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Biomedical subjects

T A Buckingham

Publications and source records attributed to T A Buckingham.

At least 37 records · Page 2Linked to original sources
PubMed1989

Natural history of potentially lethal ventricular arrhythmias in patients treated with long-term antiarrhythmic drug therapy.

To examine the natural history of long-term anti-arrhythmic therapy in patients with benign and potentially lethal ventricular premature complexes (VPCs), 28 patients with initial efficacy with moricizine (greater than 75% suppression of baseline mean VPCs/hr and greater than 90% suppression of repetitive VPCs) were prospectively followed for 1 to 56 (mean +/- standard deviation 25 +/- 17) months. Patients were examined during baseline placebo, anti-arrhythmic drug therapy and intermittent pulsed-placebo reexamination periods. The mean VPCs of all patients at baseline entry were 233 +/- 47 VPCs/hr, and after moricizine therapy 14 +/- 4 VPCs/hr. Follow-up demonstrated that antiarrhythmic efficacy decreased to 75% at 12 months and to 62% at 24 months. Loss of antiarrhythmic drug efficacy most commonly occurred as a "transient" event (10 patients [36%]), and efficacy was spontaneously reestablished without a change in antiarrhythmic therapy. In contrast, increased dose titration of moricizine was necessary to reestablish antiarrhythmic suppression efficacy in 4 patients (14%), and 4 patients (14%) lost antiarrhythmic drug responsiveness during follow-up. Spontaneous decrease in baseline VPCs resulted in discontinuation of antiarrhythmic therapy in 3 patients, and increase in baseline VPCs was associated with a loss of antiarrhythmic response in 2 patients. Late proarrhythmic effects (2 patients, 7%), delayed side effects necessitating drug withdrawal (6 patients, 21%) and medical events (4 patients, 14%) occurred during 56 months of follow-up. Individual serum moricizine levels remained in the therapeutic range throughout the study and did not correlate with changes in antiarrhythmic efficacy.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Arrhythmia Agents↗
PubMed1989

Signal-averaged electrocardiography in the time and frequency domains.

The noninvasive signal-averaged electrocardiographic detection of late potentials correlates with the spontaneous occurrence of sustained ventricular tachycardia (VT). Frequency analysis of the electrocardiographic signal from the terminal QRS and ST segment also correlates with sustained VT. This study was designed to compare these 2 methods by analysis of signals recorded from the same hardware system. Signals were recorded from 234 patients with prior myocardial infarctions with a commercially available signal-averaging system. Patients were classified into 2 groups: group 1 consisted of 84 patients with VT and group 2 consisted of 150 patients without VT. In the frequency domain, magnitude and energy area ratios and peak ratios of the spectral plot from 20 to 50 Hz over 0 to 20 Hz were calculated for a 140-ms interval starting 60 ms after the beginning of the QRS. In the time domain, the duration of the filtered QRS was 121 +/- 29 ms for group 1 and 110 +/- 25 ms for group 2 (p less than 0.002). The duration of the terminal QRS less than 40 microV was 45 +/- 21 ms in group 1 and 36 +/- 18 ms in group 2 (p less than 0.001). The root-mean-square amplitude of the terminal 40 ms of the QRS was 25 +/- 24 microV in group 1 and 36 +/- 33 microV in group 2 (p less than 0.004).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

The hemodynamic benefit of differential atrioventricular delay intervals for sensed and paced atrial events during physiologic pacing.

The ability to program different atrioventricular (AV) delay intervals for paced and sensed atrial events is incorporated in the design of some newer dual chamber pacemakers. However, little is known regarding the hemodynamic benefit of differential AV delay intervals or the magnitude of difference between optimal AV delay intervals for paced and sensed P waves in individual patients. In this study, Doppler-derived cardiac output was used to examine the optimal timing of paced and sensed atrial events in 24 patients with a permanent dual chamber pacemaker. The hemodynamic effect of utilizing separate optimal delay intervals for sensed and paced events compared with utilizing the same fixed AV delay interval for both was determined. The optimal delay interval during DVI (AV sequential) pacing and VDD (atrial triggered, ventricular inhibited) pacing at similar heart rates was 176 +/- 44 and 144 +/- 48 ms (p less than 0.002), respectively. The mean difference between the optimal AV delay intervals for sensed (VDD) and paced (DVI) P waves was 32 ms and was up to 100 ms in some individuals. The difference between optimal AV delay intervals for sensed and paced atrial events was similar in patients with complete heart block and those with intact AV node conduction. At the respective optimal AV delay intervals for sensed and paced P waves, there was no significant difference in the cardiac output during VDD compared with DVI pacing. However, cardiac output significant declined during VDD pacing at the optimal AV delay interval for a paced event and during DVI pacing at the optimal interval for a sensed event.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Hemodynamic benefit of atrioventricular synchrony: prediction from baseline Doppler-echocardiographic variables.

The purpose of this study was to determine if baseline Doppler-echocardiographic variables of systolic or diastolic function could predict the hemodynamic benefit of atrioventricular (AV) synchronous pacing. Twenty-four patients with a dual chamber pacemaker were studied. Baseline M-mode and two-dimensional echocardiograms were obtained and Doppler-echocardiographic measurements of mitral inflow and left ventricular outflow were made in VVI mode (single rate demand) and in VDD (atrial synchronous, ventricular inhibited) and DVI (AV sequentially paced) modes at AV intervals ranging from 50 to 300 ms. Forward stroke volume and cardiac output were determined in each mode at each AV interval from the left ventricular outflow tract flow velocities, and the percent increase in cardiac output over VVI mode was determined. M-mode measurements, including left ventricular end-diastolic dimension, shortening fraction and left atrial size and Doppler measurement of diastolic filling, including peak early velocity and percent atrial contribution, did not correlate with the percent increase in cardiac output during physiologic pacing. The stroke volume in VVI mode correlated significantly with the percent increase in cardiac output during physiologic pacing (r = -0.61, p less than 0.005 for VDD mode and r = -0.55, p less than 0.05 for DVI mode). Five of the 15 patients with VVI stroke volume less than 50 ml but none of the 9 patients with stroke volume greater than 50 ml had ventriculoatrial (VA) conduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Emergency catheter ablation of refractory ventricular tachycardia.

Catheter ablation, in extreme cases, can be used successfully as emergency therapy for VT in the CCU. In the hands of a physician experienced in electrophysiologic procedures, catheter ablation may prove to be an alternative to surgical or pharmacologic therapy in acutely ill patients with refractory ventricular arrhythmias.

Aged↗
PubMed1988

Effect of conduction defects on the signal-averaged electrocardiographic determination of late potentials.

To determine the effect of cardiac conduction defects on the signal-averaged electrocardiogram (ECG) and on its ability to noninvasively identify patients predisposed to ventricular tachycardia (VT), standard 12-lead ECGs and signal-averaged ECGs were obtained in 213 patients with normal conduction and 186 patients with various conduction defects. Sustained VT was induced by programmed stimulation or occurred spontaneously in 122 patients. Two-way analysis of variance showed that conduction defects and VT were associated with changes in 3 signal-averaged ECG parameters: duration of the filtered QRS, duration of the terminal QRS under 40 microV and the mean amplitude of the terminal 40 ms of the QRS. Stepwise multiple logistic regression identified 3 variables that distinguished the patient with VT with a sensitivity of 62%, a specificity of 63% and a positive predictive accuracy of 63%. These 3 variables, listed in order of importance, were conduction defect score, duration of the filtered QRS and mean amplitude of the terminal 40 ms of the QRS. These data indicate that conduction defects have systematic effects on signal-averaged ECG parameters independent of those seen in patients predisposed to VT. These effects mandate the adjustment of the definitions of late potentials in the presence of conduction defects.

Adult↗
PubMed1988

Effects of electrophysiologic studies resulting in electrical countershock or burst pacing on left ventricular systolic and diastolic function.

To determine the acute effects of electrophysiologic study on left ventricular systolic and diastolic function in patients requiring termination of induced tachyarrhythmias by either electrical countershock or burst pacing, we examined 16 patients (11 men and five women), aged 43 to 78 years (mean 58 +/- 13), undergoing programmed electrical stimulation. Indices of systolic and diastolic left ventricular function were measured by M-mode echocardiography before and within 1 minute after termination of 22 episodes of induced tachyarrhythmias by defibrillation (n = 16) and burst pacing (n = 6). The left ventricular septal and posterior endocardial surfaces were digitized immediately below the mitral valve leaflets, and indices of systolic and diastolic function were calculated. The results showed a significant impairment in both systolic and diastolic function after termination of tachyarrhythmias by defibrillation, as seen by a decrease in the shortening fraction (23.7 +/- 7.6% to 19.8 +/- 7.8%; p less than 0.005) and a decline in the peak rate of increase in left ventricular diameter during diastole called dD/dtmax (87.4 +/- 36.1 mm/sec to 71.5 +/- 28.9 mm/sec; p less than 0.01), respectively. In addition, indices of systolic and diastolic function measured at baseline were predictive of impairment in diastolic function, as seen by modest but highly significant correlations between the absolute change in dD/dtmax after defibrillation versus the peak velocity of fiber shortening (r = -0.69; p less than 0.005) and dD/dtmax (r = -0.60; p less than 0.02) measured at baseline. Left ventricular function after termination of tachyarrhythmias by burst pacing was not significantly altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Doppler echocardiographic assessment of the effect of varying atrioventricular delay and pacemaker mode on left ventricular filling.

Pulsed Doppler echocardiography was used to study the timing and dynamics of left ventricular filling in 14 patients with permanent dual-chamber programmable pacemakers. Pacemakers were programmed to atrial sensed (VDD) mode and atrial-ventricular sequential paced mode at low (DVI-L) and high (DVI-H) heart rates, and pulsed Doppler recordings of transmitral flow were analyzed at atrioventricular delays of 50 to 300 msec in each mode. There was a significant decrease in the one-third filling fraction in both VDD and DVI-L modes and a significant increase in DVI-H modes with increasing atrioventricular delay. The ratio of early filling area to atrial filling area was significantly lower at longer atrioventricular delays in both VDD and DVI-L modes. The time from pacemaker spike to mitral valve closure was highly significantly correlated with atrioventricular delay in VDD, DVI-L, and DVI-H modes (r = -0.92, p = 0.0001; r = -0.90, p = 0.0001; and r = -0.85, p = 0.0001, respectively) as was the diastolic filling time to a lesser extent (r = -0.73, p = 0.0001; r = -0.69, p = 0.0001; r = -0.61, p = 0.0001, respectively). Events reflecting atrial systole occurred at a later time in the cardiac cycle in the atrial paced vs the atrial sensed mode. Thus changes in atrioventricular delay and pacemaker mode in this group of patients are a strong determinant of the timing and dynamics of left ventricular filling.

Aged↗
PubMed1988

Effect of ventricular function on the exercise hemodynamics of variable rate pacing.

To determine the effect of ventricular function on the exercise hemodynamics of variable rate pacing, 16 selected patients underwent paired, double-blind, randomized exercise tests in single rate demand (VVI) or variable rate (VVIR) pacing modes. Ejection fraction and cardiac index were determined by two-dimensional and Doppler echocardiography at baseline and during peak exercise. Baseline ejection fraction ranged from 14 to 73% and was less than 40% in 6 patients (Group 1) and greater than or equal to 40% in 10 patients (Group 2). Duration of exercise was longer during the VVIR mode (502 s) than during the VVI mode (449 s) (p less than 0.01) and unrelated to baseline ejection fraction. Heart rate during exercise increased 9% in the VVI mode and 35% in the VVIR mode (p less than 0.005). Cardiac index increased 49% in the VVI mode and 83% in the VVIR mode. Analysis of variance for repeated measures showed a significant effect of pacing mode (p less than 0.01) and exercise (p less than 0.001), but not baseline ejection fraction, on cardiac index. Baseline ejection fraction did not correlate with the increase in cardiac index in either pacing mode or with the difference in increase between modes. There was no significant difference between Groups 1 and 2 in exercise duration, peak heart rate-blood pressure (rate-pressure) product, baseline or peak heart rate or baseline or peak cardiac index. Therefore, in selected patients, VVIR pacing during exercise results in an increase in heart rate, duration of exercise and cardiac index that is unrelated to the degree of baseline left ventricular dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Utility of ambulatory electrocardiography in detecting pacemaker dysfunction in the early postimplantation period.

The value of ambulatory electrocardiography (AECG) in detecting pacemaker dysfunction before hospital discharge was assessed in 100 patients a mean of 1.2 days after pacemaker implantation. The incidence of permanent pacemaker dysfunction detected by AECG in the early postimplantation period, the frequency that pacemaker dysfunction detected by AECG was not detected by telemetric monitoring and the frequency that results of AECG led to pacemaker reprogramming before hospital discharge were determined. AECG detected at least 1 type of pacemaker dysfunction in 35% of patients and routine telemetry identified the abnormality in only 8% (p less than 0.001). Pacemaker dysfunction occurred in 42% of patients with dual-chamber devices and 27% of those with single-chamber devices (difference not significant). In the 35 patients who had pacemaker malfunction, a total of 50 instances of pacemaker dysfunction were detected. Failure of atrial capture occurred in 2% of patients, failure of atrial sensing in 9%, failure of atrial output in 1%, failure of ventricular capture in 8%, failure of ventricular sensing in 14%, failure of ventricular output due to myopotential inhibition in 11% and pacemaker-mediated tachycardia in 5%. The results of the AECG led to a clinical intervention in 22 patients (pacemaker reprogramming in 21 patients and lead repositioning in 1 patient) in whom no pacemaker dysfunction was suspected on the basis of telemetry or clinical symptoms. In conclusion, AECG provides additional benefit beyond that of routine telemetry monitoring in identifying pacemaker dysfunction in the early period after implantation.

Aged↗
PubMed1987

Independent value of signal-averaged electrocardiography and left ventricular function in identifying patients with sustained ventricular tachycardia with coronary artery disease.

To determine if the signal-averaged electrocardiographic detection of late potentials is an independent marker of sustained ventricular tachycardia (VT) in patients with documented chronic coronary artery disease (CAD), 57 patients underwent signal-averaged electrocardiography. Mean ejection fraction was 47 +/- 13% in the 14 patients with sustained VT and 56 +/- 19% in the 43 patients without VT (difference not significant). The sensitivity, specificity and accuracy of late potentials for detecting patients with VT were 64% (9 of 14), 79% (34 of 43), and 75% (43 of 57), respectively. Univariate analysis and stepwise logistic regression of angiographic and electrocardiographic variables identified late potentials as an independent marker of the patient with sustained VT. The odds ratio for late potentials to detect patients with prior sustained VT was 2.6. Six-month follow-up revealed a cardiac mortality rate of 11% and an arrhythmia event rate of 22% in patients with late potentials vs a cardiac mortality rate of 3% and an arrhythmia event rate of 13% in patients without late potentials. Thus, signal-averaged electrocardiographic detection of late potentials is useful in identifying patients with prior sustained VT independent of left ventricular function.

Adult↗
PubMed1986

Serum digoxin concentrations during ethmozine antiarrhythmic therapy.

The potential for pharmacokinetic drug interaction between ethmozine (moricizine HCl), a phenothiazine class I antiarrhythmic investigational drug, and digoxin was evaluated in 13 cardiac patients with normal renal function. Antiarrhythmic therapy was initiated in patients with potentially lethal (nonlife-threatening) ventricular arrhythmias (greater than 30 ventricular ectopic beats [VEB]/hr) who were receiving maintenance digoxin therapy for congestive heart failure and/or atrial fibrillation. Serum digoxin concentrations of patients were measured frequently by radioimmunoassay and plasma ethmozine concentrations by high-performance liquid chromatographic methods. Patients entered a short-term (4 weeks) single-blind, placebo controlled ethmozine protocol with an option to receive long-term (1 to 6 months) open-label maintenance ethmozine therapy. Ambulatory ECGs (48 hour) used to assess antiarrhythmic efficacy of ethmozine during each week of the short-term protocol showed that 77% of patients demonstrated greater than 90% mean hourly frequency suppression of all forms of ventricular ectopy. Serum digoxin concentrations during short-term ethmozine dosing showed a nonsignificant (p greater than 0.05) increase of 10% to 15% (mean 0.91 ng/ml to 1.13 ng/ml). The short-term protocol serum digoxin levels correlated closely with serum digoxin concentrations during placebo therapy (1st week, r = 0.90; 2nd week, r = 0.87). Serum digoxin concentrations were not significantly different (p greater than 0.05) from placebo values at the end of 1, 3, and 6 months of maintenance ethmozine therapy. Thus, we conclude that ethmozine administered in an antiarrhythmic efficacious dosage (10 mg/kg/day) showed no important clinical or statistically significant change in serum digoxin concentrations of cardiac patients with normal renal function.

Adult↗
PubMed1986

Reperfusion arrhythmias during coronary reperfusion therapy in man. Clinical and angiographic correlations.

We hypothesized that patients suffering acute myocardial infarction who have reperfusion arrhythmias (RPA) during intracoronary streptokinase infusion (ICSK) would have different clinical and angiographic characteristics and a larger infarction size than those who achieved reperfusion without RPA. Of 35 patients who received intracoronary streptokinase, 27 had successful reperfusion documented by angiography. Successful reperfusion was accompanied by RPA in eight patients and no RPA in 19 patients. RPA included episodes of ventricular tachycardia in one, idioventricular rhythm in four, junctional bradycardia in one, or AV block in two patients which occurred at the time of reperfusion. Myocardial infarction size was calculated using creatine kinase-MB (CK-MB) isoenzyme time activity curves using standard methods. The mean CK-MB g equivalents (eq) for those with RPA was 71 +/- 25 (+/- 1 SD) and for those with no RPA was 45 +/- 24 (p less than .04). In patients with RPA, ejection fraction rose 5 +/- 14 percentage points before discharge, but fell 10 +/- 13 points in those with RPA (p less than .03). There was no difference between groups in total dose of streptokinase, final degree of stenosis of the affected vessel, reocclusion rate, or time from onset of symptoms to reperfusion. We conclude that patients suffering acute myocardial infarction who have RPA during ICSK in most cases have a larger infarction site or a more "stunned myocardium," as indicated by greater CK-MB release and fall in ejection fraction which is not due to increased time of ischemia.

Adult↗
PubMed1985

Long-term follow-up of asymptomatic healthy subjects with frequent and complex ventricular ectopy.

From 1973 to 1983 we followed 73 asymptomatic healthy subjects who were discovered to have frequent and complex ventricular ectopy. Ventricular ectopy in these subjects was measured by 24-hour ambulatory electrocardiography, which showed a mean frequency of 566 ventricular ectopic beats per hour (range, 78 to 1994), with multiform ventricular ectopic beats in 63 per cent, ventricular couplets in 60 per cent, and ventricular tachycardia in 26 per cent. Asymptomatic healthy status was confirmed by extensive noninvasive cardiologic examination, although cardiac catheterization of a subsample of subjects disclosed serious coronary artery disease in 19 per cent. Follow-up for 3.0 to 9.5 years (mean, 6.5) was accomplished in 70 subjects (96 per cent) and documented one sudden death and one death from cancer. Calculation of a standardized mortality ratio (Monson's U.S. data, 8th revision) for 448 person-years of follow-up indicated that 7.4 deaths were expected, whereas 2 occurred (standardized mortality ratio, 27; P less than 0.05). A comparison of survival of the study cohort with that of persons without coronary artery disease or with mild disease, patients with moderate disease, and men with unrecognized myocardial infarction showed a favorable prognosis for the study cohort over 10 years. We conclude that the long-term prognosis in asymptomatic healthy subjects with frequent and complex ventricular ectopy is similar to that of the healthy U.S. population and suggests no increased risk of death.

Adolescent↗