Accuracy of computerized electrocardiographic identification of left ventricular hypertrophy as determined by echocardiographic measurements of left ventricular mass: evaluation of a widely used computer program.

The Hewlett-Packard 1000 electrocardiographic management system employs a user-interactive computer with revisable software. The diagnostic accuracy of this system in predicting left ventricular hypertrophy has been evaluated by comparing computer-predicted with anatomic left ventricular hypertrophy. The latter was defined as a left ventricular mass greater than 247 g as determined by M-mode echocardiography within 1 week of the computerized electrocardiogram. In this study, the Hewlett-Packard system was evaluated in 134 consecutive patients having anatomic left ventricular hypertrophy and 157 similarly studied patients with a normal left ventricular mass. By means of various combinations of voltage criteria, ST-T wave changes, abnormal QRS duration or ventricular activation time, left atrial enlargement and left axis deviation, the computer correctly identified 43 of 134 patients with left ventricular hypertrophy (sensitivity 32%); left ventricular hypertrophy was suggested or identified in an additional 18 patients with a normal left ventricular mass (specificity 89%). Graded probability statements (that is, the "strength" of the left ventricular hypertrophy diagnosis) increased with ventricular mass not only in patients with anatomic left ventricular hypertrophy but also in the patients with a "false positive" computerized electrocardiogram. Overall diagnostic accuracy was improved only in men by adjusting the definition of left ventricular hypertrophy for sex (at least 300 g for men and 220 g for women). Diagnostic accuracy was significantly better in patients 65 years of age and younger than in older patients (p = 0.007). It is concluded that the overall performance of this computer program (version ECLSB6) requires modification to improve its accuracy in identifying left ventricular hypertrophy.

A working cardiac valve phantom for radiographic assessment of prosthetic heart valves.

RATIONALE AND OBJECTIVES: A working valve phantom (WVP) that both exercises the valve occluder and simulates movements of the mitral annulus is described. It was designed to develop a method for radiographic detection of a single broken leg of the two-legged Björk-Shiley convexo-concave (C/C) heart valve outlet strut. METHODS: The WVP consists of a pneumatically driven left ventricular assist device immersed in 22 cm of water. Left ventricular assist device annulus movements are generated by systolic turgor and diastolic relaxation of the aortic outflow graft within limits set by the holding fixture design. RESULTS: WVP images were comparable in attenuation, valve motion, and diagnostic sensitivity to clinical C/C valve images and were effective in assessing leaflet excursions in another valve model. Techniques developed in the WVP have proved successful in the clinical detection of C/C valves that have a single broken leg but that show normal function in all other tests. CONCLUSION: The WVP can be a useful tool for developing refined radiographic assessments of prosthetic heart valves.

A theoretical description of blood flow through the mitral orifice.

A nonlinear differential equation describing the Doppler velocity profile for blood flow through the mitral valve has been derived. This equation is based on fluid dynamics and a simple, but comprehensive model of atrial and ventricular mechanics. A numerical solution to the equation is described and provides excellent agreement with Doppler velocity curves obtained clinically. One important result of the theory is that in patients with mitral stenosis, the slope of the clinically observed straight-line descent of the velocity profile is proportional to the mitral orifice area and inversely proportional to the atrioventricular compliance.

Radiation exposure to patients undergoing diagnostic and interventional cardiac catheterization procedures.

There has been a recent wave of concern over radiation exposure to patients during cardiac catheterization. Accordingly, we measured the area-exposure product (AEP) to patients undergoing diagnostic and interventional cardiac catheterization procedures. Fluoroscopic and cinefluorographic exposures were determined for 510 patients using an AEP meter. The total AEP was higher in interventional than diagnostic cases (16,289 R.cm2 vs. 10,873 R.cm2, P < 0.00001); multi-lesion than single lesion interventions (20,311 R.cm2 vs. 15,919 R.cm2 P < 0.0001); and in patients with previous coronary bypass surgery (20,403 R.cm2 vs. 14,298 R.cm2, P < 0.00001). The highest AEPs were observed in patients with a prior history of bypass surgery who underwent diagnostic catheterization and multilesion intervention during the same procedure.

Absorption technique for OH measurements and calibration.

An absorption technique is described which utilizes a stabilized frequency-doubled tunable dye laser and a long-path White cell with high mirror reflectivities both in the red and UV. In laboratory conditions we have been able to obtain routinely a detection sensitivity of 3 parts in 10(6) over absorption paths <1 m in length and a detection sensitivity of ~6 parts in 10(5) over an absorption path of the order of 1 km. The latter number corresponds to 3 x 10(6) OH molecules/cm(3), and therefore the technique should be particularly useful for calibration of our fluorescence instrument for OH measurements. However, the presence of atmospheric fluctuations coupled with intensity variation accompanying frequency scanning appears to degrade the detection sensitivity in outdoor ambient conditions, thus making it unlikely that this technique can be employed for direct OH monitoring.

Discrimination of anterograde from retrograde atrial electrograms for physiologic pacing.

The morphology of bipolar electrograms recorded in the right atrium was examined in nine patients in an attempt to discriminate retrograde from anterograde atrial signals to an extent that would be useful for physiologic pacing. Peak-to-peak amplitude, duration, square root of energy (energy), maximum slew rate, mean slew rate, and polarity were examined in the time domain. Maximum frequency, half-power frequency, Fourier amplitude peak, and frequency of peak were measured in the frequency domain. There was a significant difference between anterograde and retrograde signals for all variables related to amplitude; these variables are peak-to-peak amplitude, energy, Fourier amplitude peak, maximum slew rate and mean slew rate. In seven of nine patients there was at least one variable sufficiently discriminating to insure reliable detection of anterograde signals while systematically rejecting retrograde signals. However, no individual variable was able to effect this discrimination in more than four patients and at least three variables were needed for all seven patients: maximum frequency, one of either energy and Fourier amplitude peak, and one of either frequency of peak or half-power frequency (six possible combinations). Thus, although differences between anterograde and retrograde atrial activity can be demonstrated in most patients, no single parameter displays sufficient discriminating power to facilitate physiologic pacing in patients exhibiting retrograde activity.

Radiographic detection of strut separations in Björk-Shiley convexo-concave mitral valves.

BACKGROUND: The outlet struts of Björk-Shiley convexo-concave heart valves can occasionally fracture. By December 31, 1994, 564 complete strut fractures had been reported to the manufacturer, approximately two thirds of which were fatal. There are no reliable diagnostic methods to detect valves that may be at risk for strut fracture. The outlet strut has two legs, and one leg often appears to break before the other, potentially permitting detection of the single-leg separation while the valve is still functionally intact. METHODS: We used high-resolution cineradiography and defined valve profiles to evaluate 315 patients selected on the basis of their having mitral convexo-concave valves with an estimated fracture rate of 0.46 percent or higher per year. Two examinations were scheduled six months apart, with early reimaging performed when initial ratings were indeterminate. RESULTS: Three patients had unsatisfactory studies, the most recent examinations in 277 patients were rated as apparently normal, 23 had findings considered minimally suspicious, and 1 had findings termed suspicious. The number of false negative results in this study group is unknown. Eleven cineradiograms were rated as showing probable or definite single-leg separations. All five "definite" ratings and five of the six "probable" ratings were confirmed by removal of the valves. One valve with a "probable" rating was intact. Two complete outlet-strut fractures occurred three and seven months after apparently normal radiographic examinations. Unsuspected new positive findings were not found at six months among 288 patients who completed the examination cycle. CONCLUSIONS: Cineradiographic imaging can detect some single-leg separations in mitral convexo-concave valves and may help the estimated 41,000 patients with these valves worldwide and their physicians decide about elective valve removal.