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Biomedical subjects

N C Flowers

Publications and source records attributed to N C Flowers.

At least 19 recordsLinked to original sources
PubMed1992

Morphologic, hemodynamic and coronary perfusion characteristics in severe left ventricular hypertrophy secondary to systemic hypertension and evidence for nonatherosclerotic myocardial ischemia.

Patients with the clinical diagnosis of ischemic heart disease who were found to be free of significant coronary artery atherosclerotic disease (n = 150) underwent coronary vasodilator reserve testing, 2-dimensional echocardiography, and dipyridamole limited-stress thallium testing. After exclusions (predominantly for technically poor coronary artery Doppler signals or suboptimal echocardiography), 100 patients formed the study population. The purpose was to characterize typical cardiac and coronary artery findings in hypertensive patients with severe left ventricular (LV) hypertrophy (n = 15) and to investigate the evidence for myocardial ischemia unrelated to coronary atherosclerosis in early and advanced hypertensive heart disease. Normotensive and hypertensive control groups without LV hypertrophy (n = 12 and 34, respectively) were used for comparison. Severe LV hypertrophy was defined as LV mass index greater than or equal to 50% above established gender specific norms using 2-dimensional-directed M-mode echocardiography and the cube equation corrected to agree with necropsy estimates of mass. Clinical characteristics more often associated with severe LV hypertrophy were black race (67%), diabetes mellitus (33%), proteinuria (47%) and elevated creatinine (1.5 +/- 0.9 mg/dl). Baseline electrocardiograms and dipyridamole limited-stress thallium scans were highly likely to be abnormal (94 and 73%, respectively). Both eccentric and concentric cardiac hypertrophies were found in the severe group. Ejection fraction was significantly lower (0.51 vs 0.68, p = 0.002) and basal coronary flow velocity higher (12.0 vs 5.0 cm/s, p = 0.0004) among these patients when compared with normotensive control patients. Coronary flow reserve did not differ between control groups but was significantly depressed in patients with severe LV hypertrophy (2.5 vs 3.9, p = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Effect of left ventricular aneurysm on risk of sudden and nonsudden cardiac death.

Although left ventricular (LV) aneurysm is associated with increased mortality, its independent prognostic significance is controversial. To determine the effect of LV aneurysm on risk, 121 patients with healed myocardial infarction (MI), 55 manifesting akinesia on ventriculography (MI group) and 66 with LV aneurysm characterized by diastolic deformity (eccentricity) and systolic dyskinesia (LV aneurysm group) were studied. At a mean follow-up of 5.7 years, there were 32 cardiac deaths (12 MI vs 20 LV aneurysm), including 9 sudden deaths (1 MI vs 8 LV aneurysm). Multivariate analysis revealed decreasing ejection fraction to be the best predictor of total cardiac death, and revascularization to be protective. Nonsudden cardiac death was predicted by ejection fraction, absence of revascularization and right coronary artery disease, whereas sudden cardiac death was predicted by LV aneurysm and the frequency of ventricular ectopic complexes on Holter monitoring. In the MI group, ejection fraction was the only significant predictor of total cardiac death and nonsudden cardiac death. In the LV aneurysm group, total cardiac death, as well as nonsudden cardiac death, were predicted by ejection fraction, ventricular tachycardia and right coronary artery disease, whereas ventricular tachycardia predicted sudden cardiac death. It is concluded that the risk profile for total cardiac death differs between LV aneurysm and MI patients, and that LV aneurysm constitutes an independent predictor of late sudden cardiac death after MI. Moreover, on a substrate of LV aneurysm, the risk factors for sudden cardiac death and nonsudden cardiac death differ, with ventricular tachycardia being the sole predictor of sudden cardiac death. Furthermore, Holter monitoring is valuable in identifying patients at persistent risk of sudden cardiac death.

Adult↗
PubMed1991

Signal-averaged electrocardiography: history, techniques, and clinical applications.

Signal averaging principles have been utilized since around 1875. Their application in medicine to enhance biologic signals was first made in 1947 for improved detection of electroencephalographic signals. The year 1963 marked the first application of this technique to cardiac signals. The more prevalent use in adult cardiology is in the detection of ventricular late potentials (VLPs) which correspond to areas of delayed ventricular activation as slowed conduction velocity. These VLPs have value in predicting the likelihood of malignant ventricular arrhythmias after myocardial infarction (MI). Negative predictive values on the order of 96-99% are convincing as to their ability to predict no arrhythmic event post-MI. Positive predictive values, on the other hand, are poor (10-29%) but improve (35-62%) in combination with other parameters such as depressed left ventricular function and frequent ventricular ectopy. Additional accepted uses for the signal-averaged electrocardiogram (SAECG) include prediction of successful ablative surgery for intractable ventricular tachycardia and facilitating evaluation of patients presenting with syncope of an unclear etiology. Potential future applications of the SAECG are (1) in following patients for rejection after cardiac transplant, (2) as a screening tool for the need for electrophysiologic study, (3) as a predictor of vessel patency after thrombolysis or percutaneous transluminal coronary angiography, and (4) as a tool to assess proarrhythmia. As the technique of signal averaging continues to evolve, its applications may become more diverse and its clinical effectiveness may improve.

Electrocardiography↗
PubMed1991

ACC policy statement. Recommended guidelines for training in adult clinical cardiac electrophysiology. Electrophysiology/ Electrocardiography Subcommittee, American College of Cardiology.

Training in clinical cardiac electrophysiology should take place in an Accreditation Council for Graduate Medical Education accredited cardiology program, and the electrophysiology training program itself should be accredited by the Council. Each trainee must be eligible for board certification in Internal Medicine and either eligible for certification in Cardiovascular Diseases or in a program leading to eligibility. Training faculty should be certified in clinical cardiac electrophysiology or demonstrate equivalent credentials. At least two training faculty members are preferred. The faculty must be dedicated to teaching, active in performing or promoting research and must spend a substantial portion of their time in research, teaching and practice of clinical electrophysiology. A curriculum of training should be established. Faculty experts in the related basic sciences should be available and involved in teaching. The institution should have a fully equipped clinical electrophysiology laboratory and complete noninvasive capabilities. A close working relation with a cardiac surgery faculty member skilled in surgical treatment of arrhythmias is required. Training in application of pharmacologic and all current nonpharmacologic therapies, in the outpatient and inpatient setting, is necessary. The clinical exposure must include all facets of arrhythmia diagnosis and treatment and must be quantitatively sufficient to allow the trainee to develop proficiency. The period of training should not be less than one year in addition to the period of cardiology fellowship required by the ABIM for board eligibility. A continuous period of training is preferred.

Anti-Arrhythmia Agents↗
PubMed1991

Standards for analysis of ventricular late potentials using high-resolution or signal-averaged electrocardiography: a statement by a task force committee of the European Society of Cardiology, the American Heart Association, and the American College of Cardiology.

Sufficient data are available to recommend the use of the high-resolution or signal-averaged electrocardiogram in patients recovering from myocardial infarction without bundle branch block to help determine their risk for developing sustained ventricular tachyarrhythmias. However, no data are available about the extent to which pharmacological or nonpharmacological interventions in patients with late potentials have an impact on the incidence of sudden cardiac death. Therefore, controlled, prospective studies are required before this issue can be resolved. As refinements in techniques evolve, it is anticipated that the clinical value of high-resolution or signal-averaged electrocardiography will continue to increase.

Analog-Digital Conversion↗
PubMed1991

Standards for analysis of ventricular late potentials using high-resolution or signal-averaged electrocardiography. A statement by a Task Force Committee of the European Society of Cardiology, the American Heart Association, and the American College of Cardiology.

Sufficient data are available to recommend the use of the high-resolution or signal-averaged electrocardiogram in patients recovering from myocardial infarction without bundle branch block to help determine their risk for developing sustained ventricular tachyarrhythmias. However, no data are available about the extent to which pharmacological or nonpharmacological interventions in patients with late potentials have an impact on the incidence of sudden cardiac death. Therefore, controlled, prospective studies are required before this issue can be resolved. As refinements in techniques evolve, it is anticipated that the clinical value of high-resolution or signal-averaged electrocardiography will continue to increase.

American Heart Association↗
PubMed1990

Relation of peri-infarction block to ventricular late potentials in patients with inferior wall myocardial infarction.

This study explores the relation of the presence of peri-infarction block to ventricular late potentials in patients with inferior wall myocardial infarction (MI). The hypothesis was that both the gross peri-infarction block pattern and subtle low-level ventricular late potentials are expressions of conduction abnormality associated with infarction. The consequent question arose whether peri-infarction block may have the same association with sustained ventricular arrhythmias that has been demonstrated in postinfarction patients with ventricular late potentials. Seventy patients with documented Q-wave MI were divided into those with (23) and those without (47) peri-infarction block. Signal-averaged electrocardiograms were obtained. Analysis of the vectormagnitude complex revealed that the total duration of that complex and the duration of terminal potential under 40 microV in the peri-infarction group exceeded that in the group without peri-infarction block (p less than 0.0001). The voltage in the last 40 ms of the vectormagnitude complex was also significantly less in the peri-infarction group (p less than 0.0005). There were 13 instances of sustained ventricular tachycardia, ventricular fibrillation or sudden death occurring subsequent to infarction not associated with the acute ischemic event, 11 of which occurred in the peri-infarction group. The significantly higher incidence of late potentials along with the significantly higher incidence of sustained ventricular arrhythmias in the peri-infarction block on the surface electrocardiogram may provide another marker for identifying persons at increased risk for these arrhythmias subsequent to MI.

Adult↗
PubMed1990

Possible triggering of paroxysmal atrial fibrillation in normal hearts by psychological stressors: a report of two cases.

Paroxysmal atrial fibrillation was triggered by psychological stress in two patients, both of whom had normal echocardiograms and coronary angiography. Neither patient was alcoholic or had ingested ethanol in relation to the onset of atrial fibrillation and both were free of metabolic derangements. Possible mechanisms involved in the triggering of atrial fibrillation are discussed.

Adult↗
PubMed1990

Application of beat-to-beat techniques.

The focus of this report is to describe a system for recording surface His-Purkinje and ventricular late potentials on a beat-by-beat basis outside of a shielded environment. An AC magnetic field monitoring device was designed for improved site selection, orientation, and quality control of the acquisition. His-Purkinje signals are detected utilizing spatial averaging and specific channel selection algorithms applied to discriminate random noise from signal. Beat-by-beat vectormagnitude complexes were generated from pairs of X, Y, and Z leads. Both infinite impulse response (IIR) filters, modified for beat-by-beat approaches, and finite impulse response (FIR) filters were utilized. Using the IIR filter, beat-by-beat recordings from test subjects were compared to the signal averaged electrocardiogram (SAECG). Measurement parameters from normal test subjects fell within the previously specified normal range for the SAECG. The IIR filter applied to beat-by-beat recordings exhibited sharp frequency response and a precisely defined cutoff frequency allowing maximal attenuation of the low frequency components in the ST segment. While filter ringing was eliminated, discontinuity and distortion of the filtered waveform resulted. The FIR filter with linear phase response retained the integrity and morphology of the complex but because of its flat frequency response, the ST segment was not as well attenuated and it was more difficult to isolate late potentials. A high order FIR filter should be used if the desire is to match the frequency response of the four-pole IIR filter, since the frequency response of the FIR filter is primarily determined by the order of the filter.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1990

Patterns of body surface potential and ventriculograms specific to occlusion of subdivisions of the coronary arteries.

The thoracic activation map patterns, the distribution of occlusions, and the ventriculograms obtained at cardiac catheterization were examined in 166 patients with multivessel coronary disease without conduction defects or prior coronary intervention. The mean potential and ventriculographic configurations were determined for 15 groups, each formed on the basis of significant luminal occlusion (less than or equal to 90%) of an individual coronary arterial subdivision. We mathematically extracted distinctive map and wall motion patterns specific for isolated occlusion of each of the 15 major subdivisions. For these prototypes we found the following: 1) Definitive change in electrical pattern (less than 2 SD from the normal mean) occurred frequently outside the electrode sites of the standard electrocardiogram. 2) Focal akinesis systematically followed lesion site down the arterial courses; early electrical activation patterns corresponded to identifiable anatomic loss. 3) Certain paradoxes arose, for example, similar wall motion change but quite dissimilar electrical patterns from posterior descending artery occlusion of right coronary versus left circumflex origin. This technique unmasks component surface electrical patterns and ventriculographic deformities otherwise unrecognized in multisite, multivessel disease.

Adult↗
PubMed1989

Relation between the ventriculographic silhouette and topography of thoracic potential in coronary artery disease.

The body surface potential map obtained within 30 days of cardiac catheterization was examined in 180 patients with coronary artery disease. Radii to the systolic and diastolic boundaries of the right anterior oblique ventriculogram were measured at 18 degrees intervals; isointegral voltages were tabulated for early and late halves of the QRS complex at 35 definitive electrode sites. Multivariate analysis showed all ray lengths depended on all 70 voltage values. Linear transformation matrices to predict ray length from voltage distribution were calculated for a training set which was successively expanded from 80 to 160 at increments of 20 patients. Training set expansion led to a progressive decrease in the error of reproduction of the ray lengths for patients outside the training set. There is a strong relation between ventriculographic contours in patients with coronary artery disease and body surface potential values during early and late QRS complexes. Even in simplified linear formulation, the relation is detectable throughout a large population despite interindividual variations in anatomic geometry.

Adult↗
PubMed1989

Recurrent resemblance in potential topography at different instants during ventricular depolarization and repolarization. Normal conduction contrasted with left bundle branch block and paced beats.

During ventricular activation and recovery, potential distribution may be exquisitely reproduced on instantaneous maps separated in time by many milliseconds. The timing and duration of these periods of strong resemblance (absolute r = 0.80 over 142 thoracic reference sites) may provide useful insight into the underlying patterns of the spread of activation and resumption of the repolarized state. This study examined 80 normal volunteers, 35 patients with left bundle branch block (LBBB), and 41 patients with permanent pacemakers. Normal subjects showed three basic patterns of recurrent surface map resemblance: (1) positive correlation between maps in early QRS and those throughout ST-T, but with greatest focus in late ST-T; (2) negative correlation between maps in early QRS and late QRS; and (3) negative correlation between maps in late QRS and early ST-T. These findings may be hypothetically attributed to the retention or recreation of similar relationships between the anatomic distributions of resting versus active or plateau versus repolarizing cells on the endocardial and epicardial surfaces, respectively. On the other hand, patients with LBBB and pacemakers were distinctly different in the timing and frequency of sustained resemblances. In these two states, there was sustained or continuing resemblance (positive correlation) between successive maps throughout QRS and again between successive maps through ST-T. In addition, the surface map pattern found throughout ST-T consistently appeared as the negative correlate of the preceding pattern that had dominated QRS.

Bundle-Branch Block↗
PubMed1989

Anatomic localization of a single electrical source within the boundary of the human torso.

A closed prolate ellipsoid was used to approximate the surface of the Rush torso model to permit recovery of the site and orientation of known dipoles in 15 cardiac locations. Localization was found to be reasonably close, usually within 2 cm. When body surface potential maps of 37 subjects with right ventricular pacemakers were similarly treated, the discrepancy between known pacemaker site and the site of earliest activation was relatively large (mean, greater than 4 cm) and rapidly increased within the ensuing millisecond. The discrepancy not only emphasizes the wide variation in body shape and tissue distribution in living subjects, but also points to probable physical separation between stimulus site and earliest detectable activation site because of ischemia, infarction, or myocardial response to variation in current strength of the stimulus.

Cardiac Pacing, Artificial↗
PubMed1989

Use of body surface maps to identify vessel site of coronary occlusion.

Body surface mapping is more sensitive than conventional electrocardiography for various cardiac regions. In this pilot study, the authors used isoarea maps of early (the first 40 msec), late (the next 40 msec), and total (early and late, or 80 msec) QRS complex to determine the site of coronary occlusion in patients with known coronary artery disease. In the absence of conduction abnormalities or axis deviation in the 12-lead electrocardiogram, isoarea body surface map data of single-vessel disease were unremarkable; however, isoarea departure maps (ie, the average isoarea map of normal population extracted from the study group) were characteristic. Early departure isoarea maps were revealing in all three coronary artery disease groups, with a large negative potential noted over the anterior thorax, midline for the right coronary artery, left anterior in the left anterior descending artery, and further laterally for the left circumflex artery groups. The late isoarea departure map was distinct in the left circumflex artery group with positive potentials leftward, anterolaterally. Discriminant function analysis revealed a high predictive accuracy for the left anterior descending artery group. Thus, isoarea departure maps hold promise for predicting the site of coronary occlusion in this training set of patients.

Adult↗
PubMed1989

A basis for determining body surface potential patterns attributable to single-site coronary arterial occlusion.

The authors focus on computational separation of the individual patterns of occlusion of the major segments of the right coronary artery. The raw patterns of occlusion throughout 15 standard subdivisions of the coronary arterial tree and body surface isoarea maps for 8 consecutive 10-msec intervals of QRS were examined in 200 patients with known coronary artery disease. Mean patterns of occlusion and of potential distribution were formed into 15 groups according to which patients showed greater than or equal to 90% occlusion of the respective segments. By diagonalization of the occlusion matrix, individual potential map patterns were obtained to represent the effect of isolated occlusion of each segment. While these patterns appeared consistent with the known anatomy of ventricular myocardial perfusion, further correlative study will be needed. The authors suggest that the use of such prototypical patterns of single-site obstruction may be helpful in forming and assessing recognition patterns in the clinical setting of multiple-site, multiple-vessel disease.

Coronary Disease↗