Ahsan T. Ali

Evidence for Improved Cerebral Function After Minimally lnvasive Bypass Surgery

Abstract Background: Neurological impairment is a major cause of morbidity after cardiac surgery and may be associated with occurrence of cerebral microemboli generated during cardiopulmonary bypass (CPB). This study evaluates cerebral dysfunction following coronary artery surgery on‐pump and off‐pump. Methods: Neurological outcome was evaluated in 322 patients with a coronary artery bypass graft (CABG). Conventional CPB was used (on‐pump) in 305 patients and in 17 patients no CPB was used (off‐pump). Intraoperatively, a pulsed‐wave transcranial Doppler with a 2‐MHZ probe measured high‐intensity transient signals (HITS) by ultrasonic insonnation of the middle cerebral artery indicating the presence of emboli within the vessel lumen. Transcranial near‐infrared spectroscopy measured cerebral venous oxygen saturation for adequate perfusion. Postoperatively, all patients were subjected to the antisaccadic eye movement (ASEM) test, a sensitive indicator of neurocognitive deficits secondary to frontal lobe dysfunction. Results: While there was no significant difference in O2 saturation, the number of microemboli HITS generated was significantly higher in the on‐pump group than the off‐pump group. In the off‐pump group, 16 (94%) of 17 patients had perfect scores on the ASEM test, while only 108 (35.4%) of 305 patients achieved a perfect score in the on‐pump group (p < 0.01). Furthermore, while all patients in the off‐pump group achieved at least 90%, 28% (86/305) in the on‐pump group scored “zero” on the ASEM test. Conclusion: Cerebral dysfunction as evidenced by ASEM errors is common following coronary bypass on‐pump, but rare with off‐pump bypass surgery. Cerebral microemboli generated during CPB may account for this difference. (J Card Surg 1998;13:27–31

Transthoracic ultrasonography is an alternative to subxyphoid ultrasonography for the diagnosis of hemopericardium in penetrating precordial trauma

BACKGROUND Surgeon-performed ultrasonography is increasingly becoming part of the initial evaluation of patients after blunt or penetrating trauma. Currently, most institutions obtain a subxyphoid or subcostal view of the heart and pericardial space, and a three-view ultrasonogram of the abdomen to detect blood in the pericardial sac or in three dependent abdominal areas. METHODS A left parastemal standard transverse transthoracic view is described in addition to the aforementioned views. This facilitates the visualization of the pericardial sac when a subxyphoid or subcostal view cannot be obtained because of anatomical reasons (narrow subxyphoid space) or local factors (pain, fractures, subcutaneous emphysema, or chest wall contusion). RESULTS The transthoracic view can be useful in patients where the subxyphoid view is difficult to obtain through the conventional approach. In most patients an excellent view of the pericardial sac and ventricles can be obtained and, therefore, expedites the diagnosis and treatment of patients with hemopericardium. CONCLUSION Surgeon-performed ultrasonography has become the diagnostic test of choice for patients suspected of having hemopericardium and cardiac tamponade. Transthoracic ultrasonography is an excellent alternative for those patients where a subxyphoid or subcostal view to visualize the pericardial sac and heart cannot be obtained owing to local or anatomical factors.

Vascular delay of the latissimus dorsi provides an early hemodynamic benefit in dynamic cardiomyoplasty.

OBJECTIVES Dynamic cardiomyoplasty (CMP) as a surgical treatment for chronic heart failure improves functional class status for most patients. However, significant hemodynamic improvement with latissimus dorsi muscle (LDM) stimulation has not been consistent. The current protocols do not allow early LDM stimulation after CMP surgery. We hypothesized that vascular delay of LDM would increase myocardial assistance after CMP and allow early (48-h) LDM stimulation after CMP. METHODS Mongrel dogs (n = 24) were divided in four groups: 1) controls (n = 6), single-stage CMP; 2) Group ES (n = 6), single-stage CMP with early LDM stimulation beginning 48 h, postoperatively; 3) Group VD (n = 6), vascular delay of the LDM followed by CMP without early LDM stimulation, and 4) Group VDES (n = 6), vascular delay of LDM (14-18 days), followed by CMP with early stimulation (48 h postoperatively). Two weeks after CMP, global cardiac dysfunction was induced by injecting microspheres into the left coronary artery. LDM-assisted (S) beats were compared with nonstimulated beats (NS) by measuring aortic pressure (AoP), LV pressure, aortic flow, and by calculating first derivative of LV contraction (+/-dP/dt), stroke volume (SV), and stroke work (SW). RESULTS In ES, LDM stimulation had no effect on the hemodynamic parameters. In the other groups, LDM stimulation significantly (p < 0.05) increased AoP, LVP, dP/dt, SV, and SW. However, these increases were much larger in VD and VDES. In VD, LDM stimulation increased peak AoP by 21.5+/-3.8 mm Hg, LVP by 22.1+/-4.1 mm Hg, dP/dt by 512+/-163 mm Hg/sec, SV by 10.4+/-2.3 mL, and SW by 22.1+/-5.4 g/m(-1). Similarly, in VDES, LDM stimulation increased peak AoP by 24.1+/-4.7 mm Hg, LVP by 26.2+/-4.3 mm Hg, dP/dt by 619+/-47 mm Hg/sec, SV by 6.5+/-0.7 mL, and SW by 16.7+/-4.1 g/m(-1). CONCLUSIONS In dogs with global LV dysfunction, CMP after vascular delay resulted in a significant improvement in hemodynamic function measured 2 weeks after surgery. This improvement was not provided by single-stage CMP with or without early stimulation. Vascular delay of the LDM before surgery may play an important role for early benefit after CMP, shorten the overall muscle training period, as well as increase hemodynamic response to LDM stimulation.

Vascular delay and intermittent stimulation: keys to successful latissimus dorsi muscle stimulation

BACKGROUND The goal of this study was to obtain physiologically significant increases in peak left ventricular (LV) systolic pressure and stroke volume with latissimus dorsi muscle (LDM) stimulation in cardiomyoplasty (CMP). We hypothesized that preserving LDM integrity by vascular delay and intermittent stimulation would significantly increase LDM cardiac assistance. METHODS In 4 control dogs and 12 dogs that had undergone a vascular delay (VD) procedure, LV dysfunction was induced by intracoronary microsphere injections. Cardiomyoplasty surgery was performed 14 days later, followed by progressive LDM conditioning. In the control dogs and in 6 of the VD dogs, the LDM was stimulated 24 hours per day (VD plus constant stimulation [CS]). In the other 6 VD dogs, LDMs were stimulated on a daily schedule of 10 hours on and 14 hours off (VD plus interrupted stimulation [IS]). Latissimus dorsi muscle stimulated beats were compared with nonstimulated beats 9 weeks later. RESULTS In the control dogs, LDM stimulation had minimal effects. In VD + CS and VD + IS, LDM stimulation increased peak LV pressure, stroke volume, stroke work, and stroke power (p < 0.05). However, these changes were greater in the VD + IS group, in which LDM stimulation increased peak aortic pressure by 17.6 +/- 1.7 mm Hg, peak LV pressure by 19.7 +/- 1.1 mm Hg, peak positive LV dp/dt by 398 +/- 144 mm Hg per second, stroke volume by 5.1 +/- 0.7 mL, stroke work by 10.9 +/- 0.9 gm.m, and stroke power by 122.7 +/- 11.6 gm.m per second (p < 0.05 compared with VD + CS). Quantitative morphometric analysis showed minimal LDM degeneration in the VD + IS group (7.5% +/- 1.1%), and VD + CS group (10.5% +/- 4.5%) compared with the control group (29.5% +/- 4.5%, p < 0.05). CONCLUSIONS VD and IS considerably increased the LV assistance with LDM stimulation. Further studies of this combined approach to CMP should be planned.

Preconditioning of the latissimus dorsi muscle in cardiomyoplasty : vascular delay or chronic electrical stimulation

OBJECTIVES In standard single stage cardiomyoplasty (CMP), the latissimus dorsi muscle (LDM) is not preconditioned prior to surgery. We hypothesized that latissimus dorsi preconditioning by vascular delay or by chronic electrical stimulation would result in an improved LV hemodynamic function early (14 days) after CMP. METHODS Mongrel dogs had preconditioning of the latissimus dorsi by a vascular delay procedure followed by CMP 14-18 days later (group I VD). Dogs in group II underwent 4 weeks of chronic stimulation (CS) of the latissimus dorsi (2 V/30 Hz, six bursts/min) followed by CMP. The latissimus dorsi muscle was fully stimulated from 48 h after cardiomyoplasty in both groups (2 V/30 Hz, three bursts/min). Two weeks after myoplasty, injecting 2.0-3.0 x 10(5) 90 microm latex microspheres in the left main coronary artery induced global cardiac dysfunction. Hemodynamic function was then evaluated for latissimus dorsi muscle assisted (S) beats and non-stimulated beats (NS) in each group by measuring peak systolic aortic pressure (AOP), left ventricular pressure (LVP) and end diastolic pressure (LVEDP), and by calculating maximum and minimum dP/dt. RESULTS Dogs with vascular delay of the latissimus dorsi showed a marked increase for all hemodynamic indices (AOP: 23.9+/-2.5%, LVP: 23.5+/-2.2%, max dP/dt: 49.4+/-3.3%) for LDM assisted (S) beats compared to non-stimulated beats (P < 0.001). Animals with chronic electrical training did not demonstrate a significant increase in any hemodynamic parameter with LDM stimulation. CONCLUSION Preconditioning the LDM may play an important role in providing early cardiac assistance in CMP. Preconditioning the LDM with vascular delay resulted in improving performance of the LDM with consistent increases in LV hemodynamics. This was not observed after preconditioning with chronic electrical stimulation. Vascular delay of the latissimus dorsi can significantly improve muscle performance in CMP and could provide hemodynamic assistance early after surgery.

Evaluation of the long-term effectiveness of extraluminal and intraluminal vasodilators in an in vitro porcine model of arterial graft spasm.

OBJECTIVE Postoperative graft spasm is a concern when arterial conduits are used because there may be insufficient arterial graft flow. Intraoperatively, vasodilators are used to increase flow and prevent spasm, but little is known about their duration of effectiveness. METHODS To examine this we attached porcine gastroepiploic and internal thoracic arteries (GEA, n = 48; ITA, n = 24, 10-12 cm long) to a computer-controlled perfusion system (constant inflow pressure 80 mm Hg) with a fixed outflow resistance. Norepinephrine (10(-9)-10(-5) M) was incrementally added to the perfusate at baseline (B), then immediately (h+0) and 2 h (h+2) after the vessels were treated with 30 min of extraluminal or intraluminal nitroglycerin, nitroprusside, verapamil or papaverine. RESULTS At (B), norepinephrine caused a dose-dependent decrease in flow in both the ITAs and GEAs. In the ITAs, at (h+0), both extraluminal and intraluminal papaverine and, to a lesser extent nitroprusside, increased initial flow and decreased graft sensitivity to norepinephrine. At (h+2), only extraluminal papaverine sustained this maximal effect (ED50 for extraluminal papaverine at (B) 2.6 E(-7) vs. (h+2) 1.3 E(-6), P = 0.01). For the GEAs, at (h+0), both extraluminal and intraluminal verapamil, papaverine, nitroprusside and nitroglycerin attenuated flow reduction due to norepinephrine. At (h+2), only extraluminal papaverine, extraluminal verapamil and intraluminal verapamil were effective in preventing norepinephrine-induced spasm (ED50 for extraluminal papaverine at (B) 1.0 E(-7) vs. (h+2) 6.4 E(-6) (P = 0.004); extraluminal verapamil at (B) 1.2 E(-7) vs. (h+2) 4.0 E(-6); intraluminal verapamil at (B) 5.8 E(-7) vs. (h+2) 5.7 E(-6), P = 0.005). CONCLUSION Verapamil-and papaverine-treated arteries have a greater duration of efficacy in resisting spasm than arteries treated with nitroglycerin and nitroprusside. In the ITA, extraluminal administration of papaverine is most efficacious, possibly due to the prolonged exposure afforded by this route of administration. The effects of verapamil and papaverine are more prolonged in the GEA when administered extraluminally, potentially due to absorption in the perivascular fat-pad and subsequent slow release. The results of this study suggest that extraluminally administered verapamil and papaverine appear to be the preferred vasodilators for preventing arterial graft spasm in the postoperative period. This may be especially important when multiple arterial grafts are used.

Diagnosis of Cardiac Injuries by Surgeon-Performed Ultrasound: a Safe and Expeditious Alternative for Suspected Cardiac Injuries

Surgeon-performed ultrasound continues to evolve as a useful, safe, and efficient diagnostic alternative to document the presence of hemopericardium in patients sustaining penetrating injuries to the precordial region. With growing experience, its excellent sensitivity and specificity in the identification of cardiac injuries have become evident. As ultrasound for blunt abdominal trauma has been able to eliminate unnecessary diagnostic peritoneal lavages, its use in the evaluation of penetrating precordial injuries holds the promise to expedite the diagnosis of cardiac injuries and eliminate unnecessary pericardial windows and their associated morbidity.Ultrasound was performed by surgeons-in-training with supervision by a trauma surgeon at a Level-I trauma center in patients sustaining penetrating injuries to the precordial area.During the review period, 34 patients underwent precordial ultrasound (22 negative, 9 positive and 3 equivocal). There were no false-positives or false-negatives. All equivocal results were followed by a subxiphoid pericardial window that demonstrated no evidence of cardiac injury.Based o these data, we recommend that surgeon-performed ultrasound replace all other clinical, radiologic, and surgical diagnostic alternatives classically used to determine the presence of hemopericardium in stable patients with penetrating precordial injuries. Ultrasonography is fast, reliable, consistent, and easy to teach and learn. In those few patients with equivocal findings, other confirmatory diagnostics modalities should be entertained.

What in-vitro method should surgeons use to evaluate the clinical behavior of arterial bypass conduits.

UNLABELLED Surgeons have traditionally relied on ring preparations to predict how arterial bypass conduits will behave in the postoperative circulation. OBJECTIVE This study compared pharmacologic [norepinephrine (NE) challenge] and physiologic [arterial preload] responses of gastroepiploic (GEA) and internal thoracic (ITA) arteries in a standard static ring preparation and a dynamic perfusion system. METHODS Six GEAs (1.0-1.5 mm dia.) and six ITAs (1.5-2.0 mm dia.) 11 cm long were harvested from adult pigs and mounted on a computer controlled perfusion system. Inflow pressure was set at 80 mmHg and outflow resistance was adjusted to simulate high (80-90 ml/min) and low (15-20 ml/min) flow demands. NE response (10(-9)-10(-5) M) was measured under low flow conditions and at high flow conditions when distal arterial pressure (load) was reduced. NE response (10(-9)-10(-5) M) was also evaluated in arterial rings (ITA N = 6, GEA N = 6) with tensions adjusted to simulate the loads occurring at low flow (80 mmHg) and high flow (60 mmHg) situations. RESULTS In the static ring preparation, NE response [ED50] was similar for both GEA and ITA and was not affected by load. The dynamic preparation demonstrated that the GEAs were significantly more responsive to NE than the ITAs [ED50 high flow ITA 6.1 +/- 0.3**, GEA 7.2 +/- 0.3***; *P < 0.05 versus baseline, **P < 0.05 versus low flow values, ***P < 0.05 versus ITA]. Furthermore, in the dynamic preparation, NE response was profoundly affected by reduced load which occurs under high flow conditions [7.18 +/- 0.3 versus 6.1 +/- 0.3 under high flow and 5.8 +/- 0.1 versus no response under low flow conditions]. CONCLUSION Static ring preparations do not discern differences between ITA and GEA susceptibility to spasm and fail to detect the effect of load. The dynamic preparation demonstrated significant differences between the GEA and ITA potential to spasm which is consistent with widespread clinical experience. Furthermore a dynamic preparation is highly sensitive to reduced load which occurs under high flow conditions. Although it is more demanding, the dynamic preparation provides superior information to the surgeon in predicting the behavior of arterial bypass grafts.