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Biomedical subjects

D B Hackel

Publications and source records attributed to D B Hackel.

At least 55 records · Page 3Linked to original sources
PubMed1980

Widespread distribution and rate differentiation of the atrial pacemaker complex.

In a study to examine the basis of rate-related changes in the electrocardiographic P wave we found a multicentric rather than unifocal origin of the atrial depolarization wave in dogs. Three to five pacemakers, or origin points, were distributed over a 30- to 40-mm area compared to the 11-mm size of the sinus node. Two or three of the sites could excite simultaneously, or one specific site would dominate excitation. Each separate origin point dominated excitation within a specific range of heart rates, and on reaching either the upper or lower limits of this range, a new focus abruptly dominated and initiated the atrial wave front. We have obtained evidence to suggest that these findings may be explained by a widely distributed atrial pacemaker complex. The spatial distribution of this system exceeded the dimensions of the canine sinus node by a factor of three to four times. The pacemaker centers, although distributed, were consistently located at specific positions along the superior vena caval-right atrial junction. Also, each separate pacemaker site appeared functionally differentiated to generate a specific range of heart rates. We propose that in addition to the sinus node there are other specialized atrial pacemaker centers, and that this specialization, including the differentiated response and coordination, is conferred by focal receptor characteristics and their inputs.

Action Potentials↗
PubMed1980

Cryosurgical ablation of the atrioventricular node-His bundle: long-term follow-up and properties of the junctional pacemaker.

We used a cryosurgical technique to ablate the atrioventricular (AV) node-His bundle in twenty-two selected patients with disabling supraventricular tachyarrhythmias unresponsive to medical management. Successful AV block was achieved in seventeen. There was no intraoperative mortality and significant surgical complications were not encountered. Electrophysiologic studies performed 7-10 days after surgery revealed that the subsidiary pacemaker had a narrow QRS complex morphology and a mean cycle length of 1244 msec. Isoproterenol (1-4 microgram/min i.v.) significantly increased (p less than 0.01) the rate of the subsidiary pacemaker (mean maximum response 1008.3 msec); atropine (2 mg i.v.) had no effect on its rate. The cycle length of the subsidiary pacemaker during long-term follow-up (mean 14.8 months) showed a small but significant (p = 0.024) increase (mean cycle length 1430 msec). Treadmill exercise in seven patients did not result in the subsidiary pacemaker exceeding the rate of the implanted demand pacemaker set at 70 beats/min. The properties of the subsidiary pacemaker suggest an intra-Hisian site of impulse formation.

Adult↗
PubMed1980

Anatomic substrate of impaired antegrade conduction over an accessory atrioventricular pathway in the Wolff-Parkinson-White syndrome.

We present a patient with Wolff-Parkinson-White syndrome who died of a myocardial infarction 19 months after clinical electrophysiologic studies. These studies suggested the presence of a left atrioventricular accessory pathway that sustained conduction well in the retrograde direction but only intermittently in the antegrade direction. Postmortem examination of the heart revealed three accessory atrioventricular pathways in proximity to each other in the posterolateral atrioventricular region. One pathway showed complete fibrosis and two showed patchy fibrosis. The fibrosis suggests an anatomic basis for the impaired antegrade conduction observed in life.

Atrioventricular Node↗
PubMed1980

Cardiac denervation and adrenalectomy. Its effects on myocardial lesions of hemorrhagic shock in dogs.

Myocardial lesions were seen in dogs subjected to experimental hemorrhagic shock. In contrast, dogs that had been previously surgically treated by cardiac denervation and adrenalectomy, showed less myocardial damage. The latter group also had a substantially decreased myocardial I-norepinephrine content and a much lower plasma I-norepinephrine response to shock when compared with the control shock dogs. In contrast, "sham shock" dogs had no myocardial lesions, and normal myocardial and plasma I-norepinephrine contents.

Adrenalectomy↗
PubMed1979

Treatment of hemorrhagic shock in dogs with verapamil: effects on survival and on cardiovascular lesions.

Dogs were subjected to a standardized hemorrhagic shock procedure. Some were treated with verapamil and others were untreated. It was found that the dogs treated with verapamil were protected from the damaging effects of hemorrhagic shock on the heart. This was true even in treated dogs that had a rapid heart rate maintained by means of an intracardiac pacing electrode. In addition, the treated dogs did not show the intestinal hemorrhage that is usually seen in dogs subjected to hemorrhagic shock. Finally, it was found that verapamil treatment increased the survival rate of shocked dogs in comparison with control dogs which were not treated.

Animals↗
PubMed1978

Hemorrhagic cerebral white matter: infarction with cerebral deep venous thrombosis and hypoxia.

Postmortem examination of the brain of a 5-week-old boy disclosed extensive thrombosis of the deep venous system and widespread necrosis of the cerebral parenchyma. As is characteristic of this uncommon form of cerebrovascular disease, malacia was present in the central gray matter but was only focal and incospicuous in contrast to a diffuse hemorrhagic softening of the centrum semiovale. This association of deep venous thrombosis and predominant white matter necrosis suggests that impairment of venous drainage should be considered in the pathogenesis of certain disorders of the cerebral white matter.

Aspergillosis↗
PubMed1978

Myocardial involvement in Rocky Mountain spotted fever.

Rocky Mountain spotted fever (RMSF), an acute febrile exanthematous illness caused by Rickettsia rickettsii and transmitted by ticks, is endemic in the southern Atlantic states. This report is based on the clinical and pathological findings of myocardial involvement in 16 children who died with severe RMSF. All 16 children had myocardial lesions to some degree, but it was not believed that these could be evaluated in terms of cardiac function and death in the face of the usual peripheral vascular collapse caused by the widespread vascular lesions throughout the body.

Adolescent↗
PubMed1978

The effects of l-norepinephrine on myocardial zonal lesions in dogs in hemorrhagic shock.

Intravenous l-norepinephrine was given to dogs in hemorrhagic shock to determine the effect on myocardial zonal lesions which are characteristically seen in hypovolemic shock. Zonal lesions produced by hemorrhagic shock in drug-treated and nondrug-treated groups were quantitatively compared both at the light microscopic and ultrastructural levels. A significantly greater percentage of myocardium was found to be involved with zonal lesions in animals treated with l-norepinephrine following shock as compared to that found in nondrug-treated animals. The effect was greater for the right ventricle than for the left ventricle. The average size of zonal lesions was slightly smaller in the drug-treated group, indicating that there must have been a greater total number of zonal lesions produced in the treated group. Zonal lesions were not present in "sham shock" animals nor in animals given l-norepinephrine alone. The results indicate that the treatment of hemorrhagic shock with l-norepinephrine can be anatomically deleterious to the heart.

Animals↗
PubMed1977

Instantaneous nonarrhythmic cardiac death in acute myocardial infarction.

From a group of 663 patients with acute myocardial infarction, 15 patients were identified with the syndrome of sudden loss of consciousness not preceded by symptoms of cardiac or respiratory failure or cardiac arrhythmias. The syndrome was accompanied by normal sinus rhythm, as assessed by electrocardiogram, but by neither a palpable pulse nor audible heart sounds. Seven of these patients had postmortem studies, and clinicopathologic correlations are presented. This syndrome has accounted for 68 percent of in-hospital monitored sudden deaths due to myocardial infarction. Four possible mechanisms are reviewed. These patients are presented to identify the problem of nonarrhythmic cardiac arrest in acute myocardial infarction and to stimulate new thoughts concerning etiology and management.

Acute Disease↗
PubMed1977

Correlation of postmortem anatomic findings with electrocardiographic changes in patients with myocardial infarction: retrospective study of patients with typical anterior and posterior infarcts.

This retrospective study correlates electrocardiographic and histopathologic findings in 24 patients with single well-circumscribed infarcts to determine 1) whether ECG terms commonly used to describe the location of myocardial infarcts are significant, and 2) whether the extent of infarct can be determined using QRS characteristics. Transverse sections of the hearts were photographed. Based on histologic sections, the infarct was outlined on the photograph and each section was planimetered via a sonic digitizer into a computer that was programmed to divide the left ventricle into 8 radial sectors and also into basal, mesial, and apical thirds. The percentage of infarct in each of these areas was then calculated. Of the 24 hearts evaluated 12 had posterior infarcts and 12 had anterior infarcts. Posterior infarcts principally involved the basal and mesial levels, whereas the anterior infarcts were more extensive in the apical and mesial thirds, with relative or total sparing of the base. Posterior infarcts were associated with Q waves in leads II, III and aVF in 11 instances. The other posterior infarct was associated with markedly diminished R waves in leads II, III and aVf in the presence of a horizontal axis. All anterior infarcts were associated with Q waves or markedly diminished R waves in the right precordial leads. Eight of the anterior infarcts exhibited circumferential apical involvement and all eight were associated with Q waves or markedly diminished R waves in the left precordial leads. This study documents the electrocardiographic identification of anterior, posterior, and apical infarcts by correlation with pathologic anatomy.

Adult↗
PubMed1977

Cryosurgical ablation of the A-V node-His bundle: a new method for producing A-V block.

A cryosurgical instrument was used to ablate atrioventricular conduction. The procedure was carried out in 20 dogs and subsequently in three patients with drug resistant, life-threatening supraventricular tachycardias. In patients, the cryosurgical unit lowered the temperature of the His bundle area to 0 degrees C, effecting complete but reversible heart block. Rewarming resulted in resumption of normal atrioventricular conduction. The His bundle region then was cooled to -60 degrees C; complete heart block was produced with two or more 90-120 second freezes. Postoperative evaluations revealed persistent atrioventricular conduction block. The lesion showed no tendency to rupture, form aneurysm, or interfere with valvular function. In the clinical cases, postoperative studies demonstrated a stable pacemaker arising proximal to the branching portion of the His bundle. A potential application of the cryosurgical technique might be ablation of sites of dysrhythmia (i.e., ectopic foci, re-entry circuits, accessory pathways).

Adult↗
PubMed1977

Effects of alpha-adrenergic blockade on coronary blood flow of dogs in hemorrhagic shock.

The present study was designed to test the hypothesis that the vasoconstrictive effects of alpha-adrenergic receptors are responsible, at least in part, for the lack of a maximal vasodilatation of coronary arteries during hemorrhagic shock. Open-chested, anesthetized, mongrel dogs were bled so as to reach an arterial pressure level of 44 mm Hg, and were monitored using an electromagnetic, non-cannulating flowmeter. During shock, two intracoronary injections were made, one of saline, the other of phenoxybenzamine (Dibenzyline). Control dogs had 2 injections of saline. Following phenoxybenzamine, coronary blood flow increased by 32%. These results indicate that although coronary blood flow may be mainly under local control, the sympathetic nervous system limits maximal coronary vasodilatation during hemorrhagic shock by virtue of activated alpha-adrenergic receptors.

Animals↗
PubMed1977

A study of methods for surgical interruption of the His bundle.

The relationship of the atrioventricular (AV) node and His bundle to surrounding structures is described from the viewpoint of the surgeon. A series of experiments were carried out for interruption of atrial to ventricular conduction that included electrocauterization of the His bundle, incision just above the tricuspid annulus to attempt to divide the His bundle, and finally excision of the right atrial wall and the insertion of the atrial septum into the right fibrous trigone to remove all connections from the AV node and atrium to the His bundle. The last procedure was the most satisfactory method, as judged by the certainty of accomplishing both His bundle interruption and interruption at its highest possible point.

Animals↗
PubMed1977

The effects of reserpine on myocardial lesions in dogs subjected to hemorrhagic shock.

Anesthetized dogs were subjected to severe hemorrhagic hypotension, with blood pressure maintained at 35 mm Hg for 30 or 90 minutes. In these dogs myocardial zonal lesions were present and subendocardial hemorrhage and necrosis resulted. In two other groups of dogs, similarly subjected to hemorrhage but previously depleted of catecholamines by a 3-day regime of reserpine treatment, there was a markedly lower or no incidence of myocardia lesions.

Animals↗