Author + information
- aDivision of Cardiovascular Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan
- bDepartment of Cardiology, Oslo University Hospital, Rikshospitalet and University of Oslo, Oslo, Norway
- ↵∗Reprint requests and correspondence:
Dr. Theodore J. Kolias, Division of Cardiovascular Medicine, Department of Internal Medicine, University of Michigan Cardiovascular Center, 1500 East Medical Center Drive, SPC 5853, Ann Arbor, Michigan 48109.
For nearly half a century, ejection fraction has been the mainstay of the assessment of left ventricular (LV) function. Although it has served clinicians well, it is only an indirect measure of cardiac function, derived from the change in volume of the LV cavity. More recently, global longitudinal strain (GLS) derived from speckle tracking echocardiography has been developed, providing a more direct measure of cardiac function. This measure has been demonstrated to be a sensitive marker of cardiac dysfunction in a host of clinical scenarios, including heart failure, myocardial infarction, valvular heart disease, diabetes, and pulmonary hypertension. GLS by speckle tracking is featured prominently in the new guidelines for assessing cardiotoxicity from chemotherapeutic agents, because it is a more sensitive marker of subclinical cardiac dysfunction that becomes abnormal earlier than ejection fraction (1).
On this background, Saito et al. (2) performed a study evaluating the prognostic implications of LV GLS and a strain risk score in asymptomatic patients with hypertensive heart disease. Their results, published in this issue of iJACC, demonstrated that LV GLS was independently associated with major adverse cardiac events (MACE), as was a deterioration of LV GLS during follow-up. One might argue that the differences in strain values seen in patients with MACE and non-MACE seem very small in this paper and could therefore be less applicable in routine clinical practice. There are, however, several reports confirming poorer prognosis in patients with a GLS value around –16% and worse, similar to what was found in the present study (3–5).
The association of LV GLS and MACE in this study, independent of LV hypertrophy and in the presence of normal ejection fraction, highlights the role that subclinical LV dysfunction measured by strain plays in determining outcome. Not only is GLS a sensitive important subclinical measure of disease, but it can be followed serially, and its deterioration is also a marker of poor outcome. These findings add ammunition to the argument that GLS should be routinely performed in all patients with hypertension. When these results are considered alongside other prior studies demonstrating the utility of strain in multiple other clinical conditions, the argument arises that strain should become a routine part of the echocardiographic assessment in all patients, much as is ejection fraction.
So why, despite this wealth of evidence, has strain not yet achieved mainstream use? One reason is that in the past, it has required complex offline analysis, relegating it to the realm of the researcher. This has improved recently, however, as ultrasound vendors have focused on making strain analysis software more streamlined, user-friendly, and easier to implement in a busy clinical laboratory.
A second reason adoption of strain imaging has been delayed has been concern about reproducibility of strain measurements, particularly among different vendors. To address this concern, the Task Force to Standardize Deformation Imaging has been established by the European Association of Cardiovascular Imaging, the American Society of Echocardiography, and industry partners. A recently published study arising from the efforts of this task force demonstrated that interobserver test-retest reproducibility for strain was better than for ejection fraction or other standard echocardiographic parameters (6). It also found that there was some degree of bias for strain measurements among vendors, although this was within acceptable limits for most vendor combinations. The Task Force has published new consensus guidelines on measuring strain that should lead to reduced intervendor variability (7), and the early results suggest that this is already occurring (8).
Finally, the finding by Saito et al. (2) in the current study that deterioration of strain on serial imaging was associated with adverse events is thought provoking, and in light of the favorable test-retest performance of strain imaging, suggests that changes in strain should be considered as a potential future target of investigation and possibly intervention. This approach is already followed in the cardio-oncology patient population, and further studies on applying it to other populations are warranted.
↵∗ Editorials published in JACC: Cardiovascular Imaging reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Imaging or the American College of Cardiology.
Dr. Edvardsen has received research grant funding from the Norwegian Research Council. Dr. Kolias has reported that he has no relationships relevant to the contents of this paper to disclose.
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