Abstract
St-Elevation Myocardial Infarction (STEMI), commonly an acute, occlusive blood clot in a major epicardial coronary artery, is the most serious of heart attacks, carrying a significant mortality and morbidity, and opening the occluded artery quickly with good distal reflow is the goal for best clinical outcomes. Slow arrival of Emergency Health Services (EHS), a lack of Cathlab availability in underdeveloped and rural areas, poor performance and bleeding risks with thrombolytic drug therapy, and a high rate of poor microvascular re-flow regardless of therapy, have prompted searches for alternative or adjunctive treatments.
Mechanical forces or pressure waves imparted to the human body (herein described as “Acoustic Therapies”) have been well studied both in vitro and in catheter-based systems in their abilities to increase blood flow and disrupt and clear blood clots. However, the search for a non-invasive acoustic therapy suitable for first-line response in the treatment of acute thrombotic arterial occlusions, including STEMI, remains elusive. Indeed, due to the vast differences of acoustic penetration windows and variabilities of at-risk adjacent tissues, there has been a historic dilemma of “threading the needle” in finding a workable waveform and mode of delivery that is intense enough to provide adequate penetration with a clot-disruptive effect, while also avoiding harm to the patient.
STEMI victims who reach professional care in view of Primary Percutaneous Coronary Intervention (PPCI) or pre-hospital IV thrombolysis, reportedly have a ~ 4-10% resultant in-hospital mortality, with the number approaching 50% if complicated by cardiogenic shock, hence there remains room for improvement. Indeed, acoustic reperfusion for STEMI could foreseeably add particular value as a stand-alone therapy or adjunctive to IV thrombolysis in rural or relatively poor areas where a Cardiac Cathlab is not readily available, as an early warning and treatment system for STEMI patients awaiting EHS, and, importantly, for treatment of the infamous "No-Reflow phenomenon" following PPCI, where many solutions have been tried and failed.
This paper provides a history and commentary on the various forwarded non-invasive acoustic STEMI reperfusion strategies to date, including High Frequency diagnostic UltraSound (HFUS) with IV Microbubbles (MBs) - a technique commonly referred to as "Sonothrombolysis", transcutaneous Low Frequency Ultrasound (LFUS), and little-known diastolic timed Low Frequency Vibration (dtLFV), which involves palpable, infrasonic to sonic frequency percussions to the chest wall as a stand-alone measure, or as an adjunct to IV thrombolysis. A discussion is provided on each of these therapies' challenges, how they could fit in the modern paradigm of care, and where they are along their respective research and development pathways.