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In addition to ventricular arrhythmias, various forms of supraventricular arrhythmias (SVA) and atrioventricular (AV) and intraventricular (IV) conduction disturbances occur also in acute myocardial infarction (AMI). In the setting of AMI, SVA may be caused by relevant atrial ischemia or infarction. SVA complicate the course especially that of inferior, posterior and lateral AMI, SVA occur frequently also in the right ventricular myocardial infarction and in pericarditis. SVA appearing in the late phase of AMI are caused particularly by hemodynamic factors especially those of both left and right ventricular dysfunctions. Atrial dilatation and the increase of intraatrial pressure are also important factors in the genesis of SVA. The autonomous nervous system, electrolyte disturbances, acidosis and global hypoxia may operate as modulating factors in the development of SVA. AV conduction disturbances are significantly more frequent in patients with inferior than with anterior AMI. In inferior AMI, they are frequently caused by reflex parasympathetic activation. In the genesis of AV conduction disturbances, a significant role may be played also by the following mechanisms: Ischemia or necrosis of AV node or AV junction and the negative dromotropic effect of adenosine and potassium which are released to a great extent during myocardial ischemia and reperfusion. A high-degree AV block complicating the course of inferior AMI has a significantly better prognosis than that occurring in the setting of anterior AMI. In inferior AMI, AV block is frequently reversible, whereas in anterior AMI, it is persistent and irreversible. Early AV conduction disturbances, appearing within 24 hours of AMI have a better prognosis than those occurring in the late phase of AMI. Bundle branch blocks (BBB) complicating the course of AMI are caused by occlusion of bundle-related coronary artery or by serious ischemia in its bed. BBB is frequently a marker of a multivessel disease. New BBB appearing in AMI especially the right bundle branch block is considered as an predictor for the development of a complete AV block. Frequent and repetitive SVA as well as serious AV and IV conduction disturbances are frequently associated with a significantly worse clinically course of AMI and with increased mortality, with that of especially hospital mortality. However, this is usually not caused by SVA or AV and IV conduction disturbances per se. The major cause of death in these patients are heart failure cardiogenic shock and malignant ventricular arrthythmias due to larger AMI, significant reduction of left ventricular function and advanced coronary heart disease. Complex SVA as well as serious AV and IV conduction disturbances are usually considered as markers, but not as independent predictors for both increased hospital mortality and in some cases also for that of posthospital mortality. Their occurrence in AMI may help to identify the patients at great risk who require a very intensive treatment including aggressive management of extensive coronary heart disease. (Ref. 62.).