Technetium-99m-tetrofosmin imaging with incremental nitroglycerin infusion to detect severely ischaemic but viable myocardium: a comparative study with thallium-201

Could myocardial viability be related to left ventricular dyssynchrony? Simultaneous evaluation by gated SPECT-MPI

BACKGROUND

Left ventricular contraction dyssynchrony (LVCD) has been related to induced ischemia and transmural scar but the interplay of myocardial viability and dyssynchrony is unknown. The aim of the present study was to establish the role of dyssynchrony in the context of a viability study performed with nitrate augmentation gated single photon emission computed tomography (GSPECT) myocardial perfusion imaging (MPI).

METHODS

Fifty-four consecutive patients with ischemic dilated cardiomyopathy (IDC) and depressed left ventricular ejection fraction (LVEF) were included. They underwent a two-day rest/nitroglycerine (NTG) study GSPECT MPI to determine the myocardial viability. Patients with a nitrate-induced uptake increase of > 10% vs baseline, in at least, two consecutive dysfunctional segments were considered viable as well as those who showed no improvement in the uptake but the uptake was > 50% on post NTG study. Patients with no nitrate-induced uptake increase of > 10% and the uptake of < 50% were considered non-viable. Perfusion, function and LVCD were compared in 25 viable patients vs 29 non-viable patients at baseline and after NTG administration.

RESULTS

After NTG administration, in the viable group, the LVEF increased (36.44 ± 6.64% vs 39.84 ± 6.39%) and the end-systolic volume decreased significantly (119.28 ± 31.77 mL vs 109.08 ± 33.17 mL) (P < 0.01). These patients also experienced a significant reduction in the LVCD variables: phase standard deviation was reduced in the post NTG study (57.77° ± 19.47° vs 52.02° ± 17.09°) as well as the phase histogram bandwidth (190.20° ± 78.83° vs 178.0° ± 76.14°) (P < 0.05). Functional and LVCD variables remained similar in the non-viable patients (P > 0.05).

CONCLUSION

In patients with IDC and depressed LVEF, the myocardial viability detected by rest/ NTG GSPECT MPI, might determine LVCD improvement.

Effects of nitroglycerine on coronary flow velocity before and during adenosine provocation

BACKGROUND

Transthoracic echocardiography-assessed coronary flow velocity reserve (CFVR) evaluates coronary microvascular arterial function. Coronary flow velocity measurements at baseline and during hyperemia are used to calculate CFVR. Adenosine infusion induces hyperemia but it is not known if it causes a maximal response. We hypothesized that pre-treatment with nitroglycerine before adenosine provocation enhances hyperemia.

METHODS

Twenty-three healthy study subjects (mean age 27.5 ± 5.5, 35% women) underwent CFVR measurements before and after pretreatment with sublingual nitroglycerine (0.5 mg). Hyperemia was induced by adenosine infusion (140 μg/kg/min). In addition, the effect of nitroglycerin on left main coronary artery diameter was assessed.

RESULTS

Pretreatment with nitroglycerine increased median CFVR from 3.6 (range 2.8-4.3) to 5.0 (4.1-6.0), p = 0.002. The increase was caused by a marked reduction in baseline coronary flow velocity 17 (15-24) vs 27 (19-31) cm/s, p < 0.0001) while hyperemic velocity remained unchanged (90 (68-116) vs 93 (75-105) cm/s, p = 0.48). Nitroglycerin significantly dilated the left main coronary artery (from median 3.1 (2.7-3.6) mm to 3.8 (3.1-4.3) mm, p = 0.018).

CONCLUSION

Pretreatment with nitroglycerine dilates coronary arteries and increases coronary flow velocity reserve indicating that adenosine alone causes a submaximal hyperemia.