Significance of both negative T waves and stress-induced normalization of the repolarization phase in infarcted patients: a positron-emission-tomography assessment of regulation of myocardial blood flow and viability of myocardium

Exercise-induced normalization of right precordial negative T waves in arrhythmogenic right ventricular cardiomyopathy

Negative T waves (NTWs) in right precordial leads (V₁ to V₃) may be observed on the electrocardiogram (ECG) of healthy subjects but can also represent the hallmark of an underlying arrhythmogenic right ventricular cardiomyopathy (ARVC). It has been a consistent observation that NTWs usually become upright with exercise in healthy subjects without underlying heart disease. No systematic study has evaluated exercise-induced changes of NTWs in ARVC. We assessed the prevalence and relation to the clinical phenotype of exercise-induced right precordial NTWs changes in 35 patients with ARVC (19 men, mean age 22.2 ± 6.2 years). Forty-one healthy subjects with right precordial NTWs served as controls. At peak of exercise (mean power 149 ± 43 W, mean heart rate 83.6 ± 12.6% of target), NTWs persisted in 3 patients with ARVC (9%), completely normalized in 12 (34%), and partially reverted in 20 (57%). Patients with ARVC with or without NTWs normalization showed a similar clinical phenotype. The overall prevalence of right precordial T waves changes during exercise (normalization plus partial reversal) did not differ between patients with ARVC and controls (92% vs 88%, p = 1.0), whereas there was a statistically nonsignificant trend toward a greater prevalence of complete normalization in controls (56% vs 34%, p = 0.06). In conclusion, our study demonstrated that right precordial NTWs partially or completely revert with exercise in most patients with ARVC, and NTWs normalization is unrelated to the clinical phenotype. Exercise-induced NTWs changes are inaccurate in differentiating between ARVC patients and benign repolarization abnormalities.

Normalization of abnormal T-waves during stress testing does not identify patients with reversible perfusion defects

OBJECTIVE

To determine if T-wave normalization during exercise or dobutamine stress testing identified patients with myocardial ischemia as indicated by reversible perfusion defects.

METHODS

Exercise or dobutamine stress tests with perfusion scintigraphy were performed in 1,173 patients with abnormal T-waves on their baseline electrocardiograms. The results of perfusion scintigraphy were compared in patients with and without stress-induced T-wave normalization.

RESULTS

Only 33 of 270 patients with reversible perfusion defects (12.2%) had T-wave normalization during stress while 76.4% of 140 patients who had T-wave normalization during stress did not have a reversible perfusion defect. Results were similar for patients who did or did not reach 85% of their maximal predicted heart rate, for patients with and without Q-wave infarction on the baseline EKG and for patients who did or did not have ischemic ST-segment depression during stress.

CONCLUSIONS

T-wave normalization during stress testing has low sensitivity and poor positive predictive value for stress-induced reversible myocardial ischemia.

Assessment of intermediate stenosis in the left anterior descending coronary artery with contrast-enhanced transthoracic Doppler echocardiography

BACKGROUND

Visual or quantitative assessment of coronary angiography may not exactly predict the physiological significance of intermediate (40-70%) coronary stenosis. Coronary flow reserve is a well-established marker of the functional significance of coronary stenosis.

OBJECTIVES

The aim of this study was to compare the coronary flow velocity reserve (CFVR) using contrast-enhanced transthoracic Doppler echocardiography (CE-TTDE) with thallium-201 imaging in assessment of intermediate lesions in the left anterior descending coronary artery (LAD).

METHODS

A consecutive series of 50 patients with intermediate stenosis in the LAD underwent pharmacological stress thallium-201 imaging and CFVR measured by CE-TTDE.

RESULTS

CFVR could be measured in 49 of 50 patients by the present method. A CFVR <2.0 predicted the presence of a stress thallium defect in 12 of 14 patients (agreement=90%, kappa=0.76, P < 0.001). The sensitivity and specificity of CFVR for stress thallium-201 results were 86 and 91%, respectively. In contrast, significant stenosis (>50% by diameter) showed fair agreement for stress thallium defects (agreement=59%, kappa=0.28, P < 0.05).

CONCLUSIONS

In the evaluation of intermediate lesions in the LAD, CFVR as assessed by CE-TTDE could accurately predict the presence of ischemia on stress thallium imaging, whereas angiographic stenosis did not yield reliable results.

High-resolution myocardial perfusion mapping in small animals in vivo by spin-labeling gradient-echo imaging

An ECG and respiration-gated spin-labeling gradient-echo imaging technique is proposed for the quantitative and completely noninvasive measurement and mapping of myocardial perfusion in small animals in vivo. In contrast to snapshot FLASH imaging, the spatial resolution of the perfusion maps is not limited by the heart rate. A significant improvement in image quality is achieved by synchronizing the inversion pulse to the respiration movements of the animals, thereby allowing for spontaneous respiration. High-resolution myocardial perfusion maps (in-plane resolution=234 x 468 microm2) demonstrating the quality of the perfusion measurement were obtained at 4.7 T in a group of seven freely breathing Wistar-Kyoto rats under isoflurane anesthesia. The mean perfusion value (group average +/- SD) was 5.5 +/- 0.7 ml g(-1)min(-1). In four animals, myocardial perfusion was mapped and measured under cardiac dobutamine stress. Perfusion increased to 11.1 +/- 1.9 ml g(-1)min(-1). The proposed method is particularly useful for the study of small rodents at high fields.