Our patient was having an uneventful and ordinary day. He got his children off to school, and spent the morning at the office completing paperwork. By noon he had eaten lunch, and went to the company workout center. It was Wednesday, so it was arms day. He started as he always did with 20 minutes of cardio on the elliptical machine, then shoulders, biceps, triceps, forearms — big muscle to small muscle. It was at the end of his first rep of triceps that things changed.
He felt some dizziness, and the nausea began within 30 seconds or so. He couldn't hold himself upright, and slouched sideways off the bench onto the ground, losing consciousness. Others had seen him slide to the floor, and tended to him immediately. He did not have a pulse, and chest compressions were started. Another person ran to get an AED, which advised a shock. A jolt of electricity and remarkably he had a pulse and regained consciousness.
He was brought by ambulance to the ED, and said he felt fairly well besides minor chest wall pain from the CPR. The patient didn't have exercise-related chest pain or chest tightness, and denied a sense of racing heart or palpitation prior to the event. He had not had any previous known cardiac history or previous exertional syncope. He had no family history of premature coronary artery disease, cardiomyopathy, or sudden cardiac death.
Vital signs and physical exam were unremarkable. A 12-lead ECG was obtained. (Figure 1.) The ECG shows sinus rhythm with some right axis deviation and nonspecific ST-T changes; otherwise no current of injury, infarction pattern, or ischemic changes were seen. QTc is not prolonged, and no Brugada pattern or evidence of Wolf-Parkinson-White are present.
Figure 1. 12-lead ECG on presentation to the emergency department.
An emergent transthoracic echocardiogram was performed, and a parasternal long axis view is shown in Figure 2. Left ventricular hypertrophy was present, systolic function was at the lower limits of normal, and he had a mild asynchronous kinesis of the septum. Most notably, he had an inferolateral wall motion abnormality, with a suggestion of thinned myocardium over the segment.
Figure 2a and 2b.
Watch videos of an emergent transthoracic echocardiogram in the parasternal long axis view here and here. Left ventricular hypertrophy was present, systolic function was at the lower limits of normal, and he had a mild asynchronous kinesis of the septum.
Myocardial segments with abnormal enhancement or wall motion disturbances are named and localized according to the 17 segments-model of the American Heart Association. In cross-section, the left ventricle can be divided into apex, mid, and basal sections, and then subdivided circumferentially. (Figure 3.) Individual myocardial segments can be assigned to the three major coronary arteries with the recognition that anatomic variability exists.
Figure 3. Left ventricle segment definitions.
Given the concern for coronary artery disease, coronary angiography was performed and showed no significant coronary artery disease. LVEDP was 20, and no evidence of gradient across aortic valve was seen. The initial working diagnosis was possible catecholaminergic polymorphic ventricular tachycardia (CPVT) because it followed intense exercise. Given the echocardiographic finding, this is likely to be scar-mediated, probably from previous silent myocardial infarction with possible recanalization. This can best be evaluated with a cardiac MRI. (Figure 4.)
Figure 4. Cardiac MRI.
One of the benefits of cardiac MRI is the ability to evaluate the myocardium’s response to Gadolinium contrast. The contrast is taken up in normal and injured myocardium, but it is washed out easily of normal tissue. There is a delay in eliminated the contrast in certain conditions (approximately 10-15 minutes), and is termed delayed enhancement.
The pattern of the delayed enhancement provides insight to the etiology causing the damaged myocardium. Ischemic cardiomyopathy is seen as ventricular dysfunction in a coronary artery distribution. Tissue involvement always progresses from the subendocardium through to full transmural thickness, depending on the extent of injury. Both acute and chronic myocardial infarctions demonstrated delayed enhancement. The contrast in acute infarctions enters the damaged myocardial cells through the leaky myocyte membrane, but in chronic infarctions the late enhancement is a result of retention of contrast in the fibrous interstitium. On the other hand, nonischemic myocardial disease usually does not occur in patterns consistent with a coronary artery distribution and often can be limited to midwall or epicardial regions. (Figure 5.)
Figure 5. Patterns of delayed enhancement on cardiac MRI.
Delayed enhancement can also identify two important features of ischemic myocardium: stunning and hibernation. Myocardial stunning can occur following an acute myocardial infarction despite restoration of coronary artery flow. The myocytes are dysfunctional, but can regain contractile function over time. The myocardial function is likely to improve if the delayed enhancement is less than 50 percent of the transmural thickness. Hibernating myocardium, however, occurs in chronic ischemic heart disease. Myocytes that are chronically deprived of oxygen can enter a low-energy sleep state; this is potentially reversible by revascularization. Hibernating myocardium can be identified on MRI as areas that do not enhance with contrast. The function is likely to improve after revascularization if the nonenhancing thickness is greater than 50 percent of the transmural thickness.
The cardiac MRI delayed images for our patient show an akinetic segment of marked myocardial thinning in the inferolateral wall of the mid left ventricle with near transmural delayed enhancement. (Figure 6.) This is consistent with sequelae of previous myocardial infarction, and indicates nonviable myocardium in this territory. There was no evidence for an acute or recent myocardial infarction.
Figure 6. Delayed image from patient’s cardiac MRI.
The patient later reported treating himself for heartburn several months before his cardiac arrest, which could have been an unrecognized acute coronary event that resulted in scarring. The cardiac arrest appears to be a primary arrhythmic event probably mediated by a myocardial scar. He was treated with aspirin, beta-blockade, ACE inhibitor, and high-intensity statin even in the absence of underlying obvious coronary disease based on the presence of myocardial scar and suspicious previous symptoms. An ICD was placed for secondary prevention of sudden cardiac death.