from Electrodes Separated by Increasing Distances

BLANCHARD, S. M., et al.: Interpolating Unipolar Epicardial Potentials from Electrodes Separated by Increasing Distances In cardiac mapping, potentials for unexplored areas are estimated by interpolating values from nearest neighbor electrodes regardless of distances between these sites or wave front orientation. The effects of these variables on interpolated unipolar electrograms were analyzed two ways: with a computer model and with electrograms recorded 9.9 and 14.1 mm apart. For the model, wave fronts (n = 39) were generated from electrograms recorded during right ventricular (RV) activation in five dogs following the RV isolation procedure. Each wave front was assumed to propagate radially at 0.5 m/sec from a site 30 mm from the center of a square array with electrodes located at the center and corners. Each wave front crossed the array with its tangent at an angle of 0°, 45°, or 90° to the diagonal line connecting opposite corner electrodes. Potentials for all five sites were generated from each wave front and were interpolated for the center site from the generated corner potentials. Generated and interpolated center site potentials were compared using correlation coefficients (r) and percent root mean square differences (%RMSD). Mean r values fell below 0.90 for interelectrode distances of 15.6 mm, 2.8 mm, and 1.4 mm at 0°, 45°, and 90° wave front orientations, respectively. For experimentally measured potentials recorded 9.9 mm apart, results from interpolated electrograms were similar to results from the model at 0° propagation. Electrograms interpolated from potentials measured 14.1 mm apart had poorer r and %RMS values than those from the computer model. Thus, with linear interpolation unipolar electrograms can be inaccurately interpolated from electrodes less than 3 mm apart or correctly interpolated from electrodes more than 14 mm apart depending upon wave front orientation.

Reversal of Flow through Chronic Coronary Collateral Vessels

The purpose of this study was to determine whether blood flow through chronic collateral vessels may reverse its direction to supply acutely ischemic myocardium. Ameroid constrictors were placed on the circumflex coronary artery (CCA) of 12 dogs to promote collateral flow (CQ) from the left anterior descending (LAD) to the CCA. Twelve weeks later, myocardial blood flow (MBF) was determined (ml/g/min) using radioactive tracer microspheres. Control LAD subepi-cardial (EPI) and subendocardial (ENDO) flows were 1.17 ± 0.11 and 1.00 ± 0.10 (Mean ± SEM), respectively. CCA EPI and ENDO flows were 1.25 ± 0.12 and 1.12 ± 0.20, respectively. The LAD was then occluded, and MBF to the CCA bed decreased by an average of 0.31 ± 0.03 ml/g/min (P < 0.005). This decrease in MBF quantitated the amount of CQ from the LAD to the CCA bed. An aortocoronary bypass graft was anastomosed to the distal CCA and MBF to the LAD bed immediately increased by an average of 0.30 ± 0.02 ml/g/min (P < 0.005). This increase in MBF represented reversed CQ from the CCA to the acutely ischemic LAD bed. It had a normal transmural distribution (ENDO/EPI = 0.9). Four hours later, total reversed CQ to the LAD bed remained unchanged, but was redistributed toward the EPI (ENDO/EPI = 0.6). These data document that chronic collateral vessels are capable of immediate and sustained conduction of CQ in a retrograde direction and suggest that these collateral vessels may play a role in limiting the degree and transmural extent of ischemic injury when a perioperative myocardial infarction occurs in the vascular bed of a nonbypassed coronary artery.

Diagnosis of arteriovenous fistula by venous oxygen saturation: Case report

Peripheral arteriovenous fistulas may produce significant deleterious hemodynamic effects yet their diagnosis may not be obvious. A case is described in which the diagnosis of peripheral arteriovenous fistula was suspected from pulmonary artery catheterization data. The fistula was then localized by means of venous catheterization performed at bedside and determination of oxygen content of venous blood above and below the fistula.