Clinical Investigation
Hypertrophic Cardiomyopathy
Regional Difference of Microcirculation in Patients with Asymmetric Hypertrophic Cardiomyopathy: Transthoracic Doppler Coronary Flow Velocity Reserve Analysis

https://doi.org/10.1016/j.echo.2013.03.023Get rights and content

Objective

To evaluate, by noninvasive coronary flow velocity reserve (CFVR), whether patients with asymmetric hypertrophic cardiomyopathy (HC), with or without left ventricular outflow tract obstruction, demonstrate significant regional differences of CFVR.

Methods

We evaluated 61 patients with HC (27 men; mean age 49 ± 16 years), including 20 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 41 patients without obstruction (HCM). The control group included 20 age- and sex-matched subjects. Transthoracic Doppler echocardiography CFVR of the left anterior descending coronary artery (LAD) and the posterior descending coronary artery (PD) were performed, including calculation of relative CFVR as the ratio between CFVR LAD and CFVR PD.

Results

Compared with the controls, all the patients with HC had lower CFVR LAD (2.12 ± 0.53 vs 3.34 ± 0.67; P < .001) and CFVR PD (2.29 ± 0.49 vs 3.21 ± 0.65; P < .001). CFVR LAD in HOCM group in comparison with the HCM group was significantly lower (1.93 ± 0.42 vs 2.22 ± 0.55; P = .047), due to higher basal diastolic coronary flow velocities (0.40 ± 0.09 vs 0.33 ± 0.07 m/sec; P = .002), with similar hyperemic diastolic flow velocities (0.71 ± 0.16 vs 0.76 ± 0.19 m/sec; P = .330), respectively. There was no significant difference in CFVR PD between patients with HOCM and those with HCM (2.33 ± 0.46 vs 2.27 ± 0.50; P = .636), respectively. Relative CFVR was lower in the HOCM group compared with the HCM group (0.84 ± 0.16 vs 0.98 ± 0.14; P = .001). By multivariable regression analysis, left ventricular outflow tract gradient was the independent predictor of CFVR LAD (B = −0.24; P = .008) and relative CFVR (B = −0.34; P = .016).

Conclusions

CFVR LAD and relative CFVR were significantly lower in patients with HOCM compared with patients with HCM. Regional differences of CFVR are present only in patients with significant left ventricular outflow tract obstruction, which suggests that obstruction per se, by increasing wall stress in basal conditions, leads to higher basal diastolic coronary flow velocities and results in lower CFVR in LAD compared with PD.

Section snippets

Study Population

We prospectively included 64 patients with asymmetric HC; but, due to a technical inability to assess CFVR in both arteries in 3 patients, the final group consisted of 61 patients (27 men, 34 women; mean age, 49 ± 16 years). The patients were evaluated at the Clinic of Cardiology, Clinical Center of Serbia, during the period October 2007 to March 2011. Patients' clinical characteristics, New York Heart Association (NYHA) class, the presence of arrhythmia on 24-hour Holter monitoring, and

Results

Of 64 patients, 1 patient was excluded because of a technically inadequate coronary flow signal in LAD artery during hyperemia, whereas 2 patients were excluded due to an inability to visualize baseline coronary flow in PD artery. Thus, feasibility to assess CFVR for patients with HC was 98.4% for LAD, and 96.7% for PD. According to the presence of LV outflow tract gradient at rest (≥30 mm Hg), the patients were divided into 20 patients who had HOCM, and 41 patients with HCM.

Clinical

Discussion

To the best of our knowledge, our study is the first to report dual assessment and the high feasibility of CFVR by transthoracic Doppler echocardiography in patients with HC. Similar studies to assess regional difference of microcirculation in patients with HC were done by using PET,3, 16, 17 intracoronary Doppler wire,8, 18 magnetic resonance imaging,19 and transthoracic contrast echocardiography.6 Results of our study demonstrated that regional differences of CFVR are present only in patients

Conclusions

CFVR was impaired in both hypertrophic and nonhypertrophic regions of the LV in patients with HC. CFVR LAD and relative CFVR were significantly lower in patients with HOCM compared with patients with HCM. Regional differences of CFVR are present only in patients with significant LV outflow tract obstruction, which suggests that obstruction per se, by increasing wall stress in basal conditions, leads to higher basal diastolic coronary flow velocities and results in lower CFVR in LAD compared

Acknowledgment

This study was partially supported by the grants of the Ministry of Education and Science of the Republic of Serbia (Grant Nos. III41022 and ON175086).

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      The SE assessment might include an evaluation – feasible today – of all major variables potentially involved in generating symptoms in HCM patients, including those missed in the present study, such as diastolic function and mitral regurgitation. It is interesting that the only SE variable recommended today by the guidelines on the basis of the available evidence (i.e. left ventricular outflow tract obstruction during stress in symptomatic patients with resting gradient < 50 mm Hg, class IB) was by far less useful for risk stratification purposes than wall motion abnormalities (usually discarded as a frequent source of false positive responses also occurring in patients with angiographically normal coronary arteries) and reduction in CFVR, which may occur in HCM independently of underlying epicardial coronary artery disease for left ventricular hypertrophy, microvascular disease largely unrelated to the presence and severity of left ventricular hypertrophy and increased intraparietal extravascular resistances with reduction of diastolic suction forces [8,13,33]. “False positive” SE responses based on more advanced ischemia leading to wall motion abnormalities, or more localized sub-endocardial reduction in flow reserve leading to reduction in CFVR without overt wall motion abnormalities, may overturn into prognostic truths when risk stratification, rather than diagnosis of coronary artery disease, is the purpose of imaging.

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    The authors declare no conflict of interest.

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