Evaluation the Capabilities of Cardiac Mechanical Dyssynchrony in the Diagnosis of Myocardial Microvascular Dysfunction in Chronic Ischemic Heart Disease

Each patient will have a peripheral catheter placed, blood will be drawn, followed by dynamic SPECT on a two-day rest/stress protocol, and then standard gated myocardial perfusion scintigraphy will be performed (the resting study will be followed by a study with dobutamine administration at doses of 5 and 10 µg/kg/min). The protocols will be described in detail in the Interventions section. Based on the results of dynamic SPECT, patients will be divided into 2 groups depending on the state of myocardial blood flow reserve. All nuclear examinations will be performed using a hybrid specialized SPECT/CT Discovery NM/CT570C.

1. Determination of myocardial blood flow and reserve. Myocardial blood flow and reserve will be assessed using specialized software (GE Alcyone: Dynamic Analysis Tool), two series of images will be formed from the array of primary data: 1) reflecting the passage of the radiopharmaceutical bolus through the LV cavity and myocardium from 1 to 120 seconds of the study; 2) a group of 8 dynamic tomoscintigrams (frame duration 30 s) a series of static tomoscintigrams showing the accumulation of the radiopharmaceutical in the LV walls. The next stage of data processing (bi means of of specialized software (4DM CFR) will include the analysis of static and dynamic images, with the establish of "activity-time" graphs based on areas of interest corresponding to the cavity, walls (anterior, posterior, lateral , septum and apex) and 17 segments of the polar map of the left ventricle. On the basis of the obtained graphs, indices of myocardial blood flow at rest and stress will be determined (in ml per 1 gram of tissue per minute) on the basis of which the indices of the reserve of myocardial blood flow will be determined, reflecting the MBF stress/rest ratio. These indices will be estimated for all walls, vascular regions and segments of the polar map of the left ventricle.
2. Evaluation of myocardial perfusion. To evaluate the results of myocardial perfusion, a specialized software package Corridor 4DM (University of Michigan, Ann Arbor, MI, USA) will be used with the construction of sections along the short and long axes of the heart, as well as a 17-segment polar map of the left ventricle normalized to 100%. Semi-quantitative calculation of local disorders of LV perfusion will be performed in points as follows: 0 - accumulation of radiopharmaceuticals in the myocardial segment ≥70% of the maximum; 1 - a mild decrease in accumulation (50-69%), 2 - a moderately reduced accumulation (30-49%), 3 - a pronounced decrease in accumulation (10-29%) and 4 - a severe decrease of radiopharmaceuticals accumulation (<10%). The calculation of the total violation of LV perfusion will be made as follows: a decrease <4 points will be regarded as the norm; 4-8 - as easy; 9-13 - as moderate; >13 - as a severe deterioration of myocardial perfusion. Thus, the total perfusion impairment on exercise (SSS - Summed Stress Score), at rest (SRS - Summed Rest Score), as well as SDS - Summed Difference Score - will be calculated. In addition, the indicator called transient ischemic dilatation (TID) will be determined in a specialized Quantitative Perfusion SPECT software package (QPS software, version 2013, Cedars-Sinai).
3. Evaluation of inotropic function and mechanical dyssynchrony

To assess contractile dysfunction, we will analyze the results of gMPI obtained during dynamic acquisition with ATP (early post-exercise images), after 60 minutes after the introduction of radiopharmaceuticals, obtained with dobutamine gMPI, as well as during the study at rest. The assessment of stress-induced changes will be estimated as the difference between the score during the stress test and at rest (Δ = [value at stress] - [value at rest]). To get early post-exercise images from the array of primary data obtained during dynamic SPECT, list data from 4 to 8 will be reconstructed. The resulting images will be processed in Corridor 4DM SPECT (INVIA, Ann Arbor, MI, USA), Emory Cardiac Toolbox (Emory University/ Syntermed, Atlanta, GA), and QGS/QPS (Cedars-Sinai Medical Center, CA, USA). After construction the activity-time curve, the following parameters of the LV contractile function will be automatically estimated:

End-systolic volume (ESV, ml); End-diastolic volume (EDV, ml); Ejection fraction (EF, %); Peak ejection rate (PER, EDV/s); Peak filling rate (PFR, EDV/s).

After the construction of the phase histogram according to the algorithm "time to the maximum contraction", the following MD indices will be estimated automatically: