The yearly number of invasive cardiac procedures is increasing. Since the first cardiac catheterization was performed in 1929 by Werner Forssmann of Germany, the number of annual percutaneous coronary interventions now well exceeds 500,000 cases per year in the United States and is estimated to exceed 1 million annual cases worldwide.1,2 During this generally familiar procedure, arterial access is obtained via percutaneous puncture of the femoral artery, with subsequent access to the coronary ostia. It may surprise some, however, that prophylactic temporary transvenous pacemakers are also employed for the reported 2% incidence of brady-dysrhythmias and atrioventricular blocks associated with percutaneous coronary intervention; and permanent pacemaker placement rates have also increased to an estimated 250,000 implantations per year.3,4
Typically, through a transvenous approach, a cardiac pacemaker lead is advanced into the right heart, and this procedure carries a small risk of transmural perforation, reported at approximately 1%.3,4 Although iatrogenic cardiac trauma associated with pacemaker placement requiring surgical repair has been reported at less than 1%, immediate diagnosis with prompt surgical intervention may be of vital importance to patient survival in cases with a potential for progression to cardiac tamponade.5 Although a specific cause of the iatrogenic damage may remain elusive, anatomic variations or abnormalities of the heart may play an underlying role in causation; and these sometimes subtle anomalies should be carefully searched for at autopsy. The identification of an anatomic variant that increases the risk of an iatrogenic injury may obviously have a significant impact on any potential litigation related to these procedures.
We report 2 cases of atrial endocardial injury and hemorrhage in the presence of an atrial anatomic abnormality. Both of these endocardial injuries occurred during cardiac pacemaker electrode insertion, 1 for temporary placement during cardiac catheterization and the other for permanent pacemaker placement.
This patient was a 52-year-old gentleman admitted for complaints of chest pain. An EKG showed inverted T waves in the inferior leads and a troponin level was elevated at 3.5 ng/mL. Diagnosis of a non-Q wave myocardial infarction was made and treatment with aspirin, lovenox, a beta blocker, and a proton pump inhibitor was begun. He subsequently underwent temporary bipolar electrode insertion, left ventricular angiography, left heart catheterization, and coronary angiography. There was complete occlusion of the right coronary artery. Also, 50% stenosis of the midleft anterior descending and 50% stenosis of the midfirst diagonal arteries were identified. A coronary thrombectomy with 5 passes was completed, and a coronary stent was placed in the midright coronary artery. Intracoronary ultrasound and an intravenous injection of platelet inhibitor followed. Hours later he developed recurrent chest pain and began requiring pressor support to maintain a systolic blood pressure above 90 mm Hg. He was returned to the catheterization laboratory for assessment. The right coronary artery stent was found to be widely patent with excellent antegrade flow. However, an echocardiogram showed a pericardial effusion with evidence of early tamponade. A pericardiocentesis was performed removing approximately 350 mL of bloody fluid. This resulted in marked improvement of the patient's blood pressure, and a pericardial drain was left in place. He was transferred to the intensive care unit and shortly thereafter was given pain medication for yet another episode of chest discomfort. A few hours later, the patient's heart rate fell below 60, and he was pale, cold, and unresponsive. A “code” was called, but cardio-pulmonary resuscitation was unsuccessful. An hour later, the patient was pronounced dead.
A significant finding at postmortem examination consisted of a lace-like veil of tissue spanning the region from the thebesian valve of the coronary sinus to the crista terminalis. Inferiorly, the net was firmly attached to the endocardium of the right atrial wall. At the base of this inferior attachment, there was a 1- to 2-mm hemorrhagic disruption of the endocardial lining surrounded by a large purple area of subendocardial hemorrhage (Fig. 1). Directly subjacent to the endocardial defect was a conspicuous extravasation of blood extending into the epicardial tissues. The hemorrhage extended around the adjacent circumflex artery and coronary sinus within the epicardial fat, and the hemorrhage continued through the epicardial surface, which was disrupted at the posterior aspect of the heart near the atrio-ventricular junction. Only 10 mL of blood remained in the pericardial sac, but the pericardial drain was attached to a bag containing 450 mL of bloody liquid. No other congenital abnormalities were identified. There was no dysplasia, fatty infiltration, or abnormal thinning of the right ventricular free wall. The midright coronary stent was widely patent, and the coronary atherosclerotic stenosis identified by catheterization was confirmed. No grossly obvious left ventricular myocardial lesions were identified.
Microscopically, there was a slight epicardial fibrinous surface exudate associated with an early acute inflammatory reaction. Left ventricular sections revealed mild myocardial hypertrophy. Also present in left ventricular sections were areas of focal interstitial myocardial hemorrhage, occasional wavy fibers, and a focal acute inflammatory infiltrate consistent with early infarction.
This patient was a 72-year-old woman who presented with back pain, left arm pain, and shortness of breath. She was diagnosed with an aortic dissection by computed tomography. The patient was admitted to the intensive care unit where an arterial line was placed, which showed highly variable blood pressures. She later developed rapid atrial fibrillation that was unresponsive to medical therapy. A transesophageal echocardiogram-guided cardioversion was performed with electrical cardioversion to sinus bradycardia. A few days later in this hospital course, the patient became more bradycardic, unresponsive, and was noted to be in pulseless electrical activity (PEA). Successful cardiopulmonary resuscitation (CPR) was performed. One day later, a second episode of atrial fibrillation occurred at which time a permanent right ventricular pacemaker was placed. The patient's condition did not improve and an additional episode of PEA occurred from which resuscitation was unsuccessful.
Important findings at postmortem examination included an intact type B aortic dissection and lipomatous hypertrophy of the interatrial septum and right atrial free wall. In the right atrium, directly overlying the lipomatous hypertrophy of the interatrial septum was a 3-cm area of recent subendocardial hemorrhage with a central 3-mm area of endocardial disruption, located between the fossa ovalis and the coronary sinus (Fig. 2). Grossly, the septum was bulging into the right atrial chamber, and it reached a maximum thickness of 1.3 cm on cut section. The hemorrhage was contained within the atrial septum and did not rupture into the pericardial sac.
Microscopically, the endocardial disruption (Fig. 3) was contiguous with a large area of hemorrhage, which dissected into the atrial septum. Overlying the disruption was adherent blood clot, fibrin, and granulocytes. The septum itself revealed typical features of lipomatous hypertrophy, including extensive infiltration by mature fat cells, collections of fetal (embryonic) fat cells, and somewhat bizarre hypertrophic myocardial nuclei.
Chiari's net, also called a Chiari network, or Chiari malformation, is a congenital remnant of the right valve of the sinus venosa.6 This congenital variant was first described in 1897 by Hans Chiari, who reported 11 cases in which there was a network of threads found within the right atrium. These threads were in connection with the thebesian valves at the orifice of the inferior vena cava and the coronary sinus. They also showed attachments to the upper region of the right atrium near the crista terminalis,7 and such Chiari nets have been reported to occur in 1.3% to 4.0% of autopsies.2 A recent study by Bhatnagar et al8 looking at 213 cadaver hearts and 11 fetuses during a 4-year period, found Chiari malformations in 13.6% of cadaver hearts and 10.5% of autopsied hearts.
Therefore, these delicate and inconspicuous networks are probably overlooked in some autopsies, considering their low incidence in routine autopsy reports compared with that of systematic studies.
Although generally considered to be of no clinical significance, Chiari nets have been reported in association with numerous complications. These complications have included thrombosis within the net, fragmentation of network fibers with pulmonary embolization, obstruction of cardiac blood flow, and entrapment of catheters during invasive procedures.8,9 The latter complication is documented in a German article by Muller, who reported 4 cases of traumatic lesions associated with central venous catheter placement. He reported that such endocardial injuries may occur due to horizontal fixation of the intracardiac portion of a catheter because of wall-adherent thrombus, a Chiari net, or coiling of the catheter within the atrium.9 Endocardial catheter injuries can induce cardiac arrhythmias and, in rare instances produce transmural perforation and cardiac tamponade. Such perforation of an atrium or ventricle with cardiac tamponade carries a mortality rate approaching 85%, commonly associated with a delay in recognition of the perforation.10
It is probable that the endocardial disruption in case 1 represents a complication of pacemaker insertion in which the pacemaker lead tip was diverted against the endocardium after being trapped within the Chiari network. The patient's anticoagulated state further contributed to subsequent hemorrhage into the epicardial tissue, which eventually resulted in cardiac tamponade and subsequent continuous bleeding into the pericardial sac after placement of the pericardial drain. Furthermore, the delicate strands of the Chiari network were overlooked during our initial autopsy examination, and the lesion was only identified after careful re-examination of the base of the heart after fixation.
Lipomatous hypertrophy of the interatrial septum was first described by Prior in 1964 who simply saw excessive deposition of fatty tissue in the interatrial septum.11 Since then, it has been referred to by many names such as “fatty infiltration,” “lipomatous hamartoma,” “cardiac and paracardiac masses,” and “massive fatty deposits.” Pathologically, the lesion is comprised of a nonencapsulated mass of adipose tissue, which includes both fetal and mature fat. The mass may be associated with fibrosis, inflammation, and entrapment of myocardial cells, which can exhibit a bizarre, sarcomatoid appearance but lack mitoses. Because small fatty deposits in the interatrial septum are fairly common, a minimum septal thickness of at least 1.0 cm has been suggested as a requirement for the diagnosis of lipomatous hypertrophy.12 Furthermore, the amount of septal fat has been shown to increase with age and obesity.13
The prevalence of lipomatous hypertrophy in autopsy material is approximately 1%, but the lesion is increasingly being diagnosed before death due to its unique characteristics on echocardiography, CT, and magnetic resonance imaging. Currently, the lesion is seen at a rate of 2% to 8% in echocardiography reports, suggesting that autopsy pathologists may not be carefully examining this region or appreciating the significance of these fatty deposits. Such a lesion can easily be missed if the septum is not incised, or at least palpated to appreciate its thickness. Although it may be difficult to prove that lipomatous hypertrophy is the cause of a sudden death, it has been accepted as a presumptive cause of serious arrhythmia and is associated with characteristic EKG findings.12,14 The lesion, when massive, has also been shown to cause right atrial obstruction.14 And additionally, lipomatous hypertrophy of the atrial septum is more common in patients with chronic obstructive pulmonary disease.14
We believe the endocardial disruption in case 2 was most likely caused by impact of the pacemaker lead against the bulging right atrial septum, because this region clearly protruded into the path of the advancing lead. The focal disruption was near the center of this protrusion, and the subendocardial hemorrhage was clearly tracking into the septum from this endocardial injury. Probably, this patient was able to clot over the endocardial injury, preventing transmural disruption with development of cardiac tamponade. The relationships between the septal hemorrhage, the lipomatous hypertrophy, and the patient's arrhythmias remain speculative.
In both of these cases, an abnormality of the right atrium probably caused alteration or deflection of the typical path taken by electrode/pacemaker wires through the right atrium and over the tricuspid valve into the right ventricle. This deflection resulted in pacer lead impact with the septal wall and disruption of the endocardial lining.
In case 1, this superficial disruption slowly progressed to cardiac tamponade and continued pericardial bleeding. Even though there was no actual tamponade at death, additional cardiac ischemia associated with the previous tamponade and continued hemorrhage probably played a role in his ultimate demise. The second patient was apparently able to clot over the area before dissection and rupture into the pericardial sac could occur, but she continued to experience serious arrhythmias. Both injuries were almost identical with respect to location and endocardial appearance.
In summary, we present 2 patients with atrial endocardial injury associated with cardiac pacemaker placements. In both cases, a structural abnormality of the atrium predisposed the patient to this unusual complication. The finding of such an anatomic lesion decreases the likelihood that medical negligence was a causative factor and may well decrease the probability of subsequent litigation. Furthermore, these atrial abnormalities were fairly subtle and could have been missed without careful dissection and re-examination. Such extra effort is recommended in cases of unusual complications associated with medical procedures. And finally, although imaging studies can potentially detect some of these atrial lesions, standard of care issues regarding screening for these abnormalities before pacemaker insertion is beyond the scope of this article.
The authors thank Rebecca A. Sager, MD, Baylor University Medical Center, Dallas, Texas, for her participation in the autopsy of case 2.
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