Assessment of the sensitivity of detecting drug-induced QTc changes using subject-specific rate correction.

Aims: To quantify the sensitivity of QT heart-rate correction methods for detecting drug-induced QTc changes in thorough QT studies.

Methods: Twenty-four-hour Holter ECGs were analyzed in 66 normal subjects during placebo and moxifloxacin delivery (single oral dose). QT and RR time series were extracted.

Evaluation of a subject-specific transfer-function-based nonlinear QT interval rate-correction method.

The QT interval in the electrocardiogram (ECG) is a measure of total duration of depolarization and repolarization. Correction for heart rate is necessary to provide a single intrinsic physiological value that can be compared between subjects and within the same subject under different conditions. Standard formulas for the corrected QT (QTc) do not fully reproduce the complexity of the dependence in the preceding interbeat intervals (RR) and inter-subject variability.

Extraction and analysis of T waves in electrocardiograms during atrial flutter.

Analysis of T waves in the ECG is an essential clinical tool for diagnosis, monitoring, and follow-up of patients with heart dysfunction. During atrial flutter, this analysis has been so far limited by the perturbation of flutter waves superimposed over the T wave. This paper presents a method based on missing data interpolation for eliminating flutter waves from the ECG during atrial flutter.

Modeling transport of interstitial potassium in regional myocardial ischemia: effect on the injury current.

Myocardial ischemia leads to an efflux of potassium ions from affected cells. The resulting depolarization of the resting membrane is one of the main features of ischemic myocardium. It has been shown experimentally that a part of the surplus interstitial potassium is transported out of the ischemic zone, even if no coronary blood flow is present in the affected area.

The role of extracellular potassium transport in computer models of the ischemic zone.

Ischemic heart disease is associated with large mortality and morbidity. Understanding of the relations between coronary artery occlusion, geometry of the ischemic region, physiology of ischemia, and the resulting changes in electrocardiogram (ECG) leads and catheter signals is important to support diagnosis and treatment. Computer models play an important role in understanding ischemia, by linking experimental to clinical results.

ST elevation or depression in subendocardial ischemia?

ST-segment depression in epicardial electrograms can be a "reciprocal" effect of remote myocardial ischemia (MI), and can also be due to local partial-thickness or "subendocardial" MI. Experimental studies have shown either ST elevation or depression in leads overlying a subendocardial ischemic region. Those reporting elevation have shown depression over the lateral borders of the ischemia.

Understanding ST depression in the stress-test ECG.

Objective: The electrocardiogram (ECG) obtained during stress testing often shows a typical pattern of primary ST depression. A similar pattern can occur in unstable angina. Current textbooks consider ST depression as a direct result of partial occlusion of a coronary artery.

Why do we need supercomputers to understand the electrocardiographic T wave?

Objective: Propagation of depolarisation and repolarisation in myocardium results from an interplay of membrane potential, transmembrane current, and intercellular current. This process can be represented mathematically with a reaction-diffusion (RD) equation. Solving RD equations for a whole heart requires a supercomputer.

Effects of valsartan or amlodipine alone or in combination on plasma catecholamine levels at rest and during standing in hypertensive patients.

To compare the effects of valsartan and amlodipine alone or in combination on plasma norepinephrine (NE) at rest and standing for 10 minutes in patients with hypertension, 47 patients with a sitting diastolic blood pressure (BP) (DBP)>95 mm Hg and<110 mm Hg were randomized in a double-blind fashion to either valsartan or amlodipine. During the first 4 weeks of treatment, patients received a low dose of either valsartan (80 mg) or amlodipine (5 mg). The patients were force-titrated to the high dose of either drug (160 or 10 mg) for 4 weeks.

The effect of lesion size and tissue remodeling on ST deviation in partial-thickness ischemia.

Background: Myocardial ischemia causes ST segment elevation or depression in electrocardiograms and epicardial leads. ST depression in epicardium overlying the ischemic zone indicates that the ischemia is nontransmural. However, nontransmural ischemia does not always cause ST depression.

Progressive epicardial coronary blood flow reduction fails to produce ST-segment depression at normal heart rates.

ST-segment depression is commonly seen in patients with acute coronary syndromes. Most authors have attributed it to transient reductions in coronary blood flow due to nonocclusive thrombus formation on a disrupted atherosclerotic plaque and dynamic focal vasospasm at the site of coronary artery stenosis. However, ST-segment depression was never reproduced in classic animal models of coronary stenosis without the presence of tachycardia.

Absence of clinically significant increase in pulmonary artery pressure after intravenous perflutren injection for myocardial perfusion imaging in pigs.

Objective: We sought to evaluate the impact of a continuous intravenous infusion of perflutren on systemic pulmonary artery pressures at clinically relevant doses for myocardial perfusion imaging in pigs.

Methods: Five anesthetized, ventilated, open-chest pigs were administered perflutren intravenously at a rate of 0.0364 mL/kg/min over approximately 5 minutes.

Effect of the renin-angiotensin system or calcium channel blockade on the circadian variation of heart rate variability, blood pressure and circulating catecholamines in hypertensive patients.

Objective: To determine the effects of 8 weeks of therapy with amlodipine, ramipril or telmisartan on the autonomic system over 24 h in hypertensives.

Methods: After a placebo run-in, 57 patients were included in a prospective randomized open-label design protocol for therapy with amlodipine (5 mg for 4 weeks followed by 10 mg for 4 weeks, n = 22), or ramipril (2.5 mg for 1 week, 5.

Distinction between myocardial ischemia and postural changes in continuous ECG monitoring based on ST-segment amplitude and vector orientation--preliminary results.

Background: Myocardial ischemia, commonly defined as ST-segment elevation or depression on the electrocardiogram (ECG), is plagued by a large number of false positive events.

Objectives: To present a new method that attempts to distinguish between 'highly probable ischemia' and positional changes.

Methods: Continuous three-lead orthogonal ECG monitoring was performed in three groups of subjects: 16 healthy volunteers undergoing a body position change protocol, 22 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) and 17 patients with acute coronary syndromes (ACS).