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Acoustic quantification (AQ) is a noninvasive technique which provides online left ventricular (LV) area/volume waveforms. The filling portion of the AQ waveform can be used to assess LV diastolic properties. Analysis of signal-averaged AQ curves enhances the waveforms and allows reliable, quantitative, and automated analysis. From signal-averaged AQ LV waveforms, the phases of diastole can be easily detected and several parameters of diastolic performance calculated. Analysis of signal-averaged LV waveforms is complementary to that of LV AQ analysis. AQ has been used to identify diastolic dysfunction in patients with LV hypertrophy and systemic hypertension. Normal values of these parameters are age dependent and reference values will soon be available.

Color kinesis is a relatively new echocardiographic technique that allows color encoding of endocardial motion in real time. We briefly review the literature on the current clinical uses and limitations of this technique, as well as its potential future applications based on some of our results. The major advantage of this modality is that it provides the basis for objective and automated evaluation of regional systolic and diastolic function, which may have a direct impact on the diagnosis of various myocardial disease states and, in particular, coronary artery disease.

We evaluated diastolic performance in 50 normal subjects and 50 patients with concentric left ventricular (LV) hypertrophy. Age-dependent normal values were determined for LV and left atrial (LA) acoustic quantification parameters. Pulsed wave Doppler echocardiography was also performed on all subjects. Patients with LV hypertrophy had higher peak velocities of atrial contraction and atrial contributions to filling. The acoustic quantification waveforms revealed lower rapid filling percentage of total filling and lower peak rapid filling rates. The LA acoustic quantification analysis confirmed the dependence on active atrial emptying in the patients with LV hypertrophy. There were significant correlations with age for most of the LV and LA acoustic quantification parameters. Acoustic quantification provided confirmatory results in subjects with an abnormal relaxation or restrictive Doppler pattern. In subjects with a normal Doppler pattern, the acoustic quantification was of added diagnostic value, identifying abnormalities in 77% to 80% of the patients.

Background: The aim of this study was to evaluate the clinical utility of using signal-averaged acoustic quantification (SAAQ) waveforms for improved assessment of left ventricular (LV) size and function., Methods and Results: Four separate protocols were performed in 47 subjects. SAAQ waveforms were used to assess alterations in LV function induced by dobutamine (15 microg/kg per minute) and esmolol (200 microg/kg per minute) in eight normal subjects. Subsequently, we analyzed SAAQ waveforms obtained in 12 patients with LV dysfunction secondary to dilated cardiomyopathy and 12 age-matched normal subjects. Finally, we developed computer software for monitoring of LV function on the basis of continuous acquisition and repeated analysis of SAAQ waveforms. We compared the interbeat variability in indexes of LV function obtained from raw AQ and SAAQ during 10 minutes of steady-state monitoring in eight patients undergoing transesophageal echocardiography. The feasibility of long-term monitoring in the intensive care setting was then studied in seven patients undergoing abdominal surgery. Our analysis tracked variations in LV function induced by dobutamine and esmolol. Significant differences in all measured indexes were found between normal subjects and patients with dilated cadiomyopathy. Signal averaging during steady-state monitoring significantly reduced the interbeat variability of all indexes (21% to 42%). In the operating room, the SAAQ monitoring system tracked hemodynamic changes in close agreement with invasive measurements., Conclusions: SAAQ allows fast and easy quantification of LV function and can track hemodynamic trends in the operating room setting.

Objectives: We tested the feasibility of using analysis of color kinesis images to objectively assess global and regional left ventricular (LV) diastolic function in patients with dilated cardiomyopathy (DCM). In addition, the ability of this technique to track drug-induced changes on LV diastolic properties was studied., Background: Diastolic dysfunction contributes to symptomatology in patients with DCM. The assessment of LV diastolic function using conventional Doppler echocardiography is indirect and is confounded by multiple variables. Moreover, the noninvasive evaluation of regional diastolic properties is difficult. In contrast, color kinesis directly tracks and color-encodes regional diastolic endocardial motion., Methods: We studied 24 patients with DCM and mitral regurgitation (MR) and 24 age-matched normal subjects. Transmitral and pulmonary vein flow velocities were measured using pulsed Doppler echocardiography. Diastolic color kinesis images were used to calculate indexes of magnitude and timing of global and regional diastolic function. Diastolic asynchrony was evaluated in different subgroups of patients with DCM. The effects of drug infusions (nitroprusside and dobutamine) were also studied., Results: Color kinesis indexes of global diastolic function showed significant differences between patients with DCM and normal subjects. Compared with Doppler indexes, color kinesis was less confounded by MR and was capable of differentiating between drug-induced lusitropic and vasodilator effects. Diastolic asynchrony was increased in patients with DCM and severe MR., Conclusions: Quantitative analysis of global and regional LV diastolic function in patients with DCM using color kinesis is feasible.

Background: Diastolic wall motion asynchrony is a major determinant of impaired left ventricular (LV) filling in patients with concentric hypertrophy and coronary artery disease. We evaluated the ability of Color Kinesis, a new echocardiographic technique that color-encodes endocardial motion, to quantitatively assess global and regional LV filling properties., Methods and Results: Color Kinesis images and mitral and pulmonary vein flow Doppler data were acquired in 29 patients with LV hypertrophy and 29 age-matched control subjects. In addition, Color Kinesis data were correlated to coronary angiographic findings in 15 patients with suspected coronary artery disease. Segmental analysis of Color Kinesis images was used to obtain time histograms of regional diastolic fractional area change, wherein early and late peaks (peaks 1 and 2) reflected rapid LV filling and atrial contraction, respectively. Regional mean LV filling time and filling curves were used to objectively identify diastolic endocardial motion asynchrony in patients with LV hypertrophy and coronary artery disease. None of the mitral and pulmonary vein Doppler indices differentiated patients with normalized mitral Doppler profile (n=13) from control subjects, whereas reduced peak1/peak2 ratio and prolonged mean filling time indicated augmented contribution of atrial contraction toward LV filling (P<.05). In 22 of 25 patients with LV hypertrophy and preserved systolic function and in all patients with coronary artery disease, delayed diastolic endocardial motion was observed in at least one segment., Conclusions: Analysis of Color Kinesis images provides objective assessment of global and regional LV filling properties and allows identification of both diastolic dysfunction in patients with normalized Doppler indices and wall motion asynchrony.

Color kinesis is a new echocardiographic technique that aids in the assessment of global and regional left ventricular performance during either systole or diastole. Color kinesis uses automated border detection technology based on backscatter data to display both the magnitude and timing of endocardial motion in real time. The color kinesis display superimposes a color overlay on the two-dimensional echocardiographic image; the number of color pixels represents the magnitude of endocardial motion, while the different colors represent the timing of endocardial motion according to a predefined color scheme. Because color kinesis is an operator-dependent technique, the steps involved in performing a technically adequate study will be reviewed as well as the pitfalls and technical limitations. The potential clinical applications of color kinesis will also be discussed.

For over a quarter of a century, echocardiography has made an unparalleled contribution to clinical cardiology as a major tool for real-time imaging of cardiac dynamics. Echocardiography is widely used to assess cardiac function and provides noninvasive information, which is invaluable for the diagnosis of various disease states. However, despite its numerous advantages echocardiography has remained mostly qualitative and subjective. The continued progress in our understanding of the interaction between ultrasound and tissue has brought about several new developments, which allow quantitative analysis of ultrasound data. Among these new developments are endocardial boundary detection (frequently referred to as acoustic quantification) and color kinesis, which provide a more objective, robust, and convenient evaluation of cardiac and vascular dynamics that embraces multiple clinical applications. This review describes these two techniques, focusing on their current status and the evolving clinical applications.

Transesophageal echocardiography has been used as a diagnostic tool in the critical care unit. However, long-term serial evaluation of ventricular function with transesophageal echocardiography is difficult because of the current probe sizes and intolerance to prolonged oral intubation. We performed 139 intubations (64 oral and 75 transnasal) with a new prototype probe in 128 patients referred for transesophageal echocardiography. Transnasal intubation with the prototype probe was possible in 63/75 attempts. Oral intubation was successful in all 64 attempts. Patients tolerated transnasal intubation well when mildly sedated or awake. Two-dimensional echocardiographic views obtained with the nasal probe were similar to those obtained with a standard monoplane probe. Image quality was rated as good or acceptable in nearly all cases. Transgastric short-axis imaging of the left ventricle combined with acoustic quantification provided stable left ventricular area waveforms. Using custom developed software we showed the feasibility of monitoring left ventricular performance with minimal probe adjustment while graphically displaying and updating left ventricular area and fractional area change. Thus, transesophageal echocardiography with a prototype miniaturized monoplane probe passed transnasally is feasible, safe, and well tolerated by patients. This probe provides excellent two-dimensional echocardiographic images and may allow long-term echocardiographic monitoring of ventricular performance.

Background: We describe a method for objective assessment of left ventricular (LV) endocardial wall motion based on Color Kinesis, a new echocardiographic technique that color-encodes pixel transitions between blood and myocardial tissue., Methods and Results: We developed a software that analyzes Color Kinesis images and provides quantitative indices of magnitude and timing of regional endocardial motion. Images obtained in 12 normal subjects were used to evaluate the variability in each index. Esmolol, dobutamine, and atropine were used to track variations in LV function in 14 subjects. Objective evaluation of wall motion was tested in 20 patients undergoing dobutamine stress testing. Regional fractional area change, displacement, and radial shortening were displayed as histograms and time curves. Global function was assessed by calculating magnitude and timing of peak ejection or filling rates and mean time of ejection or filling. Patterns of endocardial motion were consistent between normal subjects. Fractional area change and peak ejection rate decreased with esmolol and increased with dobutamine. Time to peak ejection and mean time of contraction were prolonged with esmolol and shortened with dobutamine. Using atropine, we proved that our findings with dobutamine were not secondary to its chronotropic effects. Dobutamine induced regional wall motion abnormalities in 10 patients in 38 segments diagnosed conventionally. Segmental analysis detected abnormalities in 36 of these 38 segments and in an additional 5 of 322 segments., Conclusions: Analysis of Color Kinesis images allows fast, objective, and automated evaluation of regional wall motion sensitively enough to evaluate clinical dobutamine stress data. This method has significant potential in the diagnosis of myocardial ischemia.

The effects of temperature on the stability of two contrast agents, Albunex and perfluoropropane filled albumin microspheres (FS069), were investigated by studying the variations in their reflective properties, induced by high dose ultrasound irradiation at different temperatures. Diluted contrast agents were introduced into a 3.5-mL latex balloon, placed in a plastic water tank, and continuously irradiated over a period of 6 minutes using different power levels: 0, 20, 25, and 30 dB. The irradiation was interrupted for imaging every 30 seconds for 2 seconds. The protocol was carried out at three different temperatures: 8 degrees C, 22 degrees C, and 37 degrees C. For each temperature, the concentration of contrast solution was matched to produce approximately the same initial video intensity. Time variations in mean video intensity in the balloon cross section were studied. Contrast enhancement was found to be directly related to temperature. Under continuous ultrasonic irradiation, video intensity gradually decreased over time. This decrease was dependent on both transmitted power and temperature, and was more pronounced with Albunex when compared to FS069 (P < 0.05). Abruptly dropping temperature consistently resulted in rapid, irreversible disappearance of contrast induced by Albunex. Temperature affects the reflectivity and stability of diluted Albunex and FS069. To enhance the reproducibility of contrast enhancement achieved by these agents, their temperature should be carefully controlled.

The effects of Albunex (Molecular Biosystems, Inc., San Diego, Calif.) and a second generation contrast agent, FS069, on left ventricular (LV) contractility were evaluated using an isolated rabbit heart model under constant loading conditions and heart rate. Contrast injections (2 ml total volume) were performed in two separate protocols (N1 = 6, N2 = 6). In protocol 1, various doses of Albunex (0.1 to 2.0 ml in saline solution) were used, and paired control injections of a matched dose of 5% solution of human albumin in saline solution were administered. In protocol 2, LV contractility was assessed during injections of the following solutions: (1) 1:250 suspension of FS069 in saline solution, which caused optimal myocardial contrast enhancement; (2) a 1:25 suspension of FS069; (3) a 1:25 suspension of FS069 prefiltered using an 8 microns pore filter; and (4) 2 ml saline solution as a control. Instantaneous LV pressure was analyzed for variations in peak systolic pressure (peak P) and maximum pressure derivative (peak P'), both indices of LV contractility under conditions of fixed heart rate and chamber volume. Albumin alone caused a transient, dose-dependent depression of LV contractility, reflected by decreases in both peak P and peak P' values. These decreases presumably were caused by the decreasing availability of ionized calcium as a result of calcium binding. No further decrease in contractility was noted when Albunex microspheres were present in the solution. Saline injections caused a transient minor increase in LV contractility, reflected by increases of 4.5% +/- 1.1% and 10.6% +/- 3.8% in peak P and peak P' values, respectively. These levels returned to baseline levels within 2 minutes. A similar response was observed when a 1:250 suspension of FS069 was used. The 1:25 suspension of FS069 caused a bimodal response, with initial rises in peak P and peak P' levels (5.2% +/- 3.6% and 12.8% +/- 6.5%, respectively), followed by minor reductions in contractility (2.0% +/- 2.4% and 1.7% +/- 2.1%, respectively). The latter decrease in contractility caused by the 1:25 suspension of FS069 was eliminated by filtering. The isolated rabbit heart model is a highly sensitive tool that allows accurate and direct assessment of possible adverse effects of intravascular contrast agents on LV contractility. Using this model, we showed that neither Albunex microspheres nor FS069 microspheres impaired myocardial contractility.

Background: Color kinesis is a new technology for the echocardiographic assessment of left ventricular wall motion based on acoustic quantification. This technique automatically detects endocardial motion in real time by using integrated backscatter data to identify pixel transitions from blood to tissue during systole on a frame-by-frame basis. In this study, we evaluated the feasibility and accuracy of quantitative segmental analysis of color kinesis images to provide objective evaluation of regional systolic endocardial motion., Methods and Results: Two-dimensional echocardiograms were obtained in the short-axis and apical four-chamber views in 20 normal subjects and 40 patients with regional wall motion abnormalities. End-systolic color overlays superimposed on the gray scale images were obtained with color kinesis to color encode left ventricular endocardial motion throughout systole on a frame-by-frame basis. These color-encoded images were divided into segments by use of custom software. In each segment, pixels of different colors were counted and displayed as stacked histograms reflecting the magnitude and timing of regional endocardial excursion. In normal subjects, histograms were found to be highly consistent and reproducible. The patterns of contraction obtained in normal subjects were used as a reference for the objective automated interpretation of regional wall motion abnormalities, defined as deviations from this pattern. The variability in the echocardiographic interpretation of wall motion between two experienced readers was similar to the diagnostic variability between the consensus of the two readers and the automated interpretation., Conclusions: Color kinesis is a promising new tool that may be used clinically to improve the qualitative and quantitative evaluation of spatial and temporal aspects of global and regional wall motion. In this initial study, segmental analysis of color kinesis images provided accurate, automated, and quantitative diagnosis of regional wall motion abnormalities.

Quantification of regional myocardial tissue blood flow (RMBF) based on contrast echocardiography has yet to be achieved. This study validated our recently proposed algorithm for quantification of RMBF with colored microspheres. Experiments were carried out in an isolated rabbit heart preparation (n = 11). Aortic root injections of perfluoropropane-filled albumin microsphere solution (FS069) and colored microspheres were performed at five levels of coronary flow achieved by altering perfusion pressure. During each injection of contrast material, consecutive end-diastolic images of the heart and an extracardiac reference chamber were acquired with a 7.5 MHz transducer and digitized. Time-intensity curves from the reference chamber and myocardial regions of interest, corresponding to the anatomic segments used for colored microsphere analysis, were analyzed for RMBF. Blood flow was calculated as the intravascular volume fraction (ratio of areas under myocardial and reference curves) divided by mean transit time (deconvolution of impulse response) and compared with those obtained with colored microspheres. Injections of FS069 resulted in highly reproducible enhancement of myocardial contrast. Analysis of time-intensity curves provided consistent measurements of RMBF (r = 0.91), which correlated highly with microsphere data (r = 0.84). The use of this new algorithm allows accurate quantification of RMBF in the isolated heart model. Further validation of this approach in an animal model with peripheral intravenous injections of contrast material will allow noninvasive clinical measurements of RMBF.

The acoustic quantification technique for on-line detection of endocardial boundaries currently provides continuous left ventricular area or volume signals and beat-to-beat ejection fraction. However, the distortion of individual waveforms by noise results in a wide beat-to-beat variability in these parameters. We developed an automated algorithm for the evaluation of left ventricular function by averaging acoustic quantification signals. End-diastolic and end-systolic area, stroke area, and fractional area change are measured directly from the average waveform. Peak ejection and peak filling rates and time to peak filling rate are obtained from its time derivative. Area signals obtained from eight normal subjects were used to evaluate the performance of this algorithm. Parameters of left ventricular function obtained with the automated algorithm were highly consistent and in excellent agreement with those obtained by repeated manual operator-dependent selections. This algorithm provides a fast and easy method for noise reduction in acoustic quantification signals, which significantly improves the noninvasive assessment of left ventricular function.

Objectives: We used an isolated, crystalloid-perfused rabbit heart model to test the hypothesis that the phasic changes in left ventricular contrast are due to bubble compression and decompression during systole and diastole, respectively., Background: Contrast enhancement of the left ventricular cavity has been shown to decrease during ventricular systole. This phenomenon has been attributed to pressure-induced microbubble destruction. Such destruction, if confirmed, would severely confound the quantitative interpretation of contrast echocardiographic data., Methods: A fixed volume of contrast solution (5% human albumin and Albunex, approximately 400:1 ratio) was introduced into a latex balloon placed within the left ventricular cavity of an isolated paced rabbit heart preparation (n = 12). Instantaneous left ventricular pressure was measured using a high fidelity microtip catheter and digitized on-line. The beating heart was placed in a water tank, and ultrasound images were obtained using a 7.5-MHz transducer and were recorded and digitized off-line at 12 frames/s. Simultaneously, the pacing signal was used for gated on-line acquisition of end-diastolic frames. A simple theoretic model based on surface tension physical principles was used to predict changes in bubble size and, consequently, the reflection intensity in response to the measured changes in left ventricular pressure., Results: We found that under peak left ventricular systolic pressures ranging from 89 to 155 mm Hg, 1) end-diastolic videointensity decreased by 8 +/- 6% (mean +/- SD) over 25 consecutive heart beats; and 2) intracyclic variations in measured videointensity were in close agreement with the theoretic calculations: 80.1 +/- 2.9% versus 80.2 +/- 4.6% of diastolic videointensity at systole., Conclusions: The major cause of systolic decrease in contrast enhancement is periodic bubble compression (as opposed to bubble destruction) induced by high systolic pressures. The minor progressive decrease in end-diastolic videointensity reflects the degree of instability of Albunex microbubbles under left ventricular pressures. However, the clinical impact of these destructive effects is likely to be only minor because of the rapid transit of microbubbles through the left heart chambers and myocardial microcirculation.

Objective: To seek in hypertensive patients rhythmic variations of the systolic blood pressure signal obtained by ambulatory blood pressure monitoring of any inherent cycle of intermediate value between 1 and 24 h., Design: Subjects (62 hypertensive, 39 normotensive) were evaluated by 24-h ambulatory blood pressure monitoring. The hypertensive group consisted of 48 patients with essential hypertension, nine with renovascular hypertension and five with phaeochromocytoma. The groups were matched for age and weight., Methods: The ambulatory systolic blood pressure recording served as the input for a filtering procedure that rejected unacceptable values according to predetermined criteria. The whole-day systolic blood pressure series thus obtained were subjected to Fourier analysis to obtain a spectral analysis of daily systolic blood pressure fluctuations. Daily (first 12 h), nightly (second 12 h) and whole-day average systolic blood pressure values were calculated and compared for the various groups., Results: The average nocturnal systolic blood pressure was found to be lower than its daily counterpart in the normal subjects and in the patients with essential hypertension, whereas in the patients with renovascular hypertension or phaeochromocytoma no such nocturnal decrease was found. The power spectrum of patients with phaeochromocytoma was statistically different from that of other aetiologies of hypertension. This was achieved due mainly to a statistically significant difference in the power spectrum integral over the low-frequency band (0-0.2 cycles/h) of the power spectrum of the 24-h systolic blood pressure signal. Resection of the phaeochromocytoma normalized the power spectrum as found by analysis of the postoperative ambulatory blood pressure monitoring data in two patients who underwent a repeat recording., Conclusions: The technique described enables the discrimination of patients with phaeochromocytoma as a cause of hypertension from other aetiologies of hypertension. Patients with renovascular hypertension could not be distinguished from those with essential hypertension on the basis of their power spectrum. However, this technique may prove to be a valuable modality for characterizing hypertensive patients of different aetiologies.

Power spectra of epicardial electrograms were studied in 13 anesthetized dogs subjected to occlusion of the left anterior descending coronary artery. Electrograms were obtained from a bipolar electrode placed on the epicardial surface of the left ventricle and recorded before and after coronary occlusion. After digitization, power spectra of the first and every 50th subsequent waveform were evaluated and compared with the power spectrum of the average waveform obtained from the baseline recording. In particular, we examined variations in relative power content in three frequency ranges: 150-250 Hz, previously shown to be directly affected by myocardial ischemia; 40-150 Hz, presumably corresponding to the fine notches and slurs on the body surface QRS; and 2-40 Hz, the low-frequency range. Apart from a mild initial rise during the first 50 heart beats, the power in the high-frequency range gradually decreased, reaching 5% of the control value at wave 500. The power in the mid-frequency range showed a monotonous decrease after the occlusion and reached 16% of the control. The power in the low-frequency range showed a gradual buildup to 140% of the control after 500 heart beats. Therefore, ischemia causes a shift of the high-frequency spectral components of the local electrographic waveform to lower frequencies. Our findings and the fact that body surface ECG is produced by spatial summation of local electric potentials over the different regions of the myocardial tissue may explain two previously described effects of acute myocardial ischemia on the body surface ECG complex. First, local loss of spectral components in the range 150-250 Hz may produce a zone of reduced amplitude within a QRS complex band-pass filtered in this range. Second, displacement of power in the frequency domain may suggest an explanation to the increased incidence of visible notches and slurs on the surface QRS complex, characteristic to various myocardial pathologies.

Clinical experience has shown that the antiarrhythmic effect of lidocaine on atrial arrhythmias, and specifically for the conversion of atrial fibrillation to normal sinus rhythm, is minimal. This study summarizes our experience in 30 dogs in which atrial fibrillation was initiated and sustained (greater than or equal to 15 minutes) under increased vagal tone achieved by either alpha-chloralose anesthesia (26 dogs) or pentobarbital sodium anesthesia combined with direct external electrical vagal stimulation (four dogs). Under increased vagal tone (regardless of the procedure), an intravenous bolus of lidocaine (2 to 3 mg/kg) was 100% effective (101 of 101 episodes) in pharmacologically converting atrial fibrillation to normal sinus rhythm. This was associated with marked slowing of intra-atrial electrical activity, as shown by fast Fourier analysis of intra-atrial electrograms. Over a period of 3 to 5 minutes, lidocaine progressively shifted the peak frequency content from 84 +/- 18 mV2/Hz in the 10 to 20 Hz frequency band during the pre-lidocaine phase to 110 +/- 34 mV2/Hz in the 0 to 10 Hz frequency band immediately prior to conversion to normal sinus rhythm. When atropine was administered or electrical vagal stimulation was discontinued, the conversion of atrial fibrillation to normal sinus rhythm followed a similar electrophysiologic pattern. When isoproterenol was infused, it was difficult to induce atrial fibrillation; when the arrhythmia was initiated, it could not be sustained even with concomitant electrical vagal stimulation. Thus in this model of parasympathetically sustained atrial fibrillation, lidocaine was 100% effective in converting atrial fibrillation to normal sinus rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)

The physiological mechanisms responsible for the high frequency components of the electrocardiographic signals in different frequency ranges are still unknown. These components have been studied in the frequency domain as well as in the time domain. Numerous clinical and experimental studies have focused upon the incidence and interpretation of high frequency notches and slurs under different conditions in the myocardium. However, the analysis of the high frequency components appeared to be tedious and imprecise, and the interpretation of its results difficult and controversial, and strongly dependent upon empirically determined standards which still require thorough evaluation. Digital methods for processing electrocardiographic signals developed during the last decade have given rise to a variety of fast and reliable approaches for analyzing the information carried by the electrocardiogram. Many researchers have applied such methods to various clinical situations in human studies and to different kinds of interventions in animal studies. These developments prompted us to review research in the field of wideband recording of the electrocardiogram and to briefly discuss some of the aspects that still require elucidation.

Hypothermia is known to affect the electrophysiology of the myocardium in various ways. A marked increase in action potential duration, combined with a decrease in rate of depolarization and conduction velocity, has been observed. We studied the effect of localized hypothermia of the ventricular myocardium on the high-frequency (HF) components of the ECG waveform. Signals were obtained from 6 anesthetized dogs using simultaneous recording of three orthogonal body surface leads before, during, and following surface cooling of different areas of the epicardium. Computer analysis included digital averaging and filtering in a frequency range of 150-250 Hz. For each intervention in each animal, the variance of the average nonfiltered QRS complex was used for a quantitative estimate of the total power, whereas the variance of the derived filtered wave (HF QRS complex) expressed the power content in the HF range. The total power increased during localized cooling of the anterior as well as the inferior epicardial surface, while a clear reduction of power was observed in the HF range. This reduction was shown to be lead dependent and nonuniformly distributed during the course of the QRS. In all cases, hypothermia of either anterior or inferior ventricular epicardium produced a zone of reduced amplitude in the HF QRS complex of at least one lead. Thus, typical changes in the morphology of the HF QRS complex are reliable markers for cooling-induced localized electrophysiological (EP) variations. Therefore, the HF analysis of the body surface ECG may provide noninvasive insight into the EP properties of the myocardium.

High-fidelity ECGs, defined as ECG signals including high-frequency components, have been studied and variations in the incidence of fine notches and slurs on the QRS complex were reported in different myocardial pathologies. These observations might be of clinical importance since they suggested a noninvasive marker for cardiac dysfunctions. We studied high-fidelity ECG waveforms displaying pronounced notches and slurs. Signals were obtained from 12 anesthetized dogs. Computer analysis included digital averaging, followed by digital filtering in different frequency bands in order to determine the frequency range corresponding to notches and slurs. Low-pass filtering of the low-noise average waveforms was performed while gradually lowering the upper frequency limit, until the fine notch (or slur) could no longer be visually detected, thus determining the lower limit of its frequency content. A band cutoff filter was then applied to the original average waveform. The lower limit of the band cutoff filter was set at the frequency previously determined as the lower limit of the notch (or slur), and its upper limit was determined by gradual raising until the notch (or slur) was visually indistinct. Following this approach, the notches were found to contribute to a frequency range of 40-185 Hz, whereas the slurs contributed only to the lower subrange of this frequency band below 100 Hz.

The very high-frequency content (150 to 250 Hz) of epicardial electrogram waveforms was studied in 19 anesthetized dogs subjected to occlusion of left anterior descending coronary artery. Computer techniques of digital averaging and digital band-pass filtering were applied. Signals were obtained from epicardial electrodes placed in the ischemic left ventricular region and on the noninjured right ventricular surface, and from the body surface electrocardiogram. All recordings were made simultaneously before, during, and after coronary occlusion and subjected to the same analysis. The waveforms obtained from the ischemic left ventricular region showed a considerable decrease in high-frequency content, while those obtained from the noninjured right ventricular surface remained unchanged. The results correlated with the appearance of a zone of reduced amplitude in the body surface high-frequency QRS complex. Therefore, this macroscopic phenomenon measured noninvasively from the body surface is explained by local reduction of high-frequency activity in the ischemic region of the myocardium.