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Biomedical subjects

G C Timmis

Publications and source records attributed to G C Timmis.

At least 73 records · Page 4Linked to original sources
PubMed1986

Twelve years of clinical experience with lithium pulse generators.

The clinical performance of 9,651 lithium pulse generators, which were implanted at our registry hospitals since 1973, was assessed by analysis of actuarial survival data and information obtained at the time of pacemaker failure. Cumulative survival estimates for all units were: 5 years, 94 percent, 7 years, 81 percent, 10 years, 62 percent. Discriminant actuarial analysis revealed no differences between lithium iodine and lithium cupric sulfide longevity. Battery depletion was found in 49.1 percent of 277 units subjected to detailed explant analysis, while 31 percent and 8.7 percent had component and hermetic seal defects, respectively. Of the pulse generators with battery depletion, all but two units exhibited normal end-of-battery life behavior. We conclude that the lithium iodine and lithium cupric sulfide batteries are safe, long-term energy sources; however, the impact of reduced battery size and dual chamber pacing on these performance parameters is unknown.

Electronics, Medical↗
PubMed1986

Hemorrhage vs rethrombosis after thrombolysis for acute myocardial infarction.

To determine whether or not the timing of heparin infusion affects either bleeding or reocclusion following intracoronary streptokinase for acute myocardial infarction, heparin was infused immediately after streptokinase in 89 patients and was delayed for 12 hours in the subsequent 93. Bleeding occurred in 22 immediate-heparin patients and was major in five (one fatal); there were 14 hemorrhages in the delayed-heparin group, all minor. At discharge, reocclusions were observed in 18% (12/68) of immediate-heparin patients, and 11% (3/27) of the latter. Bioassayed fibrinogen levels displayed sustained depression regardless of bleeding for 20 hours after streptokinase; however, defibrinogenation measured by immunoassay was much less striking. This suggests that high levels of fibrinogen degradation products spuriously affect the bioassay of fibrinogen. We conclude that bleeding is related to the anticoagulant effects of fibrinogen degradation products interacting with heparin, and may be largely independent of hypofibrinogenemia. Delaying heparin for 12 hours may decrease the risk of bleeding while little affecting the risk of reocclusion.

Coronary Disease↗
PubMed1985

Acute myocardial infarction treated with intracoronary streptokinase: a report of the Society for Cardiac Angiography.

The Society for Cardiac Angiography maintains a registry of intracoronary streptokinase therapy (IC-SK) in patients with acute myocardial infarction. Between July 1981 and August 1984, 1,029 patients were entered into the registry. The baseline and clinical characteristics of patients were determined, the early results of therapy were evaluated, and baseline characteristics of those in whom reperfusion was achieved were compared with those in whom it was not. Multivariate discriminant analysis was used to identify the predictors of reperfusion and hospital mortality. The overall rate of reperfusion was 71.2%. Reperfusion was positively associated with hypotension, absence of cardiogenic shock and early treatment. The hospital mortality rate for all patients was 8.2% and was higher for women and the elderly. The hospital mortality was significantly lower among patients in whom reperfusion was achieved compared with those in whom it was not (5.5% vs 14.7%, p less than 0.0001) and for several high-risk subgroups. Thus, coronary artery reperfusion induced by IC-SK significantly reduces hospital mortality in high-risk patients with acute myocardial infarction. High-risk patients in whom reperfusion fails with IC-SK therapy should be considered for early coronary angioplasty or coronary artery bypass surgery.

Age Factors↗
PubMed1985

Symmetric cardiac enlargement in highly trained endurance athletes: a two-dimensional echocardiographic study.

Twelve highly trained male endurance athletes and 12 normally active matched control subjects were studied by two-dimensional and M-mode echocardiography to evaluate changes in the right and left heart chambers associated with intense aerobic training. Maximal oxygen uptake, a measure of cardiovascular fitness, ranged from 62.1 to 82.6 ml/kg/min in the athletes and from 33.0 to 49.3 ml/kg/min in the control subjects (p less than 0.001). The athletes had significantly greater left ventricular wall thickness (p less than 0.01), left ventricular chamber area (p less than 0.005), left atrial area (p less than 0.01), right ventricular chamber area (p less than 0.002), right ventricular wall thickness (p less than 0.05), and right atrial area (p less than 0.01). Proportionality of cardiac chamber enlargement in the athletes was shown by similar ratios of both right-to-left ventricular areas and right-to-left atrial areas in the two groups. Left ventricular contractility was not significantly different between groups. Cardiac enlargement in endurance athletes enables a greater stroke volume for the performance of sustained, intense exercise; hypertrophy of the chamber walls normalizes wall stress. These changes occur symmetrically in both right and left cardiac chambers in the endurance athlete, reflecting bilateral hemodynamic loading. The symmetry of the endurance athlete's cardiac enlargement differs from most pathologic conditions which have heterogeneous effects on specific cardiac chambers.

Adult↗
PubMed1985

Sequence of mechanical, electrocardiographic and clinical effects of repeated coronary artery occlusion in human beings: echocardiographic observations during coronary angioplasty.

The direct manipulation of coronary blood flow to induce regional myocardial ischemia has been almost entirely limited to experimental animal models. Thus, the detection of ischemia-induced left ventricular dysfunction in human subjects has been generally limited to observations made under conditions of diagnostic loading or during spontaneous clinical events. Percutaneous coronary angioplasty requires repeated interruptions of coronary blood flow for periods as long as 1 minute. The resulting appearance of or increase in ischemia-produced changes in myocardial function were detected by two-dimensional echocardiography in 18 patients undergoing angioplasty of 22 coronary stenoses. Accordingly, left ventricular contraction was studied during 52 episodes of regional coronary blood flow interruption and reperfusion in the process of inflating and deflating the angioplasty balloon. Before angioplasty, left ventricular wall motion was normal in 14 patients. There was mild anteroapical hypokinesia in two patients, anteroapical akinesia in one and mild inferior hypokinesia in one. Balloon inflations repeatedly produced new or increased wall motion abnormalities in the distribution of the instrumented coronary artery in 19 (86.4%) of the 22 procedures, but did not alter wall motion during angioplasty of one left circumflex artery lesion, one highly collateralized left anterior descending artery stenosis and one left anterior descending stenosis that had already caused severe anteroapical dyssynergy. Hypokinesia, usually rapidly progressing to dyskinesia, began 19 +/- 8 seconds (mean +/- SD) after coronary occlusion. Wall motion began to normalize 17 +/- 8 seconds after reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Sequelae of left ventricular electrical endocardial ablation.

The endomyocardial residual effects of left ventricular endocardial electrical ablation utilizing unipolar and bipolar electrode catheters were studied in 15 dogs. Histopathologic techniques specific for contraction band necrosis revealed that the mean maximal depth and breadth of necrosis was 0.63 +/- 0.44 and 1.23 +/- 0.82 cm, respectively. The dimensions of necrosis were significantly increased when utilizing larger energy discharges, especially through unipolar electrodes. Four dogs died during the procedure, three from ventricular fibrillation and one from asystole, and two died suddenly within the succeeding 24 hours. Endocardial thrombi were noted at necropsy in two dogs. In conclusion, transcatheter endocardial electrical ablation may destroy a sufficient mass of myocardium to interrupt arrhythmogenic conduction tissue, especially when larger currents are delivered through unipolar electrodes. However, serious ventricular arrhythmias and endocardial thrombi should be anticipated.

Animals↗
PubMed1985

Enlargement of the right heart in the endurance athlete: a two-dimensional echocardiographic study.

M-mode echocardiographic studies of endurance-trained athletes have provided conflicting data for right ventricular (RV) dimensions and no data for right atrial (RA) size. Since two-dimensional echocardiography provides a more accurate measurement of the RV and RA, it was employed together with M-mode echocardiography to evaluate 12 male endurance athletes and 12 sedentary controls matched for body size and age. All subjects were screened by history, physical examination, ECG, and maximal exercise testing. RV and RA areas were planimetered in the apical four-chamber view while displaying maximal chamber sizes. Athletes had significantly greater left ventricular (LV) wall thickness (P less than 0.01), LV area (P less than 0.001), and left atrial (LA) area (P less than 0.01). They also had greater RV area (P less than 0.01), RV wall thickness (P less than or equal to 0.05), and RA area (P less than or equal to 0.01). Maintained proportionality of the cardiac chamber dimensions in the athletes was shown by similar ratios of right-to-left ventricular areas, right-to-left atrial areas, and right-to-left ventricular wall thicknesses in both groups. The symmetry of the greater athlete's heart differs from most pathological conditions which have heterogeneous effects on specific cardiac chambers.

Adult↗
PubMed1985

The influence of infarction site and size on the ventricular response to coronary thrombolysis.

To test the hypothesis that myocardial infarction (MI) size rather than location determines the ventricular response to reperfusion, we studied 69 patients receiving intracoronary streptokinase within five hours of chest pain onset who displayed sustained reperfusion at 8.4 +/- 3.4 (SD) days. Twenty reperfusion failures served as controls. There were 31 patients with anterior MIs, 18 of which were estimated to be large based on an ejection fraction (EF) at reperfusion of less than 50%; 14 of 38 patients with inferior MIs also had large MIs. The EF increased at follow-up by 6.4% +/- 2.6% in patients with large anterior MIs and by 8.2% +/- 2.5% in those with large inferior MIs; in contrast, it increased by only 1.8% +/- 2.6% in patients with small anterior MIs and significantly decreased by 5.8% +/- 1.9% in patients with small inferior MIs. Six controls with large MIs (four anterior) displayed no change in EF; in 14 with small MIs (ten inferior), it fell slightly. There were no significant group differences in the number of diseased vessels, residual stenosis, or collaterals. It is concluded that MI size, not site, largely determines the ventricular functional response to early reperfusion; thus, patients with inferior MIs cannot be disqualified on this basis alone for thrombolytic therapy.

Coronary Disease↗
PubMed1984

The effect of electrode position on atrial sensing for physiologically responsive cardiac pacemakers.

Fully automatic pacing systems rely on accurate identification of spontaneous atrial signals for physiologically responsive pacing. These signals must be discriminated from far-field ventricular activity, which might otherwise be sensed in the atrium. To amplify on the previously reported superiority of bipolar signals and high-impedance circuitry for atrial sensing, we studied the effects of various intraatrial electrode positions on the atrial and ventricular contribution to electrograms recorded in this chamber. Compared with other intraatrial endocardial sites, right atrial signals were greatest in amplitude and slew rate in the appendage (RAA), averaging 3.3 +/- 0.41 mV and 1.15 +/- 0.16 V/sec (mean +/- SEM), respectively. These values were substantially higher than in the low atrium (p less than 0.001 and 0.0005 for amplitude and slew rate, respectively) and the high lateral atrium (p less than 0.05 for slew rate). Appendage atrial electrograms also had significantly higher amplitude and slew rate than far-field R waves recorded here (p less than 0.0001 for both). Additionally, the greatest difference in spectral content between atrial and far-field ventricular signals was also observed in the RAA. Thus, parameters in the domain of both time and frequency identified the RAA as the superior location for atrial sensing. Except for phrenic nerve problems with pacing, the HRA also appears to be a suitable electrode location for sensing. These considerations are germane in light of a growing number of atrial active and passive fixation leads now being employed for physiologic pacing.

Cardiac Pacing, Artificial↗
PubMed1984

Prevalence and significance of ventriculoatrial conduction.

Because retrograde atrioventricular conduction may predispose to pacemaker-induced tachycardia when DDD pacing is employed, we assessed ventriculo-atrial conduction in 117 patients undergoing electrophysiologic studies. Ventriculo-atrial conduction was present in 40% with a mean (+/- sem) conduction time of 205 +/- 12 ms. The maximum VA conduction time following minimum extrastimulus intervals averaged 258 +/- 14 ms. Antegrade AV nodal properties predicted VA conduction in only 67% by using stepwise discriminant analysis. Only the PR interval, AH interval, and AV nodal effective refractory periods were helpful in predicting ventriculo-atrial conduction. Although ventriculo-atrial conduction time increased on most antiarrhythmic drugs, it was infrequently eliminated.

Aged↗
PubMed1984

Hemorrhage and the products of fibrinogen digestion after intracoronary administration of streptokinase.

Hemorrhage was prospectively identified in 26 of 116 consecutive patients (23%) who were receiving intracoronary streptokinase for occlusive coronary thrombi producing infarction. Bleeding was not influenced by the dose of streptokinase or the method of cardiac catheterization. Before treatment, prothrombin time and partial thromboplastin time were normal in both bleeders and nonbleeders. Fibrinogen levels measured by bioassay after streptokinase (mean +/- SEM) were 62 +/- 29 mg/dl in patients with major bleeding, 111 +/- 26 mg/dl in patients with minor bleeding, and 109 +/- 13 mg/dl in nonbleeders (p = NS). The regression slope b calculated from poststreptokinase fibrinogen time-concentration data in 71 patients was 4.7 mg/dl/hr. However, mean fibrinogen concentrations calculated at sequential 5 hr intervals revealed no net regeneration for the first 20 hr after thrombolysis. The apparent fibrinogen regeneration rate was less than normal (31 mg/kg/day) for more than 10 hr but subsequently increased to 94 +/- 10 mg/kg/day by the second day. The initial apparent latency of fibrinogen regeneration paralleled the sharp rise in fibrinogen degradation products, which began to decline after 20 hr of treatment but remained elevated well into the second day. Because of their anticoagulant effects, these products may interfere with the fibrinogen assay, causing spuriously low results. Thus, whether the early delay in fibrinogen regeneration is real or simply a reflection of the effects of fibrinogen degradation products on the bioassay, it signals the time for caution in initiating systemic heparin therapy.

Blood Coagulation Factors↗
PubMed1983

The significance of surface changes on explanted polyurethane pacemaker leads.

Although over 140,000 polyurethane leads have been implanted in humans, a controversy has recently arisen dealing with the significance of frequently detected irregularities on explanted insulator surfaces by scanning electron microscopy (SEM), and their relationship with lead failure. We therefore implanted ten, 6 Fr atrial polyurethane leads and an equal number of 4 Fr ventricular leads in dogs for a mean 26 +/- 2 and 29 +/- 2 weeks, respectively. Fourteen leads were removed utilizing metered force. The remaining leads were removed surgically without force at the termination of the study. Specimens were stored in saline prior to physical testing (tensile strength and elongation) of intravascular and extravascular lead segments. Similarly stored samples were prepared for SEM analysis. The polyurethane insulator disconnected from the electrode on forcible removal in three atrial and two ventricular leads (concordant connected from the electrode on forcible removal in three atrial and two ventricular leads (concordant for two pairs). There was no significant relationship between the results of physical testing and extraction force, lead size, integrity on removal, sample location or SEM scores. Chemical analysis of surface changes employing both x-ray and electron emission spectroscopy failed to reveal evidence of protein adsorption or liquid impregnation. Samples soaked in sodium hydroxide displayed the same SEM irregularities. The combined effects of fissuring and fluid absorption by polyurethane did not affect chronic anodal or cathodal thresholds. In conclusion, a clear relationship between chronic surface irregularities and the insulator function of polyurethane, its relationship between chronic surface irregularities and the insulator function of polyurethane, its integrity in situ, or its strength at explant has not been established by this relatively short-term study. On the other hand, a potential time-dependent impact of these changes on lead performance has not been excluded. Moreover, only a single species of medical grade polyurethane has been clinically evaluated. Thus, the ultimate place of polyurethane leads in pacing systems has yet to be determined.

Animals↗
PubMed1983

Severe transient left ventricular "hypertrophy" occurring during acute myocarditis.

We report an unusual sequence of echocardiographic abnormalities observed during the course of acute myocarditis in a young woman. Striking left ventricular "hypertrophy" transiently followed the normalization of marked segmental wall motion abnormalities. These rapid and marked alterations in left ventricular wall thickness suggest that myocardial inflammation and edema resulted in the transient appearance of myocardial hypertrophy. Our findings also indicate that contractility may be nonhomogeneously depressed in acute myocarditis.

Acute Disease↗
PubMed1982

High-density lipoprotein-cholesterol in marathon runners during a 20-day road race.

Plasma high-density lipoprotein (HDL)-cholesterol and lipid levels were measured in 12 male marathon runners (mean age, 40 years) who ran an average of 28 km/day for ten days, rested 70 hours, then continued to run for eight more days, covering a total distance for both running periods of 500 km. Blood samples were obtained on eight mornings. After one week of running, HDL-cholesterol levels increased 18% and triglyceride levels decreased 22%. However, the three-day rest period reversed these changes. As running resumed, HDL-cholesterol levels again increased and triglyceride levels decreased. There were no significant changes in total cholesterol, body weight, or skinfold thickness despite an average caloric intake of 4,800 kcal/day. Heavy beer drinking had no discernible effect on HDL-cholesterol levels, but may have caused mild hepatic injury as suggested by significantly increased serum alanine transferase and gamma-glutamyl transferase values. This study demonstrates that HDL-cholesterol levels increase with higher running mileage and decrease within days of stopping exercise when caloric and alcohol intake remain elevated.

Adult↗
PubMed1982

Intracoronary streptokinase in clinical practice.

The candidacy for streptokinase (SK) infusion was studied in 95 patients displaying ECG evidence of acute or impending infarction who were catheterized within 5 hours of the onset of chest pain. Intracoronary SK was administered to 84 patients in whom occlusions of the infarct-related vessel were identified, with early recanalization having been achieved in 74 (88%). Because of completeness of studies, a data base of 72 patients was employed for further analysis. Recanalization was sustained at follow-up in 45 of 55 patients (82%). Spontaneous thrombolysis was demonstrated at follow-up in five patients (8%) initially resistant to SK, and rethrombosis occurred in 10 patients (18%). Preservation of R waves relative to Q wave depth was limited to patients with less than 90% residual stenosis. Eight of nine patients with continuing thrombolysis and patients with recanalized occlusions of the left anterior descending coronary artery displayed more impressive increases in mean (+/- SEM) ejection fraction (47% +/- 4% to 53% +/- 5% [p less than 0.05], and 47% +/- 3% to 52% +/- 5, respectively). The ejection fraction also increased significantly in 15 patients with pre-SK values of less than 50% (41% +/- 2% to 48% +/- 3%; p less than 0.05). Ventricular function deteriorated in SK failures. Reperfusion arrhythmias occurred in 28 of 62 recanalized patients (45%). Minor bleeding tendencies were displayed in 18 of 72 patients (25%). Major hemorrhages, one of which may have been fatal, occurred in four patients (5.6%). Of 84 patients, four (4.7%) died, two of whom were in cardiogenic shock when first seen. In contrast, there were 11 deaths (11.8%) in a consecutive simultaneously enrolled series of 93 control patients with similar entry criteria (p less than 0.05). Two additional SK-treated patients died, 16 and 30 days after treatment, both more than a week after surgical revascularization. It is concluded that SK recanalization is a promising new therapy that may decrease mortality and preserve myocardial function in certain circumstances. Its efficacy in a setting closer to the mainstream of cardiologic practice extends the favorable experience issuing from earlier clinical investigations.

Adult↗