Biomedical subjects

Philip B Adamson

Publications and source records attributed to Philip B Adamson.

17 recordsLinked to original sources

PubMed2006

Induced hypothermia following out-of-hospital cardiac arrest; initial experience in a community hospital.

BACKGROUND: Successful resuscitation from sudden cardiac death is frequently accompanied by severe and often fatal neurologic injury. Induced hypothermia (IH) may attenuate the neurologic damage observed in patients after cardiac arrest. HYPOTHESIS: This study examined a population of nonselected patients presenting to a community hospital following successful resuscitation of sudden cardiac death. We sought to determine whether a program of induced hypothermia would improve the clinical outcome of these critically ill patients. METHODS: We initiated a protocol of IH at the Oklahoma Heart Hospital in August of 2003. Study patients were consecutive adults admitted following successful resuscitation of out-of-hospital cardiac arrest. Moderate hypothermia was induced by surface cooling and maintained for 24 to 36 h in the Intensive Care Unit with passive rewarming over 8 h. RESULTS: Forty-nine patients who were resuscitated and had the return of spontaneous circulation completed the hypothermia protocol. The cause of cardiac arrest was acute myocardial infarction in 24 patients and cardiac arrhythmias in 19 patients. Nineteen patients (39%) survived and were discharged. Sixteen of the patients discharged had no or minimal residual neurologic dysfunction and 3 patients had clinically significant residual neurologic injury. CONCLUSION: A program of induced hypothermia based in a community hospital is feasible, practical, and requires limited additional financial and nursing resources. Survival and neurologic recovery compare favorably with clinical trial outcomes.

Adult↗

PubMed2006

Reducing the risk of sudden death in heart failure with beta-blockers.

BACKGROUND: Heart failure (HF) is a serious cardiovascular syndrome that affects nearly 5 million people in the United States. A review of clinical data demonstrates that sudden cardiac death (SCD) accounts for approximately one-third of all HF deaths. This fatal outcome typically involves an unexpected electrical event leading to sustained cardiac arrhythmias resulting in cardiovascular collapse. METHODS AND RESULTS: A systematic review of the literature was performed to serve as the basis for this review. Factors contributing directly to incidence of SCD in the HF population may include significant remodeling of the left ventricle (hypertrophy, dilation, and fibrosis) in addition to increased sympathetic activation. Using specific therapies to limit these mechanisms are beneficial in the HF patient by preventing SCD. Beta-blockers play a key role in the prevention of SCD for patients with HF by limiting the effects of circulating norepinephrine and by reducing left ventricular remodeling. CONCLUSIONS: This review outlines the potential mechanisms and contributing factors of SCD in patients with HF and the impact of beta-blocker usage in the prevention of this fatal outcome for this growing patient population.

Adrenergic beta-Antagonists↗

PubMed2006

Integrating device monitoring into the infrastructure and workflow of routine practice.

Monitoring strategies for patients with heart failure vary. Physical assessment and patient reporting are often unreliable and inconsistent. Continuous physiologic information from implanted devices identifies the progression to congestion in patients with chronic heart failure earlier in the process than traditional methods. Common themes of a successful system will require a means to provide device-based data to interested providers who then can interpret the information in the context of either remote or face-to-face clinical assessment.

Decision Support Systems, Clinical↗

PubMed2005

The perplexing complexity of cardiac arrhythmias: beyond electrical remodeling.

Cardiac arrhythmias continue to pose a major medical challenge and significant public health burden. Atrial fibrillation, the most prevalent arrhythmia, affects more than two million Americans annually and is associated with a twofold increase in mortality. In addition, more than 250,000 Americans each year suffer ventricular arrhythmias, often resulting in sudden cardiac death. Despite the high incidence and societal impact of cardiac arrhythmias, presently there are insufficient insights into the molecular mechanisms involved in arrhythmia generation, propagation, and/or maintenance or into the molecular determinants of disease risk, prognosis, and progression. In addition, present therapeutic strategies for arrhythmia abatement often are ineffective or require palliative device therapy after persistent changes in the electrical and conduction characteristics of the heart have occurred, changes that appear to increase the risk for arrhythmia progression. This article reviews our present understanding of the complexity of mechanisms that regulate cardiac membrane excitability and cardiac function and explores the role of derangements in these mechanisms that interact to induce arrhythmogenic substrates. Approaches are recommended for future investigations focused on providing new mechanistic insights and therapeutic interventions.

Arrhythmias, Cardiac↗

PubMed2004

Ephedrine increases ventricular arrhythmias in conscious dogs after myocardial infarction.

OBJECTIVES: This study examined the hypothesis that the sympathomimetic activity of ephedrine increases the risk of lethal arrhythmias. BACKGROUND: The sympathomimetic amine, ephedrine, is used to augment physical performance and as a weight loss aid, but little is known about the cardiovascular consequences in individuals with ischemic heart disease. METHODS: Fifteen dogs at low risk for ventricular fibrillation (VF) during exercise and transient myocardial ischemia 30 days after a small anterior myocardial infarction were retested after five days of ephedrine use (Xenadrine, 0.4 mg/kg/day orally). To assess the effects of ephedrine on cardiac autonomic control, baroreceptor reflex sensitivity (BRS), heart rate (HR) variability, HR response to acute myocardial ischemia, and resting catecholamines were measured before and after ephedrine. Dogs were used as their own control when possible. RESULTS: Nine of 15 animals had increased ventricular arrhythmias during ephedrine treatment (p = 0.01) and four had VF. Three dogs that had VF could not be resuscitated. Five animals with increased arrhythmias during ephedrine treatment had none during a third exercise and ischemia test after drug washout. Heart rates were higher after 30 s of myocardial ischemia during ephedrine treatment (204 +/- 25 beats/min no drug vs. 218 +/- 26 beats/min with ephedrine, p = 0.03). All plasma catecholamines increased after ephedrine administration. No changes in BRS, HR variability, or exercise HR were noted. CONCLUSIONS: Ephedrine increases ischemia-dependent arrhythmias at doses recommended in over-the-counter preparations. Increased arrhythmia risk was associated with augmented ischemia-dependent sympathetic reflex activation.

Animals↗

PubMed2004

The evolving challenge of chronic heart failure management: a call for a new curriculum for training heart failure specialists.

Chronic heart failure (HF) is a growing epidemic, and therapy options are becoming more complex. Specifically, device management of HF represents a new "class" of therapy that can reduce mortality and alleviate morbidity of the disease syndrome. Heart failure training programs seldom provide structured opportunities for trainees to gain competence in device implantation and management. This curriculum outlines a new approach to training interventional HF cardiologists and internal medicine HF specialists to meet the growing demands for specially trained health care providers.

Cardiology↗

PubMed2004

Continuous autonomic assessment in patients with symptomatic heart failure: prognostic value of heart rate variability measured by an implanted cardiac resynchronization device.

BACKGROUND: Heart rate variability (HRV) as an indirect autonomic assessment provides prognostic information when measured over short time periods in patients with heart failure. Long-term continuous HRV can be measured from an implantable device, but the clinical value of these measurements is unknown. METHODS AND RESULTS: A total of 397 patients with New York Heart Association class III or IV heart failure were studied. Of these, 370 patients had information from their implanted cardiac resynchronization device for mortality risk stratification, and 288 patients had information for measured parameters (ie, HRV, night heart rate, and patient activity) and clinical event analyses. Continuous HRV was measured as the standard deviation of 5-minute median atrial-atrial intervals (SDAAM) sensed by the device. SDAAM <50 ms when averaged over 4 weeks was associated with increased mortality risk (hazard ratio 3.20, P=0.02) and SDAAM were persistently lower over the entire follow-up period in patients who required hospitalization or died. SDAAM decreased a median of 16 days before hospitalization and returned to baseline after treatment. Automated detection of decreases in SDAAM was 70% sensitive in detecting cardiovascular hospitalization, with 2.4 false-positives per patient-year of follow-up. CONCLUSIONS: This study demonstrates that SDAAM continuously measured from an implanted cardiac resynchronization device is lower in patients at high mortality and hospitalization risk. SDAAM declines as patient status decompensates. Continuous long-term SDAAM may be a useful tool in the clinical management of patients with chronic heart failure.

Aged↗

PubMed2003

Cardiac resynchronization therapy improves heart rate variability in patients with symptomatic heart failure.

BACKGROUND: Cardiac resynchronization therapy (CRT) using biventricular pacing improves symptoms and functional capacity in patients with moderate to severe heart failure. The present study examined whether an improvement in ventricular performance from resynchronization therapy changes the autonomic control of heart rate. METHODS AND RESULTS: Heart rate variability (HRV) was examined in 50 patients implanted with the InSync biventricular pacing system who were randomized to therapy-on (n=25) or therapy-off (n=25). HRV was computed as the standard deviation of the atrial cycle length sensed from the system over 2 months of continuous monitoring. HRV was compared between CRT-on and CRT-off groups. HRV was higher in patients randomized to CRT-on compared with CRT-off (148+/-47 ms for CRT-on versus 118+/-45 ms for CRT-off; P=0.02), despite the lack of difference in mean atrial cycle length (844+/-129 ms for CRT-on versus 851+/-110 ms for CRT-off; P=0.82). Changes in plasma catecholamines were not different between the CRT-on and CRT-off groups from baseline to the 3-month follow-up. CONCLUSIONS: Improvement in ventricular performance from CRT shifts cardiac autonomic balance toward a more favorable profile that is less dependent on sympathetic activation.

Adrenergic beta-Antagonists↗

PubMed2003

Ongoing right ventricular hemodynamics in heart failure: clinical value of measurements derived from an implantable monitoring system.

OBJECTIVES: This study examined the characteristics of continuously measured right ventricular (RV) hemodynamic information derived from an implantable hemodynamic monitor (IHM) in heart failure patients. BACKGROUND: Hemodynamic monitoring might improve the day-to-day management of patients with chronic heart failure (CHF). Little is known about the characteristics of long-term hemodynamic information in patients with CHF or how such information relates to meaningful clinical events. METHODS: Thirty-two patients with CHF received a permanent RV IHM system similar to a single-lead pacemaker. Right ventricular systolic and diastolic pressures, heart rate, and pressure derivatives were continuously measured for nine months without using the data for clinical decision-making or management of patients. Data were then made available to clinical providers, and the patients were followed up for 17 months. Pressure characteristics during optimal volume, clinically determined volume-overload exacerbations, and volume depletion events were examined. The effect of IHM on hospitalizations was examined using the patients' historical controls. RESULTS: Long-term RV pressure measurements had either marked variability or minimal time-related changes. During 36 volume-overload events, RV systolic pressures increased by 25 +/- 4% (p < 0.05) and heart rate increased by 11 +/- 2% (p < 0.05). Pressure increases occurred in 9 of 12 events 4 +/- 2 days before the exacerbations requiring hospitalization. Hospitalizations before using IHM data for clinical management averaged 1.08 per patient year and decreased to 0.47 per patient-year (57% reduction, p < 0.01) after hemodynamic data were used. CONCLUSIONS: Long-term ambulatory pressure measurements from an IHM may be helpful in guiding day-to-day clinical management, with a potentially favorable impact on CHF hospitalizations.

Adult↗

PubMed2003

Heterogeneous regional endocardial repolarization is associated with increased risk for ischemia-dependent ventricular fibrillation after myocardial infarction.

UNLABELLED: Repolarization Heterogeneity and Sudden Death Risk. INTRODUCTION: The aim of this study was to investigate whether the characteristics of endocardial ventricular repolarization are associated with differential risk for sudden death. Prolonged surface QT interval is associated with increased arrhythmic risk after myocardial infarction (MI), but the underlying mechanism of QT prolongation and its relation to lethal arrhythmias are unclear. METHODS AND RESULTS: Ventricular fibrillation (VF) risk was assessed in 12 dogs 1 month after anterior MI during an exercise test coupled with brief circumflex coronary occlusion. Susceptible dogs (n = 5) developed VF during the brief ischemic episode, whereas resistant dogs did not (n = 7). Surface QT interval was measured at rest. Endocardial electroanatomic catheter maps of left ventricular repolarization were obtained in four unique regions identified by echocardiography and compared between groups. Compared to resistant dogs, susceptible dogs were characterized by prolonged surface QT intervals (240 +/- 10 msec vs 222 +/- 7 msec, P = 0.04). In addition, they had lower baroreflex sensitivity (9.7 +/- 1.5 msec/mmHg vs 28 +/- 9.8 msec/mmHg, P < 0.01) and a tachycardic response to acute ischemia suggesting higher propensity for stronger sympathetic reflexes. Surface QT interval prolongation in susceptible dogs was due to a marked heterogeneity of endocardial left ventricular repolarization (239 +/- 42 msec, basal anterior wall vs 197 +/- 35, lateral wall; P < 0.001). Resistant animals had no regional differences in endocardial repolarization. CONCLUSION: Sympathetic activation following MI not only produces adverse structural remodeling but also contributes to adverse electrophysiologic remodeling resulting in heterogeneous ventricular repolarization and in a myocardial substrate conducive to lethal reentrant arrhythmias.

Animals↗

PubMed2003

Combined sodium and calcium channel blockade in prevention of lethal arrhythmias.

Anti-arrhythmic compounds with multiple actions reduce arrhythmic death risk in post-myocardial infarction (MI) patients. Sudden death prevention, however, may rely more on implantable defibrillators than anti-arrhythmic drugs due to ineffective pharmacologic intervention. Widespread use of implantable defibrillators should not obscure the need for development of new anti-arrhythmic drugs. This study tested the hypothesis that combined blockade of I(Na) and I(Ca(L)) prevents ischemia-dependent ventricular fibrillation (VF) in conscious dogs after MI. I(Na) and I(Ca(L)) blockade was accomplished with levosemotiadil in 11 dogs known to be at high risk for VF during 2 min of coronary occlusion during submaximal treadmill exercise 30 days after MI. Negative chronotropic effect of levosemotiadil was examined using the heart rate response to isoproterenol and comparing it with response to propranolol. Levosemotiadil prevented VF in 64% (7 of 11) of the high-risk animals. Heart rate responses to myocardial ischemia and to graded doses of isoproterenol were blunted by the high dose of levosemotiadil. Propranolol prevented VF in 73% (8 of 11) of the dogs. Levosemotiadil had approximately one half the beta-blocking activity of propranolol. The combination of I(Na) and I(Ca(L)) channel blockade coupled with partial beta-adrenergic blockade was equally effective in preventing VF as propranolol.

Adrenergic beta-Antagonists↗

PubMed2003

Autonomic modulation during acute myocardial ischemia by low-dose pirenzepine in conscious dogs with a healed myocardial infarction: a comparison with beta-adrenergic blockade.

Experimental and clinical evidence documents the beneficial effects of blocking sympathetic activity and modulating heart rate to reduce risk for lethal events in ischemic heart disease. Beside beta-adrenergic receptor blockade, vagal activation is a meaningful approach but not yet easily attainable. Promising results were shown with low-dose atropine and scopolamine, but no follow-up was done because of significant adverse side effects. Pirenzepine is an atropine analogue approved to treat peptic ulcer disease in Europe that is devoid of central actions, which are mostly responsible for anti-muscarinic agents side effects. The vagomimetic action of IV low-dose pirenzepine was studied at rest under control conditions, at rest during acute coronary artery occlusion, and during exercise in conscious dogs with a healed anterior myocardial infarction (MI). The effects of pirenzepine were then compared, by internal control analysis, with those of atenolol (1 mg/kg). Increasing doses of pirenzepine (from 0.01 to 1 mg/kg) were tested in 11 dogs at rest by measuring time and frequency domain heart rate variability (HRV). The most effective dose (0.1 mg/kg) was used in the study. At the most effective dose, pirenzepine increased all measures of time domain HRV by 40-50%. However, the vagomimetic action of pirenzepine was lost during exercise and brief ischemia and no anti-arrhythmic action was observed. Conversely, pirenzepine effectively modulated the heart rate increase during acute ischemia at rest with an effect comparable to that of atenolol. The vagomimetic action of pirenzepine in the acutely ischemic heart supports the possibility that this intervention may be helpful for chronic autonomic modulation in post-MI patients.

Acute Disease↗

PubMed2003

Hemodynamic effects of a new inotropic compound, PST-2744, in dogs with chronic ischemic heart failure.

Inotropic agents for acute decompensated heart failure are associated with a lack of efficacy or increased mortality. New compounds are needed to support patients with acute exacerbations of heart failure. This study examined the hemodynamic effects of a new inotropic agent (PST-2744) in dogs with chronic ischemic heart failure. Eight mongrel dogs at low risk for postmyocardial infarction (MI) sudden death entered the protocol. Dogs were studied after ischemic left ventricular dysfunction was induced by repeated injections of latex microspheres into the circumflex artery until the ejection fraction reached 35%. Hemodynamic parameters were measured at baseline and peak drug effect (PST-2744 5 microg.kg-1.min-1). In 5 animals, PST-2744 effects were compared with dobutamine. Heart rates, PR intervals and QT intervals were unchanged following PST-2744 administration. PST-2744 increased contractility (+dP/dt) by 56% from 1881 +/- 282 mm Hg/s to 2939 +/- 734 mm Hg/s (P < 0.01). The inotropic effect of PST-2744 was equal to that produced by 5-microg.kg-1.min-1 dobutamine (56% increase in +dP/dt), but peak heart rates were significantly higher with dobutamine (129 +/- 24 bpm PST-2744 versus 160 +/- 6 bpm 5-microg.kg-1.min-1 dobutamine, P < 0.002). No arrhythmias or conduction delays were seen with either compound. PST-2744 is an effective inotropic agent without positive chronotropic effect in subjects with stable moderate left ventricular dysfunction.

Animals↗

PubMedDate not supplied

Cardiac resynchronization therapy--how big of a miracle?

This review examines the clinical benefit of cardiac resynchronization therapy (CRT) in patients with severe heart failure symptoms and interventricular conduction delay. The magnitude of CRT effects on exercise duration, quality of life, and reversal of adverse remodeling are compared to angiotensin-converting enzyme (ACE) inhibitor therapy and combined beta-blocker/ACE inhibitor therapy. Overall, CRT delivers substantial improvement in clinical well-being to an extent similar to or greater than what would be expected with neurohormonal intervention alone.

Adrenergic beta-Antagonists↗

PubMedDate not supplied

Ambulatory hemodynamics in patients with chronic heart failure: implications for volume management in elderly patients.

Invasive hemodynamic assessment of patients with chronic heart failure is helpful in managing severe congestive symptoms associated with acute volume exacerbations that lead to hospitalizations. Information useful in guiding medication changes targeting control of left ventricular filling pressures can be obtained from measurements in the right ventricle. With the advent of implantable devices designed to treat heart failure, the logical next development is an implanted device that incorporates sophisticated monitoring systems capable of continuous acquisition of hemodynamic information over a long-term period. An implantable hemodynamic monitoring system (Chronicle; Medtronic, Inc., Minneapolis, MN) is safe to implant and has a pressure sensor with proven long-term reliability. Using transtelephonic data transmission and Internet-based information systems, ambulatory hemodynamic monitoring may reduce the need for hospitalizations and overall health care utilization in patients with symptomatic heart failure. This approach may be especially helpful for elderly patients with chronic heart failure in whom overdiuresis or volume contraction may lead to gait instability and falls. Additionally, elderly patients with heart failure from primary diastolic dysfunction may have a very narrow therapeutic window of optimal volume that is difficult to assess by daily weights and physical examination alone. This hypothesis is currently being tested in a prospective randomized clinical trial.

Aged↗

PubMedDate not supplied

Continuous heart rate variability from an implanted device: a practical guide for clinical use.

Continuous measurement of spontaneous heart rate variability is now possible from permanently implanted devices and may contain information useful in the chronic management of patients with congestive heart failure. Since heart rate variability semi-quantifies autonomic control of the heart, changes noted from continuous measurement provide insight into cardiac control system status, which may reflect clinical status of the patient. This review outlines clinical evidence supporting the use of heart rate variability derived from implanted electronic devices and suggests a practical application in an every day clinical setting for its use. Changes in continuously measured heart rate variability coupled with the absolute value of the standard deviation of the atrial-to-atrial activation period predict subsequent risk for decompensation and hospitalization. Prospective clinical trials will evaluate this approach and the use of such markers on health care utilization in populations of patients with long-term chronic heart failure.

Arrhythmias, Cardiac↗

PubMedDate not supplied

Ambulatory hemodynamic monitoring from an implanted device: components of continuous 24-hour pressures that correlate to supine resting conditions and acute right heart catheterization.

Information from an implantable hemodynamic monitoring system (IHM) aids in management of patients with heart failure. This study identified which components of 24-hour IHM data best estimate resting conditions. Thirty-two patients with heart failure received an IHM in the right ventricular (RV) outflow tract. RV hemodynamics were divided into seven components of a 24-hour recording and were compared with resting supine values. Ambulatory pressures approximating rest were then compared with acute invasive catheterization values. Resting RV pressures from the IHM averaged 41+/-16/10+/-6 mm Hg and estimated pulmonary artery diastolic pressure was 21+/-8 mm Hg. Nighttime (midnight to 4 a.m.) minimum pressures from the IHM best approximated supine resting conditions. RV and pulmonary artery pressures during catheterization were higher than the nighttime minimum, although RV diastolic pressure was not statistically different. Minimum RV and pulmonary artery pressures during nighttime approximate observed resting conditions; invasive catheterization pressures are higher than IHM resting values.

Adult↗