Hypokalemia and ventricular arrhythmias in acute myocardial infarction

In the present study, 408 patients with acute myocardial infarction were included. The serum concentration of potassium was assessed on admission. Episodes of ventricular fibrillation and/or ventricular tachycardia within the following 6 hours were registered. A significant positive correlation between hypokalemia and the incidence of malignant ventricular arrhythmias was demonstrated. Ongoing treatment with diuretics at the time of admission did not appear to be of any significance for the development of ventricular fibrillation or ventricular tachycardia. Out of 100 hypokalemic patients, only 33 were treated with diuretics. The main reason for hypokalemia in the early phase of an acute myocardial infarction is most likely an activation of the sympathetic nervous system leading to an influx of potassium from the extracellular to the intracellular body fluid compartment.     

Spontaneous and inducible ventricular arrhythmias after myocardial infarction in mice.

INTRODUCTION: Remodeling of gap junctions has been implicated in development of ventricular arrhythmias following myocardial infarction (MI) but the specific contribution of reduced electrical coupling is not known. We addressed this question using hearts from mice heterozygous for a connexin43 null allele (Cx43(+/-)). METHODS: To determine whether Cx43-deficient mice exhibit increased spontaneous ventricular arrhythmias in the setting of chronic ischemic heart disease, radiofrequency transmitters were implanted in wild-type and Cx43(+/-) mice 2 days or 9 weeks after left anterior descending coronary artery ligation or sham operations. ECGs were recorded from unanesthetized, unrestrained mice 1 and 10 weeks after MI. Isolated, perfused hearts excised 1 and 10 weeks after MI were subjected to programmed electrical stimulation to induce arrhythmias. RESULTS AND CONCLUSIONS: Hearts with infarcts exhibited more spontaneous and inducible arrhythmias, but there was no significant difference between wild-type and Cx43-deficient mice. Fewer hearts exhibited spontaneous ventricular tachycardia (VT) in vivo than were inducible in vitro, suggesting that structural and functional substrates for inducible VT in isolated hearts may not be sufficient for initiation and maintenance of sustained VT in vivo. Previous studies have shown that Cx43-deficient mice exhibit more VT than wild-type mice during acute regional ischemia. Mice with MI exhibit increased arrhythmias. However, reduced coupling in Cx43-deficient mice does not significantly enhance spontaneous or inducible VT after MI.     

Isolated right ventricular myocardial infarction. A case report

Isolated right ventricular infarction is uncommon. A 73-year-old man without previous cardial complaints was admitted pulseless to hospital. An infarct of the left ventricle was suspected. Autopsy showed a fresh thrombus located in a small branch artery of the right coronary artery accompanied by a fresh infarction of the anterior free wall of the right ventricle. Only 8 cases of isolated right ventricular infarction located in the anterior free wall were found in a review of the literature of right ventricular infarction. The diagnosis, treatment and prognosis of right ventricular infarction are discussed.     

Hypokalemia, arrhythmias and early prognosis in acute myocardial infarction

Serum potassium concentration was estimated on admission to hospital in 289 women and 785 men with acute myocardial infarction. The proportion of women in potassium subgroups was inversely related to serum potassium concentration, increasing from 8% at serum potassium greater than or equal to 5.2 mmol/l to 58% at less than or equal to 3 mmol/l. The frequency of diuretic therapy was also higher in women (35%) than in men (23%). The mortality rate was high at 3 months in patients with one or more arrhythmias (atrioventricular block grade 2, complete heart block, bundle branch block, atrial fibrillation, premature ventricular contractions, ventricular tachycardia) detected by conventional methods during the first 48 hours after admission. Hypokalemia (serum potassium less than or equal to 3.5 mmol/l) did not significantly predict increased occurrence of any of these arrhythmias. Small inhomogeneities of arrhythmias between the potassium groups may have been caused by digitalis therapy prior to admission. Hypokalemia on admission did not predict altered prognosis during the first 3 months.     

Post-myocardial infarction exercise testing: clinical significance of a left ventricular function index and ventricular arrhythmias. A prospective study

A predischarge exercise test was performed in a prospective series of 187 patients, less than 70 years old, with acute myocardial infarction. A survival analysis confirmed previous retrospective findings of a significantly increased long-term mortality in patients with a low increase in the pressure-rate-product (PRP) and/or with major exercise-induced arrhythmias. ST segment depression was without prognostic significance. By a graduated, quantitative re-evaluation of the significance of exercise-induced ventricular arrhythmias, an appropriate, significantly discriminating cutoff point for the frequency of solitary ventricular premature beats (VPBs) was found at two or more VPBs/min. Repetitive VPBs had an equal significance. The probability of 4.5-year survival in patients with these arrhythmias and a low increase in PRP was 0.49 vs. 0.85 in patients with less frequent arrhythmias and with a high increase in PRP (p less than 10(-6)).     

Mast cell inhibition and reduced ventricular arrhythmias in a swine model of acute myocardial infarction upon therapeutic administration of relaxin

Inflammation Research -     

Remodelling of action potential and intracellular calcium cycling dynamics during subacute myocardial infarction promotes ventricular arrhythmias in Langendorff-perfused rabbit hearts

We hypothesize that remodelling of action potential and intracellular calcium (Ca_i) dynamics in the peri-infarct zone contributes to ventricular arrhythmogenesis in the postmyocardial infarction setting. To test this hypothesis, we performed simultaneous optical mapping of Ca_i and membrane potential ( V _m) in the left ventricle in 15 rabbit hearts with myocardial infarction for 1 week. Ventricular premature beats frequently originated from the peri-infarct zone, and 37% showed elevation of Ca_i prior to V _m depolarization, suggesting reverse excitation–contraction coupling as their aetiology. During electrically induced ventricular fibrillation, the highest dominant frequency was in the peri-infarct zone in 61 of 70 episodes. The site of highest dominant frequency had steeper action potential duration restitution and was more susceptible to pacing-induced Ca_i alternans than sites remote from infarct. Wavebreaks during ventricular fibrillation tended to occur at sites of persistently elevated Ca_i. Infusion of propranolol flattened action potential duration restitution, reduced wavebreaks and converted ventricular fibrillation to ventricular tachycardia. We conclude that in the subacute phase of myocardial infarction, the peri-infarct zone exhibits regions with steep action potential duration restitution slope and unstable Ca_i dynamics. These changes may promote ventricular extrasystoles and increase the incidence of wavebreaks during ventricular fibrillation. Whereas increased tissue heterogeneity after subacute myocardial infarction creates a highly arrhythmogenic substrate, dynamic action potential and Ca_i cycling remodelling also contribute to the initiation and maintenance of ventricular fibrillation in this setting.     

大鼠实验性左室心肌梗塞对右室收缩性能的影响

对左室心肌梗塞(MI)是否会直接影响右室功能,至今尚有争议。本实验观察大鼠左室MI时右室dp/dt max的改变及其与左室dp/dt max和梗塞范围(IS)间的关系。结果发现冠脉结扎后1天,在左室dp/dt max显著降低的同时,右室dp/dt max也显著降低,且与左室dp/dt max呈显著的直线正相关,而与IS呈显著的直线负相关。在冠脉结扎后3天时,左室dp/dt max有显著恢复,但仍低于对照水平,而右室dp/dt max已恢复正常,且与左室的dp/dt max和IS间不再具有显著的直线相关关系。由此证明;在大鼠左室MI早期,右室收缩性能可受到直接影响,影响的程度与IS及左室收缩性能降低的程度相关;但当左室收缩性能恢复到一定程度时,这种影响消失。     

Serum-ionised magnesium in patients with acute myocardial infarction. Relation to cardiac arrhythmias, left ventricular function and mortality.

Measurement of serum-ionised magnesium has recently become available, and we report the first study of the relation of this parameter to arrhythmias, left ventricular function and mortality in patients with an acute myocardial infarction. Serum-ionised magnesium was determined in 217 consecutive patients admitted to hospital with an enzyme confirmed AMI. 70 healthy subjects acted as a control group. The main study parameters were occurrence of arrhythmias, left ventricular function estimated by echocardiography, and mortality after 10 months for the AMI patients. AMI patients had significantly lower serum-ionised magnesium compared to healthy controls but the level of serum-ionised magnesium in the acute phase of a MI was neither related to arrhythmias, left ventricular function nor mortality.     

卡维地洛缓解兔心肌梗死后心室重构

冠心病患者发生心力衰竭最常见的始动因素是心肌梗死(myocardial infarction,MI),由梗死心肌触发的一系列体液及细胞外基质的改变等因素将导致心脏结构异常,即心室重构.研究表明,MI后心室重构是发生心室功能障碍和心力衰竭的重要原因.因此,抑制心室重构已成为心血管领域备受关注的课题.本实验旨在研究卡维地洛对心室重构的影响.