Correlation between myocardial ischemia and changes in arterial resistance during coronary artery bypass surgery

A new noninvasive device for measuring central ejection dP/dt mathematical foundation of cardiac dP/dt measurement using a model for a collapsible artery

We have developed a novel non-invasive device for the measurement of one of the most sensitive indices of myocardial contractility as represented by the rate of increase of intraventricular pressure (left ventricular dP/dt and arterial dP/dt performance index (dP/dt(ejc)). Up till now, these parameters could be obtained only by invasive catheterization methods. The new technique is based on the concept of applying multiple successive occlusive pressures on the brachial artery from peak systole to diastole using a inflatable cuff and plotting the values against time intervals that leads to the reconstruction of the central aortic pressure noninvasively. The following describes the computer simulator developed for providing a mathematical foundation of the new sensor. At the core of the simulator lies a hemodynamic model of the blood flow on an artery under externally applied pressure. The purpose of the model is to reproduce the experimental results obtained in studies on patients (Gorenberg et al. in Cardiovasc Eng: 305-311, 2004; Gorenberg et al. in Emerg med J 22 (7): 486-489, 2005) and a animal model where ischemia resulted from balloon inflation during coronary catheterization (Gorenberg and Marmor in J Med Eng Technol, 2006) and to describe correlations between the dP/dt(ejc) and other hemodynamic variables. The model has successfully reproduced the trends observed experimentally, providing a solid in-depth understanding of the hemodynamics involved in the new measurement. A high correlation between the dP/dt(ejc) and the rate of pressure rise in the aorta during the ejection phase was observed. dP/dt(ejc) dependence on other hemodynamic parameters was also investigated.

Validation of a novel method to determine non-invasively the rate of central aortic pressure changes

INTRODUCTION

One of the most sensitive indices of myocardial contractility is represented by the rate of increase of intraventricular pressure during isovolumetric contraction (dP/dt) and (dP/dt(ejc)), which represents the rate of change of pressure during ejection. Today these parameters can be obtained only by invasive catheterization methods. We developed a novel technique that leads to the non-invasive reconstruction of the central aortic pressure. The technique is based on the concept of applying multiple successive occlusive pressures on the brachial artery from peak systole to diastole using an inflatable cuff and plotting the values against time intervals. The hypothesis is that the time intervals required for the aortic pressure wave to overcome a given occlusive brachial pressure applied by a sphyngomanometer on the arm are equal to time needed to reach the same pressure in the central aorta plus the propagation time to the brachial point, which is constant in the same patient throughout the measurements.

METHODS AND RESULTS

We tested the hypothesis using an animal experiment. The new non-invasive device was mounted on the left forelimb of the animal. A Millar pressure transducer catheter was inserted to the aorta and the aorta pressure was recorded at time intervals of 1 ms. A second catheter was inserted into the coronary arteries and used to create controlled occlusion of the arteries using a balloon inflated to 10 atm. Measurements were obtained before the intervention was started, and throughout the sequence of repeated occlusions and deflations. At the end of the sequence, IV dobutamine was administered and results were monitored for 10 min while the heart rate and blood pressure were rising. Non-invasive dP/dt(ejc) was reduced typically by 20% in response to balloon inflation. In long occlusion periods, stabilization and sometimes recovery of dP/dt(ejc) is observed. By plotting dP/dt(ejc) measured by the new non-invasive device versus catheter measurements a correlation factor of 0.843 was found.

CONCLUSION

A newly developed method of non-invasive measurement of central dP/dt has been found to correlate to invasive measurements in an animal model.

Acute coronary syndromes in the emergency department: diagnostic characteristics, tests, and challenges

Failure to diagnose patients who have acute coronary syndromes (ACSs)-either acute myocardial infarction (AMI) or unstable angina pectoris (UAP)-who present to the emergency department (ED) remains a serious public health issue. Better understanding of the pathophysiology of coronary artery disease has allowed the adoption of a unifying hypothesis for the cause of ACSs: the conversion of a stable atherosclerotic lesion to a plaque rupture with thrombosis. Thus, physicians have come to appreciate UAP and AMI as parts of a continuum of ACSs. This article reviews the state of the art regarding the diagnosis of ACSs in the emergency setting and suggests reasons why missed diagnosis continues to occur, albeit infrequently.

Detection of chest pain of non-cardiac origin at the emergency room by a new non-invasive device avoiding unnecessary admission to hospital

Recent advances in the treatment of acute coronary syndromes has raised awareness that prompt presentation for chest pain may be life saving. Most patients presenting with chest discomfort have a non-ischaemic ECG on presentation, but are routinely admitted to hospital because of diagnostic uncertainty for occult MI or ischaemia. We tested a new non-invasive device that measures central aortic pressure changes (dP/dtejc): an accepted index of myocardial performance that could be added to the diagnostic triage of ischaemia in the ER avoiding unnecessary admissions. We followed 85 patients presenting at the ER with acute chest pain. In 72 patients, negative ECG and myocardial enzyme dynamics ruled out coronary origin during the first 24 h after admission. In 8 of the 72 patients, coronary catheterisation found normal coronary arteries. In this group, average dP/dtejc was 163 (range 92-232). In 35 patients in whom the new non-invasive cardiac performance index dP/dtejc was above a threshold of >150, acute MI was ruled out. In 13 patients, acute chest pain had coronary origin confirmed by ECG and/or positive enzymes. The average dP/dtejc in this group was 117 (range 61-149). The dP/dtejc values were found to be significantly higher in patients without acute MI (p<0.001). Preliminary findings suggest that nearly 40% of patients presenting with acute chest pain could be spared the risks and costs of unnecessary hospital admission and more invasive cardiac testing by simply adding a easy to use, immediately obtained, test to the diagnostic protocol, and using a threshold of dP/dtejc>150 to rule out heart attack.

Assessment of peripheral artery tonometry in the detection of treadmill exercise-induced myocardial ischemia

OBJECTIVES

We sought to assess the added diagnostic value of peripheral artery tonometric (PAT) measurements, based on finger pulsatile arterial volume changes, to standard 12-lead stress electrocardiography (ECG), for detecting exercise-induced myocardial ischemia, using single-photon emission computed tomography (SPECT) as the standard of comparison in a double-blinded, multicenter protocol.

METHODS

An automated algorithm for identifying myocardial ischemia from PAT was derived from 345 training cases. The PAT outcome was combined with the ECG result (ischemic, nonischemic, or equivocal), giving a PAT-enhanced value. A threshold of normality was determined to optimize agreement with the SPECT results in the training sample. The PAT-enhanced analysis was then validated in 616 subjects, only two of whom had technically unacceptable PAT studies.

RESULTS

In the validation cohort, receiver operating characteristic curve analysis of the PAT-enhanced diagnosis yielded an area under the curve of 0.72, a sensitivity of 63.5%, compared with 44.7% for ECG alone (p < 0.0001), and a specificity of 67.8% common to both ECG and PAT-enhanced diagnoses. Similar results were found in the training sample. Although over 10% of validation subjects had equivocal ECG results, with the aid of PAT, it was possible to provide diagnostic information for all but one subject.

CONCLUSIONS

Peripheral artery tonometry may be useful for improving the diagnosis of exercise-induced myocardial ischemia by both enhancing the sensitivity without impairing the specificity and increasing the percentage of definitive test results.

What's new in monitoring the coronary surgery patient?

Monitoring has been extensively reviewed in most textbooks of cardiothoracic surgery and anaesthesia, particularly in the recent textbooks on monitoring edited by Carol L Lake 1 and Casey D Blitt 2 and in the Journal of Clinical Monitoring. Although monitoring properly includes both pre- and postoperative periods, this review will concentrate exclusively on the operative period. I will also concentrate on new approaches or information which relate to more traditional approaches to monitoring. The emphasis in this review will not be on what we can monitor, but rather on what we should monitor. In this regard, I will analyse accuracy and identify sources of error and try to answer the following questions. Does the device or parameter measure (monitor) what we want to know? Does it improve patient outcome and safety? Is it cost-effective? Unfortunately, data are not always available to answer all these questions at present, but hopefully the discussions will make us aware of what we do and do not know, and what we should look for in the near future.