Biomedical subjects

S G Keim

Publications and source records attributed to S G Keim.

6 recordsLinked to original sources

PubMed1999

The clinical utility of adenosine in difficult to diagnose tachyarrhythmias.

BACKGROUND: The use of intravenous adenosine to help differentiate the origin of tachyarrhythmias has been suggested to be beneficial. However, the benefit of this intervention to physicians with different levels of training in electrocardiographic (ECG) interpretation is unknown. HYPOTHESIS: The purpose of the study was to determine whether intravenous adenosine improved the diagnostic accuracy of difficult to diagnose tachyarrhythmias when used by physicians with different levels of training in ECG interpretation. METHODS: We studied 28 consecutive patients presenting with wide and narrow complex tachyarrhythmias, in whom adenosine was given specifically for diagnostic purposes. Two groups of physicians, attending (n = 14) and housestaff (n = 10), reviewed each ECG before and after the administration of adenosine. RESULTS: For narrow complex tachyarrhythmias, neither physician group derived diagnostic benefit from the use of adenosine. However, for wide complex tachyarrhythmias, the diagnostic accuracy of the housestaff group significantly improved with the use of adenosine (pre = 54%, post = 70%, p < 0.01), while the attending physician group had no significant improvement (pre = 61%, post = 71%, p = NS). CONCLUSION: This study suggests that adenosine provides useful diagnostic information to physicians less experienced in ECG interpretation when presented with patients having wide complex tachyarrhythmias of uncertain origin.

Adenosine↗

PubMed1991

Accelerated idioventricular rhythm detected during elective surgery in a healthy man.

Accelerated idioventricular rhythm (AIVR) is found most commonly in the presence of underlying heart disease. It is characterized by acceleration of a latent pacemaker that normally depolarizes slowly. We describe a 30-year-old man who was found to have episodes of accelerated idioventricular rhythm (AIVR) on cardiac monitoring during elective orthopedic surgery. Noninvasive evaluation including two-dimensional echocardiography was unremarkable. No late potentials were detected on a signal-averaged electrocardiogram. During an exercise tolerance test, AIVR was suppressed as heart rate increased. A 24-h Holter monitor revealed that the AIVR rate was consistently 73-76 beats/min, which appeared whenever the sinus rate slowed to this level. The patient has been asymptomatic, and the rhythm has persisted at least through a 5-month follow-up period.

Accelerated Idioventricular Rhythm↗

PubMed1991

A method for analysis of the local atrial evoked response for determination of atrial capture in permanent pacing systems.

We developed a method for detection and analysis of the local atrial evoked response. Eleven patients undergoing permanent dual chamber pacemaker implantations for standard clinical indications were included in the study. Using a pacing system emulator, charge balancing using a variable triphasic stimulus waveform to reduce polarization artifact amplitude was performed first. This could not be completed in one patient because of a poor signal-to-noise ratio. Subsequent analysis of the local atrial evoked response in the remaining ten patients showed the typical signal to be a biphasic waveform with an initial negative deflection followed by a positive deflection nearly equal in amplitude. The mean amplitude of the atrial evoked response was 3.1 +/- 1.4 mV, while the intrinsic P wave amplitude in these same patients averaged 5.6 +/- 3.0 mV. The summed evoked response, a parameter that is directly proportional to the area of the signal, was used to determine atrial pacing threshold. The median atrial pacing threshold determined by the algorithm was 1.00 V. There was no instance of failure to detect loss of capture, nor was loss of capture inaccurately determined when there was still successful atrial pacing. Atrial capture in permanent pacing systems can thus be determined using an algorithm to record and analyze the local atrial evoked response. This method could potentially be useful in the automatic determination of atrial pacing threshold.

Algorithms↗

PubMed1991

A new algorithm for minimizing pacemaker polarization artifact: universally applicable in permanent pacing systems.

Polarization artifacts that result from pacing may interfere with analysis of paced evoked responses during, e.g., automatic threshold tracking. We have developed a method for reduction of such artifacts that relies on the introduction of pacing stimuli during the refractory period of unipolar or bipolar paced captured beats after previous identification of a refractory period "template" or baseline. The refractory pacing stimuli cannot capture the heart, and thus any deviation from the template is due to polarization artifact alone. The artifact amplitude is measured and the precharge duration of the triphasic stimulus waveform is changed each time until artifact is minimized, as detected by repeated reversals in the polarity of the polarization artifact. In a series of 11 patients with unipolar and bipolar permanent pacing leads, mean initial artifact before balancing was 1.44 +/- 0.84 mV, which was reduced to 0.44 +/- 0.30 mV after balancing (P = 0.001). Initial precharge duration was 3.2 msec by design; mean final precharge duration was 3.30 +/- 0.34 msec. This algorithm is universally applicable in permanent pacing systems, as it is valid in unipolar and bipolar pacing and it does not require an intrinsic cardiac rhythm.

Algorithms↗

PubMed1991

Left ventricular regional wall motion assessment by radionuclide ventriculography: a comparison of cine display with Fourier imaging.

Radionuclide ventriculography and contrast ventriculography were performed in two comparable projections on 50 patients with suspected coronary artery disease. The efficacy of conventional cine display and Fourier image analysis of the radionuclide ventriculogram was compared using contrast ventriculography as the gold standard. Of seven different combinations of Fourier images, the combination of left anterior oblique amplitude and phase and left posterior oblique amplitude and phase provided the highest sensitivity (87%), specificity (83%), accuracy (86%), and kappa coefficient (0.64). To increase statistical power, segment data were collapsed to global data in which a heart was considered normal if all segments were normal and abnormal if one or more segments were abnormal. Fourier images had higher sensitivity (Fourier 87%, cine 47%); lower specificity (Fourier 83%, cine 92%), higher accuracy (Fourier 86%, cine 58%), and higher kappa coefficient (Fourier 0.64, cine 0.25), and these differences were statistically significant (p less than 0.01).

Coronary Disease↗

PubMed1990

Value of right-sided cardiac catheterization in patients undergoing left-sided cardiac catheterization for evaluation of coronary artery disease.

The value of right-sided cardiac catheterization was assessed prospectively in 200 patients undergoing left-sided catheterization for evaluation of known or suspected coronary artery disease. Before catheterization, data from right-sided catheterization was not felt to be necessary for clinical management. There were 6 +/- 2 extra minutes of procedure time and 86 +/- 63 extra seconds of fluoroscopy time used. Abnormalities were detected in 69 (35%) patients. These findings were unexpected in 37 of these patients and in 3 patients, further evaluation was prompted. However, management was altered in only 3 (1.5%) patients as a result of data obtained by right-sided catheterization. In conclusion this additional procedure rarely adds clinically useful information about patients undergoing left-sided catheterization and angiography for coronary artery disease without a clinical indication for right-sided catheterization.

Cardiac Catheterization↗