This invention relates generally to the field of cardiovascular medicine, and in particular to the treatment of patients suffering from a spectrum of cardiac states, ranging from shock to pulseless electrical activity, in which the patient appears to be lifeless and in cardiac arrest yet retains some mechanical activity in the myocardial wall motion.
One common technique for treating persons suffering from cardiac arrest is the use of cardiopulmonary resuscitation (CPR). In this procedure, the patient's chest is repeatedly compressed, often in combination with periodic ventilations. Administration of electrical countershock and drugs intended to assist in restoration of cardiopulmonary function to chest compression and ventilation, constitutes advanced life support. For a variety of reasons, the effectiveness of CPR has been limited. Hence, devices or techniques which can improve the effectiveness of CPR are greatly needed.
In additional to sudden cardiac arrest, refractory-shock (which is referred to herein as “shock”) is often fatal. For example, if not properly stabilized, a person suffering from shock can progress into cardiac arrest, which, because it is not sudden in nature, is usually fatal. Emergency medicine and critical care practitioners approach the treatment of shock principally by attempting to alleviate the cause because there are no non-invasive techniques that may beneficial in assisting circulation. Hence, devices and techniques are also needed to treat those suffering from refractory shock and shock that is progressing toward cardiac arrest.
There is no general consensus as to when it is the appropriate to start administering CPR as the patient's blood pressure progressively decreases. This relates to a lack of demonstrated efficacy and concern that chest compression may interfere with residual cardiac function, even though CPR may at some point be beneficial in shock patients as they progress to cardiac arrest. Hence there a need for a device or technique to prevent CPR from interfering with residual cardiac function.
Unlike cardiac arrest caused by ventricular fibrillation, pulseless electrical activity (PEA) is a heterogeneous entity with respect to cardiac function and hemodynamics. PEA is a clinical condition characterized by unresponsiveness and lack of palpable pulse in the presence of organized cardiac electrical activity. Pulseless electrical activity has previously been referred to as electromechanical dissociation (EMD). During PEA, electrical activity of the heart may or may not be indicative of cardiac mechanical movements and particularly cardiac output.
Pulseless electrical activity is not necessarily a condition of complete mechanical quiescence in the heart. In PEA, the heart may have a regular organized electrical rhythm such as supraventricular or ventricular rhythms. These cardiac rhythms may not be associated with mechanical activity of the heart in PEA.
As an example of cardiac mechanical patterns during PEA, patients may have weak ventricular contractions and detectable aortic pressure—which is a condition referred as pseudo-PEA. Various studies have documented that between 40-88% of patients with PEA had residual cardiac mechanical activity (pseudo-PEA). In pseudo-PEA, the patient may appear lifeless and without a pulse, despite some degree of residual left ventricle function and hemodynamics. The outcome of patients suffering PEA has tended to be worse than those in ventricular fibrillation, possibly reflecting the potential of CPR chest compressions and residual myocardial mechanical activity to interfere with each other's efficacy. Hence there is a need for a device or technique to enhance the efficacy of CPR in PEA.