The apex cardiogram in ischaemic heart disease

Changes in Forcecardiography Heartbeat Morphology Induced by Cardio-Respiratory Interactions

The cardiac function is influenced by respiration. In particular, various parameters such as cardiac time intervals and the stroke volume are modulated by respiratory activity. It has long been recognized that cardio-respiratory interactions modify the morphology of cardio-mechanical signals, e.g., phonocardiogram, seismocardiogram (SCG), and ballistocardiogram. Forcecardiography (FCG) records the weak forces induced on the chest wall by the mechanical activity of the heart and lungs and relies on specific force sensors that are capable of monitoring respiration, infrasonic cardiac vibrations, and heart sounds, all simultaneously from a single site on the chest. This study addressed the changes in FCG heartbeat morphology caused by respiration. Two respiratory-modulated parameters were considered, namely the left ventricular ejection time (LVET) and a morphological similarity index (MSi) between heartbeats. The time trends of these parameters were extracted from FCG signals and further analyzed to evaluate their consistency within the respiratory cycle in order to assess their relationship with the breathing activity. The respiratory acts were localized in the time trends of the LVET and MSi and compared with a reference respiratory signal by computing the sensitivity and positive predictive value (PPV). In addition, the agreement between the inter-breath intervals estimated from the LVET and MSi and those estimated from the reference respiratory signal was assessed via linear regression and Bland-Altman analyses. The results of this study clearly showed a tight relationship between the respiratory activity and the considered respiratory-modulated parameters. Both the LVET and MSi exhibited cyclic time trends that remarkably matched the reference respiratory signal. In addition, they achieved a very high sensitivity and PPV (LVET: 94.7% and 95.7%, respectively; MSi: 99.3% and 95.3%, respectively). The linear regression analysis reported almost unit slopes for both the LVET (R² = 0.86) and MSi (R² = 0.97); the Bland-Altman analysis reported a non-significant bias for both the LVET and MSi as well as limits of agreement of ±1.68 s and ±0.771 s, respectively. In summary, the results obtained were substantially in line with previous findings on SCG signals, adding to the evidence that FCG and SCG signals share a similar information content.

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.

A Comparison of Heart Pulsations Provided by Forcecardiography and Double Integration of Seismocardiogram

Seismocardiography (SCG) is largely regarded as the state-of-the-art technique for continuous, long-term monitoring of cardiac mechanical activity in wearable applications. SCG signals are acquired via small, lightweight accelerometers fixed on the chest. They provide timings of important cardiac events, such as heart valves openings and closures, thus allowing the estimation of cardiac time intervals of clinical relevance. Forcecardiography (FCG) is a novel technique that records the cardiac-induced vibrations of the chest wall by means of specific force sensors, which proved capable of monitoring respiration, heart sounds and infrasonic cardiac vibrations, simultaneously from a single contact point on the chest. A specific infrasonic component captures the heart walls displacements and looks very similar to the Apexcardiogram. This low-frequency component is not visible in SCG recordings, nor it can be extracted by simple filtering. In this study, a feasible way to extract this information from SCG signals is presented. The proposed approach is based on double integration of SCG. Numerical double integration is usually very prone to large errors, therefore a specific numerical procedure was devised. This procedure yields a new displacement signal (DSCG) that features a low-frequency component (LF-DSCG) very similar to that of the FCG (LF-FCG). Experimental tests were carried out using an FCG sensor and an off-the-shelf accelerometer firmly attached to each other and placed onto the precordial region. Simultaneous recordings were acquired from both sensors, together with an electrocardiogram lead (used as a reference). Quantitative morphological comparison confirmed the high similarity between LF-FCG and LF-DSCG (normalized cross-correlation index >0.9). Statistical analyses suggested that LF-DSCG, although achieving a fair sensitivity in heartbeat detection (about 90%), has not a very high consistency within the cardiac cycle, leading to inaccuracies in inter-beat intervals estimation. Future experiments with high-performance accelerometers and improved processing methods are envisioned to investigate the potential enhancement of the accuracy and reliability of the proposed method.

A Novel Broadband Forcecardiography Sensor for Simultaneous Monitoring of Respiration, Infrasonic Cardiac Vibrations and Heart Sounds

The precordial mechanical vibrations generated by cardiac contractions have a rich frequency spectrum. While the lowest frequencies can be palpated, the higher infrasonic frequencies are usually captured by the seismocardiogram (SCG) signal and the audible ones correspond to heart sounds. Forcecardiography (FCG) is a non-invasive technique that measures these vibrations via force sensing resistors (FSR). This study presents a new piezoelectric sensor able to record all heart vibrations simultaneously, as well as a respiration signal. The new sensor was compared to the FSR-based one to assess its suitability for FCG. An electrocardiogram (ECG) lead and a signal from an electro-resistive respiration band (ERB) were synchronously acquired as references on six healthy volunteers (4 males, 2 females) at rest. The raw signals from the piezoelectric and the FSR-based sensors turned out to be very similar. The raw signals were divided into four components: Forcerespirogram (FRG), Low-Frequency FCG (LF-FCG), High-Frequency FCG (HF-FCG) and heart sounds (HS-FCG). A beat-by-beat comparison of FCG and ECG signals was carried out by means of regression, correlation and Bland–Altman analyses, and similarly for respiration signals (FRG and ERB). The results showed that the infrasonic FCG components are strongly related to the cardiac cycle (R² > 0.999, null bias and Limits of Agreement (LoA) of ± 4.9 ms for HF-FCG; R² > 0.99, null bias and LoA of ± 26.9 ms for LF-FCG) and the FRG inter-breath intervals are consistent with ERB ones (R² > 0.99, non-significant bias and LoA of ± 0.46 s). Furthermore, the piezoelectric sensor was tested against an accelerometer and an electronic stethoscope: synchronous acquisitions were performed to quantify the similarity between the signals. ECG-triggered ensemble averages (synchronized with R-peaks) of HF-FCG and SCG showed a correlation greater than 0.81, while those of HS-FCG and PCG scored a correlation greater than 0.85. The piezoelectric sensor demonstrated superior performances as compared to the FSR, providing more accurate, beat-by-beat measurements. This is the first time that a single piezoelectric sensor demonstrated the ability to simultaneously capture respiration, heart sounds, an SCG-like signal (i.e., HF-FCG) and the LF-FCG signal, which may provide information on ventricular emptying and filling events. According to these preliminary results the novel piezoelectric FCG sensor stands as a promising device for accurate, unobtrusive, long-term monitoring of cardiorespiratory functions and paves the way for a wide range of potential applications, both in the research and clinical fields. However, these results should be confirmed by further analyses on a larger cohort of subjects, possibly including also pathological patients.

Invasive and noninvasive assessment of exercise-induced ischemic diastolic response using pressure transducers

Left ventricular (LV) pressure curve shows early high-magnitude changes in the presence of induced ischemia. A dramatic rise in LV and left atrial end-diastolic pressures occurs within seconds to minutes in the presence of ischemia induced by dynamic or handgrip exercise as well as pacing of 38 to 183% and during short coronary balloon occlusion of 32 to 208% of baseline. Changes in relaxation or volumetric filling rate or ejection fraction were significantly less pronounced.

Similar end-diastolic abnormalities occurring mainly in patients with coronary artery disease (CAD) have been shown in noninvasive recordings obtained by pressure transducer placed over the point of maximal LV beat (pressocardiograms). Specifically, the amplitude of the A wave to total excursion of pressocardiogram showed a similar high-magnitude increase after dynamic or handgrip exercise in average by 60 to 142% of baseline; however, changes in pressocardiographic relaxation time indexes were only slightly abnormal. A well-defined “ischemic pattern” of pressocardiographic diastolic changes with handgrip, showed a high prevalence in CAD patients.

The assessment of diastolic changes in the presence of handgrip-inducible ischemia using noninvasive pressure transducers might provide after further studies a simple complementary diagnostic tool to assist in identification of patients with atypical or asymptomatic CAD.

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.

Ratio of total amplitude to diastolic wave on the apexcardiogram. Findings in aortic regurgitation and other cardiac lesions

Utilizing the apexcardiogram, the ratio of total amplitude to the height of the total diastolic wave was determined. Compared with a mean (+/- 1 SD) value of 21 +/- 4% for normal subjects there were statistically significant differences in those patients with isolated aortic regurgitation (30 +/- 10%, P = 0.01), aortic stenosis (12 +/- 11%, P less than 0.025) and mitral insufficiency (14 +/- 8%, P less than 0.025). There were no significant changes of this ratio in subjects with combined aortic stenosis and insufficiency (24 +/- 9%, P less than 0.25), triple vessel coronary artery disease (19 +/- 7%, P less than 0.25) and mitral valve prolapse (23 +/- 10%, P less than 0.35). There was a trend for higher ratio values in patients with greater angiographic evidence of aortic insufficiency, but no correlation between the ratio and left ventricular end-diastolic pressure. These alterations of the apexcardiogram accord with hemodynamic findings in the presence of each respective lesion. It is concluded that this ratio is useful for the noninvasive assessment of isolated aortic regurgitation, aortic stenosis and mitral insufficiency.

Noninvasive diagnosis of coronary artery disease: the cardiokymographic stress test

Stress-induced abnormalities of regional left ventricular wall motion were assessed by cardiokymography (CKG) during the course of maximal treadmill exercise tests in 157 patients, of whom 122 subsequently underwent coronary angiography. Seventy patients had significant angiographic coronary artery disease and 52 were normal. Forty-one of the 70 patients developed greater than 0.1 mV ST-segment depression (ECG sensitivity 59%) and 52 of 70 patients developed abnormal systolic outward motion by CKG (CKG sensitivity 74%). Among the 52 normals, 36 had negative ECG stress tests (ECG specificity 69%) and 49 had normally sustained systolic inward motion by CKG (CKG specificity 94%). The stress CKG was normal in 15 of the 16 false-positive stress ECGs; the stress ECG was correctly normal in two of the three false-positive stress CKG tests. Only one normal patient had concordantly false-positive ECG and CKG tests. The predictive accuracy of concordant ECG and CKG interpretations was, therefore, higher than either test alone. These data suggest that regional wall motion abnormalities, which are sensitive and specific markers of myocardial ischemia, may be detected noninvasively by CKG. We concluded that CKG helps identify false-positive and false-negative ECG stress tests and improves the diagnostic accuracy of stress testing for detection of coronary artery disease.

Noninvasive assessment of cardiac motion: comparison of the apexcardiogram and cardiokymorgram

The apexcardiogram (ACG) and cardiokymogram (CKG) (displacement cardiogram) tracings were compared in 45 patients with a variety of cardiac diseases and in 16 normal subjects. The ACG and CKG were generally comparable in waveform and timing of standard tracing intervals; however, on a case by case comparison frequent discrepancies between the ACG and CKG were observed. In 13 patients where no ACG could be recorded, an interpretable CKG tracing was obtained. However, the CKG produced frequent artifacts, mirror images, was very sensitive to probe position, and was judged to be of limited advantage over the ACG.

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.

Measurement of diastolic events by apexcardiogram: correlation with hemodynamic state and prognosis after myocardial infarction

Apexcardiograms and hemodynamic studies were performed in 32 postmyocardial infarction patients. Group 1 patients (5) had markedly elevated left ventricular end diastolic (LVED) pressures but normal LVED volumes; apexcardiograms included tall A waves (31 percent of the E to O points), prolonged A-wave durations of 134 msec or greater, short rapid filling wave durations (55 msec) and slow-filling waves replaced by plateaus in three patients. Group 2 patients (10) had markedly elevated LVED pressures and elevated LVED volumes, and had similar apexcardiographic findings: A-wave heights had a mean of 23.4 percent of E to O points, A-wave durations were 113 msec or more, rapid filling wave (RFW) durations were 93 msec and diastolic plateaus occurred in five patients. Group 3 patients (11) had intermediate hemodynamic findings and the apexcardiograms were varied; three patients with mild congestive heart failure (CHF) had apexcardiograms similar to Group 1 and five without CHF had apexcardiograms similar to those in Group 4. Group 4 patients (6) had normal hemodynamic findings; the mean A-wave height was 6 percent of the E to O point height, A-wave durations 90 msec or less RFW durations were 117.5 msec or more and the slow-filling wave duration (SFW) was normal in the configuration. Fourteen of 15 patients in Groups 1 and 2 developed CHF and six died on follow-up. Group 4 patients showed no evidence of CHF on follow-up and there were no deaths. Group differences were significantly different for A-wave height and duration, and for RFW duration at 0.05 or 0.01.Tall prolonged A waves and short RFWs were associated with poor left ventricular (LV) compliance and dysfunction, and diastolic plateau immediately following the RFW when present were confirmatory. Thus, the apexcardiogram is a reproducible useful noninvasive tool for clinical assessment, and predicting prognosis in postmyocardial infarction patients.

The fourth heart sound in patients without demonstrable heart disease

One hundred patients, 17 to 67 years of age, had normal hearts diagnosed on the basis of complete right and left heart catheterization and coronary cineangiography. Phonocardiograms were obtained from each patient, providing an average of 17 recordings per subject for analysis; 75/100 (75%) subjects had a recordable fourth sound; 60/75 (80%) of the latter group had an audible fourth heart sound. It is concluded that recordable and audible fourth heart sounds are common findings in subjects without catheterization evidence of cardiovascular disease.

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.

Left ventricular function in ischemic heart disease: assessment by noninvasive techniques

1. Thirty-two patients (29 men and 3 women), admitted to a coronary-care unit with either acute coronary insufficiency or acute myocardial infarction, had their systolic time intervals and the a/E ratio of the apexcardiogram studied on days 1,2, and 7 of their hospital stay. 2. Only the LVETc and PEP/LVET were found to undergo any statistically significant change. Although all figures were in the abnormal range, they had no discriminative value in individuals. None of the other commonly accepted noninvasive indices or left ventricular function, including the a/E ratio of the apexcardiogram, were found to be of assistance in the early distinction between acute coronary insufficiency and acute myocardial infarction.

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 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.

Examination of the heart in supine and left lateral positions

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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.

Coronary artery reperfusion. I. Early effects on local myocardial function and the extent of myocardial necrosis

The effects of coronary artery reperfusion 3 hr after coronary occlusion on contractile function and the development of myocardial damage at 24 hr was studied experimentally. In 14 control and 6 reperfused dogs, relationships between epicardial ST segment elevation 15 min after coronary occlusion and myocardial creatine phosphokinase activity (CPK) and histologic appearance 24 hr later were examined. The electrocardiograms were recorded from 10 to 15 sites on the left ventricular epicardium and transmural samples for CPK and histology were obtained from the same sites where epicardial electrocardiograms had been recorded. An inverse relation existed between ST segment elevation (mv) 15 min after occlusion and log CPK activity (IU/ mg of protein) 24 hr later, log CPK = - 0.06ST + 1.26. In dogs subjected to coronary artery reperfusion, there was significantly less CPK depression (log CPK = - 0.01ST + 1.31, [P < 0.01]) than that expected from the control group. In the control group 97% of specimens showing ST segment elevations over 2 mv at 15 min showed abnormal histology 24 hr later. In contrast, in the reperfused group 43% of sites exhibiting elevated ST segment at 15 min showed abnormal histology 24 hr later. In six additional dogs it was shown that the paradoxical movement of the left ventricular wall could be reversed within 1 hr of perfusion. Therefore, by enzymatic and histologic criteria, as well as by functional assessment, coronary artery reperfusion 3 hr after occlusion resulted in salvage of myocardial tissue.

Abnormalities of ventricular motion induced by atrial pacing in coronary artery disease

In order to study left ventricular performance and motion under ischemic stress, incremental atrial pacing was performed in 10 patients with angiographically proven coronary artery disease until angina pectoris or segmental S-T depression appeared. Single-plane left ventricular cineangiograms were obtained in both the resting and the transiently ischemic state induced by pacing.

Abnormal motion appeared with pacing in two of three patients with normal contraction at rest; in one of them, gross dyskinesis of the cardiac apex was noted. Seven patients had abnormal contraction at rest; six showed an increase in either the severity or the topographic distribution of abnormality, while one showed no change.

Left ventricular end-diastolic pressure and cardiac index were not altered significantly despite changes in the pattern of contraction. Left ventricular end-diastolic volume decreased irrespective of the development of asynergy, but ejection fraction decreased markedly in those patients in whom asynergy was induced de novo or increased.

Thus left ventriculography during pacing-induced ischemia may reveal segmental or generalized abnormalities of contraction not necessarily reflected in the usual hemodynamic parameters of function. Moreover, asynergy induced by pacing is associated with a decreased ejection fraction.

The apexcardiogram in ischemic heart disease

The apexcardiogram (acg), when recorded serially in patients with acute myocardial infarction (ami), preinfarction angina (pia) and stable ischemic heart disease (ihd), appeared to reflect the abnormal patterns of contraction of the left ventricle in these conditions. Thus, paradoxical bulging (dyskinesis) of the systolic wave or increased "a" wave amplitude with gradual recovery over several weeks was found in all 60 patients with documented ami and in 18 of 20 patients with pia. Electrocardiogram changes were noted, however, in only eight of the pia patients. Changes in the acg frequently antedated ischemia in the ecg. Paradoxical bulging of the systolic wave of the acg was additionally noted in patients during the pain of angina pectoris but this promptly disappeared after the administration of nitroglycerine. Patients with classic angina often had normal resting ecg's but abnormal resting acg's. In contrast to the relatively transient abnormalities noted above, the acg remained unchanged in most patients with stable ihd during follow-up of three months to two years. Patients undergoing coronary bypass operations, however, showed immediate improvement in the acg in the postoperative period. These results suggest the acg reflects the contractile pattern of the left ventricle, and may be an indirectly recorded ventriculogram. Its enhanced sensitivity and the earlier development of changes in comparison to the ecg make this a valuable tool in the study of patients with heart disease.