Integration of longitudinal and circumferential strain predicts volumetric change across the cardiac cycle and differentiates patients along the heart failure continuum

Abstract

Background: Left ventricular (LV) circumferential and longitudinal strain provide important insight into LV mechanics and function, each contributing to volumetric changes throughout the cardiac cycle. We sought to explore this strain-volume relationship in more detail, by mathematically integrating circumferential and longitudinal strain and strain rate to predict LV volume and volumetric rates of change.

Methods: Cardiac magnetic resonance (CMR) imaging from 229 participants from the Alberta HEART Study (46 healthy controls, 77 individuals at risk for developing heart failure [HF], 70 patients with diagnosed HF with preserved ejection fraction [HFpEF], and 36 patients with diagnosed HF with reduced ejection fraction [HFrEF]) were evaluated. LV volume was assessed by the method of disks and strain/strain rate were assessed by CMR feature tracking.

Results: Integrating endocardial circumferential and longitudinal strain provided a close approximation of LV ejection fraction (EF_Strain), when compared to gold-standard volumetric assessment (EF_Volume: r = 0.94, P < 0.0001). Likewise, integrating circumferential and longitudinal strain rate provided a close approximation of peak ejection and peak filling rates (PER_Strain and PFR_Strain, respectively) compared to their gold-standard volume-time equivalents (PER_Volume, r = 0.73, P < 0.0001 and PFR_Volume, r = 0.78, P < 0.0001, respectively). Moreover, each integrated strain measure differentiated patients across the HF continuum (all P < 0.01), with the HFrEF group having worse EF_Strain, PER_Strain, and PFR_Strain compared to all other groups, and HFpEF having less favorable EF_Strain and PFR_Strain compared to both at-risk and control groups.

Conclusions: The data herein establish the theoretical framework for integrating discrete strain components into volumetric measurements across the cardiac cycle, and highlight the potential benefit of this approach for differentiating patients along the heart failure continuum.

Keywords: Ejection fraction; Ejection rate; Filling rate; Strain; Volume-time.

Fig. 1

Left ventricular ejection fraction (EF) can be calculated by integrating peak longitudinal (LS) and circumferential strain (CS), with changes in ventricular volume being linearly related to changes in chamber length and quadratically related to changes in chamber circumference (A).[15] In a randomly chosen sample of 79 individuals with varying EF and clinical status, EF calculated using the integrated strain approach (EF_Strain) and EF measured using the gold-standard method of disks volume-time relationship (EF_Volume) were strongly related (B), with good agreement between the two measures across a range of EF (C)

Fig. 2

Data from a representative individual showing the circumferential and longitudinal strain rate curves as well as how using the integrated strain approach can be used to calculate the volumetric rate of change curve (A). From the integrated strain curve, peak ejection rate (PER_Strain) and peak filling rate (PFR_Strain) can be identified. PER_Strain, calculated using the integrated strain approach and peak ejection rate measured using the gold-standard volume-time relationship (PER_Volume) was correlated with good agreement between the two measures across a range of ventricular systolic performance (B). Similarly, PFR_Strain calculated using the integrated strain approach and peak filling rate measured using the gold-standard volume-time relationship (PFR_Volume) was correlated with good agreement between the two measures in participants with varying degrees of diastolic dysfunction (C). These data were generated using the same randomly chosen sample of 79 individuals as in Fig. 1. s’ – peak systolic strain rate; e’ – peak early diastolic strain rate; a’ – peak late diastolic strain rate

Fig. 3

When applied to the entire cohort of subjects (n = 229), the integrated strain approach for measuring left ventricular ejection fraction (EF_Strain), peak ejection rate (PER_Strain) and peak filling rate (PFR_Strain) successfully differentiated groups according to their heart failure diagnosis (all P < 0.01, Panels A–C). *indicates significantly different from control; ^#indicates significantly different from At-Risk. ^†indicates significantly different from HFpEF

Fig. 4

Three representative case examples are shown, highlighting the strain-volume relationship and the influence each individual strain component has on left ventricular ejection fraction (EF). Top: 63-year-old male with heart failure with preserved EF. Middle: 55-year-old female control participant. Bottom: 80-year-old female with heart failure with reduced EF. Note how a reduction in strain in one direction can be compensated for by a higher strain in the other direction to achieve the same EF, while reductions in both strain components ultimately leads to a reduction in EF. Together, these examples highlight the potential advantages of integrating discrete strain components when interpreting global left ventricular function. Green arrows and numbers represent normal strains, while red arrows and numbers represent impaired strains, relative to the mean of the control group (LS: − 21.5 ± 3.3%; CS: − 29.6 ± 3.9%; EF: 62.0 ± 6.2%)