Clinical Vignette XIX

Which of the following mechanisms of the action best describes the medication most likely responsible for this patient’s presenting signs and symptoms

A 52-year-old male is evaluated in the Medtigo Medical Clinic for several weeks of slowly worsening dyspnea, non-productive cough, low-grade fever, and malaise. He denies any associated chest pain, arm pain, jaw pain, palpitations, near-syncopal episodes, fever, chills, or night sweats. The patient has no family history of early heart disease. He does not consume alcohol or use recreational drugs. He has a smoking history of 21-pack-years but quit five months ago after being hospitalized for three days due to chest pain and palpitations caused by sudden onset of recurrent episodes of non-sustained monomorphic ventricular tachycardia. During the hospitalization five months ago, the patient underwent a full cardiac workup which included a 2-D transthoracic echocardiographic imaging assessment, multiple 12-lead electrocardiographs, serial cardiac enzymes with various other blood tests, 24-hour telemetry monitoring, and an exercise stress test with single-photon emission computed tomography imaging. The transthoracic echocardiogram revealed an LVEF of 60% +/-5% with normal left ventricular and right ventricular size and systolic function, no structural abnormalities, no hemodynamically significant valvular disease, and no thrombi or vegetations. The serial cardiac enzymes and other blood tests were all within reference range. The exercise stress test with single-photon emission computed tomography imaging revealed no evidence of cardiac ischemia. The serial electrocardiographs were unremarkable. However, 24-hour telemetry monitoring revealed recurrent episodes of non-sustained monomorphic ventricular tachycardia which was finally controlled with amiodarone. Even though the medical team was unable to identify a primary etiology of the patient’s recurring episodes of non-sustained monomorphic ventricular tachycardia despite a thorough workup, the patient was subsequently discharged with a prescription for amiodarone since it proved highly effective at maintaining sinus rhythm. He was also scheduled to follow-up with a cardiac electrophysiologist. The rest of his medical history is notable for hypertension, hyperlipidemia, type 2 diabetes mellitus, and gout. His other current medications are lisinopril, hydrochlorothiazide, low-dose aspirin, rosuvastatin, metformin, and allopurinol.  

On physical examination, temperature is 98.9°F (37.2°C), blood pressure is 131/81 mm Hg, pulse rate is 92 beats/min and regular, respiration rate is 18/min, and oxygen saturation is 94% breathing ambient air. Body mass index is 24.4 kg/m². Cardiac exam reveals a normal S1 and S2. Pulmonary exam reveals diffuse rales bilaterally. The remainder of the physical exam is unremarkable.

ECG and chest radiographs obtained in the clinic reveal the following: 

ECG: Normal sinus rhythm, rate of 90 bpm, no significant ST-segment or T-wave abnormalities

PA/Lateral view chest radiographs: multiple patchy areas of interstitial infiltrates bilaterally

PA/Lateral view chest radiographs: normal (obtained 5 months ago)