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Biomedical subjects

L A Saxon

Publications and source records attributed to L A Saxon.

At least 37 records · Page 2Linked to original sources
PubMed1997

Electrocardiographic and electrophysiologic characterization of atypical atrial flutter in man: use of activation and entrainment mapping and implications for catheter ablation.

INTRODUCTION: Although the circuit in typical counterclockwise atrial flutter has been clearly delineated, the mechanisms of "atypical atrial flutters" have been less well characterized. The purpose of this study was to investigate the ECG and electrophysiologic (EP) characteristics of atypical atrial flutter. METHODS AND RESULTS: Thirty-three patients with at least one form of atypical atrial flutter underwent EP evaluation with multipolar atrial activation and entrainment mapping. Nineteen patients with clockwise flutter had: (1) stereotypic ECG morphology; (2) same cycle length as counterclockwise flutter; (3) clockwise activation around the tricuspid annulus; (4) recording of discrete split potentials along the length of the crista terminalis, suggesting the presence of conduction block; (5) concealed entrainment from the low right atrial isthmus; (6) successful ablation in this isthmus. Twenty patients with atypical flutter not consistent with a clockwise mechanism ("true atypical flutter") showed: (1) heterogeneous ECG morphology; (2) cycle length shorter than that of clockwise flutter; (3) frequent transitions from and to atrial fibrillation; (4) could be entrained in only six patients and, when accomplished, demonstrated surface fusion when entraining from the low right atrial isthmus. CONCLUSIONS: Atypical flutter falls into two broad categories. Clockwise flutter uses the same circuit with the same endocardial barriers as its counterclockwise counterpart and is best considered a form of typical flutter. True atypical flutter induced in the EP laboratory is a heterogeneous group of arrhythmias that are transitional to atrial fibrillation. Although it may superficially resemble clockwise or counterclockwise flutter based on the 12-lead ECG alone, the distinction can be readily made from a combined evaluation including activation and entrainment mapping.

Adult↗
PubMed1997

Preferential locations for critical reentry circuit sites causing ventricular tachycardia after inferior wall myocardial infarction.

INTRODUCTION: For relatively slow monomorphic ventricular tachycardia (VT) after myocardial infarction, entrainment can be used to identify reentry circuit "isthmus sites" (exit sites and sites proximal to the exit) where radiofrequency (RF) catheter ablation has the greatest likelihood of interrupting reentry. Similarities in coronary and ventricular anatomy may cause such sites to form in preferential locations. The objective of this study is to determine if there are preferential locations for reentry circuit isthmus regions in chronic inferior wall infarctions causing VT. METHODS AND RESULTS: Catheter mapping and RF catheter ablation was performed in 21 patients with an old inferior wall myocardial infarction and VT. The inferior wall was divided into 9 anatomic regions: 3 apical, 3 mid, and 3 basal segments. Of 46 different VTs, an endocardial isthmus site was identified in one or more zones in 28 (61%), with 10 VTs having isthmus sites in two or more adjacent regions. Isthmus zones were found in a basal region of the left ventricle in 24 (86%) of 28 VTs, in a mid segment in 9 (32%) VTs, and in an apical segment in 1 (4%) (P = 0.002). Of 30 RF current applications that terminated VT, 21 (70%) were at basal isthmus sites. CONCLUSION: The high prevalence of endocardial isthmus zones near the base of the left ventricle suggests that the mitral annulus often plays a role in defining the margins of reentry circuits that cause relatively slow VTs after inferior wall myocardial infarction.

Aged↗
PubMed1996

Improving survival for patients with atrial fibrillation and advanced heart failure.

OBJECTIVES: We attempted to determine whether changes in heart failure therapy since 1989 have altered the prognostic significance of atrial fibrillation. BACKGROUND: Atrial fibrillation occurs in 15% to 30% of patients with heart failure. Despite the recognized potential for adverse effects, the impact of atrial fibrillation on prognosis is controversial. METHODS: Two-year survival for 750 consecutive patients discharged from a single hospital after evaluation for heart transplantation from 1985 to 1989 (Group I, n = 359) and from 1990 to April 1993 (Group II, n = 391) was analyzed in relation to atrial fibrillation. In Group I, class I antiarrhythmic drugs and hydralazine vasodilator therapy were routinely allowed. In Group II, amiodarone and angiotensin-converting enzyme inhibitors were first-line antiarrhythmic and vasodilating drugs. RESULTS: A history of atrial fibrillation was present in 20% of patients in Group I and 24% of those in Group II. Patients with atrial fibrillation in the two groups had similar clinical and hemodynamic profiles. Among patients with atrial fibrillation, those in Group II had a markedly better 2-year survival (0.66 vs. 0.39, p = 0.001) and sudden death-free survival (0.84 vs. 0.70, p = 0.01) than those in Group I. In each time period, survival was worse for patients with than without atrial fibrillation in Group I (0.39 vs. 0.55, p = 0.002) but not in Group II (0.66 vs. 0.75, p = 0.09). CONCLUSIONS: The prognosis of patients with advanced heart failure and atrial fibrillation is improving. These findings support the practice of avoiding class I antiarrhythmic drugs in this group and may reflect recent beneficial changes in heart failure therapy.

Adult↗
PubMed1996

Activation and entrainment mapping defines the tricuspid annulus as the anterior barrier in typical atrial flutter.

BACKGROUND: The importance of anatomic barriers in the atrial flutter reentry circuit has been well demonstrated in canine models. It has been shown previously that the crista terminalis and its continuation as the eustachian ridge form a posterior barrier. In this study we tested the hypothesis that the tricuspid annulus forms the continuous anterior barrier to the flutter circuit. METHODS AND RESULTS: Thirteen patients with typical atrial flutter were studied. A 20-pole halo catheter was situated around the tricuspid annulus. A mapping catheter was used for activation and entrainment mapping from seven sequential sites around the tricuspid annulus and from three additional sites including the tip of the right atrial appendage, at the fossa ovalis, and in the distal coronary sinus. Sites were considered to be within the circuit when the postpacing interval minus the flutter cycle length and the stimulus time minus the activation time were < or = 10 ms; sites were considered to be outside the circuit when these intervals were > 10 ms. All seven annular sites were within the circuit; activation occurred sequentially around the annulus and accounted for 100% of the flutter cycle length. The fossa ovalis, the distal coronary sinus, and the right atrial appendage were outside the circuit. CONCLUSIONS: Closely spaced sites around the tricuspid annulus are activated sequentially, and are all within the flutter circuit according to entrainment criteria. This demonstrates that the tricuspid annulus constitutes a continuous anterior barrier constraining the reentrant wave front of human counterclockwise atrial flutter.

Aged↗
PubMed1996

Results of radiofrequency catheter ablation for atrial flutter.

RF catheter ablation for symptomatic typical atrial flutter is associated with a high procedural success rate, but a second RF procedure may be required in up to one third of subjects, particularly those with right atrial enlargement. In those subjects with both established AF and flutter, RF ablation for atrial flutter may decrease the recurrence rate of AF. However, patients remain at risk for the development of newly documented AF, most likely secondary to the high incidence of underlying structural heart disease.

Aged↗
PubMed1996

Ablation of 'incisional' reentrant atrial tachycardia complicating surgery for congenital heart disease. Use of entrainment to define a critical isthmus of conduction.

BACKGROUND: Intra-atrial reentrant tachycardia occurs frequently after surgery for congenital heart disease and is difficult to treat. We tested the hypotheses that intra-atrial reentrant tachycardia in patients who had undergone prior reparative surgery for congenital heart disease could be successfully ablated by targeting a protected isthmus of conduction bounded by natural and surgically created barriers and that entrainment techniques could be used to identify these zones. METHODS AND RESULTS: Eighteen consecutive patients with 26 intra-atrial reentrant tachycardias complicating surgery for congenital heart disease (9 atrial septal defect repair, 4 Fontan, 2 Mustard, 2 Senning, and 1 Rastelli procedure) underwent electrophysiological study and ablation attempts. Mapping of activation was facilitated by the deployment of catheters with multiple electrodes. Sites for ablation were sought that demonstrated entrainment with concealed fusion and at which the postpacing interval minus the tachycardia cycle length and the stimulus to P wave minus the activation time were < 30 ms. These sites were considered to be within a narrow isthmus critical to the tachycardia mechanism. Anatomic barriers bordering the critical isthmus of conduction were identified on anatomic grounds, by the presence of areas of electrical silence or by the demonstration of split potentials signifying a line of block. Success was achieved in 15 patients with 21 arrhythmias. The median number of radiofrequency applications was 5. There was a wide range of activation times at successful sites (-30 to -250 ms). At a mean duration of follow-up of 17 +/- 8 months, 11 patients were asymptomatic and 9 did not require antiarrhythmia therapy. CONCLUSIONS: Successful ablation of intra-atrial reentrant tachycardia complicating surgery for congenital heart disease may be achieved by creation of an ablative lesion in a critical isthmus of conduction bounded by anatomic barriers. This isthmus may be identified by the presence of entrainment with concealed fusion and an analysis of the relationship between the postpacing interval and the tachycardia cycle length and between the activation time and the stimulus time. Because this isthmus is invariably confined on at least one aspect by a surgical repair site that is of central importance to the tachycardia mechanism, we suggest that this type of arrhythmia be given the descriptive designation of "incisional reentry."

Adolescent↗
PubMed1995

Improving survival for patients with advanced heart failure: a study of 737 consecutive patients.

OBJECTIVES: This study sought to determine whether survival and risk of sudden death have improved for patients with advanced heart failure referred for consideration for heart transplantation as advances in medical therapy were systematically implemented over an 8-year period. BACKGROUND: Recent survival trials in patients with mild to moderate heart failure and patients after a myocardial infarction have shown that angiotensin-converting enzyme inhibitors are beneficial, type I antiarrhythmic drugs can be detrimental, and amiodarone may be beneficial in some groups. The impact of advances in therapy may be enhanced or blunted when applied to severe heart failure. METHODS: One-year mortality and sudden death were determined in relation to time, baseline variables and therapeutics for 737 consecutive patients referred for heart transplantation and discharged home on medical therapy from 1986 to 1988, 1989 to 1990 and 1991 to 1993. Medical care was directed by a single team of physicians with policies established by consensus. From 1986 to 1990, the hydralazine/isosorbide dinitrate combination or angiotensin-converting enzyme inhibitors were the initial vasodilators, and class I antiarrhythmic drugs were allowed. After 1990, captopril was the initial vasodilator, given to 86% of patients compared with 46% of patients before 1989. After mid-1989, class I agents were routinely withdrawn, and amiodarone was used for frequent ventricular ectopic beats or atrial fibrillation (53% of patients after 1990 vs. 10% before 1989). RESULTS: The total 1-year mortality rate decreased from 33% before 1989 to 16% after 1990 (p = 0.0001), and sudden death decreased from 20% to 8% (p = 0.0006). Adjusted for clinical and hemodynamic variables in multivariate proportional hazards models, total mortality and sudden death were lower after 1990. CONCLUSIONS: The large reduction in mortality, particularly in sudden death, from advanced heart failure since 1990 may reflect an enhanced impact of therapeutic advances shown in large randomized trials when they are incorporated into a comprehensive approach in this population. This improved survival supports the growing practice of maintaining potential heart transplant candidates on optimal medical therapy until clinical decompensation mandates transplantation.

Adult↗
PubMed1995

Amiodarone and torsades de pointes in patients with advanced heart failure.

Amiodarone is considered to be safe in patients with prior QT prolongation and torsades de pointes taking class I antiarrhythmic agents who require continued antiarrhythmic drug therapy. However, the safety of amiodarone in advanced heart failure patients with a history of drug-induced torsades de pointes, who may be more susceptible to proarrhythmia, is unknown. Therefore, the objective of this study was to assess amiodarone safety and efficacy in heart failure patients with prior antiarrhythmic drug-induced torsades de pointes. We determined the history of torsades de pointes in 205 patients with heart failure treated with amiodarone, and compared the risk of sudden death in patients with and without such a history. To evaluate the possibility that all patients with a history of torsades de pointes would be at high risk for sudden death regardless of amiodarone treatment, we compared this risk in patients with a history of torsades de pointes who were and were not subsequently treated with amiodarone. Of 205 patients with advanced heart failure, 8 (4%) treated with amiodarone had prior drug-induced torsades de pointes. Despite similar severity of heart failure, the 1-year actuarial sudden death risk was markedly increased in amiodarone patients with than without prior torsades de pointes (55% vs 15%, p = 0.0001). Similarly, the incidence of 1-year sudden death was markedly increased in patients with prior torsades de pointes taking amiodarone compared with such patients who were not subsequently treated with amiodarone (55% vs 0%, p = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Risk of arterial embolization in 224 patients awaiting cardiac transplantation.

Of patients awaiting cardiac transplantation, 10% to 20% die before a donor heart becomes available. Embolization of left ventricular thrombus is a source of morbidity and mortality in this population. To define the incidence and possible risk factors for systemic arterial embolization, we examined the frequency of arterial embolic events and their relation to clinical, hemodynamic, and echocardiographic variables in 224 consecutive outpatients awaiting cardiac transplantation (left ventricular ejection fraction 0.20 +/- 0.07 and left ventricular end-diastolic dimension 76 +/- 11 mm). Over a follow-up period of 301 +/- 371 days, during which 82 (37%) patients received warfarin, arterial embolization occurred in 6 (3%) patients, 1 of whom was receiving and 5 of whom were not receiving warfarin (difference not specifically significant). The risk of embolization was not statistically different in patients with atrial fibrillation, previous embolization, or left ventricular thrombus on transthoracic echocardiogram, regardless of warfarin therapy. Cumulative risk of sudden death was similar for patients with or without echocardiographically documented left ventricular thrombus. Nonfatal bleeding complications associated with warfarin therapy occurred in 2 (2%) patients. Thus in patients who are awaiting cardiac transplantation and who receive anticoagulation therapy for left ventricular thrombus, atrial fibrillation, or previous arterial embolization, the incidence of clinically detectable arterial embolization is low despite severe ventricular dilatation. Embolization is not likely a major cause of sudden death or morbidity in this population.

Cardiomyopathy, Dilated↗
PubMed1995

Implantable defibrillators for high-risk patients with heart failure who are awaiting cardiac transplantation.

The objective of this study was to assess the operative risk and efficacy of implantable defibrillators for preventing sudden death in patients with heart failure awaiting transplantation. The average waiting time for elective cardiac transplantation is 6 months to 1 year. Sudden cardiac death is the major source of mortality in outpatients in stable condition awaiting cardiac transplantation. The efficacy of implantable defibrillator therapy in this population is not established. We analyzed the operative risk, time to appropriate shock, and sudden death in 15 patients determined to be at high risk of sudden death who were accepted onto the outpatient cardiac transplant waiting list. Nonfatal postoperative complications occurred in two (13%) subjects with epicardial defibrillating lead systems and in none with transvenous lead systems. Defibrillation energies were 16 +/- 2 J versus 24 +/- 2 J with epicardial and transvenous lead systems, respectively. Sudden death free survival until transplantation was 93%. Most of the patients (60%) had an appropriate shock during a mean follow-up of 11 +/- 12 months. The mean time to an appropriate shock was 3 +/- 3 months. Hospital readmission was required in three (20%) subjects to await transplantation on an urgent basis. However, two of these subjects had received appropriate shocks before readmission. In selected patients at high risk for sudden death while on the outpatient cardiac transplant waiting list, the operative risk is low and adequate defibrillation energies can be obtained to allow implantable defibrillator placement. Most subjects will have an appropriate shock as outpatients before transplantation, and sudden death free survival is excellent.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1995

Relation of pace mapping QRS configuration and conduction delay to ventricular tachycardia reentry circuits in human infarct scars.

OBJECTIVES: This study sought to determine the relation of the paced QRS configuration and conduction delay during pace mapping to reentry circuit sites in patients with ventricular tachycardia late after myocardial infarction. BACKGROUND: The QRS configuration produced by ventricular pacing during sinus rhythm (pace mapping) can locate focal idiopathic ventricular tachycardias during catheter mapping, but postinfarction reentry circuits may be relatively large and contain regions of slow conduction. We hypothesized that for postinfarction ventricular tachycardia, 1) pacing during sinus rhythm at reentry circuit sites distant from the exit from the scar would produce a QRS configuration different from the tachycardia; and 2) a stimulus to QRS delay during pace mapping may be a useful guide to reentry circuit slow conduction zones. METHODS: Catheter mapping and ablation were performed in 18 consecutive patients with ventricular tachycardia after myocardial infarction. At 85 endocardial sites in 13 patients, 12-lead electrocardiograms (ECGs) were recorded during pace mapping, and participation of each site in a reentry circuit was then evaluated by entrainment techniques during induced ventricular tachycardia or by application of radiofrequency current. RESULTS: Pace maps resembled tachycardia at < 30% of likely reentry circuit sites identified by entrainment criteria and at only 1 (9%) of 11 sites where radiofrequency current terminated tachycardia. Analysis of the stimulus to QRS interval during entrainment with concealed fusion showed that the conduction time from the pacing site to the exit from the scar was longer at sites where the pace map did not resemble tachycardia. Evidence of slow conduction during pace mapping, with a stimulus to QRS interval > 40 ms was observed at > or = 70% of reentry circuit sites. CONCLUSIONS: At many sites in postinfarction ventricular reentry circuits, the QRS configuration during pace mapping does not resemble the ventricular tachycardia QRS complex, consistent with relatively large reentry circuits or regions of functional conduction block during ventricular tachycardia. A stimulus to QRS delay during pace mapping is consistent with slow conduction and may aid in targeting endocardial sites for further evaluation during tachycardia.

Aged↗
PubMed1993

Transesophageal echocardiography during radiofrequency catheter ablation of ventricular tachycardia.

Radiofrequency lesion formation requires stable catheter tip/endocardial contact. Energy delivery is limited when temperatures are > 100 degrees C due to coagulum formation at the catheter tip. Transesophageal echocardiographic imaging may be useful for monitoring catheter position and detecting boiling. Transesophageal echocardiographic images were recorded during production of 22 radiofrequency lesions in bovine myocardium in a saline bath. Lesion size, tissue temperature and appearance of echo contrast (bubbles) were assessed. In 11 patients, transesophageal echocardiography was used to guide catheter movement and detect boiling during radiofrequency ablation for ventricular tachycardia. In the tissue bath, the appearance of echo bubbles was associated with visual bubbling at the catheter tip, tissue temperatures > 60 degrees C and larger lesions (284 +/- 165 vs 30 +/- 54 mm3; p < 0.001). In humans, transesophageal images easily identified the catheter tip in either ventricle and enabled continuous observation of electrode-tissue contact during radiofrequency application. Transesophageal echocardiographic bubbles appeared in 59 of 217 radiofrequency applications (27%). Continued radiofrequency application after appearance of bubbles was followed by an increase in impedance. Prolonged placement of the probe in heavily sedated patients resulted in a mild sore throat, but no other complications. Transesophageal echocardiographic imaging enables continuous monitoring of catheter position during radiofrequency energy application. The abrupt appearance of echo bubbles indicates boiling and impending coagulum formation at the catheter tip.

Adult↗
PubMed1993

Predicting death from progressive heart failure secondary to ischemic or idiopathic dilated cardiomyopathy.

Data were retrospectively reviewed on 528 consecutive patients hospitalized for treatment of advanced heart failure (left ventricular ejection fraction 0.2 +/- 0.07) and cardiac transplant evaluation, who were stabilized with medical therapy and discharged home. Predictors of heart failure death or rehospitalization for urgent transplantation were identified using the Cox proportional-hazards model. Within 1 year, 59 patients (11%) died suddenly and 70 (13%) died of heart failure or required urgent transplantation. A serum sodium < or = 134 mEq/liter, pulmonary arterial diastolic pressure > 19 mm Hg, left ventricular diastolic dimension index > 44 mm/m2, peak oxygen consumption during exercise testing < 11 ml/kg/min and the presence of a permanent pacemaker were independent predictors of hemodynamic deterioration. In the absence of these risk factors the risk of hemodynamic deterioration within 1 year from this study was only 2%. This risk increased to > 50% in the presence of hyponatremia and any 2 additional risk factors. Thus, patients with advanced heart failure at highest risk for progressive hemodynamic deterioration can be identified from clinical variables that could aid in triaging such patients to earlier cardiac transplantation.

Actuarial Analysis↗