Hemodynamic consequences of arrhythmias

Hemodynamic effects during arrhythmias may be caused by underlying pathology (i.e., infarction) as well as disturbance of rate or conduction pattern. In all arrhythmias, compensatory mechanisms tend to restore normal hemodynamics, and with good left ventricular function this can be achieved despite wide disturbance of rhythm. Hemodynamic effects of ectopic beats can result in dramatic fall of stroke volume and reduction in cardiac output, which is greater for ventricular than for atrial ectopics. Prolonged tachycardias are also tolerated up to far higher rates (180/min) if they are atrial, not ventricular, in origin. Mean blood pressure is often maintained even when systolic pressure and cardiac output are reduced. Even in healthy young subjects it is possible for cardiac ischemia to be induced by excessive heart rates. Some of the most deleterious effects are produced by simultaneous atrial and ventricular contraction, which results in continued suppression of cardiac output, both during tachycardias and at normal heart rates. Such situations are often highly symptomatic. Few measurements are available during external chest compression, and these suggest only marginal improvement in hemodynamics, with low pressures and output.