Ventricular Interdependence

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Right and left ventricles are situated inside the same non compliant pericardium. This means that they are both exposed to the same intrathoracic and intraalveolar pressures. Changes in volume and pressure of one ventricle will directly affect the other. Normally LV pressure is greater than RV pressure and the interventricular septum bows into the RV. However, the thin free wall of the RV makes it more sensitive to increases in afterload than the LV, and any increase in afterload (e.g. pulmonary hypertension) will lead to dilatation of the RV. Under these circumstances the trans-septal pressure gradient can reverse and the septum can shift to the left compromising LV filling during diastole. Interaction between the two ventricles occurs during systole and diastole, and is called ventricular interdependence (Figure HE.35).

Ventricular Interdependence
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Figure HE.35 Ventricular interdependence

Cardiac Failure

Cardiac failure is a state of inadequate circulation due to cardiac dysfunction. The condition manifests itself through two aspects. First, there is a failure to provide adequate arterial pressure and CO ("forward failure') into the systemic circulation. Second, there is a failure to pump away the venous return that causes congestion in the pulmonary or systemic venous beds ("backward failure').

The course of cardiac failure may be acute or chronic. The commonest cause of acute cardiac failure is myocardial infarction, while chronic failure often arises in ischaemic heart disease, hypertension and valvular disease. In acute cardiac failure hypotension without peripheral oedema may occur. While in chronic failure, blood pressure is usually maintained, but signs and symptoms due to congestion develop.

Some of the common signs and symptoms of cardiac failure are shown in Figure HE.36.

Many of the physiological parameters and indices reflecting aspects of cardiac performance change in cardiac failure. These are outlined in Figure HE.37.

SIGNS AND SYMPTOMS OF CARDIAC FAILURE

Physiological change

Sign or symptom

Congestion in the pulmonary vascular system

Pulmonary oedema Dyspnoea on exertion Orthopnoea

Paroxysmal nocturnal dyspnoea

Congestion in the systemic vascular system

Dependent oedema (e.g. ankle) Hepatomegaly

Raised jugulovenous pressure

Inadequate systemic circulation

Fatigue

Sodium retention Increased intravascular volume

Figure HE.36

CHANGES IN PHYSIOLOGICAL INDICES IN CARDIAC FAILURE

Change in heart

Change in physiological index

i Ventricular contractility

X decreased CO

Shift of ventricular function curve down

Ventricular dilatation

CVP

systolic ventricular wall stress EDV

Ventricular diastolic dysfunction

Shift of EDPVR curve up and left

Altered cardiovascular coupling

Displacement of operating point on ventriculo-arterial and ventriculovenous coupling diagrams

Figure HE.37

Figure HE.37

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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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