Toshihiro Nozato

Cyclin A/cdk2 Activation Is Involved in Hypoxia-Induced Apoptosis in Cardiomyocytes

Abstract— Cardiomyocytes are terminally differentiated cells characterized as withdrawal cell-cycle machinery, but nonetheless they are known to express cell-cycle regulators. Because many proteins related to the cell cycle induce apoptosis in proliferating cells, we examined the involvement of these proteins in the apoptosis pathway in cardiomyocytes. Primary rat cardiomyocytes were exposed to a severe hypoxic condition to induce apoptosis. The apoptosis rate of cardiomyocytes increased to ≈40% under 24 hours of hypoxia as evaluated by the TUNEL method. The cyclin A protein level assessed by immunoblot analysis accumulated in a time-dependent manner in cardiomyocytes, but there was no increase in nonmyocytes. Hypoxia increased the activity of cyclin A–associated kinase but not the activity of cyclin E–associated kinase, and the apoptosis was inhibited by infection of dominant-negative cdk2 adenovirus, suggesting that cyclin A and its associated kinase play significant roles in the apoptosis of cardiomyocytes. To investigate the cyclin A–mediated apoptosis, we infected cultured cells with cyclin A adenovirus. Apoptosis was induced in 63±12% of the infected cardiomyocytes in contrast to only 12±3% of the LacZ-infected control cells. In addition, the cells in the hypoxic condition showed an increase in caspase-3 activity and a subsequent decrease in p21cip1/waf1 protein, which is partly cleaved by caspase-3. These findings confirm that cyclin A–associated kinase mediates hypoxia-induced apoptosis in cardiomyocytes, and they also suggest that additional elements of the cell-cycle–dependent machinery participate in this mechanism.

Quantitative Measures of Coronary Stenosis Severity by 64-Slice CT Angiography and Relation to Physiologic Significance of Perfusion in Nonobese Patients: Comparison with Stress Myocardial Perfusion Imaging

Coronary stenosis severity by 64-slice CT angiography (CTA) is acceptably correlated with intravascular ultrasound. Stress myocardial perfusion imaging using SPECT is an established method for assessment of the functional significance of coronary stenosis. Our aim was to assess a clinical validation of quantitative measurements of coronary stenosis severity by 64-slice CTA and the relation to the physiologic significance of myocardial perfusion. Methods: One hundred four patients with suspected coronary artery disease underwent 64-slice CTA and stress 201Tl SPECT. The stenosis severities of 105 coronary lesions assessed by CTA with sufficient image quality were compared with the results of stress 201Tl SPECT. The body mass index (BMI) of the patients was 23.8 kg/m2 (range, 21.1–25.6 kg/m2). Results: Reversible defects began to increase progressively when the area of stenosis was at least 60%, and the prevalence of these reversible defects and their severity significantly increased as the degree of stenosis increased. When stenosis severity by CTA is < 60%, ischemia is seldom observed; when stenosis severity is ≥80%, ischemia is common (86%). For intermediate stenosis severity values of 60%–70%, the prevalence of reversible defects was 9 of 27 vessels (33%), and for stenosis severity values of 70%–80%, the prevalence was 20 of 37 vessels (54%). When evaluating the diagnostic accuracy of stenosis severity by CTA to identify patients with ischemia excluding all nonevaluable vessels, applying stenosis thresholds of >70% results in 79% sensitivity, 92% specificity, 66% positive predictive value, and 96% negative predictive value. A lesion minimal luminal cross-sectional area of < 3.7 mm2 was a good accurate cutoff value for significant coronary narrowing using stress SPECT, with a sensitivity of 88% and specificity of 83% by receiver-operating-characteristic analysis. Conclusion: Despite an excellent negative predictive value to rule out the presence of ischemia, 64-slice CTA alone is a poor discriminator of the functional significance of myocardial ischemia in a highly selected patient population with a low BMI.

Incremental value of combining 64-slice computed tomography angiography with stress nuclear myocardial perfusion imaging to improve noninvasive detection of coronary artery disease.

BackgroundTo compare the accuracy of combined 64-slice computed tomography angiography (CTA) and stress nuclear myocardial perfusion imaging (MPI) in the noninvasive detection of coronary artery disease (CAD) with that of 64-slice CTA alone.Methods and resultsOne hundred thirty symptomatic patients with suspected CAD underwent both 64-slice CTA and stress thallium-201 MPI before invasive coronary angiography (ICA). Coronary lesions with ≥50% luminal narrowing were considered as significant stenoses on CTA and ICA. Of 390 arteries in 130 patients, 54 (14%) were nonevaluable by CTA due to severe calcifications, motion artifacts, and/or poor opacification. All nonevaluable arteries were considered positive. The sensitivity, specificity, PPV and NPV were 95%, 80%, 69%, and 97%, respectively, for CTA alone and 94%, 92%, 85%, and 97%, respectively, for CTA with stress nuclear MPI for all nonevaluable arteries on CTA. Per-patient analysis showed significant increase in specificity and PPV. The majority (75%, 9/12) of nonevaluable severely calcified vessels in the left anterior descending artery were positive on stress nuclear MPI, whereas the majority (89%, 8/9) of nonevaluable vessels with motion artifacts in the right coronary artery were negative.ConclusionsCombined CTA and stress nuclear MPI provide improved diagnostic accuracy for the noninvasive detection of CAD.

Early validation study of 64-slice multidetector computed tomography for the assessment of myocardial viability and the prediction of left ventricular remodelling after acute myocardial infarction

AIMS We aim to validate the ability of multidetector computed tomography (MDCT) for assessing myocardial viability and predicting left ventricular (LV) remodelling after acute myocardial infarction (AMI). METHODS AND RESULTS In 52 consecutive patients with first AMI, 64-slice MDCT without iodine re-injection was performed immediately following coronary stenting. Electrocardiogram-gated thallium-201 single-photon emission tomography was performed using QGS programs within 5 days and 6 months after onset. Among the 52 patients, 18 patients (Group A) showed transmural contrast-delayed enhancement on MDCT images, 20 patients (Group B) showed subendocardial contrast-delayed enhancement, and 14 patients (Group C) had no contrast-delayed enhancement. In the acute phase, peak creatine kinase-MB [497 (189-744), 182 (90-358), 85 (40-204) IU/mL, respectively, P = 0.0004] was significantly higher in Group A, while the incidence of myocardial blush grade 3 (22, 67, 75%, respectively, P = 0.001) and LV ejection fraction (41 +/- 7, 53 +/- 12, 62 +/- 11%, respectively, P < 0.0001) were significantly lower in Group A. During the 6-month period, LV remodelling (P = 0.001) and the number of rehospitalization for heart failure (P = 0.0017) were more significantly observed in Group A. CONCLUSION Myocardial contrast-delayed enhancement patterns provide promising information regarding myocardial viability, LV remodelling, and prognosis in AMI.

Electrophysiological Characteristics of Localized Reentrant Atrial Tachycardia Occurring After Catheter Ablation of Long‐Lasting Persistent Atrial Fibrillation

Background: Mapping of recurrent atrial tachycardia (AT) after extensive ablation for long‐lasting persistent atrial fibrillation (AF) is complex. We sought to describe the electrophysiological characteristics of localized reentry occurring after ablation of long‐lasting persistent AF.

Effects of serum n-3 to n-6 polyunsaturated fatty acids ratios on coronary atherosclerosis in statin-treated patients with coronary artery disease.

A low ratio of n-3 to n-6 polyunsaturated fatty acids has been associated with cardiovascular events. However, the effects of this ratio on coronary atherosclerosis have not been fully examined. The purpose of the present study was to evaluate the correlations between the n-3 to n-6 polyunsaturated fatty acid ratio and coronary atherosclerosis. Coronary atherosclerosis in nonculprit lesions in the percutaneous coronary intervention vessel was evaluated using virtual histology intravascular ultrasound in 101 patients at the time of percutaneous coronary intervention and 8 months after statin therapy. Forty-six patients (46%) showed atheroma progression and the remaining 55 patients (54%) showed atheroma regression at 8-month follow-up. Significant negative correlations were observed between percentage change in plaque volume and change in the eicosapentaenoic acid (EPA)/arachidonic acid (AA) ratio (r = -0.190, p = 0.05), docosahexaenoic acid (DHA)/AA ratio (r = -0.231, p = 0.02), and EPA+DHA/AA ratio (r = -0.240, p = 0.02). Furthermore, percentage change in the fibrous component volume was negatively and significantly correlated with change in the EPA/AA ratio (r = -0.206, p = 0.04) and EPA+DHA/AA ratio (r = -0.217, p = 0.03). Multivariate regression analysis showed that change in the EPA+DHA/AA ratio was a significant predictor of percentage change in plaque volume and fibrous component volume (β = -0.221, p = 0.02, and β = -0.200, p = 0.04, respectively). In conclusion, decreases in serum n-3 to n-6 polyunsaturated fatty acid ratios are associated with progression in coronary atherosclerosis evaluated using virtual histology intravascular ultrasound in statin-treated patients with coronary artery disease.

Prognostic Value of Myocardial Contrast Delayed Enhancement With 64-Slice Multidetector Computed Tomography After Acute Myocardial Infarction

OBJECTIVES This study evaluated the clinical value of myocardial contrast delayed enhancement (DE) with multidetector computed tomography (MDCT) for predicting clinical outcome after acute myocardial infarction (AMI). BACKGROUND Although some studies have described the use of MDCT for assessment of myocardial viability after AMI, clinical experience remains limited. METHODS In 102 patients with first AMI, 64-slice MDCT without iodine reinjection was performed immediately following successful percutaneous coronary intervention (PCI). We measured the size of myocardial contrast DE on MDCT and compared it with clinical outcome. Primary composite cardiac events were cardiac death or hospitalization for worsening heart failure. RESULTS Among the 102 patients (24 ± 10 months follow-up), 19 patients experienced primary composite cardiac events (cardiac death, n = 7; heart failure, n = 12). Kaplan-Meier analysis showed higher risk of cardiac events for patients in the third tertile of myocardial contrast DE size (≥ 36 g) than for those in the other 2 tertiles (p < 0.0001). Multivariable Cox proportional hazards regression analysis indicated that myocardial contrast DE size (adjusted hazard ratio [HR] for tertile 3 vs. 1: 16.1, 95% confidence interval [CI]: 1.45 to 72.4, p = 0.022; HR for tertile 3 vs. 2: 5.06, 95% CI: 1.25 to 22.7, p = 0.039) was a significant independent predictor for cardiac events after adjustment for Thrombolysis In Myocardial Infarction risk score, left ventricular ejection fraction, total defect score on single-photon emission CT with technetium tetrofosmin, and transmural extent of myocardial contrast DE on MDCT. CONCLUSIONS Myocardial contrast DE size on MDCT immediately after primary PCI may provide promising information for predicting clinical outcome in patients with AMI.

Clinical Characteristics of Patients With Persistent Atrial Fibrillation Successfully Treated by Left Atrial Ablation

Background—We sought to characterize patients with persistent atrial fibrillation (AF) who were successfully treated by ablation targeting the left atrium (LA). Methods and Results—Ninety-three patients (58±10 years, 79 male) undergoing ablation of persistent AF were studied. During the first procedure, ablation was performed in the LA and coronary sinus, consisting of pulmonary vein isolation, linear ablation, and electrogram-based ablation. During follow-up after the first procedure, 35 patients (38%) remained free from tachyarrhythmias, 27 patients (29%) had atrial tachycardia, and 31 patients (33%) had AF. Duration of persistent AF according to medical history and whether AF was terminated by ablation were associated with the outcome (P=0.005, P=0.004, respectively). In multivariate analysis, the duration of persistent AF was the only predictor of freedom from AF (sinus rhythm or atrial tachycardia) (odds ratio, 0.80 for a 1-year increase; 95% confidence interval, 0.67 to 0.95; P=0.01). Of 31 patients in whom AF recurred during follow-up, electrogram-based ablation was performed in the right atrium in 26 patients. Sixteen of those patients (62%) remained free from AF during follow-up. Overall, 82% of patients were free from any tachyarrhythmias at 2-year follow-up after a median of 2 procedures. Conclusions—Patients with shorter duration of persistent AF were more likely to be free from AF by LA ablation. Right atrial ablation may provide incremental efficacy in patients who are refractory to LA ablation.

Incremental Prognostic Values of Serum Tenascin-C Levels With Blood B-type Natriuretic Peptide Testing at Discharge in Patients With Dilated Cardiomyopathy and Decompensated Heart Failure

BACKGROUND This study investigates the predictive value of serum tenascin-C (TN-C), which is observed at the active sites of ongoing tissue remodeling, for cardiac events of patients with dilated cardiomyopathy (DCM). METHODS AND RESULTS In this trial, 110 consecutive patients hospitalized with heart failure (HF) resulting from DCM underwent assessments of serum TN-C and plasma brain natriuretic peptide (BNP) levels at discharge and were followed up for 22.4 months. Cardiac function and hemodynamics were assessed invasively in 60 of these patients at discharge. There were 19 cardiac events (14 rehospitalizations, 3 deaths from refractory HF, and 2 sudden deaths) during follow-up. The average levels of TN-C and BNP were 73 +/- 38 ng/mL and 279 +/- 414 pg/mL, respectively. The optimal cutoff value for serum TN-C levels predicted cardiac events were >or=78.4 ng/mL, whereas BNP levels were >or=219 pg/mL. Patients with levels higher than this had significantly higher cardiac events and serum TN-C >or=78.4 ng/mL had an incremental predictive power with BNP for cardiac events. Left ventricular end-diastolic volume was significantly larger, and mean pulmonary arterial pressure was elevated in patients with serum TN-C >or=78.4 ng/mL. CONCLUSIONS The combined index of serum levels for TN-C and BNP at discharge predicts cardiac events from decompensated HF. Additionally, elevated serum TN-C levels reflect left ventricular and pulmonary vascular remodeling in DCM patients.

Clinical characteristics of massive air embolism complicating left atrial ablation of atrial fibrillation: lessons from five cases.

AIMS This study aimed to elucidate the clinical characteristics of massive air embolism occurring during atrial fibrillation (AF) ablation. METHODS AND RESULTS Of 2976 patients undergoing AF ablation, 5 patients complicated by serious air embolism were examined. Atrial fibrillation ablation was performed with the use of three long sheaths for circular mapping and ablation catheters under conscious sedation. Two patients had air spontaneously introduced through a haemostasis valve of the long sheaths, at the end of long apnoea caused by the sedation, even though the catheters were placed within the long sheaths. The remaining three patients, all of whom also exhibited long apnoea, had air entry at the circular mapping catheter exchanges. Air accumulated in the right and left ventricles, left atrial appendage, right coronary artery, and ascending aorta. Haemodynamic collapse and hypoxaemia occurred in all and two patients, respectively, and supportive treatment and the accumulated air were aspirated. ST elevation, haemodynamic collapse, and hypoxaemia persisted for 10-35 min; however, all patients recovered completely. After we changed the sedative to one with less respiratory depressive effects and the timing of the saline flush at the circular mapping catheter exchanges, we never experienced such serious complications any further. CONCLUSION Serious air embolism can occur in patients with long apnoea under sedation during AF ablation with the use of long sheaths. Supportive therapy and air aspiration were effective in resolving the complication. A sedative that causes less respiratory depression and the timing of the saline flush were important for preventing air embolism.