Heart Failure...Pathophysiology and Drugs

Heart failure occurs when the heart inability to pump(contract) properly causing reduced in cardiac output(CO). Several mechanisms are activated in order to compensate with low CO.
1) Increase in sympathetic activities which can lead to stimulation of vasoconstriction. Thus this mechanism sure increasing the cardiac filling pressure that lead to cardiac remodeling.
2) Reduced cardiac output can stimulate the release of renin that stimulate the production of angiotensinogen to angiotensin 1 and eventually produces angiotensin 2. ACE is enzyme that stimulate conversion of angiotensin 1 to angiotensin 2. Angiotensin 2 is a very strong vasoconstrictor which can increase cardiac filling pressure above. Angiotensin 2 also stimulate formation of aldosterone to helps in sodium and water retention and eventually increase cardiac filling pressure.
However this mechanism is not in under control will lead to heart failure.

Drugs used in heart failure are :

1) Positive inotropic
a) cardiac glycoside : inhibit Na / K channel, increase Ca ion intracellularly thus increase strength of the myocyte contraction
b) PDE-i : reduce cAMP breakdown, increase level of cAMP which can lead to inrease myocardial contractility and vasodilation
c) beta agonist : stimulation of beta receptor in low dose stimulate vasodilation, in median dose stimulate mycardial contraction which can lead to increase stroke volume.

2) Diuretics
used in patient with high retention volume due to heart failure to pump or increase in aldosterone level that can cause water Na retention.

3) ACE-i and ARB, helps in reducing the effect of angiotensin 2.

$) Beta-blocker, slow action to recover the normal heart within 2-4 months