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Biomedical subjects

A G Wallace

Publications and source records attributed to A G Wallace.

At least 19 recordsLinked to original sources
PubMed1979

Cholesterol metabolism in non-obese women--Failure of physical conditioning to alter levels of high density lipoprotein cholesterol.

The effects of a 6-week program of vigorous exercise were studied in 14 non-obese females aged 22--26. Preceding and following a regimen consisting of 30--45 min of jogging 5 days per week, treadmill performance, body weight, total plasma cholesterol, and plasma high density lipoprotein (HDL) cholesterol were assessed. Aerobic performance improved markedly after training as demonstrated by a reduced heart rate at each submaximal treadmill workload, and by an increase in maximal attainable workload. In the absence of a significant change in body weight, total cholesterol fell significantly after training (171 +/- 6 vs 161 +/- 5 mg/dl, P less than 0.05) whereas HDL cholesterol was not significantly altered (63 +/- 5 vs 58 +/- 3 mg/dl). The ratio of total cholesterol to HDL cholesterol fell insignificantly (2.92 +/- 0.19 vs 2.86 +/- 0.14). Our findings differ from prior reports of elevations of high density lipoprotein levels following physical conditioning in men. We suggest that hormonal or other factors leading to higher baseline levels of HDL in women counteract the expected alterations in lipoprotein metabolism induced by physical training.

Adult↗
PubMed1979

Transfer of coupling of premature ventricular contractions to an ectopic ventricular tachycardia: a mechanism for atypical bidirectional tachycardia.

Bidirectional tachycardia was observed on Holter tracings recorded from a dog three days after the production of a small freeze lesion on the wall of the left ventricle. A bigeminal rhythm with fixed coupling of ventricular premature contractions was interrupted by a burst of ventricular tachycardia of different morphology. The ventricular premature contractions, originally coupled to the sinus beats, became coupled to the new ventricular tachycardia with an identical coupling interval. This resulted in a dibirectional tachycardia, created by the "transfer" of coupling of premature ventricular contractions to a separate ectopic ventricular tachycardia.

Animals↗
PubMed1979

Electrophysiologic effects of disopyramide phosphate on sinus node function in patients with sinus node dysfunction.

The electrophysiologic effects of intravenously administered disopyramide (2 mg/kg) on three parameters of sinus node function were examined in 16 symptomatic patients with sinus node dysfunction. Based on their ECG data before study, patients were subdivided into group A (n = 8), those with sinus pauses and/or sinoatrial (SA) exit block; and group B (n = 8), those with sinus bradycardia. Disopyramide shortened spontaneous cycle length in 10 of 16 patients and lengthened it in six--markedly so (91%) in one patient. Estimated SA conduction time decreased in seven of 14 patients and increased in seven. Two patients developed second degree SA exit block after disopyramide. Maximum sinus node recovery time was prolonged by disopyramide in 11 of 16 patients and markedly so in four. For the group as a whole there was no significant difference in spontaneous cycle length, maximum sinus node recovery time or estimated SA conduction time. P-wave and QRS durations and H-V intervals were significantly lengthened by disopyramide. Marked depression of the three parameters of sinus node function occurred in three group A patients and in one group B patient who had persistent severe sinus bradycardia. These four patients also had secondary pauses after termination of rapid atrial pacing under control conditions. Disopyramide should be administered cautiously to patients with sinus node dysfunction, particularly those with sinus pauses, SA exit block or secondary pauses.

Adult↗
PubMed1979

Reaction of the myocardium to cryosurgery: electrophysiology and arrhythmogenic potential.

The acute and chronic electrophysiological effects of a cryolesion produced in the left ventricle were studied in six dogs. All dogs had frequent ventricular premature beats (VPB) and five of six dogs had ventricular tachycardia during the first 4 days after the cryolesion; only one of the six dogs continued to have VPBs after 1 week, and this dog had identical VPBs before the creation of the cryolesion. Neither control dog had VPBs. Two additional dogs underwent epicardial and transmural mapping studies immediately after production of a cryolesion. VPBs in these animals were shown to originate at the border of the cryolesion. Epicardial activation sequence during normal sinus rhythm was not altered by the chronic cryolesion. The border zone of the chronic cryolesion was sharply demarcated with normal potentials recorded outside of the lesion and "extrinsic" potentials recorded within.

Animals↗
PubMed1979

Reentry within the atrioventricular node: surgical cure with preservation of atrioventricular conduction.

Paroxysmal supraventricular tachycardia (PSVT) is commonly caused by reentry within the atrioventricular (AV) node. This arrhythmia was abolished by operative dissection of the AV junction in a patient with disabling tachycardia that was not controlled by drugs. The operation was intended to create complete AV block, but AV conduction persisted after surgery. An electrophysiologic study 1 year after the operation revealed that the operation changed AV conduction in both the antegrade and retrograde directions, which may explain the absence of tachycardia. The patient has been free of arrhythmias for 18 months.

Atrioventricular Node↗
PubMed1979

Epicardial mapping of the onset of ventricular tachycardia initiated by programmed stimulation in the canine heart with chronic infarction.

The initial beats of ventricular tachycardia (VT) induced by programmed stimulation (PS) of the heart have frequently been observed to differ in QRS configuration from the subsequent uniform QRS complexes of tachycardia. The transient nature of these initial beats has made their study difficult during epicardial mapping with conventional, hand-held recording electrodes. Twenty-four dogs were studied with PS 1-10 months after coronary ligation. Twenty-six epicardial electrograms were recorded simultaneously during PS. The data were digitized for computer generation of isochronic maps for any desired beat. Three patterns of initiation were observed in episodes of tachycardia in which the initial beats differed from the subsequent beats of VT (11 of 18 runs of VT). Most frequently, the initial beats of VT originated near the pacing electrode before moving to a stable infarction zone location. Less frequently, the initial beats were due to transient reentry in the bundle branches or a transient shifting of early breakthrough sites in the infarction zone.

Animals↗
PubMed1979

An analysis of the effects of acetylcholine on conduction and refractoriness in the rabbit sinus node.

The effects of acetylcholine (ACh) on sinus node automaticity, atrio-sinus conduction, and refractoriness were studied in 41 isolated rabbit right atrial preparations. Average control rate was 126 beats/min, and ACh 5 x 10(-8) M, 5 x 10(-7) M, and 5 x 10(-6) M significantly decreased heart rate by 7, 15, and 43%, respectively (P less than 0.01, 0.001, and 0.001). Atrio-sinus conduction time at a pacing cycle length of 400 msec did not significantly change during exposure to ACh 5 x 10(-8) and 5 x 10(-7) M. However, the mean effective refractory period (ERP) of the sinus node, at a pacing cycle length of 400 msec, increased from 183 +/- 16 msec to 210 +/- 24 msec during exposure to ACh 5 x 10(-7) M (P less than 0.025). The change in ERP followed the change in action potential duration. In contrast to the lack of effect of ACh 5 x 10(-7) M on atrio-sinus conduction time, ACh 5 x 10(-6) M caused 2:1 atrio-sinus block in 8 of 10 experiments. The site of block was identified using multiple microelectrode impalements, and occurred between the perinodal fibers bordering on the edge of the sinus node and the pacemaker area in the sinus node proper. When the pacing cycle length was increased and 1:1 atrio-sinus conduciton was present, conduction time did not significantly differ from control. At this longer pacing cycle length the mean ERP of the sinus node was 380 msec greater than control and lasted well after repolarization was completed. Thus, atrio-sinus block during exposure to ACh 5 x 10(-6) M resulted from a marked prolongation of refractoriness.

Acetylcholine↗
PubMed1979

Sinus node disease.

Sinus node dysfunction may be clinically asymptomatic or may lead to serious arrhythmias and sudden death. Symptomatology relates to the resulting brady- or tachyarrhythmias. Clinical and electrocardiographic assessements fail to identify the cause in many patients. Ambulatory electrocardiography establishes the diagnosis in a greater percentage of patients and permits the direct correlation of symptoms with rhythm disturbances. Functional electrophysiologic testing which examines the sinus node response to constant atrial pacing and premature atrial stimulation may be performed for further evaluation of these patients. Sensitivity and specificity of sinus node recovery times (SNRT) and sino- atrial conduction time (SACT) derived by functional testing vary markedly in different reports. This variation may relate to differences in patient population, limitations of testing procedures, and the uncertainties as to the normal limits of SNRT and SACT. As a result, the full value of these tests in diagnosis and in furthering our understanding of sinus node disease remains to be established. At present, permanent pacing remains the definitive treatment in symptomatic patients.

Animals↗
PubMed1978

Hospital discharge one week after acute myocardial infarction.

Sixty-seven consecutive patients who had suffered an acute myocardial infarction but no serious complications during the first to fourth hospital days were considered for a trial of hospital discharge at one week. Thirty-three of the 67 patients were discharged at one week, the remainder having a mean hospital stay of 11 +/- 2 days. The incidence of late complications and recurrent infarctions, as well as mortality and functional status, were determined in all patients six months after discharge. No serious complications occurred in either subgroup within three weeks after discharge. There were no deaths in either subgroup and no difference in functional status at six months. Patients without serious complications during the four days after an acute myocardial infarction can be spared the economic costs and psychologic stress of prolonged hospitalization.

Aged↗
PubMed1978

Cryoablation of drug-resistant ventricular tachycardia in a patient with a variant of scleroderma.

A 37-year-old man with a benign variant of scleroderma (CRST syndrome: calcinosis circumscripta, Raynaud's phenomenon, sclerodactyly, and telangiectasia) presented with recurrent ventricular tachycardia. Preoperative electrophysiologic study suggested that the mechanism of tachycardia was an ectopic pacemaker focus in the right ventricle. Right ventricular dilatation, tricuspid insufficiency, normal pulmonary pressures, and normal coronary arteries were also demonstrated. At surgery, epicardial mapping localized the site of origin of ventricular tachycardia to the anterior right ventricle near the crista supraventricular. Intramural recordings of the site of tachycardia demonstrated autonomous activity unreflected on the peripheral ECG during brief periods of sinus rhythm. Local epicardial cooling of this area with a cryoprobe promptly terminated ventricular tachycardia with resumption of tachycardia on warming. The focus was ablated by freezing the area at -60 degrees C. The patient remained free of dysrhythmia on no anti-arrhythmic agents for eight months at which time he had a single recurrence of ventricular tachycardia from a different site in the right ventricle. This technique offers a method for ablating sites of dysrhythmia arising in diffusely diseased myocardium.

Adult↗
PubMed1978

The role of the exercise test in the evaluation of patients for ischemic heart disease.

A cohort of 1472 patients who underwent both exercise stress testing and coronary angiography within six weeks was examined. The data indicated that a combination of exercise parameters is both diagnostically and prognostically important. Almost all patients (greater than 97%) who had positive exercise tests at Stage I or Stage II had significant coronary artery disease. More than half of these (greater than 60%) had three vessel disease and over 25% had significant narrowing (greater than 50%) of the left main coronary artery. Patients who achieved Stage IV or greater exercise durations with either negative or indeterminate ST-segment response had less than a 15% prevalence of three vessel disease and less than a 1% prevalence of left main coronary artery disease. A low risk subgroup (75% of all non-operated patients) was identified with a twelve month survival greater than 99%. A high risk subgroup (11% of all nonoperated patients) was identified with a twelve month survival of less than 85%. The exercise test is a noninvasive, reproducible method to assess the presence and extent of anatomic disease and the prognosis when significant disease has been defined. It should be used in conjunction with other noninvasive tests to determine optimal management in patients evaluated for ischemic heart disease.

Angiocardiography↗
PubMed1978

Characteristics of atrioventricular conduction and the spectrum of arrhythmias in lown-ganong-levine syndrome.

Electrophysiological characteristics of atrioventricular (A-V) conduction and refractoriness were examined in 12 patients with Lown-Ganong-Levine (LGL) syndrome referred for assessment of the following arrhythmias: (group I) regular narrow QRS tachycardia 6/12 (50%), (group II) atrial fibrillation (AF) 2/12 (17%), group III) ventricular tachycardia (VT) 4/12 (33%). A-V node refractory periods were shorter, and enhanced A-V conduction more frequent (7/12, 58% vs 7/28, 25%) in LGL patients compared to similar studies in 28 normal controls. During laboratory study reciprocating tachycardia (RT) due to re-entry within the A-V node occurred in 4/12 (33%) LGL patients, and exhibited a shorter cycle length (294 +/- 60.4 msec) than did the same arrhythmia in 11/28 (39%) controls 372 +/- 51.8 msec, P less than 0.05). Similarly, RT utilizing a concealed accessory pathway had a shorter cycle length (228 +/- 3.5 msec) in 2/12 (17%) LGL patients than in 11/28 (39%) controls (314 +/- 24.3 msec, P less than 0.001). In AF, the shortest R-R intervals in 4/12 (33%) LGL patients (2 group I, 2 group II) were shorter than in 15/28 (54%) control patients (254 +/- 42.2 msec vs 325 +/- 64.2 msec, P less than 0.05). The mean R-R internvals did not differ significantly (LGL 372 +/- 89 msec vs control 428 +/- 82.6 msec). This study suggests that the characteristics of A-V conduction and refractoriness may permit development of more rapid heart rates during certain arrhythymias in LGL patients compared to normal controls. Furthermore, the occurrence of VT in patients with LGL sydrome indicates that symptomatic arrhythmias require specific diagnosis.

Adolescent↗
PubMed1978

Epicardial mapping in the Wolff-Parkinson-White syndrome.

Epicardial mapping provides a method for defining antegrade and retrograde sites of pre-excitation. It is best undertaken only after a careful, detailed preoperative electrophysiological study has been performed. The potential pitfalls of the technique are many and technical expertise must be constantly available to maintain a functioning system. For these reasons, it is not likely to lend itself to widespread application. The same techniques can be applied to localization of the site of origin of atrial or ventricular dysrhythmias, localization of myocardial ischemia and infarction, as well as to differentiate between epicardial delays due to conduction delay and those caused by intramural myocardial delay.

Arrhythmias, Cardiac↗