While the ECG provides information about the electrical performance of the heart HFM assesses the mechanical performance of the heart through capturing cardiac vibrations, such as the seismocardiograph (SCG). Cardiac contractility can be obtained directly by estimating measures of contractility such as stroke volume or indirectly through the measurement of systolic time intervals which are related to contractility.
Myocardial contractility is the intrinsic ability of the heart to contract. Different levels of contractility are achieved by the binding between myosin and actin filaments of the cardiac muscle fibers. In a variety of cardiac abnormalities, myocardial contractility is affected and reduced. The gold standard for assessment of myocardial contractility is the invasive measurement of change in pressure in the left ventricle per unit time. Through the use of intra-cardiac catheters, a calculation of the maximum first derivative of pressure (dP/dtmax) can be determined. SCG has been proposed for the assessment over time (trending) of dP/dtmax (REF).Stroke volume is also an indicator of myocardial contractility and a close correlate of dP/dt max. Different clinical conditions can result in abnormal stroke volume, such as hypovolemic shock from severe bleeding (hemorrhage), myocardial infarction and cardiomyopathy. Some of these conditions may coexist and a non-invasive trending of stoke volume, as an index of contractility, could help physicians to treat these conditions. The seismocardiogram (SCG) has been proposed for the estimation of stroke volume (REF) (REF) (REF).
Systolic Time Intervals
The systolic time intervals were first defined by Wiggers, please refer to Figure 1. The recent advances in technology have provided the tools for non-invasive measurement of the systolic time intervals (STI). The assessment of STIs were one of the first methods in cardiology where the term non-invasive was applied . Commonly used systolic time intervals are total electromechanical systole (QS2), the left ventricular ejection time (LVET), pre-ejection period (PEP), isovolumic contraction period (IVCP) and electromechanical lag (EML). l lag (EML).
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A. Definitions and Terminologies
In the past SCG has also been called by other names such as sternal acceleration ballistocardiography (REF) , sternal ballistocardiography (REF), digital ballistocardiography …read more
B. Frequency Range
Recording the acceleration of the chest created by beating heart can range from frequencies below 20 Hz to beyond 1 KHz depending on the accelerometer and the sampling frequency.