Special Clinical Situations Right Ventricular Infarction

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In the SHOCK registry, the prognosis of patients with shock due to primarily left ventricular or right ventricular shock was similar (61 vs 54%) (283).

The initial management of patients with shock from right ventricular infarction involves administration of volume to augment right ventricular function and maintain adequate left ventricular preload. Venous dilatation with drugs such as nitroglycerin must be avoided. Volume loading alone may not optimize hemodynamic parameters. This may result from accentuated right ventricular distension and adverse ventricular interdependence effects. The use of inotropic agents, such as dobutamine, have been reported to increase the cardiac output in this situation (284).

Maintenance of right atrial contraction is important and may require AV sequential pacing or cardioversion of arrhythmias. Intra-aortic balloon counterpulsation should be employed with persistent hypotension, especially in the presence of multivessel coronary artery disease. Percutaneous cardiopulmonary bypass, right ventricular assist devices, and pulmonary artery counterpulsation have also been utilized (50).

Revascularization therapy has been shown to improve the hemodynamic status and outcome of patients with right ventricular infarction (283,285,286). Bowers et al. (285) reported a series of 53 patients with acute right ventricular infarction who underwent primary angioplasty. In patients with successful complete reperfusion of the right main coronary artery and major right ventricular branches, marked improvement in right ventricular function occurred. Unsuccessful reperfusion resulted in more frequent hypotension and low cardiac output (83 vs 12%, p = 0.002) and a higher mortality (58 vs 2%, p = 0.001) than in those with successful reperfusion.

Acute Ischemic Syndromes without ST-Elevation

In two large trials evaluating patients with non-ST-elevation acute coronary syndromes, cardiogenic shock developed 2.5% of patients (91,287). In both the SHOCK registry and GUSTO lib trial, patients developing shock without ST-elevation were older and had more frequent comorbid factors, including more prior infarction, congestive heart failure, and bypass surgery compared to shock patients with ST-elevation (95,287). The onset of shock in the GUSTO-IIb trial was significantly later (76.2 vs 9.6 h, p < 0.001) in patients without ST-elevation (287).

Although mechanical causes of shock are uncommon in this setting, the pathogene-sis of this syndrome is heterogeneous. Compared with ST-elevation infarction, recurrent ischemia and reinfarction are more common. Triple vessel disease is significantly more likely. The left circumflex coronary artery is more frequently identified as the culprit artery (95,287). It is known that total occlusion of the left circumflex artery may occur without ST-elevation on a standard 12-lead ECG (288).

Despite typically smaller infarctions in patients with shock secondary to non-ST-elevation infarction, the outcome is similar to patients with ST-elevation. In the SHOCK registry, hospital mortality occurred in 62.5% with non-ST-elevation compared with 60.4% of ST-elevation infarction (95). The 30-d mortality of patients without ST-elevation in the GUSTO-IIb trial was actually higher than with ST-elevation (72.5 vs 63%, p = 0.05) (287).

The role of revascularization for patients with shock secondary to non-ST-elevation syndromes remains uncertain (95). In the PURSUIT trial, the 30-d mortality was lower in patients who received eptifibatide (58.2 vs 73.5%,p = 0.02) (91).

The Elderly

Approximately 85% of deaths from myocardial infarction occur in patients >65 yr (289). The senescent cardiovascular system has a reduced capacity to compensate for myocardial injury sustained during infarction (290,291). In the GUSTO-I trial, older age is the variable most strongly predictive of the development of shock and 30-d mortality with shock (79,292).

The advantage of primary angioplasty over thrombolysis is magnified in the elderly (293). However, in the SHOCK trial patients >75 yr in the early revascularization group had a higher mortality at 30 d compared to those assigned to medical stabilization (53

vs 75%) (6). Echocardiographic data accumulated during the trial suggested that elderly patients in this small cohort (n = 56) had a significant excess of low ejection fractions and remote zone hypokinesis at randomization compared to younger patients (294). In contrast, in the SHOCK registry, there was an apparent survival benefit for those aged >75 yr who were clinically selected for early revascularization (4,295).

A decline in hospital fatality rate was noted for elderly patients (>65 yr) over time in the Worcester Heart Attack Study. Early revascularization was an independent predictor of hospital survival (296). The excess mortality and complex comorbid status in the elderly patient with cardiogenic shock impedes definition of the expected advantages of revascularization. Further investigation is necessary to refine selection for therapy in this high risk group.

Prior Coronary Bypass Surgery

Patients presenting with infarction and previous coronary bypass surgery are older and have more extensive coronary artery disease, worse left ventricular function, and more associated comorbidities (297,298). In the GUSTO-I trial, patients with prior CABG exhibited a higher 30-d mortality (10.7 vs 6.7%, p < 0.001) and more cardiogenic shock (9 vs 5.8%, p < 0.001) (299). Although angioplasty was performed on equivalent proportion of patients with (26.5 vs 29.6%) and without prior bypass surgery in the SHOCK registry, very few patients in the latter group underwent repeat bypass surgery (300). There was a reduction in mortality associated with revascularization in the prior bypass surgery group (56.5 vs 84.45, p = 0.018) similar to those without prior surgery (44 vs 80%,p < 0.001). Revascularization should be considered for cardiogenic shock in patients with prior coronary bypass surgery.

The Left Main Shock Syndrome

As one might expect, the extensive myocardial insult resulting from left main coronary artery occlusion is characterized commonly by a dramatic presentation and a substantial hemodynamic derangement. The timing of shock onset and mortality related to the culprit infarct vessel is depicted in Table 1 (17,18). The rapid onset of shock is associated with widespread ST-elevation, especially associated with ST-elevation in a VR (94).

Quigley et al. (301) reported a 94% mortality for the "left main shock syndrome" (acute anterior infarction, severe left main stenosis, and cardiogenic shock) and suggested that conservative therapy may be indicated in this subset. Although infarction and shock arising from left main obstruction is often a catastrophic event, several reports have demonstrated survival with an aggressive approach including emergency catheter-ization and revascularization with either surgery and/or transluminal revascularization (302-304).

Shock and Mechanical Complications of Myocardial Infarction

Ventricular Septal Rupture

Cardiogenic shock associated with rupture of the interventricular septum is a highly lethal event. In the shock registry (n = 55) the hospital mortality was 87% (69). Risk factors for this complication include advanced age, female gender, hypertension, and lack of previous infarction (63,69).

Intra-aortic balloon counterpulsation may stabilize the patients' hemodynamic status (137), but the potential for sudden decompensation remains (305). Previous data suggested a lower operative mortality when surgery was delayed. However, a deadly selection process occurs with a substantial proportion of patients unable to survive until a late operation. Early surgical repair is a necessary strategy. Very few patients in cardiogenic shock survive without surgery (57,69,305). In the SHOCK registry, mortality was reduced with surgery (81 vs 96%) (69). Other surgical reports suggest better outcome (306,307), but preoperative cardiogenic shock is a predictor of operative mortality (308,309). Patients with inferior infarction and posterior septal rupture have an increased mortality due to more complex defects and extensive right ventricular involvement (63,69,71). Recently, successful closure of postinfarction septal defects has been reported with transcatheter septal occluder devices (310-313). Future trials will clarify the role of these devices in the management of this lethal complication (314).

Papillary Muscle Dysfunction or Rupture

Acute severe mitral regurgitation resulting in shock during myocardial infarction is also likely to resultant in death without prompt surgical intervention (315-317). In the SHOCK registry, patients with this complication were more likely female (52 vs 37%, p < 0.004) and were less likely to exhibit ST-elevation (41 vs 63%, p < 0.001) compared to shock due to left ventricular failure (318). Shock developed at a median of 12.8 h after onset of the infarction.

As with septal rupture, intense medical therapy and balloon pump support may stabilize the patient, but the prognosis is poor without surgical intervention (137). Again, surgical delay often leads to rapid clinical deterioration and death. Early surgery is recommended (319). Several series have documented success with this approach (92,320). In the SHOCK registry, mortality was lower with early (16.6 h) surgery (318). Valve repair without replacement was possible in 6 out of 42 patients. A few patients with papillary muscle dysfunction have been treated successfully with angioplasty (321,322). However, this approach must be taken cautiously. Tcheng et al. reported higher mortality with angioplasty compared with medical or surgical treatment (323). In the SHOCK registry 9 patients were treated with angioplasty and 6 died (318).

Free Wall Rupture

Free wall rupture of the left or right ventricle is commonly a fatal event. Risk factors include advanced age, female gender, hypertension, and less prior infarction (60,324,325).

Patients identified by electromechanical dissociation requiring ongoing cardiopulmonary resuscitation have rarely survived, although a few successful surgical cases have been reported (253). Surgical results in subacute rupture are more favorable (50% survival) (67,326,327). Hemodynamic improvement may occur through the maneuvers of volume administration, inotropic agents, and pericardiocentesis, allowing stabilization for transfer to the operating room. Medical management of selected patients with left ventricular free wall rupture has been reported by Figueras and colleagues (328). Survivors (15 out of 19) were successfully treated with intravenous volume and dobutamine and survived with subsequent bedrest and b-blocker administration. A method utilizing pericardiocentesis, followed by injection of "fibrin glue" (composed of fibrinogen, Factor XIII, and aprotinin) in the pericardial space, has also been reported to successfully

Fig. 7. The modem strategic approach to cardiogenic shock. IABP, intra-aortic balloon pump; CABG, coronary artery bypass graft surgery; PCI, percutaneous coronary intervention.

treat this complication (329). Thus, survival is possible through cautious medical management in some patients who recover from the initial tamponade.

In the SHOCK registry, 28 patients (2.7%) presented in shock with free wall rupture or tamponade (327). Nearly all (27 out of 28) patients were treated with surgical repair (n = 21, 38% survival) or pericardiocentesis (n = 6, 50% survival). Rapid diagnosis with echocardiography in patients with shock is an essential component in the management of patients with free wall rupture.

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