INOTROPES AND VASOPRESSORS

PADRAIG HEADLEY ST7

OBJECTIVES•Review physiology of cardiac contraction and inotropy

•Classify inotropes

•Discuss their mechanism of action

•Overview of vasopressors

•Choosing the right one????

•The future??

Positive inotropes increase the force of contraction of the myocardium

The smallest unit functional unit of the myocardium is the actin-myosin unit

Cross bridge cycle

•Ca binds troponin C and alters tropomysin uncovering actin for binding

•ATP attaches to myosin head and causes rotation and breakdown to ADP and binding to actin

•On attachment to actin --- further rotation and displacement ADP --produces force (on time) --- detaches and enters non force state (off time).

•This process cycles

The extent of the force produced per unit time depends on the amount of cross-bridges activated. This depends on:

a) the amount of Ca available

b) its affinity to troponin C

c) cross bridge function and co-operativity

European Heart Journal (2011) 32, 1838–1845 doi:10.1093/eurheartj/ehr026

Removal of calcium is also an

active process

HOW DOES THE HEART CONTROL IT'S FORCE OF CONTRACTION PHYSIOLOGICALLY??

•Length dependant activation of cross bridges :- the frank starling mechanism -- improves co-operativity and therefore most energy efficient means

•Frequency dependant activation - in normal hearts increase in heart rate will result in increased intracellular calcium, defective in disease states and other factors involved -- energy dependant

•Catecholamine mediated activation

Positive inotropy

Increased work,

imbalances in supply and

demand, risk of arrhythmia and ischaemia

It's increasingly recognised that the economics of these processes may mean that some inotropes may work without increasing energy

requirements.

Both contraction and relaxation are active processes reflecting types of heart dysfunction - systolic and diastolic

INOTROPES

CLASSIFICATION

BETA ADRENORECEPTORS

β-1 adrenergic

β-2 adrenergic

CATECHOLAMINES

• Natural or synthetic

• Most commonly used agents act on multiple receptors in a dose-dependent manner

• Have multisystem effects also - central, respiratory, endocrine, immune

Natural catecholamines

ADRENALINE• Potent β-1, moderate α-1 & β-2

• Low dose – chronotrope and inotrope

• Increased CO, decreased SVR, variable MAP

• High dose – α effect increases• Increased CO, increased SVR

DOPAMINE• Dose range dependent effects:

• 1 – 2 μg/kg/min dopamine-1 receptors in the renal, mesenteric,

cerebral, and coronary beds, resulting in selective vasodilation

• 5 -10 μg/kg/min β-1 stimulation – increased SV, variable effect on

HR

• >10 μg/kg/min adrenergic stimulation – vasoconstriction &

increased SVR

DOBUTAMINE• Synthetic derivative of isoprenaline

• Overall an inotrope with vasodilatory properties

• Predominantly β-1 - inotropy, chronotropy, decreased LV filling pressure

• Minimal α and β-2 – overall vasodilation

PHOSPHODIESTERASE INHIBITORS

• Selective or non selective

• PDE3 inhibitors - Inotropic and vasodilatory

• Mainly in impaired cardiac function and medically refractory heart failure

• Limitations in sepsis due to vasodilatation

LEVOSIMENDAN

•Inodilator

•Enhances sensitivity of troponin C to Ca without increase in intracellular Ca

•Only acts in presence of high Ca therefore does not affect relaxation phase

•Opening of ATP K channels causes vasodilation and reduced afterload

•Overload cardiac output is augmented with improved diastolic relaxation without an increase in workload

•In vitro PDE III inhibitor ? In vivo effect

•Long half life due to active metabolites

•Given as loading dose followed by 24hr infusion, effects last up to 9 days

Glucagon

OTHERS Insulin

VASOPRESSORS

ALPHA ADRENORECEPTORS

ADRENALINE• Potent β-1, moderate α-1 & β-2

• Low dose – chronotrope and inotrope

• Increased CO, decreased SVR, variable MAP

• High dose – α effect increases• Increased CO, increased SVR

DOPAMINE• Dose range dependent effects:

• 1 – 2 μg/kg/min dopamine-1 receptors in the renal, mesenteric,

cerebral, and coronary beds, resulting in selective vasodilation

• 5 -10 μg/kg/min β-1 stimulation – increased SV, variable effect on

HR

• >10 μg/kg/min adrenergic stimulation – vasoconstriction &

increased SVR

NORADRENALINE

• α-1 & β-1

• Potent vasoconstriction, less pronounced increase in CO

• Reflex bradycardia

PHENYLEPHRINE• Purely alpha-adrenergic agonist

• Increased afterload

• CO usually actually maintained in patients without prior cardiac dysfunction

• CO falls in patients with impaired ventricular function

VASOPRESSIN•Nanopeptide produced by hypothalamus & released by posterior pituitary.

•3 receptors

•V1 – G-protein coupled - vasoconstriction

•V2 - aquaporins insertion in renal tubules, release vWF and factor VIII

•V3 - anterior pituitary release of ACTH and endorphins

•Synthetic derivatives - desmopressin (high V2 effect), terlipressin longer acting

WHICH INOTROPE / VASOPRESSOR??

WHICH AGENT?•Depends on individual patient and type of shock

•Potential Pitfalls and options

•Knowing the patient's current cardiovascular status - ? more cardiac output monitors

•Recognising that things can change due to multiple factors including the natural history of the underlying process eg phases of sepsis, tachyphylaxis to adrenergic agents - therefore choice of agent may need to change during course of illness

SEPSIS

• Vasopressin and Septic Shock Trial (VASST)• 778 patients with septic shock randomly assigned to either low dose vasopressin

(0.01 to 0.03 units per minute) norepinephrine (5 to 15 mcg per minute)

• similar 28-day and 90-day mortality rates, similar incidence of serious adverse events

• Russell JA, Walley KR, Singer J, Gordon AC, Hébert PC, Cooper DJ, Holmes CL, Mehta S, Granton JT, Storms MM, Cook DJ, Presneill JJ, Ayers D, VASST Investigators. Vasopressin versus norepinephrine infusion in patients with septic shock. N Engl J Med. 2008;358(9):877

SEPSIS

• Annane et al, Lancet 2007; 370: 676–84, 330 patients with septic shock in French ICU’s

• Titrated to maintain MAP at 70mmHg, Primary outcome 28 day mortality

CARDIOGENIC SHOCK•Little evidence to guide inotropic or vasopressor therapy. ESC guidelines suggest dobutamine first line+/- noradrenaline if required to maintain perfusion pressures

•Those that require these agents have a high mortality

•Revascularisation if required is key

•Inotropes and vasopressors may actually have a detrimental effect in longer term- everything we know to improve outcome in heart failure works opposite in effect to these agents.

•commonly used drugs may be less effective given changes in the myocardial cells due to the disease state and also due to pretreatment with beta blockade - leading to theory that agents such as PDEi may be more beneficial in these cases

•However direct studies between PDEi and dobutamine are all small studies not showing any difference in outcome

LEVOSIMENDAN

•Little evidence base to date to direct critical care use

•Biggest trials to date have been on Decompensated chronic heart failure - REVIVE and SURVIVE - excluded shocked or ventilated patients - use associated with reduction in BP particularly with loading dose

•Meta analysis suggested potential survival advantage compared with dobutamine but not with placebo.... Is dobutamine actually doing harm in these cases??

THE FUTURE???

BETA BLOCKERS PLUS INOTROPES??

CONCLUSIONS•These are commonly used agents in critical care - has appeared as viva topic in FFICM

•Evidence base is limited to guide use of one agent over another, choice should be based on individual patient characteristics

•Our understanding of basic science behind inotropy etc is leading to novel agents / ideas