Which of the following patients is NOT a candidate for ICD implantation?

Patients who exhibit persistent New York Heart Association (NYHA) class 4 symptoms are not considered ideal candidates for implantable cardioverter-defibrillator (ICD) implantation because their functional status is severely compromised. This classification indicates that the patient experiences significant limitations in physical activity, with symptoms occurring even at rest.

In contrast, the other patients listed exhibit conditions that generally make them more favorable candidates for ICD implantation. A patient with a history of sustained ventricular tachycardia (VT) and syncope has shown a previous serious arrhythmia and loss of consciousness, which is a clear indication for potential ICD placement to prevent life-threatening arrhythmias. A patient with structural heart disease may also be at risk for arrhythmias, making them suitable candidates for ICD therapy. Lastly, a patient with unexplained syncope, particularly if they have risk factors or underlying conditions associated with arrhythmias, can also be considered for ICD placement to prevent sudden cardiac death. Therefore, the key distinction for B is the severity and chronicity of heart failure symptoms, which outweigh the potential benefits of an ICD in this scenario.