Mnemonics:
Remember again, the heart has 4 chambers =>  4 stages of classifications => ABCD.
Remember the heart has 2 atrium & 2 ventricles => AB = at risk for HF; CD = Heart failure.
A                          B                       C                   D
Structural             Structural          HF                HF
Heart                    Heart
Not yet                 No s/s               W/ s/s           S/s not abated

Memory aids:
The keyword here is 'structural heart disease'. Remember that ACC/AHA is very scientific => they dont' just do symptom based like NYHA, they want to do sth that you can visualize = structural heart disease.
Now, the progression of HF starts early from HTN, hyperlipidemia (atherosclerosis), diabetes, etc. to structural heart disease. From structural heart disease when the heart already has anatomical changes such as Left ventricular hypertrophy. However, to be considered as Heart failure (stage C), pt must have those symptoms associated with HF. Finally, when those symptoms, despite being treated aggressively, still recurrent => refractory.

A----Developing structural heart disease---->B----developing HF symptoms---->C------Tx-resistant symptoms---->D

Stage A: Who's at risk HF & developing structural heart disease?:
- HTN
- Coronary artery or other atherosclerotic vascular dz
- Diabetes
- Obesity
- Metabolic syndrome

Stage B: What causes Structural heart disease?:
- Previous MI
- Left-ventricular hypertrophy
- Left ventricular systolic dysfunction

Stage C: HF:
- Left ventricular systolic dysfunction and symptoms such as dyspnea, fatigue & reduced exercise tolerance

Stage D: Who's considered as resistant to HF therapy?:
- Those who has symptoms at rest (stage IV NYHA) despite maximal medical therapy, meaning those who's requiring recurrent hospitalization (despite being compliant with medications)
- Those who cannot be discharged without mechanical assist devices or inotropic therapy.