Diastolic amplitude time index: a new apexcardiographic index of left ventricular diastolic function in human beings

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.

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.

Identification of patients with coronary artery disease by assessing diastolic abnormalities during isometric exercise

BACKGROUND

Previous clinical studies using invasive and noninvasive methods have shown handgrip-induced diastolic abnormalities in patients with coronary artery disease (CAD).

HYPOTHESIS

The study was undertaken to determine the utility of Doppler echo- and pressocardiography during hand-grip in discriminating patients with coronary artery disease (CAD) and in those with normal coronary arteries.

METHODS

Both methods were obtained in 96 patients with suspected CAD within 24 h before coronary angiography. An abnormal handgrip-Doppler was defined by an early (E) to late (A) transmitral flow velocities ratio (E/A) < 1 during handgrip and a positive handgrip pressocardiographic test (HAT) by an abnormal increase in the A wave/total excursion or prolongation of the absolute or relative (heart-rate corrected) total relaxation time during isometric exercise.

RESULTS

Of the 96 patients studied, 23 had normal coronary arteries and 73 showed CAD. In patients with normal coronary arteries, handgrip-Doppler showed an abnormal average E/A at rest and during handgrip, whereas all variables of HAT were within normal limits. In patients with CAD, handgrip-Doppler showed only a moderate handgrip-induced increase in average A (+ 19%, p < 0.001), whereas HAT showed a significant (p < 0.001) increase in mean A wave/total excursion (+ 60%) and decrease in the relative total relaxation time (- 17%). Furthermore, handgrip-Doppler and HAT were abnormal in 15 of 23 (65%, specificity 35%) and the HAT in 5 of 23 (22%, specificity 78%) patients with normal coronary arteries, as well as in 57 of 73 (sensitivity 78%) and 69 of 73 (95%) patients with CAD.

CONCLUSIONS

Our study demonstrates that these noninvasive stress tests can become a useful new diagnostic modality for detecting patients with unknown or suspected CAD.

Usefulness of noninvasive detection of left ventricular diastolic abnormalities during isometric stress in hypertrophic cardiomyopathy and in athletes

We showed previously that the handgrip apexcardiographic test (HAT) is a useful method for detecting left ventricular (LV) diastolic abnormalities in patients with coronary artery disease and systemic hypertension. This study evaluates the use of HAT for assessing the prevalence and types of exercise-induced diastolic abnormalities in patients with obstructive (n = 31) and nonobstructive (n = 35) hypertrophic cardiomyopathy (HC) as well as its potential value for separating healthy subjects and athletes from patients with HC. We obtained a HAT in 66 consecutive patients with HC and in 72 controls (52 healthy volunteers and 20 athletes). A positive HAT was defined by the presence of one of the following: (1) relative A wave to total height (A/H) during or after handgrip > 21% (compliance type), (2) total apexcardiographic relaxation time (TART) > 143 ms or the heart rate corrected TART (TARTI) during handgrip < 0.14, (relaxation type), (3) both types present (mixed type), and (4) diastolic amplitude time index (DATI = TARTI/[A/D]) during handgrip < 0.27. Of the controls, only 1 of 52 healthy subjects and 1 of 20 athletes showed a positive HAT, whereas of the total HC cohort 63 of 66 patients (95%) had a positive result. There was no significant difference in the distribution of these types between obstructive and nonobstructive HC. Further, no LV diastolic abnormalities were present in 10 of 35 patients (29%) with nonobstructive HC at rest and in 3 of 35 patients (9%) during handgrip, whereas of the patients with obstructive HC only 1 of 31 (3%) had no LV diastolic abnormalities at rest and none during handgrip. Based on HAT data, our study demonstrates that in HC (1) LV diastolic abnormalities are very frequent during handgrip; (2) patients with nonobstructive HC show significantly fewer LV diastolic abnormalities at rest than those with obstructive HC; and (3) no significant difference exists between obstructive and nonobstructive HC in the prevalence of types of handgrip-induced LV diastolic abnormalities. Consequently, HAT appears to be of clinical value as an additional tool for separating normal patients and athletes from patients with HC.

Noninvasive detection of coronary artery disease by assessing diastolic abnormalities during low isometric exercise

The handgrip-apexcardiographic test (HAT) is a simple low-level (40% of maximal voluntary handgrip during 2 min) stress test which can detect left ventricular (LV) diastolic abnormalities. To determine whether it contributes to the diagnosis of coronary artery disease (CAD), HAT was obtained in 68 patients--47 with and 21 without angina pectoris--who prospectively underwent coronary arteriography. According to the highest or lowest individual values of diastolic apexcardiographic indices in 255 healthy volunteers, a pathologic or positive HAT was defined by the presence of at least one of the following new criteria: (1) A wave relative to total height of apexcardiogram during and/or after handgrip > 21%, (2) total apexcardiographic relaxation time (TART) during handgrip > TART at rest > 143 ms and/or TART corrected for the duration of diastole (TARTI) during handgrip < 0.14, or (3) diastolic amplitude time index (DATI), given by dividing TARTI and A wave relative to total diastolic amplitude of apex tracing during handgrip < 0.27. HAT was positive in 20 of 21 patients with single-vessel disease (sensitivity 95%), 21 of 24 patients with double-vessel disease (sensitivity 88%), and in 22 of 23 patients with triple-vessel disease (sensitivity 96%). Furthermore, HAT was positive in 20 of 21 (95%) patients without symptoms. Thus, the overall sensitivity of HAT for detecting CAD was 93%. This study is the first to demonstrate the high sensitivity of HAT in identifying patients with CAD with or without symptoms by assessing diastolic apexcardiographic abnormalities during low-level isometric stress. Thus, HAT potentially could become an additional simple diagnostic tool for noninvasive detection of patients with CAD.