The normal and abnormal apexcardiogram

Respiratory-Induced Amplitude Modulation of Forcecardiography Signals

Forcecardiography (FCG) is a novel technique that records the weak forces induced on the chest wall by cardio-respiratory activity, by using specific force sensors. FCG sensors feature a wide frequency band, which allows us to capture respiration, heart wall motion, heart valves opening and closing (similar to the Seismocardiogram, SCG) and heart sounds, all simultaneously from a single contact point on the chest. As a result, the raw FCG sensors signals exhibit a large component related to the respiratory activity, referred to as a Forcerespirogram (FRG), with a much smaller, superimposed component related to the cardiac activity (the actual FCG) that contains both infrasonic vibrations, referred to as LF-FCG and HF-FCG, and heart sounds. Although respiration can be readily monitored by extracting the very low-frequency component of the raw FCG signal (FRG), it has been observed that the respiratory activity also influences other FCG components, particularly causing amplitude modulations (AM). This preliminary study aimed to assess the consistency of the amplitude modulations of the LF-FCG and HF-FCG signals within the respiratory cycle. A retrospective analysis was performed on the FCG signals acquired in a previous study on six healthy subjects at rest, during quiet breathing. To this aim, the AM of LF-FCG and HF-FCG were first extracted via a linear envelope (LE) operation, consisting of rectification followed by low-pass filtering; then, the inspiratory peaks were located both in the LE of LF-FCG and HF-FCG, and in the reference respiratory signal (FRG). Finally, the inter-breath intervals were extracted from the obtained inspiratory peaks, and further analyzed via statistical analyses. The AM of HF-FCG exhibited higher consistency within the respiratory cycle, as compared to the LF-FCG. Indeed, the inspiratory peaks were recognized with a sensitivity and positive predictive value (PPV) in excess of 99% in the LE of HF-FCG, and with a sensitivity and PPV of 96.7% and 92.6%, respectively, in the LE of LF-FCG. In addition, the inter-breath intervals estimated from the HF-FCG scored a higher R2 value (0.95 vs. 0.86) and lower limits of agreement (± 0.710 s vs. ±1.34 s) as compared to LF-FCG, by considering those extracted from the FRG as the reference. The obtained results are consistent with those observed in previous studies on SCG. A possible explanation of these results was discussed. However, the preliminary results obtained in this study must be confirmed on a larger cohort of subjects and in different experimental conditions.

Identification of cardiac events by optical Vibrocardiograpy: comparison with Phonocardiography

Laser Doppler vibrometry has been recently applied for non-contact monitoring of the cardiac activity, both in terms of cardiac rate and heart rate variability, measuring the velocity of the skin surface of the chest wall and the neck (optical Vibrocardiography, VCG). To go further insight in the analysis of VCG recordings, in this study authors have compared heart sounds by digital Phonocardiography (PCG) with the motion of the skin on the chest wall by optical VCG, the final aim being the identification of some events of cardiac mechanics in the VCG signals. PCG and VCG traces were synchronously recorded on 10 healthy subjects, along with ECG. To reach this goal, multiresolution analysis together with Hilbert transforms for envelope calculation on PCG and VCG have been applied, temporal and morphological features were extracted from the signals. Data collection and signal processing allowed us to identify some events of cardiac mechanics, correlating the heart sounds relative to the closure of the mitral valve, and the following closure of the aortic and pulmonary valve with characteristic deflections identifiable on VCG traces.

The apical impulse in coronary heart disease

Forty patients (36 with coronary artery disease), who had angiographic assessment of left ventricular function were studied using apexcardiography with a new method of standardization, the objective being to define the parameters of the apical impulse which reflect changes in the left ventricular function and correlate them with clinical assessment of the apical impulse. Based on measurements from patients with normal left ventricular function, abnormalities in apexcardiograms were identified. An increase in amplitude of percent A wave alone (greater than 13.3%) (palpable as an atrial kick in approximately half of these patients) was not associated with significant left ventricular dysfunction. An isolated abnormality in isovolumic slopes, although associated with mild left ventricular dysfunction, could not be detected clinically. Moderate to severe left ventricular dysfunction was always associated with abnormal ejection phase slopes and all had sustained apical impulses. The additional presence of a palpable atrial kick or an increased percent A wave on the apexcardiogram was more indicative of moderate rather than severe dysfunction. Thus this study clearly establishes that left ventricular function does in fact affect the nature of the apical impulse in patients with coronary artery disease and these can be easily defined.

Laser method for recording displacement of the heart and chest wall

Several non-invasive methods are in use for recording mechanocardiograms. In this paper a new laser technique will be presented to measure heart motion, chest wall displacement and other displacement curves of cardiovascular structures. Principles of the laser displacement technique are described. The measurement range within which displacement is sensed, is 32 mm with a detector to object distance of 25 cm and a resolution of 8 micron (digital output) or 16 micron (analogue output). The specific surface of which motion is sensed is 1 mm2. The sensitivity of the system is 156 mV/mm at a frequency bandwidth of 0-2 kHz. Assessment of the laser displacement technique was carried out during 6 dog experiments on the closed chest, on the exposed heart, on blood vessels and also on the chest wall of 5 normal subjects. Displacement of the chest wall at the apical site ranges between 0.3-0.8 mm and of the exposed heart between 3-10 mm.

Hall effect transducer for apexcardiography and sphygmography

Recording of mechanograms (Recording of mechanical activity of internal organs and vessels, often non-invasively eg. apex cardiogram) can be performed by applying different kinds of mechano-electric transducers. In this paper the idea and construction of a new transducer with Hall-generator are presented. This transducer is self-adjusting in the range of its linear characteristics, and exerts practically constant touching pressure independent of the configuration of the patients thorax. This facilitates the measuring process and allows for calibration of the obtained records. The sensitivity of the transducer is 250 mV/mm, frequency bandwidth 0-45 Hz and it has a linearity of +/- 1.5% in the range of displacements +/- 1.5 mm. The transducer also generates the signal of the first derivative of the investigated vibrations. Assessment of the transducer was carried out in a cardiology clinic on 27 patients with a normal heart and with different kind and degree of heart damage. The mechanograms obtained from different transducers for each patient were compared in respect of the essential time intervals and morphological elements. The comparison shows a good detecting capability, correctness and reproducibility of the data obtained by means of the Hall-effect transducer. Some recordings of mechanograms (apexcardiograms and different kinds of pulse) from patients with normal heart, valvular aortic stenosis and atrial heart defect are shown and discussed in the paper.

High-fidelity, infinite time constant calibrated pressure apexcardiogram and its correlation with high-fidelity left ventricular pressure

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Use of apexcardiography to evaluate left ventricular diastolic compliance in human beings

The relation between various relative amplitude measurements of the left apexcardiogram and internally derived indexes of diastolic compliance of the left ventricle was studied in 29 patients. Simultaneous high fidelity recordings of the left apex tracing and left ventricular pressure were obtained in 11 patients without left ventricular disease (group I) and 18 patients with congestive cardiomyopathy (group II). In 204 normal subjects the ratio of the A wave amplitude to the total diastolic deflection (A/D ratio) of the left apexcardiogram was 31.4 +/- 11.4 (mean +/- standard deviation) percent, the ratio of the A wave amplitude to the total height (A/H ratio) 8.9 +/- 4.3 percent and the D/H ratio 30.4 +/- 14.7 percent. The A/D and A/H ratios were significantly (P less than 0.001 and P less than 0.005) increased in group II (69.2 +/- 12.2 percent and 16.8 +/- 8.2 percent, respectively); they were within normal limits in group I. In contrast, the D/H ratio was within normal limits in both groups of patients. The A/D ratio correlated significantly better with specific compliance (deltaV/deltaP.V) (r = -0.87) than did the A/H ratio (r = -0.53), whereas similar correlations were obtained with end-diastolic volume compliance (dV/dPV) (r = -0.61 and r = - 0.64, respectively). In contrast, the D/H ratio correlated significantly only with end-diastolic distensibility index (dV/dP) (r = -0.52). It is concluded that A wave amplitude/total diastolic deflection (A/D) ratio and, to a lesser degree, the A wave amplitude/total height (A/H) ratio of the left apexcardiogram correspond best to diastolic compliance and are useful noninvasive measurements of this property of the left ventricle.

Relation between apexcardiographic a wave and posterior aortic wall motion

Left ventricular end-diastolic pressure, an apexcardiogram and an aortic root echocardiogram were recorded in 24 patients. Eleven patients (46%) had a ratio of atrial to total amplitude (a/OE ratio) greater than 14% in the apexcardiogram, and all patients had a left atrial systolic posterior aortic wall motion after the conduit period that was greater than 50% of the total posterior aortic wall excursion as measured from the O to V points (A/OV ratio) on the echocardiogram. Only 2 of 24 patients (8%) had an echographic A/OV ratio greater than 0.5 with an apexcardiographic a/OE ratio of less than 14%. There was a significantly (P less than 0.001) high degree of positive correlation between the apexcardiographic a/OE ratio and the echographic A/OV ratio (r = 0.81), the a/OE ratio and left ventricular end-diastolic pressure (r = 0.82), and the A/OV ratio and left ventricular end-diastolic pressure (r = 0.75). It is concluded that the amplitude of posterior aortic root motion during atrial systole in relation to total posterior aortic wall motion may provide a useful index for the noninvasive assessment of left ventricular compliance and end-diastolic pressure.

Slow filling period/rapid filling period ratio in the apexcardiogram: relation to the diagnosis of coronary artery disease

Apexcardiograms were performed in 68 consecutive patients who had either normal findings or coronary artery disease on cardiac catheterization. The height of the a wave in relation to the total apexcardiographic deflection (a/H) and the duration of both the rapid (RFW) and the slow (SFW) filling periods were determined in each case. The patients were classified into three gorups: I, no evidence of heart disease on catheterization; II, significant coronary artery disease with elevated left ventricular end-diastolic pressure; and III, coronary artery disease with normal filling pressure. There was a significant difference (P less than 0.001) between the SFW/RFW values (mean +/- 1 standard deviation) in control subject (group I, 2.3 +/- 0.5) and in subjects with coronary artery disease (group II, 4.7 +/- 1.6 and group III, 4 +/- 1.7). Setting the upper limit of normal for SFW/RFW at 2.8 (mean + 1 standard deviation) identified 94 percent of patients, in group II, 71 percent of patients in group III and 86 percent of all patients with coronary disease (group II plus group III). This sensitivity appeared greater than that of the a/H ratio. Only 2 of 17 patients (12 percent) without coronary atherosclerosis had an SFW/RFW ratio greater than 2.8. It is concluded that (1) the slow/rapid filling period ratio is a useful noninvasive measurement for identifying subjects with ischemic heart disease; (2) the increased values for slow/rapid filling period ratio associated with obstructive coronary lesions may be caused by impairment of early left ventricular distensibility; and (3) this ratio should be determined in patients with other forms of heart disease to determine its specificity.

The influence of atrial activity on ventricular capture by failing artificial pacemakers. I. Report of two new cases and review of the literature

Atrial activity can influence the ability of a failing artificial pacemaker to excite the heart. An appropriately timed atrial beat may cause failure in excitation by pacemaker stimuli which are usually successful in ventricular capture. Conversely, stimuli which usually fail in excitation may be made to succeed by an appropriately timed atrial beat. Two case reports and a review of the literature are presented. Alternative mechanisms for this influence of atrial activity are electrotonic effects (Wedensky facilitation or inhibition) and mechanical effects (motion of the pacing catheter or ventricular myocardium). The authors consider the latter mechanism preferable.

Magnet noncontact apexcardiography. A new technique for registering chest motion

A new apexcardiographic recording system has been developed which is free of certain technical limitations. This noncontact magnetic transducer was tested alternately with a commonly used pneumatic piezoelectric transducer in a comparative study on ten normal subjects. The magnetic registration offered a more accurate timing and configuration of the ACG. Signal distortion, such as peaked waves and an early fall of the systolic wave, was eliminated. The magnetic transducer was capable of recording directional apex point tracings, as well as pulsations of a larger apical area. The new system proved to possess definite advantages and eliminated some of the inconveniences inherent in the pneumatically coupled system.

Value of serial apexcardiograms during and after myocardial infarction

Apexcardiograms were systematically recorded serially in 40 patients after acute myocardial infarction, in an additional 21 patients with proven aneurysms, and in 18 patients with good ventricular performance following myocardial infarction. Abnormalities of the "A" wave and systolic waves of the apexcardiogram correlated well with akinesia or dyskinesia proven by cinefluoroscopic and cineangiographic studies. Third and fourth heart sounds and apical systolic murmurs also correlated well with evidence of ventricular dysfunction. This study indicates that the apexcardiogram is a good qualitative tool for serially assessing patients following acute myocardial infarction and that the results on invasive study may be predicted in most patients.

Measurement of cardiac muscle relaxation in hypothyroidism

The isovolumetric relaxation time of the left ventricle (IRT) in 20 hypothyroid patients (133 +/- (SE of mean) 4 ms) was significantly longer than that in 23 normal subjects (95 +/- 3 ms). During a trial of thyroxine replacement the IRT in 12 hypothyroid patients fell from 143 +/- 4 ms to 107 +/- 4 ms. The IRT seems to be a useful index of end-organ function in hypothyroidism.

Relationship between duration of systolic upstroke of apexcardiogram and internal indexes of myocardial function in man

In 11 patients with nonobstructive cardiomyopathy and coronary heart disease and decreased myocardial function of the left ventricle, as well as in nine patients without left heart valvular or myocardial disease, left apexcardiograms were recorded during diagnostic heart catheterization, wherein micromanometers were used; ACG's were registered additionally in 54 healthy volunteers in order to establish the normal range of apexcardiographic parameters. In all cases the apex tracings were recorded by means of a pulse transducer with infinite time constant. The most important finding of this study was the close correlation between the duration of the systolic upstroke (SUT) of the apex tracing and some accepted isovolumic indexes of left heart function (isovolumic contraction time, time interval from the onset to peak of the first derivative of left ventricular pressure, maximal value of the first derivative of left ventricular pressure, and the peak measured velocity of shortening of the contractile elements). Further, the mean value of SUT in patients with impaired left myocardial function was significantly prolonged, compared to the control subjects; an overlap was apparent due to the fact that some of these patients showed a normal left myocardial performance at rest, having an abnormal response only to exercise tests. The apexcardiographic SUT can practically always be measured when the first derivative of apex tracing is simultaneously recorded. It showed itself to be only slightly influenced by the resting heart rate. The mentioned relationship of the systolic upstroke time of the ACG to internal isovolumic indexes of myocardial function makes this noninvasive measurable parameter an additional excellent tool for the evaluation of the left myocardial state, thus supporting a new aspect of the value of quantitative apexcardiography.

Normalized first derivative ofthe left apex cardiogram in assessment of left ventricular function

The relation between the left displacement apex cardiogram and the left ventricular pressure during isovolumic contraction was studied in 30 patients with cardiac disease. Using the instantaneous relation between the first time derivative and the magnitude of both the left apex cardiogram and the left ventricular pressure, normalized derivatives were obtained. These noramized velocities were correlated with each other and with several indexes of left ventricular function. The normalized derivatives of the left apex cardiogram (dD/dt/D) and the left ventricular pressure (dP/dt/P) were similar in magnitude, standard deviation and variation coefficient. No such similarity was present when the first time derivatives of each tracing (dD/dt and dP/dt) were compared. A highly significant relation was found between normalized displacement velocity and normalized pressure velocity using both total (r = 0.76, P less than 0.001) and developed (r = 0.75, P less than 0.001) displacement and pressure. Significant correlations with several other indexes of left ventricular function (end-diastolic pressure, peak dP/dt, maximal velocity of the contractile elements at zero load[Vmax]) were also observed. It is concluded that the index dD/dt/D of the left apex cardiogram is an important noninvasive tool for assessing left ventricular function in man.

Time relation between apex cardiogram and left ventricular events using simultaneous high-fidelity tracings in man

In 10 patients without left heart valvular disease and having normal function of the left ventricle, the left ventricular apex cardiogram with its first derivative (dA/dt), left ventricular pressure with its first derivative (dP/dt), aortic pressure, electrocardiogram, and phonocardiogram were reocrded simultaneously during cardiac catheterization. The apex cardiographic tracings were obtained by means of a transducer with infinite time constant and very high resonant frequency and the LV and aortic pressures with catheter tip-manometers. The onset of the systolic rise of apex cardiographic and LV pressures were found to occur almost simultaneously with the upstroke of LV pressure, preceding that of the apex cardiogram by only 2 +/- 4 ms (mean +/- 1 SD). The summit of the systolic upstroke of the apex cardiogram (called E-point) occurred 37 +/- 9 ms after opening of the aortic valve and 41 +/- 9 ms after peak dP/dt. The peak of dA/dt preceded peak dP/dt by 10 +/- 4 ms. The protodiastolic nadir of the apex cardiogram (called-O-point) occurred slightly earlier (19 +/- 16 ms) than the nadir of the LV pressure curve, with considerable variation. In conclusion, this study using external and internal transducers with similar characteristics gives a new definition of the time relation between the externally recorded apex cardiogram and the haemodynamic events within the left heart in human subjects with normal left ventricular function.

The use of echocardiography to measure isometric contraction time

The current methods for estimating isometric contraction time were discussed. Ultrasonically derived isometric contraction time, using external carotid pulse tracing, phonocardiogram, and the B-point of the mitral echogram was also measured. Recordings were performed in 10 normal subjects, and 15 patients. Hypertrophic cardiomyopathy (5), congestive cardiomyopathy (6), and ischemic heart disease (4). In 11 patients, the results were correlated with the internal isometric contraction time. The ultrasound isometric contraction time showed good correlation with the internal isometric contraction time (r equals 0.92, P less than 0.01). The external isometric contraction time showed less correlation with the internal isometric contraction time and was significantly shorter (P less than 0.01). The ultrasound isometric contraction time showed a superior discriminating value to the external isometric contraction time for differentiation the normal subjects from the patients' group.

The apical A wave versus the fourth heart sound in assessing the severity of aortic stenosis

The height of the "a" wave of the apexcardiogram was evaluated as a marker for critical aortic stenosis in patients over 40. Critical aoritc stenosis was defined as an aortic valve area less than .75 cm-2 with no more than mild aortic insufficiency. Phonocardiograms and apexcardiograms were performed on 72 patients with catheterization proven aortic stenosis and on 14 normal controls, all over age 40. The height of the "a" wave of the apexcardiogram was measured as a percentage of the e to o excursion (a/e-o). Fourth heart sound gallops ( S4G) were recorded in 71% (11 of 14) of normal controls, 86% (6 of 7) of patients with less than critical aortic stenosis, and 85% ( 55 of 65) of patients with critical aortic stenosis. The a/e-o was less than 16% in all normals or patients with less than critical aortic stenosis. The a/e-o exceeded 16% in 45% (29 of 65) with critical aortic stenosis. Audibility of the S4G bore no relationship to recordability, apical "a" wave geight, or the severity of the aortic stenosis. In conclusion, therefore, we believe that when one is confronted with findings suggestive of aortic stenosis, the finding of a palpable apical "a" wave (or an "a" wave height of greater than 16% of the total complex on the apexcardiogram) is an important positive feature, suggesting severe aortic stenosis. Its absence, however, does not exclude severe valvar obstruction. Probably because of auscultatory inaccuracy in this condition, the apparent presence or absence of an S4G has not been of much aid in this evaluation. This sound, however, might be more useful in a carefully performed prospective study.

The A wave of the apexcardiogram and left ventricular diastolic stiffness

This study was made to determine whether the A wave of the apexcardiogram (ACG), a reflection of the late diastolic response of the left ventricle to atrial systole, corresponded in a quantifiable way to left ventricular late diastolic stiffness (LVDS). Using a combined ultrasonic and hemodynamic technique, the slope of the late diastolic left ventricular pressure/diameter relationship (ΔP/ΔD) was calculated in 25 patients and used as a measure of effective LVDS. Most patients had valvular heart disease, all were in sinus rhythm and none had regional abnormalities of contraction. An ACG was recorded in all and the ratio of the size of the A wave to the total amplitude of the ACG wave (A/H) was calculated. When A/H was more than 11%, left ventricular hypertrophy (LVH) and the presence of a fourth heart sound were the rule in the group of patients studied.

Using A/H as an independent variable, correlation coefficients were obtained for ΔP, ΔD, ΔP/ΔD, left ventricular end diastolic pressure (LVEDP), and left ventricular end diastolic volume (LVEDV). Correlation coefficients ( r ) were: ΔP = 0.68; ΔD = –0.05; ΔP/ΔD = 0.87; LVEDP = 0.73; LVEDV = 0.21. It is concluded that A/H corresponds best to LVDS and is a useful noninvasive measurement of this property of the left ventricle.

Physical signs, apexcardiography, phonocardiography, and systolic time intervals in angina pectoris

Coronary artery disease and angina pectoris are frequently associated with disordered myocardial function which may cause abnormalities in precordial motion, heart sounds, and/or systolic time intervals. The pathophysiologic basis for these abnormalities has been studied by correlating them with more direct measurements of myocardial function. Large a waves on the apexcardiogram and atrial gallops are related to accentuated left ventricular a waves which reflect diminished left ventricular compliance. Uncoordinated left ventricular contraction (asynergy) may cause abnormal systolic motion which can sometimes be recorded on the apexcardiogram. Ventricular (early diastolic) gallops in coronary artery disease are usually associated with extensive obstructive lesions, left ventricular asynergy, and a low cardiac output. Transient paradoxic splitting of the second sound in angina pectoris has been reported though rarely documented by phono-cardiography. Mitral insufficiency due to papillary muscle dysfunction implies significant damage to the papillary muscles and the surrounding ventricular wall, usually by severe coronary artery disease. Systolic time intervals are a sensitive technic which may reflect diminished contractility (prolonged preejection period) or low stroke volume (shortened left ventricular ejection time) in patients with coronary artery disease. However, systolic time intervals are also sensitive to many other pharmacologic and hemodynamic influences, including changes in left ventricular preload and afterload which may result in misleading values. Therefore, as a technic for evaluating individual patients with coronary artery disease and angina pectoris, the role of systolic time intervals remains limited.

Apex cardiogram and systolic time intervals in acute myocardial infarction

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Electromechanical correlation of leftatrial function after cardioversion

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Auscultatory and phonocardiographic characteristics of supracristal ventricular septal defect

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Jugular, hepatic, and praecordial pulsations in constrictive pericarditis

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