Study population. Eighty middle-aged individuals including two subgroups of healthy individuals (i) and CAD patients (ii) (mean age 56 ± 17 years; 48 males) were enrolled (Table 1). All subjects were in sinus rhythm. CMR revealed regular biventricular function and morphological dimensions in all individuals (LVEF 62 ± 6%, LVEDV 145 ± 33ml, LV mass 103 ± 28g). Fifty-two subjects (65%) underwent the study examination on 1.5 Tesla MR scanner, the others on a 3 Tesla clinical MR scanner. Mean systolic blood pressure at rest was 124 ± 10mmHg, diastolic blood pressure at rest was 78 ± 7mmHg.
Dynamic handgrip exercise. Seventy-four persons (93%) fully completed DHE, a minor portion of six persons (7%) had to abort prematurely due to peripheral fatigue (Table 1). The lightest handgrip ring resistance (30lb) was used by the majority of subjects (74%), whereas 25% relied on medium resistance (50 lb) and a single person utilized the highest resistance (70lb).
Mean resting HR was 68 ± 10 bpm. DHE induced a significant increase of HR to 91 ± 13 bpm (p < 0.001, Figure 4A). Figure 3 shows a representative course of HR during DHE in a healthy subject. HR increased steadily as DHE progressed. A HR plateau was not evident after two minutes of DHE. After the end of DHE, HR fell rapidly towards the resting HR.
GLSrest was -19.4 ± 1.9%. GLS significantly increased to -20.6 ± 2.1% (p < 0.001) following DHE, according to a relative increase of 7 ± 7%. The majority of our study population (70%) responded with a relevant increase of GLS (DGLS < -0.5%) on a paired comparison, whereas GLS remained unchanged in 25% of individuals and decreased in 5% (Figure 4B). On a segmental level (Figure 4C), DHE induced a significant increase of LS in every segment of apical and midventricular layer (p < 0.01). However, in most basal segments no significant changes of LS could be observed.
Subgroup analysis of CAD patients. Patients in subgroup ii (CAD patients) had a mean age of 64±15 years (23 men, 77%). 4 patients (13%) aborted DHE due to peripheral fatigue. Compared to subgroup i, no significant differences were observed for HR at rest and after DHE (p = n.s.). In subgroup ii, GLS also increased significantly after DHE (GLSrest: -18.8 ± 2.2% vs. GLSrest: -19.5 ± 2.3%, p < 0.001).
In comparison to intermediate dobutamine stress (Figure 5), a significantly higher HR (HRDHE: 89 ± 14bpm, HRDobuInterm: 78 ± 15bpm, p < 0.001) as well as a trend towards a higher GLS was observed after DHE in subgroup ii of CAD patients (GLSDHE: -19.5 ± 3.1%, GLSDobuInterm: -19.1 ± 3.1%, p = 0.22). At peak dobutamine/atropine stress, heart rate was significantly higher compared to DHE and rest (HRDobuMax= 140 ± 12bpm, p < 0.001), GLS though was significantly lower (GLSDobuMax= -15.6 ± 3.6%, p < 0.001). However, fSENC sequences were not evaluable in 14 patients at maximum stress level (47%). Whilst physiologic DHE stress including the acquisition of fSENC sequences at rest and after DHE took at median 2:20 (2:01-3:23) min, intermediate dobutamine stress already lasted 6:20 (6:02-6:58) min and maximum dobutamine/atropine stress 19:36 (18:03-22:04) min – implying a significant time saving of DHE-fSENC (p < 0.001).
Subgroup analysis of subgroup i (healthy individuals) for gender and age differences. Gender-related subgroup analysis revealed no significant differences regarding LVEF (p = n.s.). Significantly more women used the lowest (30lb) handgrip ring (24 women (96.0%) vs. 12 men (48.0%), p < 0.001). No significant gender differences were found for HRrest and HRDHE. In contrast, GLSrest (men: -19.0 ± 1.3%, women: -20.5 ± 1.5%, p < 0.001) and GLSDHE (men: -20.5 ± 1.5%, women: -21.9 ± 1.3%, p < 0.05), but not DGLS (men: -1.7 ± 1.1%, women: -1.3 ± 1.4%, p = n.s.) were significantly different between male and female subjects.
Divided at the median age (53.7 years), two age-dependent subgroups were created: younger (n=25, mean age = 36.8 ± 10.4 years) and older adults (n=25, mean age = 65 ± 7 years). Except HRDHE (young HRDHE = 96 ± 12bpm vs. old HRDHE = 88 ± 12bpm; p < 0.05), no significant differences were observed between younger and older adults related to DHE study. Neither age, gender nor handgrip ring strength were significant confounders for heart rate or GLS stress response.
Observer variability. Quantification of both GLSrest and GLSDHE by fSENC featured an excellent reproducibility. ICC for the intraobserver variability of GLSrest was 0.98 (95% CI: 0.93-1.00), for the interobserver variability 0.98 (95% CI: 0.95-1.00). For GLSDHE, the ICC for intraobserver variability was 0.99 (95% CI: 0.89-1.00) and for interobserver variability 0.97 (95% CI: 0.88-0.99).