Why alpha-antiplasmin must be converted to a derivative form for optimal function.

BACKGROUND: Human alpha(2)-antiplasmin (alpha(2)AP), the primary inhibitor of fibrinolysis, is secreted from the liver into plasma as a 464-residue protein with Met as the N-terminus. An R6W polymorphism has been suggested to affect fibrinolytic rate. Within circulating blood, antiplasmin-cleaving enzyme (APCE) cleaves Met-alpha(2)AP(R6) faster than Met-alpha(2)AP(W6) at the Pro12-Asn13 bond to yield Asn-alpha(2)AP. OBJECTIVES: To compare Met-alpha(2)AP(R6), Met-alpha(2)AP(W6) and Asn-alpha(2)AP for crosslinking with fibrin and the ability to protect fibrin from digestion by plasmin. METHODS AND RESULTS: Asn-alpha(2)AP utilizes Gln2 (Gln14 in Met-alpha(2)AP) to become crosslinked to fibrin approximately twelvefold faster than Met-alpha(2)AP(R6) or Met-alpha(2)AP(W6), and this enhances the resistance of fibrin to plasmin. All three forms of alpha(2)AP inhibit plasmin at identical rates. The N-terminal 12-residue peptide of Met-alpha(2)AP slows crosslinking of Met-alpha(2)AP(R6) or Met-alpha(2)AP(W6) by limiting access of factor XIIIa to Gln14 rather than shifting crosslinking to other Gln residues. Edman sequencing and mass analyses of tryptic peptides from each alpha(2)AP crosslinked with 5-(biotinamido)pentylamine showed Gln14 as the only major crosslinking site. Residues 5-8, GRQL in Met-alpha(2)AP(R6), and residues 1-8, MEPLGWQL in Met-alpha(2)AP(W6), slow fibrin crosslinking. CONCLUSION: Gln14 in both Met-alpha(2)AP(R6) and Met-alpha(2)AP(W6) is sheltered by the N-terminal 12-residue peptide, which, when cleaved, yields Asn-alpha(2)AP, which is rapidly crosslinked to fibrin and maximally protects it from plasmin. The R6 W polymorphism in Met-alpha(2)AP does not affect its crosslinking to fibrin, but it does slow cleavage by APCE and reduces the amount of Asn-alpha(2)AP available for rapid crosslinking to fibrin.

Regional attitudes of generalists, specialists, and subspecialists about management of atrial fibrillation.

BACKGROUND: It is unknown whether physicians' attitudes about the management of atrial fibrillation (AF) reflect the recommendations of published guidelines. METHODS: To obtain information about physicians' attitudes about management of AF, a questionnaire was returned by 904 (20.1%) of 4500 physicians involved in managing AF (385 cardiologists, 326 internists, and 193 electrophysiologists). The cardiologists and internists were from Massachusetts or California; the electrophysiologists were from around the United States. The questionnaire called for 86 separate answers about use of resources and drug therapy for different types of AF, including recent-onset AF, paroxysmal AF, and chronic AF of less than 6 months' and more than 3 years' duration. RESULTS: Transthoracic echocardiography and thyroid function were requested by more than 90% of physicians; transesophageal echocardiography and catheterization were requested by 10% of physicians. To control ventricular response, digoxin was the overwhelming first-line therapy; calcium channel blockers were favored over beta-blockers for adjunct therapy. To prevent thromboemboli, warfarin sodium was preferred for chronic AF; warfarin or aspirin were equally considered for paroxysmal AF. In considering sinus rhythm, respondents agreed about factors determining whether to revert, the number of drug trials, and the first-line drug choice (quinidine sulfate) but disagreed about second-line antiarrhythmic drugs and whether to hospitalize the patient before initiating drug therapy. CONCLUSIONS: Physicians ranging from primary care providers to subspecialists agree on issues of AF management such as heart rate control and anticoagulation. Attitudes vary widely about issues such as antiarrhythmic drugs.

Should physicians participate in affirming the best approach to atrial fibrillation management?

While all patients with atrial fibrillation should receive anticoagulation and control of ventricular response, it is not clear whether conversion to sinus rhythm is associated with a good long-term outcome. Data are presented detailing current physician practices regarding conversion to sinus rhythm (preferred by 90%) and why participation in the new National Institute of Health trial of atrial fibrillation is desirable.

Life-threatening alterations in heart rate after the use of adenosine in atrial flutter.

Adenosine has become the preferred treatment for common types of supraventricular tachycardia because it is extremely effective and rarely associated with with serious side effects. It has also been advocated as an intervention for diagnostic use to assess uncommon types of tachycardia. Evidence is shown in this report that adenosine was associated with dangerous worsening of arrhythmia in patients with atrial flutter. In two patients, adenosine precipitated acceleration of ventricular response, in one case necessitating emergent cardioversion. Both patients had atrial flutter with 2 to 1 atrioventricular block that evolved into 1 to 1 atrioventricular conduction. In three other patients, adenosine was associated with prolonged bradyasystole and hypotension. In each of the five patients, adenosine was given in a standard fashion (6 or 12 mg). In summary, adenosine should be recognized as a potentially dangerous intervention in patients with atrial flutter. If it is used for diagnostic purposes, resuscitative equipment should be readily available.

Modern concepts of atrial fibrillation.

Atrial fibrillation (AF) is recognized as a common cardiac arrhythmia associated with significant morbidity and mortality. The mechanism of AF depends on the type, paroxysmal (P) AF is usually secondary to autonomic imbalance and chronic (C) AF is typically secondary to cardiovascular dysfunction. There is significant overlap as most patients with PAF will eventually develop CAF. Therapeutic considerations depend mostly on the clinical situation ranging from emergent electrical therapy for unstable patients to no therapy for asymptomatic patients. Most patients are mildly symptomatic from rapid heart rate (ventricular response) and benefit from drugs designed to create AV block. Anticoagulation is important additional therapy in order to prevent thromboemboli. Reversion of AF and maintenance of sinus rhythm would be the ideal goals of therapy except for the toxicity of available agents. As a result many patients would be best left in AF as the rhythm of choice.