A 58-year-old man with hypertension and diabetes presents with palpitations and dyspnea for 2 days. On examination, the pulse is irregularly irregular at 120 bpm, and BP is 148/92 mmHg. A 12-lead ECG shows absent P waves with an irregular ventricular rate and a baseline that appears to undulate. What is the investigation of choice to confirm the diagnosis and assess structural cardiac involvement?

## Investigation of Choice in Atrial Fibrillation **Key Point:** Transthoracic echocardiography (TTE) is the first-line imaging investigation in all patients with newly diagnosed atrial fibrillation (AF) to assess left ventricular function, atrial size, valvular disease, and structural abnormalities that may guide management. ### Role of Transthoracic Echocardiography 1. **Assessment of left ventricular ejection fraction (LVEF)** — critical for determining whether the patient has AF with preserved ejection fraction (AFpEF) or reduced ejection fraction (AFrEF), which guides choice of rate-control or rhythm-control strategy 2. **Atrial dimensions** — enlarged left atrium (>40 mm) predicts AF recurrence and guides anticoagulation intensity 3. **Valvular pathology** — detects mitral stenosis, mitral regurgitation, or prosthetic valves that may necessitate anticoagulation regardless of CHA₂DS₂-VASc score 4. **Structural abnormalities** — identifies cardiomyopathy, hypertrophic disease, or pericardial effusion 5. **Baseline assessment** — essential for monitoring response to therapy and detecting AF-related complications **High-Yield:** TTE is recommended as a Class I investigation in all newly diagnosed AF patients per ACC/AHA guidelines [cite:Harrison 21e Ch 226]. ### Why TTE is Superior to Other Modalities in Initial Workup | Investigation | Indication | Limitation in AF | | --- | --- | --- | | **Transthoracic echo** | First-line; all AF patients | Limited acoustic window in obese patients | | **Transesophageal echo (TEE)** | AF with thrombus risk; cardioversion planning | Invasive; reserved for specific indications | | **Cardiac MRI** | Detailed tissue characterization; arrhythmogenic substrate | Expensive; not first-line; contraindicated with pacemakers | | **Coronary angiography** | Acute coronary syndrome; ischemic evaluation | Not diagnostic for AF; reserved for CAD assessment | **Clinical Pearl:** In this patient with new-onset AF, rapid ventricular response, and hypertension, TTE will determine if there is underlying LV dysfunction (which would favor rate control with beta-blockers or diltiazem rather than flecainide) and assess for structural causes such as hypertensive heart disease or valvular disease. ### When TEE is Considered Transesophageal echocardiography is NOT first-line but is indicated when: - Planning cardioversion and need to exclude left atrial thrombus - Suspicion of endocarditis - Inadequate TTE images - Evaluation of complex structural disease **Mnemonic:** **STRUCTURE** — what TTE assesses in AF: - **S**ystolic function (LVEF) - **T**hrombus (LA appendage) - **R**ight ventricular function - **U**nderlying valvular disease - **C**hamber size (atrial dimensions) - **T**issue abnormalities - **U**nderlying structural disease - **R**egurgitation severity - **E**jection fraction trends