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Biomedical subjects

D David

Publications and source records attributed to D David.

At least 145 records · Page 8Linked to original sources
PubMed1986

The role of animal models in electrophysiologic studies of life-threatening arrhythmias.

Animal models have made substantial contributions to the understanding of basic electrophysiologic principles and arrhythmia mechanisms, as well as to the development of antiarrhythmic drugs, devices and procedures. The field of clinical electrophysiology has progressed very dramatically and there have also been advances in the basic laboratory that bear relevance to the methods, design and interpretation of clinical electrophysiologic testing, and to the application of new, potential antiarrhythmic interventions.

Animals↗
PubMed1986

Diastolic 'locking' of the mitral valve: possible importance of diastolic myocardial properties.

The effects of pharmacologically induced changes in myocardial properties on diastolic mitral valve mechanics were studied in five open-chest dogs. After the induction of complete atrioventricular block, the dogs were subjected to a protocol of programmed pacing. During prolonged diastolic pauses, programmed atrial contractions were induced at progressively increasing coupling intervals. Echocardiographically determined mitral valve reopening time was established for each coupling interval in the control state as well as under the influence of calcium or verapamil. Compared with control, calcium caused an increase in myocardial tension from 23.8 +/- 3.0 to 30.0 +/- 4.6 g/cm2 (mean +/- SD, p less than .005) as well as an increase in mean septal contraction and relaxation velocities from 142 +/- 25.9 and 144 +/- 15.2 mm/sec to 188 +/- 21.7 and 174 +/- 19.5 mm/sec, respectively (each p less than .001). Conversely, verapamil caused a decrease in mean myocardial tension from 23.8 +/- 3.0 to 19.4 +/- 5.3 g/cm2 (p less than .001) and in mean septal contraction and relaxation velocities from 142 +/- 25.9 and 144 +/- 15.2 mm/sec to 112 +/- 32.7 and 112 +/- 21.6 mm/sec, respectively (each p less than .001). At every coupling interval, calcium significantly (p less than .01 to .001) prolonged, whereas verapamil significantly shortened (p less than .01 to .001), mitral reopening time compared with the control state. These pharmacologically induced changes in mitral valve mechanics occurred despite variations in left ventricular volume, as well as left ventricular and left atrial pressures that under normal conditions exert opposite effects on mitral valve mechanics.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Self-stabilizing osteotomy for frontal bar advancement.

This technique is simple, quick to perform, and produces a rigid block against posterior relapse of the advanced frontal bar in surgery for bicoronal synostosis. This stability is achieved without the need to place a bone graft across the craniectomy site in small infants with rapidly expanding brains. Finer and fewer interosseous wires are required, decreasing the chance of transcutaneous palpation, and this principle can be incorporated into most osteotomy patterns around the orbits.

Craniosynostoses↗
PubMed1985

[Critical study of the stress electrocardiogram after aortocoronary bypass, based on 95 coronary angiographic correlations].

This paper studies the correlations between the stress electrocardiogram and the angiographic findings after aorto-coronary bypass grafts. 95 correlations were established in 75 patients (coronary angiography and stress tests were performed on two occasions after the operation in 20 patients). 32 patients had a past history of myocardial infarction. The stress test was positive when the ST depression was equal to or greater than 1 mm, over more than 80 milliseconds. Four groups could be defined on the basis of the angiography: patient graft(s) with no residual stenosis; old or new coronary lesions; occlusion of one or more grafts; malfunction of the graft(s). The stress test and the coronary angiography were separated by a mean delay of 4.6 days. The stress test was positive in 43 cases, due to the residual postoperative stenoses in 63% of cases, due to occlusion of the graft(s) in 25% of cases and due to malfunction of the graft(s) in 9% of cases. In 3% of cases, the signs of ischaemia were due to an old infarct. The stress test was negative in 52 cases. This negative result corresponded to the 66% of cases with complete revascularisation of the coronary system; in 34% of cases, there were persistent angiographic abnormalities, consisting of uncorrectable coronary stenoses in half of the cases. When the coronary revascularisation was complete, the stress test was negative in every case. Residual coronary lesions were associated with a positive stress test in 66% of cases and with a negative test in 34% of cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Angiography↗
PubMed1985

Asynchronous intraventricular recovery as a basis for apparent 'supernormality'.

Various mechanisms have been postulated for the supernormal phase of intraventricular conduction where relatively early impulses are conducted with normal intraventricular conduction and relatively late impulses with abnormal intraventricular conduction. The cases presented here illustrate how asynchronous recovery of conducting tissue may result in fortuitous momentary synchrony early on in the recovery phase with asynchronous conduction properties in the later phases of recovery. This will facilitate potential synchronous conduction early on in the cycle which would result in a normal QRS complex, and potential asynchronous conduction in the later phases which would manifest with a bundle branch block QRS complex.

Aged↗
PubMed1985

An electromyographic study of elbow motion during postexercise muscle soreness.

Postexercise muscle soreness was induced in the elbow flexors of human volunteer subjects through the use of a regimen of eccentric contractions. Physical examination before and 48 h after the exercise included measurements of range of elbow motion at the elbow and of arm diameter. Electromyographic (EMG) observations, utilizing fine wire electrodes introduced into each of the elbow flexors, were carried out before and 48 h after the exercise. These observations included resting EMG levels, EMG activity under various isometric loads, and activity during active and passive extensions. The soreness induced was accompanied by a reduction in resting elbow angle while the subjects stood with arms relaxed at their sides, decreased range of both flexion and extension of the elbow, and swelling of the arm. EMG measurements showed no increase in EMG activity as the sore arms were extended passively at the elbow, indicating that the extra resistance to extension associated with the soreness was not a result of stretch receptor-induced activity in the flexors. The results rule out the possibility that neuromuscular activity is responsible for the restriction of motion and are consistent with the idea that edematous changes within the perimuscular connective tissue alter the elastic behavior of the muscles and cause restriction of motion.

Adult↗
PubMed1985

[Clinical and electrophysiological aspects of median intra-His bundle block with normal electrocardiogram at rest].

The clinical and electrophysiological features and the natural history of median intra-His block with a normal resting electrocardiogram were studied: 11 patients had a fixed split H1-H2 potential with a spontaneous or induced block between H1 and H2. The patients (5 men and 6 women) were aged 17 to 70 years (average 53 years). Associated pathology included 2 cases of aortic stenosis (1 severe), 1 case of ischaemic heart disease (effort angina), 1 case of mitral valve prolapse and 2 cases of hypertension. The presenting symptoms were syncope (4 cases), dizziness (2 cases), effort angina (1 case) and tiredness (3 cases); 1 patient was asymptomatic. Holter monitoring (24 hours) was performed in 8 patients and s-owed paroxysmal conduction defects in 6 cases; 4 Mobitz II 2nd degree AV block, 1 3rd degree AV block with narrow QRS complexes and 1 case of blocked atrial extrasystoles at coupling intervals longer than 480 ms and sinus cycle lengths of over 800 ms. Exercise testing by bicycle ergometry (4 patients) was normal in 1 case and revealed Mobitz II 2nd degree AV block in 3 cases. Baseline electrophysiological studies showed an A-H1 interval ranging from 60 to 100 ms (average 78 ms), a H1-H2 interval of 20 to 40 ms (average 31 ms) and a H2-V interval of 30 to 50 ms (average 32 ms). Block between H1 and H2 was observed: "spontaneously" during electrophysiological investigation in 6 cases, after IV atropine in 1 case, during overdrive atrial pacing at rates slower than 150/min in 7 cases, after atrial extrastimulus with a functional intra-His refractory period of over 420 ms in 7 cases, after ajmaline in 3 of the 4 cases in which this test was performed. A cardiac pacemaker was implanted in 10 patients in whom the initial symptoms have all regressed; the remaining patient considered to be "epileptic" had another syncopal attack under therapy and was finally paced. This series demonstrates that the diagnosis of median intra-His block depends on precise electrophysiological criteria and should be looked for even when the presenting symptoms are atypical; some of our patients complained only of tiredness. The value of Holter monitoring and careful endocavitary investigation is emphasised. Median intra-His block should be distinguished from longitudinal and functional His bundle dissociation.

Adolescent↗
PubMed1984

R-wave amplitude responses to rapid atrial pacing: a marker for myocardial ischemia.

Atrial pacing-induced changes in the sum of R-wave amplitude were measured in leads V5, X, Y, and Z at rates of 100 bpm (phase I), 150 bpm (phase II), and immediately after pacing (phase III) in 33 patients undergoing cardiac catheterization for evaluation of chest pain. Seventeen (51%) patients showed evidence of ischemia during atrial pacing (typical anginal pain and/or at least a 1 mm ST-segment depression) and 16 (49%) showed no evidence of ischemia. Mean R-wave amplitude changes from baseline in the ischemic patients were: phase I: -8% (p = not significant), phase II: +3% (p = not significant), and phase III: +13% (p less than 0.01); and in nonischemic patients: phase I: -11% (p less than 0.02), phase II: -18% (p less than 0.01), and phase III: +2% (p = not significant). These two distinct patterns of R-wave amplitude changes were highly sensitive (85%), specific (92%), and predictive (92%) for identifying patients with myocardial ischemia but did not correlate (p = not significant) with either the angiographically determined extent of coronary artery obstructive disease (CAD), resting left ventricular function, or the dynamic, atrial pacing-induced changes in left ventricular dimensions determined by M-mode and two-dimensional echocardiography. Thus, R-wave amplitude changes induced by atrial pacing can be used to identify patients with myocardial ischemia independent of coronary anatomy or resting left ventricular function.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

The cardiokymography exercise test compared to the thallium-201 perfusion exercise test in the diagnosis of coronary artery disease.

To determine the usefulness of exercise cardiokymography (CKG) compared to thallium-201 perfusion scanning in the diagnosis of coronary artery disease (CAD), 179 patients with a mean age of 54 +/- 10 years (73% men) were studied. Previously documented CAD was present in 73 patients (41%); 13 (7%) were asymptomatic and 93 (53%) had chest pain syndrome. Exercise stress testing, CKG, and thallium-201 perfusion scanning were independently correlated with coronary angiographic data. Treadmill exercise stress test alone without CKG had a sensitivity of 68% and specificity of 62%. CKG showed a sensitivity of 76% and a specificity of 90%, and easily interpreted cardiokymograms were obtained in 78% of patients studied. Thallium-201 scans had a sensitivity of 79% and a specificity of 88%. However, when the CKG and treadmill exercise test results were concordant (both positive or both negative), the CKG exercise test had a sensitivity of 87% and specificity of 100%. Thus, when the CKG and exercise test results are concordant, the sensitivity and specificity are equal to or better than thallium-201 perfusion scanning for the prediction of CAD. Since CKG is an inexpensive and noninvasive test, its adjunctive use with routine exercise stress testing may be of great value.

Adolescent↗
PubMed1983

Prosthetic mitral valve motion during cardiac dysrhythmias as determined by echocardiography.

To assess the changes and physiologic mechanisms of prosthetic valve motion during cardiac dysrhythmias as well as the role of atrial systole in the closure of the mitral valve, M-mode echocardiography was performed in 36 patients with normally functioning prosthetic mitral valves (Björk-Shiley, Starr-Edwards, and Beall valve). Premature closure of the prosthetic mitral valve in diastole with a "sharp" closing motion was seen during first-degree atrioventricular block, atrial fibrillation with ventricular rates less than 60 beats/min, and atrial flutter. A "rounded" premature valve closure due to atrial systole was seen during atrial tachycardia and complete heart block. Atrial systole initiates a closing motion of the prosthetic mitral valve at end-diastole, and ventricular systole completes this closure during normal sinus rhythm. When first-degree atrioventricular block is present, atrial systole alone completes this closure before ventricular contraction. Atrial contraction alone also can effectively close the prosthetic mitral valve during atrial flutter and atrial tachycardia. Other factors (such as left ventricular diastolic volume) may play a role in the effective closure of the prosthetic mitral valve during atrial fibrillation with slow ventricular rates and complete heart block. These findings must be considered in the echocardiographic evaluation of suspected malfunctioning prosthetic mitral valves. A baseline postoperative echocardiogram after prosthesis insertion is important for future evaluation when clinically indicated.

Aged↗
PubMed1983

The hemodynamic consequences of cardiac arrhythmias: evaluation of the relative roles of abnormal atrioventricular sequencing, irregularity of ventricular rhythm and atrial fibrillation in a canine model.

To evaluate the hemodynamic consequences of various cardiac arrhythmias, hemodynamic and angiographic studies were performed on 20 open-chest, atrioventricular (AV) heart-blocked dogs during various programmed pacing protocols. Protocols included AV pacing at intervals of 100 msec and -100 msec, ventricular (V) pacing during AV dissociation, and V pacing during atrial fibrillation (AF). In addition, the effects of regular versus irregular V pacing were also evaluated. During regular V pacing, cardiac output was optimal at an AV interval of 100 msec, but decreased by 25% at AV -100 msec and by 18% during both AV dissociation and AF. During irregular V cycles, cardiac output decreased further (e.g., by an additional 7% during AF). Pulmonary venous regurgitation was observed only during AV dissociation and during regular pacing at AV -100 msec. Notably, mitral valvular regurgitation was observed only during irregular V cycles, but not during regular V pacing, even in the presence of AV dissociation or AF. Using these methods it was possible to resolve some previously reported controversies regarding the relative importance of AV sequencing, atrial systole versus AF, regular versus irregular rhythms, as well as the possible contribution of mitral and/or pulmonary venous regurgitation to the adverse hemodynamics of various cardiac arrhythmias.

Animals↗
PubMed1983

Verapamil improves exercise capacity in chronic atrial fibrillation: double-blind crossover study.

Oral verapamil has previously been shown to reduce heart rate at rest and during mild exercise in chronic atrial fibrillation. Its efficacy in improving cardiovascular performance at higher levels of exercise and its safety were investigated in a prospective, randomized, placebo controlled double-blind study preceded by an open label titration phase in 20 digitalized patients with chronic atrial fibrillation. Maximal exercise capacity was improved (from 522 +/- 257 to 806 +/- 348 work units, p less than 0.0005) when tested by a standardized multistage ergometry exercise test. Heart rate was also reduced at rest, at the end of 3 minutes of 300 KPM exercise, and at the point of maximal exercise. Blood pressure and double product were also reduced. Its efficacy and safety may make verapamil the treatment of choice in chronic atrial fibrillation.

Adult↗
PubMed1983

Reevaluation of the role of atrial systole to cardiac hemodynamics: evidence for pulmonary venous regurgitation during abnormal atrioventricular sequencing.

Twenty open-chest dogs with experimental AV heart block were evaluated hemodynamically, angiographically, and by M-mode echocardiography to further elucidate mechanisms whereby abnormal AV sequencing results in decreased cardiac hemodynamics. During fixed-rate AV pacing, there was a consistent decrease in cardiac output, left ventricular and aortic pressures, and left ventricular dimensions with an increase in left atrial pressure as the AV interval was decreased from 100 to 0 msec, and there were further changes when the AV interval was set at -50 and -100 msec. The hemodynamic consequences of atrial fibrillation with regular ventricular rhythms were similar to the effects of an AV interval of 0 msec. It is important to note that retrograde blood flow into the pulmonary venous system (pulmonary venous regurgitation) was demonstrated by left atrial angiography at AV intervals of both -50 and -100 msec. However, left ventricular angiography failed to reveal mitral regurgitation during fixed-rate pacing at any AV interval or during atrial fibrillation with regular ventricular rates. Thus, during tachyarrhythmias characterized by abnormal AV sequencing, not only is there the loss of active atrial contribution to ventricular filling but there is also evidence for a retrograde or "negative atrial kick" further compromising cardiac hemodynamics.

Animals↗
PubMed1983

The acute hemodynamic effects of intravenous verapamil in coronary artery disease. Assessment by equilibrium-gated radionuclide ventriculography.

The acute hemodynamic effects of an i.v. bolus of verapamil, 0.1 mg/kg or 0.06-0.075 mg/kg, were examined by serial radionuclide studies in 46 patients with coronary artery disease. In 20 patients with ejection fractions (EFs) greater than 35% (group 1A), verapamil, 0.1 mg/kg given over 1-11/2 minutes, had a biphasic effect: first, a transient decrease in EF accompanied by increased left ventricular (LV) volumes and cardiac output equivalents; then, an overshoot of EF to values above control, accompanied by a decrease in peripheral vascular resistance and a drastic decrease in LV volumes, while cardiac output equivalent remained slightly elevated. In eight patients with EFs less than 35% (group 1B), only the first effect on EF was noted. In 10 patients with EFs greater than 35% (group 2), verapamil, 0.06-0.075 mg/kg, exerted qualitatively similar but milder effects on hemodynamic function. Finally, verapamil, 0.1 mg/kg given more slowly, over 2-21/2 minutes, produced no significant changes in EF or LV volumes in another eight patients (group 3). The acute effects of verapamil are thus both time-related and dose-dependent. They are also related to the baseline functional reserve of the left ventricle. This study documents that verapamil exerts a depressant effect on LV function. However, the transient nature of this depression and the quick recovery to normal or above-normal values indicate that verapamil, in the doses used in this study, is safe to use intravenously in patients with coronary artery disease.

Adult↗
PubMed1983

The early recognition of right ventricular infarction: diagnostic accuracy of the electrocardiographic V4R lead.

The sensitivity and specificity of ST-segment elevation in the right precordial lead V4R as an early indicator of right ventricular infarction were examined in a consecutive series of 110 patients admitted for acute inferior myocardial infarction. The sensitivity was 82.7%, the specificity 76.9% and the positive predictive value 70% in 58 patients with right ventricular infarction documented by autopsy or a combination of radionuclide ventriculography and one or more of the following tests: echocardiography, technetium-99m pyrophosphate scintigraphy and hemodynamic monitoring. The negative predictive value was 87.7%. Because of its simplicity and its high sensitivity and specificity, recording of V4R should be an intrinsic part of the early evaluation and electrocardiographic examination of acute inferior wall infarction.

Adult↗
PubMed1983

Diastolic "locking" of the mitral valve: the importance of atrial systole and intraventricular volume.

Diastolic mitral valve "locking," defined as sustained diastolic closure of the mitral valve after atrial systole, was investigated by simultaneous hemodynamic and echocardiographic recordings during a protocol of programmed pacing in six dogs with surgically induced atrioventricular block. Atrial extrasystoles were introduced at progressively increasing coupling intervals during programmed prolonged pauses in ventricular pacing. As the coupling interval of the atrial extrasystole was increased, both the mitral reopening time (MRT) and the calculated left ventricular volume (LVV) at the end of the MRT increased proportionally. These interrelations could be best expressed by a general logarithmic function of the form y = a + b ln (x), where x = the coupling interval of the atrial extrasystole and y = the MRT or the LVV. Correlations between the measured data and the predicted data were excellent (r greater than or equal to 0.95). In each dog, a specific LVV had to be attained to allow a diastolic "locking" of the mitral valve. Atrial standstill and atrial fibrillation were also induced in each dog to study the relative role of atrial systole in locking of the mitral valve. During either atrial standstill or atrial fibrillation, the mitral valve closed transiently, but did not lock, despite the accumulation of a LVV larger than the LVV necessary to lock the valve during sinus rhythm. Thus, diastolic locking of the mitral valve has several determinants, including the presence of active atrial systole and the accumulation of a sufficient intraventricular volume.

Animals↗