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Biomedical subjects

D David

Publications and source records attributed to D David.

At least 163 records · Page 9Linked to original sources
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↗
PubMed1983

Superiority of oral verapamil therapy to digoxin in treatment of chronic atrial fibrillation.

The efficacy and safety of oral verapamil, 240 mg, with or without digoxin were studied in 52 patients with chronic atrial fibrillation at rest, and during mild and maximal exercise. Twenty-four patients were studied during the following therapeutic modalities: no therapy; digoxin, 0.25 mg and 0.5 mg daily; digoxin, 0.25 mg and verapamil; and verapamil alone. Heart rate at rest and during all levels of exercise was decreased significantly (p less than 0.005), either by combining digoxin with verapamil or by verapamil therapy alone. In contrast, the excessive heart rate response to exercise was not prevented by digoxin even with good serum concentrations. The improved control of heart rate with verapamil was associated with a significantly improved exercise capacity. Verapamil is an important and safe modality of treatment, with or without digoxin, in the long-term control of heart rate in chronic atrial fibrillation. It is superior to digoxin in controlling the ventricular rate and in improving exercise capacity.

Administration, Oral↗
PubMed1983

Effect of variations in room temperature on measured values of blood gas quality-control materials.

We compared four commercial quality-control materials equilibrated in sealed ampoules at 21 or 26 degrees C in three models of blood gas machines and found po2 differences of about 13.3 Pa (10 mmHg) for an aqueous mixture with hemoglobin; about 6.7 Pa (5 mmHg) for two aqueous buffers without hemoglobin, and none for a fluorocarbon-containing emulsion. Differences for pco2 and pH were small but statistically significant. Variability within machines for pco2, po2, and pH was small but differences among machines were large, especially for po2. These results emphasize that aqueous solutions and hemoglobin-containing mixtures used for proficiency testing and quality control should be equilibrated at the temperature recommended by the manufacturer, opened, and sampled promptly.

Blood Gas Analysis↗
PubMed1982

Role of early cycle ventricular extrasystoles in initiation of ventricular tachycardia and fibrillation: evaluation of the R on T phenomenon during acute ischemia in a canine model.

Eighteen open chest dogs anesthetized with pentobarbital sodium were studied to determine the role of early cycle premature ventricular beats in the initiation of ventricular tachycardia and fibrillation during the initial 30 minutes of acute myocardial ischemia. The coupling interval and prematurity index (R-R'/R-R) of every premature beta after a sinus beat were determined during both the "immediate" (2 to 12 minutes) and "delayed" (13 to 30 minutes) phases of ventricular arrhythmias that follow acute coronary ligation. During the immediate phase, characterized by marked fractionation of local electrograms and delayed intramyocardial conduction, early cycle beats were infrequent (8 percent of extrasystoles) and initiated only 3 (4 percent) of 75 episodes of ventricular tachycardia and fibrillation. However, during the delayed phase, characterized by less fractionation and more uniform conduction, early cycle beats were both more frequent (24 percent of extrasystoles, p less than 0.001) and more successful (20 [34 percent] of 59 episodes, p less than 0.001) in initiating ventricular tachycardia and fibrillation. Thus, the underlying electrophysiologic derangements appeared to be of primary importance in determining both the frequency and relative malignancy of early cycle beats during acute myocardial ischemia.

Acute Disease↗
PubMed1982

Q-T prolongation and polymorphous ("torsade de pointes") ventricular arrhythmias associated with organophosphorus insecticide poisoning.

It is not generally appreciated in the Western world that organophosphorus poisoning may be associated with a serious and often fatal cardiac complication: Q-T interval prolongation with malignant ventricular arrhythmias of the "torsade de pointes" type. This insidious complication may lead to delayed, sudden death after the patients appears to be well on the way to recovery from the other, more dramatic respiratory and neurologic symptoms. In this study 15 patients with organophosphorus poisoning are described. Q-T prolongation was observed in 14 and malignant tachyarrhythmias in 6. In view of the dismal prognosis of these patients, ventricular pacing, previously used with success in other conditions associated with this syndrome, was tried in four patients and successfully shortened the Q-T interval and eliminated the arrhythmias. Isoproterenol did the same in a fifth patient. Awareness of this lethal, but preventable complication of organophosphorus poisoning is called for. Careful electrocardiographic monitoring is necessary until the Q-T interval returns to normal. Electrical pacing appears to be the treatment of choice for the tachyarrhythmias.

Adolescent↗