3.3.4. Positive Ionotropic Drugs

Question 1

Cardiac performance is determined by what four factors?

Answer 1

preload, afterload, contractility, heart rate

Question 2

what is another way to describe ‘contractility ‘?

Answer 2

“inotropic state”

Question 3

list 5 things that can increase contractility

Answer 3

• neural input (NE)
• circulating catechols (Epi, NE)
• Digoxin
• (+) inotropic drugs
• increased intracellular [Ca]

Question 4

Acidosis, ischemia, (-) inotropic drugs, Ca-channel blockers, and beta-blockers all do what?

Answer 4

DECREASE contractility

Question 5

what is cardiogenic shock?

Answer 5

When the blood pressure is too low to meet the needs of the vital organs due to cardiogenic pump failure
(inadequate CO)

Question 6

two physiological factors that define cardiogenic shock

Answer 6

SBP < 100 mmHg; Cardiac Index < 1.8 L/min/m2

Question 7

what are the symptoms of cardiogenic shock?

Answer 7

Poor urine output, cool extremities (due to vasoconstriction in an attempt to shunt more blood), confusion, and acidosis

Question 8

of oral and IV agents, which do you use first? last?

Answer 8

Use oral agents FIRST when there is chronic heart failure with symptoms; IV agents are a last resort

Question 9

list the two classes of sympathomimetic agents that can be used as positive inotropic agents

Answer 9

1) beta adrenergic AGONISTS; 2) catechols (NE, dopamine, dobutamine)

Question 10

what other category of positive ionotropic agent inhibits intracellular enzymes?

Answer 10

phosphodiesterase (PDE) inhibitors - these guys prevent cAMP breakdown, allowing for a greater force of contraction

Question 11

When might you PDE inhibitors for a patient w/heart failure?

Answer 11

If they’re on beta-blockers that aren’t showing any signs of improvement. (Recall that sympathomimetics - beta agonists - wouldn’t be logical to use if the beta blockers the Pt is on would counteract them anyway)

Question 12

Describe the symptoms of cardiogenic shock for a Pt that would indicate the use of DOBUTAMINE

Answer 12

Asymptomatic, SBP 70-100 mmHg

AKA, mildly low BP with no symptoms

Question 13

Describe the symptoms of cardiogenic shock for a Pt that would indicate the use of DOPAMINE

Answer 13

Symptomatic, SBP 70-100 mmHg

When symptoms exist, you need to give something with more alpha agonistic activity

Question 14

Describe the symptoms of cardiogenic shock for a Pt that would indicate the use of NOREPINEPHRINE

Answer 14

SBP < 70 mmHG

NE has a slight reduction for cardiac arrhythmias

Question 15

What are the dangers of using positive inotropic agents (other than digoxin)?

Answer 15

Because they increase mortality (arrhythmias, MI), you need to continually monitor the patient’s BP and evaluate ECGs.

Question 16

describe the clinical uses of digoxin, and when it is indicated

Answer 16

• Symptomatic CHF (in systolic dysfunction only; with or without atrial fibrillation)
• Supraventricular arrhythmias (to control ventricular rate)

Question 17

what is a CONTRAINDICATION of digoxin (specifically relating to pharmacokinetics)?

Answer 17

because digoxin is eliminated by the kidney (some GI), anyone with HF likely has kidney problems as well. This can lead to digoxin toxicity

Question 18

what is a consideration you must take when administering digoxin?

Answer 18

Combining digoxin with any drug that decreases clearance, volume of distribution, or both, is extremely dangerous (puts the Pt in the toxic range).

For example: Propafenone, quinidine, verapamil, amiodarone

Question 19

what does taking digitalis/digoxin do for your patients in the long run?

Answer 19

It eventually restores the angiotensin-renin system and instead relies on increased contractility, i.e. inotropy. While it alleviates HF symptoms and keeps Pts out of the hospital, IT DOES NOT PROLONG LIFE

Question 20

Describe digoxin’s mechanism of action

Answer 20

• digoxin blocks the Na-K-ATPase, causing an increase in cytosolic Na
• the increase in intracellular [Na] prevents Ca efflux via the Ca-Na antiporter (because the Na gradient is equalized)
• increased intracellular [Ca] causes increased contractility at the level of the sarcomere

Question 21

What are the ABSOLUTE contraindications of digoxin use?

Answer 21

1. AV NODAL block is greater than first degree (don’t want to give a drug that makes conduction worse unless they have a pacemaker)
2. Wolff-Parkinson-White (WPW) syndrome (will increase conduction through the “wrong” pathway, increasing the risk for severe arrhythmia)
3. Hypertrophic or restrictive cardiomyopathy (Digoxin increases the tension in the heart)
4. Cardiac amyloidosis

Question 22

What are the RELATIVE contraindications of digoxin use?

Answer 22

Renal insufficiency, hypokalemia, hyperthyroidism, acute coronary syndrome, normal systolic cardiac function

Question 23

list the signs of digoxin toxicity

Answer 23

Nausea, vomiting, diarrhea, Blurred vision, scotomas and yellow-green (halo) vision, Bi-directional VTach (doesn’t cause Torsades)

Question 24

How do you treat digoxin toxicity?

Answer 24

Stop the drug and admit for ECG monitoring.
Correct electrolytes (low [K+] or [Mg2+] common; high [K+] is more dangerous).
Give Fab Digibind, correct electrolytes, and MgSO4.
Cardioversion, calcium, CCB are relatively contraindicated.
Give Lidocaine and phenytoin if VTach seen.

Question 25

in two general situations, when is digoxin indicated?

Answer 25

Digoxin is used in symptomatic systolic dysfunction and poorly controlled atrial fibrillation

Question 26

in general, contractility and SV INCREASE with what four things?

Answer 26

• Catecholamines (increase activity of the Ca++ pump in sarcoplasmic reticulum)
• digitalis (increased intracellular Na+, causing increased intracellular Ca++)
• decreased extracellular Na+
• increased intracellular Ca++

Question 27

in general, contractility and SV DECREASE with what four things?

Answer 27

• beta-1 blockade
• heart failure
• narcotic overdose
• hypoxia/hypercapnia
• acidosis