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Biomedical subjects

Andrew Krahn

Publications and source records attributed to Andrew Krahn.

10 recordsLinked to original sources
PubMed2006

Delayed enhancement magnetic resonance imaging predicts response to cardiac resynchronization therapy in patients with intraventricular dyssynchrony.

OBJECTIVES: We evaluated the ability of delayed enhancement magnetic resonance imaging (DE-MRI) to predict clinical response to cardiac resynchronization therapy (CRT). BACKGROUND: Cardiac resynchronization therapy reduces morbidity and mortality in selected heart failure patients. However, up to 30% of patients do not have a response. We hypothesized that scar burden on DE-MRI predicts response to CRT. METHODS: The DE-MRI was performed on 28 heart failure patients undergoing CRT. Patients with QRS > or =120 ms, left ventricular ejection fraction < or =35%, New York Heart Association functional class II to IV, and dyssynchrony > or =60 ms were studied. Baseline and 3-month clinical follow-up, wall motion, 6-min walk, and quality of life assessment were performed. The DE-MRI was performed 10 min after 0.20 mmol/kg intravenous gadolinium. Scar measured by planimetry was correlated with response criteria. RESULTS: Twenty-three patients completed the protocol (mean age 64.9 +/- 11.7 years), with 12 (52%) having a history of myocardial infarction. Thirteen (57%) patients met response criteria. Percent total scar was significantly higher in the nonresponse versus response group (median and interquartile range of 24.7% [18.1 to 48.7] vs. 1.0% [0.0 to 8.7], p = 0.0022) and predicted nonresponse by receiver-operating characteristic analysis (area = 0.94). At a cutoff value of 15%, percent total scar provided a sensitivity and specificity of 85% and 90%, respectively, for clinical response to CRT. Similarly, septal scar < or =40% provided a 100% sensitivity and specificity for response. Regression analysis showed linear correlations between percent total scar and change in each of the individual response criteria. CONCLUSIONS: The DE-MRI accurately predicted clinical response to CRT. This technique offers unique information in the assessment of patients referred for CRT.

Aged↗
PubMed2006

Prevention of Syncope Trial (POST): a randomized, placebo-controlled study of metoprolol in the prevention of vasovagal syncope.

BACKGROUND: Previous studies that assessed the effects of beta-blockers in preventing vasovagal syncope provided mixed results. Our goal was to determine whether treatment with metoprolol reduces the risk of syncope in patients with vasovagal syncope. METHODS AND RESULTS: The multicenter Prevention of Syncope Trial (POST) was a randomized, placebo-controlled, double-blind, trial designed to assess the effects of metoprolol in vasovagal syncope over a 1-year treatment period. Two prespecified analyses included the relationships of age and initial tilt-test results to any benefit from metoprolol. All patients had >2 syncopal spells and a positive tilt test. Randomization was stratified according to ages <42 and > or =42 years. Patients received either metoprolol or matching placebo at highest-tolerated doses from 25 to 200 mg daily. The main outcome measure was the first recurrence of syncope. A total of 208 patients (mean age 42+/-18 years) with a median of 9 syncopal spells over a median of 11 years were randomized, 108 to receive metoprolol and 100 to the placebo group. There were 75 patients with > or =1 recurrence of syncope. The likelihood of recurrent syncope was not significantly different between groups. Neither the age of the patient nor the need for isoproterenol to produce a positive tilt test predicted subsequent significant benefit from metoprolol. CONCLUSIONS: Metoprolol was not effective in preventing vasovagal syncope in the study population.

Adrenergic beta-Antagonists↗
PubMed2004

Analysis of cause-specific mortality in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study.

BACKGROUND: Expectations that reestablishing and maintaining sinus rhythm in patients with atrial fibrillation might improve survival were disproved in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study. This report describes the cause-specific modes of death in the AFFIRM treatment groups. METHODS AND RESULTS: All deaths in patients enrolled in AFFIRM underwent blinded review by the AFFIRM Events Committee, and a mode of death was assigned. In AFFIRM, 2033 patients were randomized to a rhythm-control strategy and 2027 patients to a rate-control strategy. During a mean follow-up of 3.5 years, there were 356 deaths in the rhythm-control patients and 310 deaths in the rate-control patients (P=0.07). In the rhythm-control group, 129 patients (9%) died of a cardiac cause, and in the rate-control group, 130 patients (10%) died (P=0.95). Both groups had similar rates of arrhythmic and nonarrhythmic cardiac deaths. The numbers of vascular deaths were similar in the 2 groups: 35 (3%) in the rhythm-control group and 37 (3%) in the rate-control group (P=0.82). There were no differences in the rates of ischemic stroke and central nervous system hemorrhage. In the rhythm-control group, there were 169 noncardiovascular deaths (47.5% of the total number of deaths), whereas in the rate-control arm, there were 113 noncardiovascular deaths (36.5% of the total number of deaths) (P=0.0008). Differences in noncardiovascular death rates were due to pulmonary and cancer-related deaths. CONCLUSIONS: Management of atrial fibrillation with a rhythm-control strategy conferred no advantage over a rate-control strategy in cardiac or vascular mortality and may be associated with an increased noncardiovascular death rate.

Aged↗
PubMed2004

Prognostic differences between atrial fibrillation and atrial flutter.

This report presents the outcome of a cohort of 94 patients with atrial fibrillation from the Canadian Registry of Atrial Fibrillation, in which we paid particular attention to the probability of stroke and death. We also evaluated warfarin use over time and compared left atrial dimensions in patients with atrial flutter with those with atrial fibrillation.

Aged↗
PubMed2004

Cryoablation: potentials and pitfalls.

The use of cryoablation in the electrophysiology lab provides some distinct advantages not seen with conventional radiofrequency ablation. Ice mapping allows a functional assessment of a putative ablation site prior to the formation of a permanent lesion. This provides a distinct advantage adjacent to the AV node for para-hisian pathways and difficult cases of AVNRT. Cryoablation also produces minimal endothelial disruption and thrombus formation and causes no collagen shrinkage. This is likely advantageous when ablation is required within venous structures. There is also mounting experimental evidence that cryoablation is safe adjacent to the arterial system, especially within the middle cardiac vein or distal coronary sinus. As the technology evolves and further iterations of the catheter proceed, the role for this new but well-established technology is likely to grow.

Animals↗
PubMed2004

Management of vasovagal syncope: 2004.

Vasovagal syncope is a common disorder that affects at least 20% of people at some time in their lives. Probably half of these patients faint recurrently; for many this causes physical trauma, a substantial reduction in quality of life, and difficulties with driving, employment and education. The last 15 years have seen striking advances in diagnostic approaches and prognostic understanding. A number of physiological, pharmacological and electrical therapies have been developed and tested to various degrees in patients. These include counterpressure manoeuvres, salt and fluid recommendations, and attempted treatment with fludrocortisone, midodrine, beta-blockers, serotonin reuptake inhibitors, and permanent pacemakers. This review highlights the most important of these advances and suggests strategies for managing this often difficult problem.

Adrenergic alpha-Agonists↗
PubMed2003

Combined head-up tilt and lower body negative pressure as an experimental model of orthostatic syncope.

INTRODUCTION: The combination of head-up tilt and incremental lower body negative pressure has shown promise in the diagnosis of orthostatic hypotension and neurocardiogenic syncope, although prior methodologies limited conclusions as to the reproducibility of the test. The aim of this study was to assess the efficacy and reproducibility of a protocol combining tilt and stages of incremental lower body negative pressure. METHODS AND RESULTS: Ten volunteers (6 men and 4 women; mean age 21 +/- 1 years) participated in the study, which was composed of three sessions, 1 month apart, each consisting of 60 degrees tilt followed by lower body suction in incremental levels of -10 mmHg for 5 minutes at each level. The primary outcome variable was the time to presyncope. Secondary variables were the levels of heart rate, blood pressure, cerebral blood flow, and end-tidal CO2 at each level of the test. Presyncope could be achieved in all subjects. The mean times to presyncope were 24.6 +/- 1.4 minutes, 26.2 +/- 1.8 minutes, and 31.8 +/- 1.6 minutes and were not different across tests (P = 0.3). Intrasubject variability was assessed by determining the mean average deviation from the mean, which was 3.2 +/- 2.0 minutes. Changes in heart rate, blood pressure, end-tidal CO2, and cerebral blood flow were consistent with repeat testing. CONCLUSION: Lower body negative pressure combined with head-up tilt in a staged protocol can safely and reliably induce presyncope in all normal subjects tested. The test is a potent and reproducible investigational tool for inducing hypotension and transient cerebral hypoperfusion.

Adult↗
PubMed2003

Biophysical characteristics of a new mutation on the KCNQ1 potassium channel (L251P) causing long QT syndrome.

The congenital long QT syndrome (LQTS) is a hereditary cardiac disease characterized by prolonged ventricular repolarization, syncope, and sudden death. Mutations causing LQTS have been identified in various genes that encode for ionic channels or their regulatory subunits. Several of these mutations have been reported on the KCNQ1 gene encoding for a potassium channel or its regulatory subunit (KCNE1). In this study, we report the biophysical characteristics of a new mutation (L251P) in the transmembrane segment 5 (S5) of the KCNQ1 potassium channel. Potassium currents were recorded from CHO cells transfected with either wild type or mutant KCNQ1 in the presence or in the absence of its regulatory subunit (KCNE1), using the whole-cell configuration of the patch clamp technique. Wild-type KCNQ1 current amplitudes are increased particularly by KCNE1 co-expression but no current is observed with the KCNQ1 (L251P) mutant either in the presence or in the absence of KCNE1. Coexpressing KCNE1 with equal amount of cDNAs encoding wild type and mutant KCNQ1 results in an 11-fold reduction in the amplitude of potassium currents. The kinetics of activation and inactivation and the activation curve are minimally affected by this mutation. Our results suggest that the dominant negative effect of the P251L mutation on KCNQ1 channel explains the prolonged repolarization in patients carrying this mutation.

Adolescent↗