Myocardial perfusion in patients with permanent ventricular pacing and normal coronary arteries.

OBJECTIVES: The purposes of this study were to test the specificity of dipyridamole myocardial perfusion scintigraphy in patients with permanent ventricular pacing (PVP) and to evaluate coronary blood flow and reserve in these patients. BACKGROUND: Permanent ventricular pacing is associated with exercise perfusion defects on myocardial scintigraphy in the absence of coronary artery disease (CAD). On the basis of studies in patients with left bundle brunch block, coronary vasodilation with dipyridamole has been proposed as an alternative to exercise testing for detecting CAD in paced patients, but this approach has never been tested. METHODS: Fourteen patients with a PVP and normal coronary arteries underwent stress thallium-201 scintigraphy and cardiac catheterization. In these patients and in eight control subjects, coronary flow velocities were measured in the left anterior descending coronary artery (LAD) and in the dominant coronary artery before and after adenosine administration. RESULTS: In the paced patients, coronary flow velocities in the LAD and in the dominant coronary artery were significantly lower than those in the control subjects. In addition, seven patients showed perfusion defects on dipyridamole thallium-201 single-photon emission computed tomography, with a specificity of 50% for this test. The defect-related artery in these patients had lower coronary flow reserve (2.6 +/- 0.5) as compared with those without perfusion defects (3.9 +/- 1.0, p < 0.05) or the control group (3.5 +/- 0.5, p < 0.05). CONCLUSIONS: Permanent ventricular pacing is associated with alterations in regional myocardial perfusion. Furthermore, abnormalities of microvascular flow, as indicated by reduced coronary flow reserve in the defect-related artery, are at least partially responsible for the uncertain specificity of dipyridamole myocardial perfusion scintigraphy.

Phasic coronary flow pattern and flow reserve in patients with left bundle branch block and normal coronary arteries.

OBJECTIVES: The purpose of this study was to determine whether scintigraphic myocardial perfusion defects in patients with left bundle branch block (LBBB) and normal coronary arteries are related to abnormalities in coronary flow velocity pattern and/or coronary flow reserve. BACKGROUND: Septal or anteroseptal defects on exercise myocardial perfusion scintigraphy are common in patients with LBBB and normal coronary arteries. METHODS: Thirteen patients (7 men, age 61+/-8 years) with LBBB and normal coronary arteries underwent stress thallium-201 scintigraphy and cardiac catheterization. In all patients and in 11 control subjects coronary blood flow parameters were calculated from Doppler measurements of flow velocity in the left anterior descending coronary artery (LAD) before and after adenosine administration. RESULTS: The time to maximum peak diastolic flow velocity was significantly longer both for the seven patients with (134+/-19 ms) and for the six without (136+/-7 ms) exercise perfusion defects than for controls (105+/-12 ms, p < 0.05), whereas the acceleration was slower (170+/-54, 186+/-42 and 279+/-96 cm/s2, respectively, p < 0.05). Coronary flow reserve in the patients with exercise perfusion defects (2.7+/-0.3) was significantly lower than in those without (3.7+/-0.5, p < 0.05) or in the control group (3.4+/-0.5, p < 0.05). CONCLUSIONS: Patients with LBBB have an impairment of early diastolic blood flow in the LAD due to an increase in early diastolic compressive resistance resulting from delayed ventricular relaxation. Furthermore, exercise scintigraphic perfusion defects in these patients are associated with a reduced coronary flow reserve, indicating abnormalities of microvascular function in the same vascular territory.

Effects of asynchronous ventricular activation on myocardial adrenergic innervation in patients with permanent dual-chamber pacemakers; an I(123)-metaiodobenzylguanidine cardiac scintigraphic study.

AIMS: To evaluate myocardial sympathetic innervation abnormalities in patients with DDD pacemakers for complete heart block. METHODS: We studied 39 patients, chronically paced in DDD mode because of complete atrioventricular block. Twenty-three healthy individuals served as a control group. All patients underwent planar and single-photon emission computed tomography (SPECT) myocardial imaging 4 h after intravenous infusion of 185 MBq I(123)-MIBG. The heart to mediastinum ratio was calculated to quantify cardiac I(123)-MIBG accumulation, while the SPECT study was performed to investigate the regional distribution of adrenergic innervation. All patients underwent a SPECT thallium(201)myocardial study during the same week as the I(123)-MIBG study. RESULTS: The heart to mediastinum ratio was significantly smaller in paced patients than in the controls (P<0.001). 89.7% of paced patients had regional abnormalities of I(123)-MIBG uptake, mainly in the inferior (92.3%) and apical (38.5%) wall. 46.2% of paced patients had regional perfusion defects, also mainly in the inferior (46.2%) and apical (10.3%) wall. Neither the I(123)-MIBG abnormalities nor the perfusion defects were related to the duration of pacing. CONCLUSIONS: Stimulation from the apex of the right ventricle leads to regional disturbances of the adrenergic innervation of the left ventricular myocardium, as assessed by I(123)-MIBG activity.

Segmental pattern of myocardial sympathetic denervation in idiopathic dilated cardiomyopathy: relationship to regional wall motion and myocardial perfusion abnormalities.

BACKGROUND: Iodine 123-labeled metaiodobenzylguanidine (MIBG) has been used to study cardiac adrenergic nerve activity. Cardiac MIBG uptake is diminished in patients with heart failure. However, it is not known how this reduction is related to regional abnormalities of myocardial wall motion or perfusion. METHODS AND RESULTS: We studied 24 patients with idiopathic dilated cardiomyopathy (ejection fraction <45%) and 15 healthy control subjects using I-123 MIBG cardiac imaging, echocardiographic assessment of wall motion abnormalities, technetium 99m sestamibi perfusion scintigraphy, and hemodynamic assessment. Cardiac MIBG was significantly correlated with ejection fraction (r = 0.67), cardiac index (r = 0.57), left ventricular wall motion score index (r = -0.68), and systolic wall stress (r = -0.61). MIBG was lower in patients than in control subjects (1.43 +/- 0.19 vs 2.05 +/- 0.02; P <.01), whereas the washout rate was higher (P <.01). Moreover, a significant correlation was found between the reduction in MIBG uptake and the severity of echocardiographic wall motion abnormalities in the anterior wall (r = 0.543), apex (r = 0.530), and septum (r = 0.675), as well as with the severity of decrease in resting myocardial perfusion in the anterior wall (r = 0.480) and septum (r = 0.580). CONCLUSIONS: Patients with idiopathic dilated cardiomyopathy show not only global but also regional abnormalities of cardiac sympathetic innervation. The severity of these changes is partially correlated with abnormalities of regional wall motion and myocardial perfusion.