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Biomedical subjects

A J Solomon

Publications and source records attributed to A J Solomon.

At least 19 recordsLinked to original sources
PubMed2001

Treatment of patients with myocardial infarction who present with a paced rhythm.

BACKGROUND: A paced rhythm can mask the electrocardiographic features of an acute myocardial infarction, complicating timely recognition and treatment. OBJECTIVE: To evaluate characteristics, treatment, and outcomes among patients presenting with paced rhythms during myocardial infarction. DESIGN: Retrospective cohort study. SETTING: U.S. acute care hospitals. PATIENTS: 102 249 Medicare beneficiaries at least 65 years of age who were treated for acute myocardial infarction between 1994 and 1996. MEASUREMENTS: Provision of three treatments for acute myocardial infarction (emergent reperfusion, aspirin, and beta-blockers), death at 30 days, and long-term follow-up. RESULTS: 1954 patients (1.9%) presented with paced rhythms during myocardial infarction. These patients were older; were predominantly male; and had higher rates of congestive heart failure, diabetes, and previous infarction. They were significantly less likely to receive emergent reperfusion (relative risk [RR], 0.27 [95% CI, 0.22 to 0.33]), aspirin (RR at admission, 0.91 [CI, 0.88 to 0.94]; RR at discharge, 0.87 [CI, 0.83 to 0.92]), and beta-blockers at admission (RR, 0.89 [CI, 0.82 to 0.96]). In addition, there was a trend toward decreased use of beta-blockers at discharge (RR, 0.91 [CI, 0.76 to 1.06]). Crude mortality rates were higher among patients with paced rhythms than among those without at 30 days (25.8% vs. 21.3%; P = 0.001) and at 1 year (47.1% vs. 36.1%; P = 0.001). Among patients with paced rhythms, risk for death at 30 days decreased after adjustment for illness severity and decreased use of therapy (RR, 1.03 [CI, 0.93 to 1.14]). Patients with paced rhythms remained at additional risk for long-term mortality (hazard ratio, 1.12 [CI, 1.06 to 1.18]). CONCLUSIONS: Patients with paced rhythms were less likely than those without to receive treatment for acute myocardial infarction and had poorer short- and long-term outcomes. However, this mortality risk diminished after adjustment for treatment. This suggests that improved recognition and treatment of myocardial infarction may improve outcomes, particularly in the short term.

Adrenergic beta-Antagonists↗
PubMed2001

Acute myocardial infarction complicated by heart block in the elderly: prevalence and outcomes.

BACKGROUND: Although second- and third-degree heart block (HB) are common conduction disorders associated with acute myocardial infarction (MI), patient characteristics and HBs association with outcomes, particularly among the elderly, remain poorly defined. METHODS: We evaluated 106,780 Medicare beneficiaries aged 65 years and older treated for acute MI between January 1994 and February 1996 for development of HB. HB and non-HB patients were compared by univariate analysis, and the influence of HB on outcomes was evaluated by unadjusted and multiple logistic regression. RESULTS: HB was documented in 5048 (4.7%) patients; 1646 presented with HB and 3402 developed HB during hospitalization. HB was more common among patients with inferior infarctions than anterior infarctions (7.3% vs 3.0%, P =.001), particularly the cohort of patients with inferior MI treated with reperfusion therapy (8.3%). HB patients had higher rates of in-hospital mortality (29.6% vs. 17.5% vs. non-HB patients, P =.001). After adjustment for demographic and clinical factors, HB remained an independent predictor of in-hospital mortality (relative risk [RR] 1.41, 95% confidence interval [CI] 1. 34-1.48), but HB had no prognostic significance at 1 year among hospital survivors (RR 0.94, 95% CI 0.88-1.01). Mortality risks varied on the basis of MI location. Both anterior MI (RR 1.46, 95% CI 1.30-1.63) and inferior MI (RR 1.52, 95% CI 1.39-1.66) patients with HB had increased risks of in-hospital mortality. There was a trend toward increased mortality among patients with anterior MI (RR 1.15, 95% CI 0.99-1.32) at 1 year, whereas those with inferior MI were at lower risk (RR 0.83, 95% CI 0.75-0.98). CONCLUSIONS: HB is a common complication of acute MI in elderly patients, particularly among patients with inferior MIs who received reperfusion therapy. HB is independently associated with short-term but not long-term mortality.

Age Factors↗
PubMed2001

The role of reperfusion therapy in paced patients with acute myocardial infarction.

BACKGROUND/OBJECTIVE: Our purpose was to evaluate the effectiveness of reperfusion therapy among elderly paced patients with acute myocardial infarction (MI). Current guidelines make no recommendation for the use of reperfusion therapy among patients who have a paced rhythm during MI. METHODS: We evaluated 1954 Medicare beneficiaries 65 years and older treated for acute MI between 1994 and 1996 who had a paced rhythm for use of reperfusion therapy. Use of reperfusion therapy was evaluated for associations with outcomes by logistic regression and Cox proportional hazards models incorporating propensity score analysis. RESULTS: Reperfusion therapy was used in 171 (8.8%) patients; 70 were treated with primary PTCA and 101 with thrombolytic therapy. Patients who received reperfusion therapy had 30-day mortality rates similar to those who did not receive reperfusion (26.3% vs 25.7%, P =.87). Multivariate adjustment for mortality risk factors and treatment propensity indicated no survival benefit associated with reperfusion therapy at 30 days (relative risk [RR] 1.07, 95% confidence interval [CI] 0.77-1.43) or long-term follow-up (hazard ratio [HR] 0.86, 95% CI 0.68-1.10). Mortality risks varied by type of reperfusion therapy. Patients treated with primary percutaneous transluminal coronary angioplasty were at comparable risk of mortality at 30 days (RR 0.73, 95% CI 0.40-1.23) but at lower risk at long-term follow-up (HR 0.60, 95% CI 0.40-0.88). Mortality risks were unchanged among patients treated with thrombolytics at 30 days (RR 1.32, 95% CI 0.92-1.79) and long-term follow-up (HR 1.08, 95% CI 0.82-1.43). CONCLUSION: We find suggestive evidence that primary percutaneous transluminal coronary angioplasty provides a long-term survival benefit in the treatment of elderly patients with acute MI who have a paced rhythm.

Age Factors↗
PubMed2000

Acute myocardial infarction complicated by atrial fibrillation in the elderly: prevalence and outcomes.

BACKGROUND: Although atrial fibrillation (AF) is a common complication of acute myocardial infarction (MI), patient characteristics and association with outcomes remain poorly defined in the elderly. METHODS AND RESULTS: We evaluated 106 780 Medicare beneficiaries > or =65 years of age from the Cooperative Cardiovascular Project treated for acute MI between January 1994 and February 1996 to determine the prevalence and prognostic significance of AF complicating acute MI in elderly patients. Patients were categorized on the basis of the presence of AF, and those with AF were further subdivided by time of AF (present on arrival versus developing during hospitalization). AF and non-AF patients were compared by univariate analysis, and logistic regression modeling was used to identify clinical predictors of AF. The influence of AF on outcomes was evaluated by unadjusted Kaplan-Meier survival curves and logistic regression models. AF was documented in 23 565 patients (22. 1%): 11 510 presented with AF and 12,055 developed AF during hospitalization. AF patients were older, had more advanced heart failure, and were more likely to have had a prior MI and undergone coronary revascularization. AF patients had poorer outcomes, including higher in-hospital (25.3% versus 16.0%), 30-day (29.3% versus 19.1%), and 1-year (48.3% versus 32.7%) mortality. AF remained an independent predictor of in-hospital (odds ratio [OR], 1. 21), 30-day (OR, 1.20), and 1-year (OR, 1.34) mortality after multivariate adjustment. Patients developing AF during hospitalization had a worse prognosis than patients who presented with AF. CONCLUSIONS: AF is a common complication of acute MI in elderly patients and independently influences mortality, particularly when it develops during hospitalization.

Aged↗
PubMed2000

Contemporary management of angina: part II. Medical management of chronic stable angina.

Except for a small subset of patients with angina whose survival is improved with coronary artery bypass surgery, chronic stable angina can be appropriately managed with medical therapy in the vast majority of patients. Drug therapy includes aspirin, beta-adrenergic blockers, cholesterol-lowering agents and other anti-ischemic drugs that can ameliorate angina and improve the patient's quality of life. Understanding how and when to use these medicines involves knowledge of the mechanisms of these drugs as well as familiarity with the literature supporting their efficacy in various patient populations.

Adrenergic beta-Antagonists↗
PubMed2000

The combination of propranolol and magnesium does not prevent postoperative atrial fibrillation.

BACKGROUND: Atrial fibrillation is a common complication of cardiovascular surgery. Beta-blockers have been shown to decrease the incidence of postoperative atrial fibrillation. However, the use of magnesium is more controversial. It was our hypothesis that adjunctive magnesium sulfate would improve the efficacy of beta-blockers alone in the prevention of postoperative atrial fibrillation. METHODS: We prospectively randomized 167 coronary artery bypass patients (mean age 61+/-10 years, 115 men) to receive propranolol alone (20 mg four times daily) or propranolol and magnesium (18 g over 24 hours). Magnesium was begun intraoperatively, and propranolol was started on admission to the intensive care unit. RESULTS: Using an intention-to-treat analysis, the incidence of postoperative atrial fibrillation was 19.5% in the propranolol-treated patients and 22.4% in propranolol + magnesium-treated patients (p = 0.65). Because combination therapy resulted in an excess of postoperative hypotension, which required withholding doses of propranolol, an on-treatment analysis was also performed. In this analysis, the incidence of atrial fibrillation was still not significantly different (18.5% in propranolol-treated patients and 10.0% in propranolol + magnesium-treated patients, p = 0.20). CONCLUSIONS: Adjunctive magnesium sulfate, in combination with propranolol, does not decrease the incidence of postoperative atrial fibrillation.

Administration, Oral↗
PubMed2000

Atrial pacing for the prevention of atrial fibrillation after cardiovascular surgery.

OBJECTIVE: The purpose of this study was to determine the efficacy of atrial pacing in the prevention of atrial fibrillation following cardiovascular surgery. BACKGROUND: Although pharmacologic therapy has been used to help prevent postoperative atrial fibrillation, it suffers from limited efficacy and adverse effects. In the nonoperative setting, novel pacing strategies have been shown to reduce recurrences of atrial fibrillation and prolong arrhythmia-free periods in patients with paroxysmal atrial arrhythmias. METHODS: A total of 154 patients (115 men; mean age, 65 +/- 10 years; ejection fraction, 53 +/- 10%) undergoing cardiac surgery (coronary artery bypass surgery, 88.3%; aortic valve replacement, 4.5%; coronary bypass + aortic valve replacement, 7.1%) had right and left atrial epicardial pacing electrodes placed at the time of surgery. Patients were randomized to either no pacing, right atrial (RAP), left atrial (LAP) or biatrial pacing (BAP) for 72 h after surgery. Beta-adrenergic blocking agents were administered concurrently to all patients following surgery. RESULTS: There was a reduction in the incidence of postoperative atrial fibrillation from 37.5% in patients receiving no postoperative pacing to 17% (p < 0.005) in patients assigned to one of the three pacing strategies. The length of hospital stay was reduced by 22% from 7.8 +/- 3.7 days to 6.1 +/- 2.3 days (p = 0.003) in patients assigned to postoperative atrial pacing. The incidence of atrial fibrillation was lower in each of the paced groups (RAP, 8%; LAP, 20%; BAP, 26%) compared with patients who did not receive postoperative pacing (37.5%). CONCLUSION: Postoperative atrial pacing, in conjunction with beta-blockade, significantly reduced both the incidence of atrial fibrillation and the length of hospital stay following cardiovascular surgery. Additional studies are needed to determine the most effective anatomic pacing site.

Aged↗
PubMed2000

Cardiac complications of end-stage renal disease.

Cardiovascular disease is the leading cause of death in patients receiving dialysis. This is attributed in part to the shared risk factors of cardiovascular disease and end-stage renal disease. The risk factors for coronary artery disease include the classic cardiac risk factors of diabetes mellitus, hypertension, dyslipidemia, and smoking. Also in this population, hyperparathyroidism, hypoalbuminemia, hyperhomocysteinemia, elevated levels of apolipoprotein (a), and the type of dialysis membrane may play a role. Management begins with risk factor modification and medical therapy including aspirin, beta blockers, angiotensin converting enzyme (ACE) inhibitors, and lipid-lowering agents. Revascularization is often important, and coronary artery bypass grafting appears to be preferable to percutaneous transluminal coronary angioplasty. This is especially true for those with multivessel disease, impaired left ventricular function, severe symptoms, or ischemia. Congestive heart failure is another common problem in dialysis patients. The management includes correction of underlying abnormalities, optimal dialysis, and medical therapy. Data obtained from the general population indicate obvious benefits from ACE inhibitors and beta blockers, and these agents would be considered the therapies of choice. Erythropoetin is also an essential component of therapy, but the ideal hemoglobin concentration has yet to be determined. Peritoneal dialysis may be helpful in severe cases of heart failure. Pericarditis is seen in less than 10% of dialysis patients and is best diagnosed by clinical examination and echocardiography. Intensive dialysis is often the best initial therapy. Pericardiocentesis is reserved for the setting of pericardial tamponade, but a pericardial window is more definitive.

Heart Diseases↗
PubMed1999

Treatment of postoperative atrial fibrillation: a nonsurgical perspective.

Atrial fibrillation is a common complication of cardiovascular surgery. The 2 most important risk factors for its development are advancing age and a preoperative history of atrial fibrillation. Long-term sequelae, such as a stroke, are uncommon; however, atrial fibrillation frequently results in an increased length and cost of hospitalization. Strategies to prevent postoperative atrial fibrillation include perioperative beta-blockers, amiodarone, and atrial pacing. These strategies are most effective in high-risk patients. When atrial fibrillation does occur, treatment includes control of the ventricular rate, systemic anticoagulation, and conversion back to sinus rhythm.

Adrenergic beta-Antagonists↗
PubMed1999

An abdominal active can defibrillator may facilitate a successful generator change when a lead failure is present.

AIMS: Defibrillator generator changes are frequently performed on patients with an implantable cardioverter defibrillator in an abdominal pocket. These patients usually have epicardial patches or older endocardial lead systems. At the time of a defibrillator generator change defibrillation may be unsuccessful as a result of lead failure. We tested the hypothesis that an active can defibrillator implanted in the abdominal pocket could replace a non-functioning endocardial lead or epicardial patch. METHODS AND RESULTS: An abdominal defibrillator generator change was performed in 10 patients, (mean age = 67 +/- 13 years, nine men). Initially, a defibrillation threshold (DFT) was obtained using a passive defibrillator and the chronic endocardial or epicardial lead system. DFTs were then performed using an active can emulator and one chronic lead to simulate endocardial or epicardial lead failure. We tested 30 lead configurations (nine endocardial and 21 epicardial). Although a DFT of 7.3 +/- 4.2 joules was obtained with the intact chronic lead system, the active can emulator and one endocardial or epicardial lead still yielded an acceptable DFT of 19.9 +/- 6.1 joules. In addition, a successful implant (DFT < or = 24 joules) could have been accomplished in 28 of 30 (93%) lead configurations. CONCLUSION: An active can defibrillator in an abdominal pocket may allow for a successful generator change in patients with defibrillator lead malfunction. This would be simpler than abandoning the abdominal implant and moving to a new pectoral device and lead or tunnelling a new endocardial electrode. However, loss of defibrillation capability with a particular complex lead may be a warning of impending loss of other functions (eg. sensing and/or pacing).

Abdomen↗
PubMed1999

Contemporary management of angina: part I. Risk assessment.

Ischemic heart disease is one of the most common disorders managed by family physicians. Stratifying patients according to risk is important early in the course of the disease to identify patients who require invasive (percutaneous or surgical) treatment. Physical examination, clinical history, noninvasive tests and angiography are all helpful in determining who will benefit most from medical therapy, percutaneous revascularization or coronary artery bypass surgery. Surgery improves morbidity and mortality in a well-defined group of patients with left ventricular dysfunction and left main coronary artery disease or triple-vessel disease. Patients with proximal left anterior descending artery disease and moderate or severe ischemia benefit from surgery as well. In all other patients, definitive treatment includes aspirin, beta-adrenergic blockers and lipid-lowering agents. Percutaneous revascularization should be considered primarily a palliative measure, because it has never been shown to improve mortality more than medical therapy.

Algorithms↗
PubMed1998

Management of chronic stable angina: medical therapy, percutaneous transluminal coronary angioplasty, and coronary artery bypass graft surgery. Lessons from the randomized trials.

PURPOSE: To review the available data on the treatment of chronic stable angina and formulate a rational approach to the use of pharmacologic therapy, percutaneous transluminal coronary angioplasty (PTCA), and coronary artery bypass graft surgery (CABG). DATA SOURCES: A MEDLINE search of English-language literature published between 1976 and 1996 and the bibliographies of relevant articles. STUDY SELECTION: Primary research articles, meta-analyses, and meeting abstracts related to the management of chronic stable angina with an emphasis on comparisons of medical therapy, PTCA, and CABG. DATA EXTRACTION: Three trials comparing medical therapy with PTCA, seven trials comparing medical therapy with CABG, and nine trials comparing PTCA with CABG. DATA SYNTHESIS: Low-risk patients with single-vessel coronary artery disease and normal left ventricular function had greater alleviation of symptoms with PTCA than with medical treatment; mortality rates and rates of myocardial infarction were unchanged. In high-risk patients (risk was defined by severity of ischemia, number of diseased vessels, and presence of left ventricular dysfunction), improvement of survival was greater with CABG than with medical therapy. In moderate-risk patients with multivessel coronary artery disease (most had two-vessel disease and normal left ventricular function), PTCA and CABG produced equivalent mortality rates and rates of myocardial infarction. CONCLUSIONS: In low-risk patients, a strategy of initial medical therapy is reasonable. In moderate-risk patients, PTCA and CABG produce similar mortality rates and rates of myocardial infarction but PTCA-treated patients require more revascularization procedures. In high-risk patients, CABG is usually preferred.

Angina Pectoris↗
PubMed1998

Adjunctive therapy after reperfusion therapy in acute myocardial infarction.

The current era has witnessed dramatic improvement in the treatment of acute myocardial infarction, due in large part to the more widespread use of thrombolytic therapy aimed at quickly restoring perfusion in the infarct-related artery. This review addresses the role of adjunctive pharmacologic therapy in the thrombolytic era, recognizing that much of the available clinical trial data supporting the role of adjunctive pharmacologic treatment strategies was conducted in patient populations not widely exposed to reperfusion therapy. This review, therefore, explores the data supporting the incremental benefit of therapy with beta blockers, nitrates, angiotensin-converting enzyme inhibitors, or magnesium in addition to thrombolytic therapy. Heparin and aspirin will not be discussed.

Adrenergic beta-Antagonists↗
PubMed1998

Early discharge of patients with new-onset atrial fibrillation after cardiovascular surgery.

BACKGROUND: Atrial fibrillation is one of the most frequent complications after cardiovascular surgery. It may result in thromboembolic events, hemodynamic deterioration, and an increased length and cost of hospitalization. METHODS: We retrospectively studied 504 consecutive adult patients undergoing cardiovascular surgery to determine whether patients with new-onset postoperative atrial fibrillation could be safely discharged in atrial fibrillation after ventricular rate had been controlled and anticoagulation initiated. RESULTS: Postoperative atrial fibrillation occurred in 79 (16.2%) of the 487 survivors. Of these patients, 67 were discharged in sinus rhythm, whereas the remaining 12 were discharged in atrial fibrillation. Patients discharged in atrial fibrillation tended to be older, have higher Parsonnet risk scores, and have an increased incidence of valvular heart surgery. Despite this result, this cohort had a shorter length of hospital stay (7.3+/-2.0 days vs 10.9+/-9.3 days, p = 0.006), decreased hospital costs ($14,188+/-$2635 vs $23,016+/-$21,963, p = 0.002), and decreased hospital charges ($37,878+/-$7420 vs $58,289+/-$50,980, p = 0.003) compared with patients with atrial fibrillation discharged in sinus rhythm. In the 12 persons discharged home in atrial fibrillation, no repeat hospitalizations, bleeding complications, or thromboembolic events occurred. CONCLUSION: A strategy of early discharge of patients with persistent postoperative atrial fibrillation appears promising and deserves prospective testing on a larger scale.

Adult↗
PubMed1997

Alterations in heart rate following radiofrequency ablation in the treatment of reentrant supraventricular arrhythmias: relation to alterations in autonomic tone.

To determine the relation between the creation of endocardial lesions and alterations in autonomic tone, we analyzed heart rate variability in patients undergoing radiofrequency catheter ablation for symptomatic supraventricular tachycardia. Elevated heart rates are frequently noted after radiofrequency catheter ablation for supraventricular arrhythmias. It has been postulated that this elevation may be secondary to alterations in cardiac autonomic tone. Since heart rate variability is a measure of autonomic nervous system activity, we used this technique to examine the heart rate elevation and to characterize postablation autonomic changes. Thirty-eight patients undergoing 44 radiofrequency catheter ablation procedures were included in the study. Total arrhythmic substrates treated included 34 accessory pathways and 13 AV nodes with dual physiology. Twenty-four hour ambulatory electrocardiographic recordings were obtained in a drug-free state prior to, ablation early postablation, and late postablation. Spectral and nonspectral analyses of heart rate variability were performed. Subgroup analyses were also done on specific cohorts. Subgroups included patients undergoing accessory pathway ablations, AV node modifications, and ablation of septal and nonseptal targets. To determine whether the amount of tissue damage was related to changes in heart rate variability, we analyzed the relation between the total energy delivered to the endocardium and the peak change in creatine kinase and heart rate variability. In this population, a significant transient increase in heart rate was noted following radiofrequency ablation. All time and frequency domain parameters of heart rate variability showed significant reversible decreases. These changes were independent of target site and arrhythmia substrate. There was no correlation noted between the changes in heart rate variability and either the total amount of energy applied to the endocardium or the change in creatine kinase. Increased heart rates and decreased heart rate variability occur following radiofrequency catheter ablation for supraventricular tachycardia. Clinically, the predominant effect is that of decreased parasympathetic tone. Since these transient changes are independent of arrhythmic substrate or ablation site in the atria, a rich parasympathetic innervation of the heart is proposed.

Adolescent↗
PubMed1996

A second defibrillator chest patch electrode will increase implantation rates for nonthoracotomy defibrillators.

Nonthoracotomy defibrillator systems can be implanted with a lower morbidity and mortality, compared to epicardial systems. However, implantation may be unsuccessful in up to 15% of patients, using a monophasic waveform. It was the purpose of this study to prospectively examine the efficacy of a second chest patch electrode in a nonthoracotomy defibrillator system. Fourteen patients (mean age 62 +/- 11 years, ejection fraction = 0.29 +/- 0.12) with elevated defibrillation thresholds, defined as > or = 24 J, were studied. The initial lead system consisted of a right ventricular electrode (cathode), a left innominate vein, and subscapular chest patch electrode (anodes). If the initial defibrillation threshold was > or = 24 J, a second chest patch electrode was added. This was placed subcutaneously in the anterior chest (8 cases), or submuscularly in the subscapular space (6 cases). This resulted in a decrease in the system impedance at the defibrillation threshold, from 72.3 +/- 13.3 omega to 52.2 +/- 8.6 omega. Additionally, the defibrillation threshold decreased from > or = 24 J, with a single patch, to 16.6 +/- 2.8 J with two patches. These changes were associated with successful implantation of a nonthoracotomy defibrillator system in all cases. In conclusion, the addition of a second chest patch electrode (using a subscapular approach) will result in lower defibrillation thresholds in patients with high defibrillation thresholds, and will subsequently increase implantation rates for nonthoracotomy defibrillators.

Adult↗
PubMed1995

Relation between repolarization and refractoriness during programmed electrical stimulation in the human right ventricle. Implications for ventricular tachycardia induction.

BACKGROUND: Although programmed electrical stimulation is widely used for provoking sustained ventricular tachycardia (VT), the mechanism by which repetitive extrastimulation evokes VT is still little understood. Specifically, it is not clear why several closely coupled extrastimuli are frequently required to induce VT. Although regularly paced human ventricular myocardium exhibits a near constant relation between myocardial repolarization and refractoriness, the effect of repetitive extrastimulation on the relation between repolarization and excitability in the human heart and its relevance for arrhythmia induction by programmed stimulation are unknown. We hypothesized that the induction of VT by repetitive extrastimulation is facilitated by an altered relation between repolarization and refractoriness, and this leads to disturbances in ventricular impulse propagation, which trigger the onset of VT. METHODS AND RESULTS: Twenty-one patients undergoing routine electrophysiological study were paced from the right ventricular apex and outflow tract endocardium with monophasic action potential-pacing catheters placed at both sites simultaneously Monophasic action potential durations (APDs) and effective refractory periods (ERPs) were measured simultaneously at each site, during regular stimulation (S1-S1) at 400-ms cycle length and during three consecutive extrastimuli (S2 through S4) at the closest coupling intervals at which all three extrastimuli still resulted in capture. Measurements further included the repolarization level at which the earliest capture occurred, the ratio between ERP and APD, and the propagation time between the pacing and distant recording site. APD and ERP both shortened progressively with each extrastimulus. APD at 90% repolarization decreased from a baseline (S1) of 238.1 +/- 19.7 ms by 14.9% at S2, 18.9% at S3, and 22.9% at S4 (P < .0001, S1 versus S4). ERP decreased from 233.1 +/- 19.7 ms (S1) to 180.0 +/- 41.9 ms (S3) (P < .0001, S1 versus S3). While ERP shortening occurred mainly on the basis of APD shortening, there was an additional factor that contributed to ERP shortening independent of APD shortening. Each consecutive extrastimulus was able to elicit a propagated response at earlier repolarization levels than the previous one: the earliest capture for S2 occurred at 85.5 +/- 10.2% of complete repolarization, for S3 at 83.9 +/- 10.5%, and for S4 at 78.4 +/- 11.2% (P < .05 for S2 versus S3; P < .05 for S3 versus S4; P < .01 for S2 versus S4). This progressive "encroachment" of the earliest capture stimulus onto the preceding repolarization phase (at progressively less repolarized levels) correlated with a progressive delay of impulse propagation between the pacing site and the second recording site: propagation time increased from baseline (S1) by 10.5 +/- 1.3% with S2 to 19.0 +/- 1.6% with S3 and to 22.5 +/- 2.8% with S4 (P < .05, S4 versus S1). VT was induced in 11 of 21 patients. Nine of these had VT induced only when significant encroachment of extrastimuli on the preceding repolarization phase (< 81.3 +/- 7.0%) and associated conduction slowing (> 16.6 +/- 1.8%) were present. CONCLUSIONS: Repetitive extrastimulation not only shortens APD and subsequently ERP but also alters the ERP/APD relation by allowing capture to occur at progressively less complete repolarization levels. This progressive encroachment onto the preceding repolarization phase is associated with impaired impulse propagation and a high incidence of VT induction. This may help explain how repetitive, closely coupled extrastimulation induces ventricular tachycardia in the human heart.

Aged↗