Diagnosing cardiac amyloidosis is challenging and requires a high index of suspicion in patients with an increased left ventricular wall thickness (LVWT). Low QRS voltage on electrocardiogram (ECG) has been regarded as the hallmark ECG finding in cardiac amyloidosis; however, the presence of low voltage can range from 20-74% and the voltage/mass ratio carries a greater diagnostic accuracy than QRS voltage alone. Patients with cardiac amyloidosis can have conduction system infiltration and this may result in a BBB. Therefore, the ECG or mass/voltage criteria established for patients with a narrow QRS in the diagnosis of cardiac amyloidosis may not be applicable in patients with a BBB. We sought to identify criteria to aid in the diagnosis of cardiac amyloidosis in patients with increased LVWT on echocardiogram and with a BBB on ECG. We calculated the total QRS score/LVWT, limb lead QRS score/LVWT, R in lead aVL/LVWT, R in lead I/LVWT, and Sokolow index/LVWT. In patients with an increase in LVWT and BBB, total QRS voltage that is indexed to wall thickness can help distinguish between patients with increased wall thickness who have cardiac amyloidosis from those who have LVH related to a pressure overload state. A unique index of Total QRS Score/LVWT is the best predictor of cardiac amyloidosis with a cutoff value of 92.5 mV/cm which is 100% sensitive and 83% specific for the diagnosis of cardiac amyloidosis. This may be a useful screening tool in patients with an increased wall thickness to raise diagnostic suspicion for cardiac amyloidosis.
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