Early post-stress decrease in cardiac performance by impedance cardiography and its relationship to the severity and extent of ischemia by myocardial perfusion imaging.

BACKGROUND: While single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is a well-established noninvasive procedure for the evaluation of patients with coronary artery disease (CAD), it is unable to detect the presence of, or underestimates the extent of CAD in certain patients. We aimed to show that a bio-impedance device can detect early post-stress changes in several hemodynamic parameters, thereby serving as a potential marker for the presence of significant ischemia. METHODS: Prospectively enrolled patients, referred to our Medical Center for clinically-indicated MPI, underwent testing using a Non-Invasive Cardiac System (NICaS) before and immediately after exercise. The differences between rest and stress hemodynamic parameters were compared with the severity and extent of myocardial ischemia by MPI. The study included 198 patients; mean age was 62 years, 26% were women, 54% had hypertension, and 29% diabetes mellitus. Of them, 188 patients had ≤10%, and 10 had > 10% of myocardial ischemia. RESULTS: In the first group, there was a significantly greater increase in post-exercise stroke index, stroke work index, cardiac index and cardiac power index (19.2, 29.1, 90.5 and 107%, respectively) compared with the second group (- 2.7, 3.8, 43.7 and 53.5%, respectively), as well as a significantly greater decrease in total peripheral resistance index (- 38.7% compared with - 16.3%), with corresponding p values of 0.015, 0.017, 0.040, 0.016, and < 0.001, respectively. CONCLUSIONS: Our data suggest that immediate post-stress changes in several hemodynamic parameters, detected by the NICaS, can be used as an important adjunct to SPECT MPI for the early detection of myocardial ischemia.

A novel heart rate variability algorithm for the detection of myocardial ischemia: pilot data from a prospective clinical trial.

BACKGROUND: Heart rate variability (HRV) analysis has been shown to be a predictor of sudden cardiac death and all-cause mortality in patients with cardiac disease. OBJECTIVES: To examine whether newer HRV analysis algorithms, as used by the HeartTrends device, are superior to exercise stress testing (EST) for the detection of myocardial ischemia in patients without known coronary artery disease (CAD). METHODS: We present pilot data of the first 100 subjects enrolled in a clinical trial designed to evaluate the yield of short-term (1 hour) HRV testing for the detection of myocardial ischemia. The study population comprised subjects without known CAD referred to a tertiary medical center for EST with single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI). All patients underwent a 1 hour electrocardiographic acquisition for HRV analysis with a HeartTrends device prior to ESTwith MPI. Sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively) were calculated for EST and HRV analysis, using MPI as the gold standard for the non-invasive detection of myocardial ischemia. RESULTS: In this cohort 15% had a pathologic MPI result. HRV analysis showed superior sensitivity (85%), PPV (50%) and NPV (97%) as compared to standard EST (53%, 42%, 90%, respectively), while the specificity of the two tests was similar (86% and 85%, respectively). The close agreement between HRV and MPI was even more pronounced among patients > 65 years of age. CONCLUSIONS: Our pilot data suggest that the diagnostic yield of the novel HeartTrends HRV algorithm is superior to conventional EST for the non-invasive detection of myocardial ischemia.

Poor outcome among patients undergoing myocardial perfusion imaging with intermediate-zone troponin.

BACKGROUND: Intermediate zone troponin elevation is defined as one to five times the upper limit of normal. Approximately half the patients presenting with chest pain to the emergency department have initial intermediate zone troponin. OBJECTIVES: We aimed to investigate the long-term outcome of patients hospitalized with chest pain and intermediate zone troponin elevation. METHODS: We investigated 8269 patients hospitalized in a tertiary center with chest pain. All patients had serial measurements of troponin during hospitalization. Patients were divided into three groups based on their initial troponin levels: negative troponin (N = 6112), intermediate zone troponin (N = 1329) and positive troponin (N = 828). All patients underwent myocardial perfusion imaging (MPI) as part of the initial evaluation. RESULTS: Mean age of the study population was 68 ± 11, of whom 36% were women. Patients with an intermediate zone troponin were older, more likely to be males, and with significantly more cardiovascular co-morbidities. Multivariate analysis adjusted for age, gender, cardiovascular risk factors, and abnormal MPI result found that patients with intermediate zone troponin had a 70% increased risk of re-hospitalization at 1 year (HR 1.70, 95%CI 1.48-1.96, p-value < 0.001) and 5.3 times higher risk of total mortality at 1-year (HR 5.33, 95%CI 3.65-7.78, p-value < 0.001). sub-group analysis found that among the intermediate zone troponin group, patients with double intermediate zone troponin had the poorest outcome. CONCLUSIONS: Intermediate zone troponin elevation is an independent risk factor associated with adverse outcomes and therefore patients with an initial value in this range should be closely monitored and aggressively managed.

Stress-induced ST-segment elevation in patients without prior Q-wave myocardial infarction.

BACKGROUND: Stress-induced ST-segment elevation is an uncommon finding that usually occurs in patients with prior myocardial infarction (MI). Our purpose was to assess the angiographic and clinical significance of this finding in patients without prior MI. METHODS: Of the 29002 consecutive ambulatory patients who underwent stress myocardial perfusion imaging over a 5-year period, 205 (0.7%) developed stress-induced ST-segment elevation, of whom 39 (19%) had no Q-wave MI in leads showing ST-segment elevation during either exercise (n = 31) or dipyridamole (n = 8) stress myocardial perfusion imaging. All 39 patients were hospitalized and underwent coronary angiography. RESULTS: Significant coronary artery disease was found in all 39 patients: 87% had critical (>or=90%) stenosis, and 59% had multiple vessel disease. During hospitalization, 37 patients (95%) underwent revascularization. CONCLUSIONS: In patients without prior Q-wave MI, stress-induced ST-segment elevation is associated with critical coronary artery disease. Therefore, these patients should be considered for early coronary investigation.

Comparison of the usefulness of heart rate variability versus exercise stress testing for the detection of myocardial ischemia in patients without known coronary artery disease.

Heart rate variability (HRV) has been shown to be attenuated in patients with coronary artery disease (CAD) and may, therefore, be possibly used for the early detection of myocardial ischemia. We aimed to evaluate the diagnostic yield of a novel short-term HRV algorithm for the detection of myocardial ischemia in subjects without known CAD. We prospectively enrolled 450 subjects without known CAD who were referred to tertiary medical centers for exercise stress testing (EST) with single-photon emission computed tomography myocardial perfusion imaging (MPI). All subjects underwent 1-hour Holter testing with subsequent HRV analysis before EST with MPI. The diagnostic yield of HRV analysis was compared with EST, using MPI as the gold standard for the noninvasive detection of myocardial ischemia. All subjects had intermediate pretest probability for CAD. Mean age was 62 years, 38% were women, 51% had hypertension, and 25% diabetes mellitus. HRV analysis showed superior sensitivity (77%) compared with standard EST (27%). After multivariate adjustment, HRV was independently associated with an 8.4-fold (p <0.001) increased likelihood for the detection of myocardial ischemia by MPI, whereas EST did not show a statistically significant association with a positive MPI (odds ratio 2.1; p = 0.12). Of subjects who were referred for subsequent coronary angiography, the respective sensitivities of HRV and EST for the detection of significant CAD were 73% versus 26%. Our data suggest that HRV can be used as an important noninvasive technique for the detection of myocardial ischemia in subjects without known CAD, providing superior sensitivity to conventional EST in this population.

Noninvasive detection of collateral flow to the infarct-related coronary artery in patients after myocardial infarction by Tl-201 tomographic imaging.

BACKGROUND: The determination of viability and perfusion within the infarct zone in post-myocardial infarction patients has both therapeutic and prognostic significance. Reversibility of thallium 201 uptake within the territory of the infarct-related coronary artery (IRA) as shown by single photon emission computed tomography (SPECT) is associated with a jeopardized but viable myocardium. We aimed to test the hypothesis that for post-myocardial infarction patients undergoing Tl-201 stress-redistribution SPECT, a scintigraphic pattern of distal reversibility without proximal reversibility within a defect corresponding to the IRA territory is a marker of collateral flow to the occluded culprit artery. METHODS AND RESULTS: We assessed Tl-201 SPECT imaging results of 78 patients with IRA occlusion as demonstrated by angiography 7 +/- 1 months after myocardial infarction. Angiography demonstrated the presence of collateral flow in 57 patients and its absence in 21 patients. Distal reversibility was present in 42 of the 57 patients with collateral flow (sensitivity, 74%) and was absent in 16 of the 21 patients without collateral flow (specificity, 76%). Collateral flow to the IRA was demonstrated in 42 of 47 patients with distal reversibility (group A) (positive predictive value, 89%) and absent in 16 of 31 patients with a fixed defect without reversibility (group B) (P <.001) (negative predictive value, 52%). CONCLUSIONS: In patients after myocardial infarction, a Tl-201 SPECT redistribution pattern of distal reversibility without proximal reversibility within a defect in the IRA territory is a noninvasive marker of collateral flow to the culprit artery with a high positive predictive value that may provide valuable information on patient management. A larger prospective study in an unselected patient population is needed to further evaluate the clinical value of this marker.