COMPARATIVE STUDY OF THE “BLUEBERRY-ON-TOP" PHENOMENON. A RECENTLY RECOGNIZED STRAIN PATTERN IN PATIENTS WITH APICALVARIANT HYPERTROPHIC CARDIOMYOPATHY (RF_FR_413)

Background: We have recently described the “Blueberry-On-Top” phenomenon as a novel strain pattern in patients with apical HCM (ApHCM). This pattern is identified when there is impaired global longitudinal strain (GLS) with paradoxically advanced time to peak strain (TPS) in a hypertrophied apex with relative basal sparing. On a standard polar map, GLS shows a pale center while TPS depicts a more robust blue center.^[1] While this pattern has been observed in a few prior reports ^[2-5], its prevalence in ApHCM is currently unknown.

Methods: This is a single-center retrospective study. A series of patients diagnosed with ApHCM (confirmed by CMR) were included and compared to a series of normal controls. All patients underwent cardiovascular magnetic resonance imaging (CMR) and transthoracic echocardiogram (TTE). For uniform reporting, all TTEs were post-processed using Tomtec which is a vendor-independent speckle tracking software.

To develop a GLS ratio, we first obtained patient-specific GLS values across the six standard segments of a region. Segments are arranged as anteroseptal, anterior, anterolateral, inferolateral, inferior, and inferoseptal. The three regions are: basal, mid, and distal. GLS ratio is then defined as (GLS_Mid + GLS_Distal) ÷ GLS_Basal

Whereas NTPS ratio is defined as: (NTPS_Mid - NTPS_Distal) ÷ NTPS_Basal

NTPS denotes the time to peak strain with normalization relative to R-R

Results: From a cohort of 340 patients with HCM, 15 patients with ApHCM were included and comparted to 15 normal controls. Mean scar burden by LGE quantification was 13% which was mostly localized to the hypertrophied apex. In patients who had genetic testing (n=10), 50% had either pathogenic mutation or variant of unknown significance (VUS). Two thirds of patients with ApHCM had a strain pattern (deeply inverted T waves) on resting electrocardiogram (ECG).

The Blueberry-On-Top pattern was observed in 93% (n=14) of patients with ApHCM, but in none of the controls. Pixel-averaged polar maps for ApHCM patients and normal controls are shown in Figure 1. When GLS ratio threshold of 1.26 and NTPS ratio threshold of 0.09 are met, the Blueberry-On-Top phenomenon has nearly 100% sensitivity and 93% specificity for diagnosis of ApHCM (Figure 2). However, we do not suggest using these individual ratios as standalone tests for making a clinical diagnosis of ApHCM, but rather as integrated parameters in a more comprehensive approach (Figure 3).

Conclusion: This is the first-in-human report establishing the prevalence of the Blueberry-On-Top strain pattern in ApHCM. This newly recognized strain pattern is unique and can be used as a supportive diagnostic feature in ApHCM. These strain findings can be seen on CMR strain analysis. Further studies could potentially integrate the Blueberry-On-Top pattern in a more comprehensive CMR evaluation of patients with ApHCM including CMR strain as well as parametric mapping to exclude ‘‘mimickers’’ of ApHCM.