When do you require a crtd for a congestive heart failure patient? what is differences between crtd, crtp, crt, icd?

CRT: Cardiac re synchronization therapy is a pacemaker that corrects the loss of synchronization of both ventricles in CHF patients with marked intraventricular conduction delay. Because it is used in patients with low ef we often use it with defibrillator capability. Icd is a defibrillator device generally single chamber for patients who just need that function.