T1 Troubles: Ironing Out Abnormal T1 Values in a Case of Infiltrative Cardiomyopathy

Description of Clinical Presentation: An 83-year-old woman with a history of heart failure with preserved ejection fraction and atrial fibrillation presented for elective pituitary tumor resection. On arrival, she reported progressive dyspnea on exertion. Physical examination revealed lower extremity edema, elevated jugular venous pressure, and decreased breath sounds at the lung bases. The surgery was postponed for cardiac optimization and diuresis. Laboratory testing demonstrated an elevated BNP (1470 pg/ml) and troponin (0.16 μg/L). Chest X-ray revealed bilateral moderate pleural effusions and pulmonary edema. Electrocardiogram (ECG) showed atrial fibrillation with LBBB. Transthoracic echocardiography (TTE) demonstrated a new global reduction in LV systolic function, with an EF of 40% and moderate concentric LV hypertrophy (LVH). Global longitudinal strain was reduced at –12.1% with apical sparing (Fig. 1). The patient was referred to CMR for evaluation of suspected cardiac amyloidosis.

Diagnostic Techniques and Their Most Important Findings: CMR cine images showed normal LV size with reduced systolic function and concentric hypertrophy, with maximal wall thickness of 13 mm, and LGE images demonstrated severe diffuse enhancement in a pattern consistent with cardiac amyloid (Fig 2). Myocardial native T1 mapping revealed unexpectedly normal myocardial native T1 (1132 ms), and a surprisingly low blood pool native T1 (1237 ms) (Fig. 3a). Post contrast T1 values were 433 ms and 406 ms for the myocardium and blood pool respectively (Fig. 3b). Notably the extracellular volume (ECV) was markedly elevated at 57%. Further laboratory evaluation demonstrated a paraprotein spike on serum protein electrophoresis, IgG lambda positivity on immunofixation, and an abnormally low kappa/lambda ratio (0.10). Diagnosis of cardiac amyloidosis was confirmed via fat pad biopsy which showed lambda AL amyloidosis.

Learning Points from this Case: The low blood-pool native T1 suggested the possibility that the patient had recently received intravenous (IV) iron supplementation, which was confirmed from the medical record. The administration of IV iron significantly reduced the Native T1 of the myocardium and blood-pool in this case resulting in a “normal” native T1 despite significant infiltration. Given the long half-life of IV iron, we assumed that its effect on T1 was constant on the time scale of the CMR exam, which allowed us to calculate the ECV assuming the additional T1 shortening post-contrast should be related to the Gd concentration as [Gd] = 1/R*(1/T1post-1/T1pre) where R is the relativity of the contrast agent. In this case, understanding the effect of IV iron on T1 values allowed the clinical team to appropriately pursue confirmatory testing, ultimately leading to the diagnosis of AL cardiac amyloidosis.

Fig 1. LV global longitudinal strain (GLS) demonstrating reduced values at -12.1%. In addition, LV GLS is relatively preserved at the LV apex in a pattern consistent with cardiac amyloidosis.
Fig 2. SSFP cine short axis images in end diastole demonstrating significant LV hypertrophy of the (A) (B) LV base, (C) LV mid cavity, and (D) (E) LV apex. The second row of images demonstrate short axis views with the presence of diffuse late gadolinium in the (F) (G) LV base, (H) LV mid cavity, and (I) (J) LV apex.
Fig 3. (A) Native T1 mapping of the LV base demonstrating a normal myocardial value of 1132ms and an unexpectedly low blood pool value of 1237ms (Acquired on a 3T machine). (B) Post-contrast T1 mapping of the LV base demonstrating a normal myocardial value of 433ms and blood pool value of 406ms. These myocardial values are inappropriately low for a patient with biopsy confirmed AL amyloidosis given concurrent use of supplemental IV iron.