Cardiac ischemia is a condition that results from insufficient oxygenation to heart muscle and may pose an inherent risk in addition to potentially being a precursor to a life threatening event, such as myocardial infarction (MI). Detecting ischemia may be carried out by a variety of methods, some of which are amendable to implantable monitoring devices. Ischemia, and particularly, unstable ischemia, in a patient may be treated in a clinical setting by a variety of modalities.
A patient with severe unstable ischemia may be a candidate for immediate intervention, such as coronary angioplasty or bypass surgery. However, less severe cases may be treated by pharmaceutical methods as well as others. Even with such treatment modalities available, most ischemic events occur initially outside the clinical environment or at a place or time when such clinical assessment and treatment is not immediately available.
For ICD patients experiencing transient ischemia, standard ventricular pacing therapy in order to increase cardiac output is contraindicated as the increased heart rate induced as a result of the pacing will typically increase the oxygen demand on the heart tissue, and particularly the ischemic heart tissue, which may further exacerbate any damage caused by the ischemia. In addition, generally speaking, a paced rhythm is not as mechanically efficient as a normal sinus rhythm, and, as such, the blood flow output may even be further reduced. Thus, typical single chamber ventricle pacing therapy for an ischemic patient may increase oxygen demand of the heart tissue undergoing ischemic trauma and decrease the pumping efficiency of the heart overall or both.
As such, what has been needed are methods and devices for treating a patient with transient ischemia immediately after onset of the ischemia that do not generate a substantial increase in oxygen consumption by the heart.