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Ventricular interdependence is the term used to describe the dysfunction of one ventricle secondary to a disorder of the other, mainly due to the involvement of the interventricular septum which is common to both ventricles. During spontaneous inspiration, right ventricular volume increases, pushing the interventricular septum towards the left ventricle. This leads to an increase in left ventricular filling pressure with an unchanged or lower left ventricular end diastolic volume. This is a diastolic interventricular interaction which is always present .
Studies have shown that twenty to forty percent of right ventricular output and systolic pressure generation are contributed by left ventricular contraction .
Right ventricular diastolic dysfunction can be associated with left ventricular dysfunction even in the absence of pulmonary hypertension or direct involvement of the right ventricle by the same disease process as coronary artery disease. Similarly pressure or volume overload of the right ventricle can affect the systolic or diastolic function of the left ventricle due to the effect on the interventricular septum. This has been documented in certain cases of chronic obstructive pulmonary disease, pulmonary hypertension and atrial septal defect.
Right ventricular function is more important in generating the flow than pressure and hence more difficult to measure. Though this aspect is very important in the critically ill, often we go by the pressures generated by the left ventricle and forget the role of right ventricle in generating the flow component of cardiac output. That is why right ventricular dysfunction is not well recognized in the critical care setting .
Eccentricity index measured by echocardiography is a useful indicator of ventricular interdependence in the presence of pulmonary hypertension . Marked early systolic anterior motion of the septum occurs if the septum had been deviated to the left ventricle in diastole. The exercise capacity is lower in those cases and is associated with extensive ventricular remodeling and reduced ventricular function.
The effect of ventricular interdependence is also striking in cardiac tamponade when the filling of the ventricles is limited by a fixed total pericardial space. Dornhorst’s theory states that inspiratory filling of the right ventricle causes collapse the left ventricle in this situation, reducing left ventricular output and explains the pulsus paradoxus in cardiac tamponade .
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