59 THE SHARK-FIN THAT EMERGES AND IMMERGES: A CASE REPORT OF TRANSIENT AND RIPETITIVE TRIANGULAR QRS-ST-T.
Authors: Valcher Stefano , Alessandro Villaschi , Letizia Bertoldi , Martina Briani , Elena Corrada , Mauro Chiarito , Condorelli Gianluigi 
Published: December 2022

Abstract

Introduction
Shark fin sign, also known as triangular QRS-ST-T waveform (TW), is characterized by a giant R wave (amplitude ≥ 1 mV) resulting from the fusion of the QRS complex, the ST-segment and the T wave and showing triangular morphology. TW pattern is quite uncommon and reveals a life-threatening condition that needs aggressive management. Early recognition is important to prevent acute complications such as ventricular arrhythmias and cardiogenic shock.

Case presentation
A 45-years old black man with history of arterial hypertension presented with out-of-hospital cardiac arrest (OHCA) at his workplace. Extracorporeal cardiopulmonary resuscitation started immediately and return of spontaneous circulation occurred after 11 minutes and 2 DC shocks. Then he was transferred to our emergency department (ED). At arrival he was hemodynamically stable, ECG showed atrial fibrillation without any repolarization abnormalities and echocardiogram revealed left ventricular hypertrophy (IVS 12mm, PW 12mm) and normal biventricular function. Normal electrolytes and high-sensitivity troponin level of 14 (n.v. 0.01-19.8 ng/L) were found at the blood test. Sedation in the ED was needed due to psychomotor agitation. He was then transferred to the CCU where spontaneous cardioversion to sinus rhythm occurred, and no additional arrhythmias were noted at continuous ECG monitoring. After ten hours, while the patient was still under sedation, ECG monitoring revealed a progressive QRS-ST segment elevation in inferior leads up to a triangular QRS-ST-T giant waveform (“Shark fin sign”), without hemodynamic deterioration. After approximately 3 minutes the ECG showed a progressive and complete regression to a normal waveform. An emergent beside echocardiogram demonstrated inferior wall hypokinesia, but normal pump function. The episode repeated 5 more times in the following hour, waiting for cath lab personnel. Coronary angiography revealed a sub-occlusive mid RCA stenosis without any thrombotic lesion. Percutaneous coronary intervention (PCI) with the implantation of one drug eluting stent (DES) was performed. After the procedure the patient was hemodynamically and electrically stable. ECG did not show any other abnormality and no episodes of recurrent ST-elevation occurred. Sedation was suspended and no focal neurological deficits were noted.

Discussion
Shark fin sign is the expression of abrupt total deprivation of blood flow in large areas of myocardium that cause massive slowing of transmural electrical conduction. These electrical differences may be at the base of the triangular R waves and predispose to VF induction and cardiogenic shock. This sign is very rare, with an annual incidence of 0.7% in patients admitted for STEMI, and in most of the cases is described in the occlusion of the LAD.
In our case we assisted to transient but repetitive inferior triangular ST-elevation with complete regression to normal ECG. The coronary angiogram showed non-obstructive lesion of the RCA. This phenomenon was probably the expression of RCA's plaque coronary vasospasm that caused the ECG shark fin sign and cardiac arrest.

Conclusion
Shark fin electrocardiographic waveform is an uncommon pattern of STEMI and may be the expression of thrombotic coronary occlusion as well as massive coronary vasospasm. This sign correlates with high risk of cardiogenic shock, electrical instability, and cardiac arrest, thus requiring prompt and aggressive management.