For which condition is Combined CRT/ICD therapy shown to significantly reduce mortality?

Combined Cardiac Resynchronization Therapy (CRT) and Implantable Cardioverter-Defibrillator (ICD) therapy has been shown to significantly reduce mortality in patients who meet the criteria for both therapies. This population typically includes those with severe heart failure and a reduced ejection fraction, who also have a high risk of life-threatening arrhythmias.

The rationale behind this combination therapy is that CRT helps improve the heart's pumping efficiency by synchronizing the contractions of the heart chambers, while the ICD serves to prevent sudden cardiac death due to ventricular tachyarrhythmias. When used together, these interventions can lead to an overall improvement in patient outcomes, including reduced mortality rates.

In contrast, the other conditions do not specifically relate to the synergistic benefits of both CRT and ICD therapy. Patients who only partially meet the criteria or those without prior interventions may not experience the same level of benefit or mortality reduction as those who fully meet the stringent guidelines for both CRT and ICD therapy. Thus, option D correctly identifies the population in which the combined therapy is most effective.