Yousuf Mahomed

Electrophysiologic evaluation of diaphragm by transcutaneous phrenic nerve stimulation

Phrenic nerve function was evaluated by transcutaneous stimulation in the neck and recording the diaphragmatic potential from surface electrodes placed at the ipsilateral seventh intercostal space (7CS) and the xiphoid process (XP). Simultaneous recordings from 7CS and XP electrodes connected together (XP-7CS) and each connected to a remote reference (knee-7CS and knee-XP) disclosed that the 7CS electrode was always more active and showed electropositive activity, whereas the XP electrode, which was only minimally active, showed electronegative response. Out-of-phase summation of opposite polarity activity at the two electrodes resulted in a higher amplitude response in XP-7CS derivation. Phrenic nerve studies are useful in establishing phrenic nerve injury following cardiothoracic operation. They may also provide evidence of phrenic nerve or diaphragmatic involvement in demyelinative neuropathies, motor neuron disease, and muscular dystrophies.

Early Experience with an Implantable Cardioverter

We tested the efficacy and safety of a fully programmable cardioverter weighing 95 g, in terminating sustained ventricular tachycardia. The device was implanted tranvenously under local anesthesia in seven patients. On command from a programmer or automatically, the cardioverter delivered shocks through a lead inserted to the apex of the right ventricle. It also served as a demand ventricular pacemaker and could perform programmed ventricular stimulation or overdrive pacing. Cardioversion of ventricular tachycardia required less than 0.5 J (mean) and was well tolerated by the patients, who were awake and not sedated. In one patient, a shock terminated ventricular tachycardia with the device in the automatic mode but produced atrial fibrillation with a rapid ventricular response that was intermittently recognized as ventricular tachycardia, triggering additional shocks. One such shock in the ST segment produced ventricular fibrillation that was terminated transthoracically in the emergency room, without residual impairment. We conclude from these preliminary observations that cardioversion of sustained ventricular tachycardia by means of an implantable catheter device is feasible, but for the present its use in the automatic mode must be cautious and selective. The units small size, ease of implantation, usefulness for noninvasive electrophysiologic studies, programmability, and bradycardia pacing functions are advantages. The next-generation device must be able to defibrillate and provide better differentiation of arrhythmias.

Postoperative Phrenic Nerve Palsy in Patients with Open-Heart Surgery

We prospectively studied patients undergoing open-heart surgical procedures to evaluate the role of phrenic nerve palsy in the causation of the high incidence of pulmonary complications reported in these patients. Although atelectasis, or infiltrates, or both developed in the left lower lobe of 98% of the patients (43 of 44) with or without similar changes on the right side, only 5 (11%) of the 44 patients had diaphragmatic dysfunction following operation. In 1, the left phrenic nerve became inexcitable; 2 had paresis of the left hemidiaphragm, and 2 had paresis of the right hemidiaphragm. Although damage to the phrenic nerve can occur during open-heart operations, a relatively low incidence of this complication does not support it as the major cause of postoperative pulmonary complications.

Left anterior descending coronary artery wall thickness measured by high-frequency transthoracic and epicardial echocardiography includes adventitia☆

High-frequency, 2-dimensional transthoracic echocardiography (HR-2DTTE) measurements of the left anterior descending (LAD) coronary artery wall thickness are larger than measurements obtained by intravascular ultrasound. We hypothesize that this difference is due to inclusion of the third vascular layer, which may represent adventitia by HR-2DTTE, and that this layer must be increasing in thickness with the development of atherosclerosis. We evaluated the contribution of this third layer to the wall thickness of the normal and atherosclerotic LAD artery imaged by HR-2DTTE using high-frequency epicardial echocardiography (HFEE) as the reference standard. Eighteen patients (10 men, mean age 62 years), 13 with coronary atherosclerosis and 5 with normal coronary arteries, referred for open-heart surgery, underwent preoperative HR-2DTTE evaluation of the LAD artery (SONOS 5500; 3- to 8-MHz transducer) and intraoperative HFEE of the LAD artery (SONOS 5500; 6- to 15-MHz transducer). Wall thickness was greater in patients with coronary atherosclerosis than in those with normal coronary arteries by both HR-2DTTE (1.9 +/- 0.3 vs 1.0 +/- 0.1 mm, p = <0.001) and HFEE (1.8 +/- 0.2 vs 1.0 +/- 0.2 mm, p = <0.001). On HFEE, the average intima plus media thickness was greater in patients with coronary atherosclerosis than in those with normal coronary arteries (0.78 +/- 0.3 vs 0.34 +/- 0.1 mm, p = 0.005). The average thickness of adventitia was also greater in patients with coronary atherosclerosis than in those with normal coronary arteries (0.92 +/- 0.2 vs 0.54 +/- 0.2 mm, p = 0.0005). HR-2DTTE and HFEE measurements of the wall thickness correlated well (r = 0.83 [reader 1], p <0.001; r = 0.61 [reader 2], p <0.01). A third vascular layer, which likely included adventitia, represents a significant portion of the LAD wall thickness imaged by HR-2DTTE and HFEE, and it significantly increases in thickness with the development of atherosclerosis.

Surgical Division of Wolff-Parkinson-White Pathways Utilizing the Closed-Heart Technique: A 2-Year Experience in 47 Patients

Kent bundle interruption for ventricular preexcitation has been successfully accomplished utilizing several different surgical techniques. The external closed-heart technique of Guiraudon combining surgical dissection and cryoablation has been used to interrupt 52 accessory pathways in 47 consecutive patients since May, 1985. The 35 male and 12 female patients ranged in age from 10 to 67 years (mean, 30 years). There were 25 left free wall, 13 right free wall, 13 posterior septal, and 1 anterior septal accessory pathways. Preoperative and intraoperative electrophysiological studies were performed in all patients to induce the arrhythmia and localize all accessory pathways. The operation consisted of dissection of the atrioventricular fat pad. Following this, the delta wave and retrograde accessory pathway conduction disappeared, thereby indicating successful pathway ablation. In 4 patients with right-sided accessory pathways, interruption of the pathway required cryoablation. Cryolesions (made with cryoprobe at -60 degrees C for two minutes) were created in the region of the accessory pathway insertion. All accessory pathways were successfully ablated without any deaths or heart block. Concomitant surgical procedures were performed in 4 patients. Two patients required a second operation the next day for an accessory pathway not found at the initial operation. Three patients had postpericardiotomy syndrome, and 4 had recurrent atrial fibrillation requiring therapy. The remaining patients have had no arrhythmia recurrence and have remained drug free after a follow-up of 1 month to 22 months (mean, 12.5 months). We conclude that the closed-heart technique of accessory pathway ablation is safe and reproducible, obviates the necessity for aortic cross-clamping and cardioplegic arrest, and allows instantaneous monitoring of conduction over the pathway.

Effects of hypothermia on short latency somatosensory evoked potentials in humans

Short latency somatosensory evoked potentials (SSEPs) elicited by median nerve stimulation were monitored in 14 adult patients undergoing cardiac surgery under cardiopulmonary bypass and induced hypothermia. SSEPs were recorded at 1-2 degrees C steps as the body temperature was lowered from 37 degrees C to 20 degrees C to determine temperature-dependent changes. Hypothermia produced increased latencies of the peaks of N10, P14 and N19 components, the prolongation was more severe for the later components so that N10-P14 and P14-N19 interpeak latencies were also prolonged. The temperature-latency relationship had a linear correlation. The magnitude of latency prolongation (msec) with 1 degree C decline in temperature was 0.61, 1.15, 1.56 for N10, P14 and N19 components, respectively, and 0.39 and 0.68 for interpeak latencies N10-P14 and P14-N19, respectively. The rise time and duration of the 3 SSEP components increased progressively with cooling. Cortically generated component, N19, was consistently recordable at a temperature above 26 degrees C, usually disappearing between 20 degrees C and 25 degrees C. On the other hand, more peripherally generated components, N10 and P14, were more resistant to the effect of hypothermia; P14 was always elicitable at 21 degrees C or above, whereas N10 persisted even below 20 degrees C. The amplitude of SSEP components had a poor correlation with temperature; there was a slight tendency for N10 and P14 to increase and for N19 to decrease with declining temperature. Because incidental hypothermia is common in comatose and anesthetized patients, temperature-related changes must be taken into consideration during SSEP monitoring under these circumstances.

Anomalous drainage of the right superior vena cava into the left atrium

A 22 year old man with asymptomatic hypoxemia was found to have a large right to left shunt due to a rare congenital anomaly: total drainage of the right superior vena cava into the left atrium. The anomaly was first suspected after radionuclide angiocardiography was performed using technetium-99m macroaggregated albumin and was confirmed by cardiac catheterization. Contrast echocardiographic and surgical findings are discussed. Other reports on this anomaly are reviewed.

Midterm Results of Ross Aortic Valve Replacement: A Single-Institution Experience

BACKGROUND We reviewed our institutional midterm experience to assess autograft and homograft hemodynamics and reoperative frequency after Ross aortic valve replacement. METHODS Between June 1993 and January 2009, 212 consecutive patients (mean age, 24.8 +/- 15.5 years; range, 1 month to 67 years) underwent Ross aortic valve replacement; 49% were younger than 19 years old. One hundred forty-two additional procedures were required in 101 of the 212 patients (48%) at the time of the Ross aortic valve replacement. One hundred ninety-three patients had isolated aortic valve disease, and 19 pediatric patients had more complex, multilevel left ventricular outflow tract obstruction. RESULTS There were 2 early (1%) and 2 late deaths (1%), with a mean follow-up of 7.9 +/- 4.2 years (range, 1 month to 15 years). Actuarial survival at 15 years was 98%. To date 28 patients (13%) have required reoperation. At 15 years, freedom from autograft sinus or ascending aortic dilatation was 79%, autograft dysfunction, 91%, autograft reoperation, 89%, and autograft replacement, 96%. Freedom from pulmonary allograft replacement was 96% at 15 years. CONCLUSIONS The Ross aortic valve replacement can be performed in children and adults with good midterm results. The late complications of autograft regurgitation, sinus or ascending aortic dilatation, can usually be corrected with a valve-sparing root replacement. These complications can often be prevented by (1) aggressive treatment of postoperative systemic hypertension, (2) replacement of a dilated ascending aorta at the initial Ross procedure, or (3) external fixation of the autograft annulus or sinotubular junction. The potential of late autograft insufficiency, ascending aortic and sinus dilatation, or homograft stenosis and insufficiency warrants annual follow-up.

Effect of omental, intercostal, and internal mammary artery pedicle wraps on bronchial healing☆

Bronchial transection and devascularization is necessary in the course of sleeve resection or lung transplantation, leaving distal bronchial segments ischemic and subject to stricture or dehiscence. Thirty mongrel dogs underwent left lung autotransplantation. The bronchial anastomosis was wrapped with omentum (n = 9), intercostal muscle pedicle (n = 9), or internal mammary artery pedicle grafts (n = 6). Six control animals underwent bronchial anastomosis without an external wrap. Bronchial revascularization by capillary ingrowth from the pedicle to the bronchial submucosal plexus was demonstrated with all three types of vascular pedicle grafts; however, more consistent and confluent vascular ingrowth was provided by internal mammary artery pedicle grafts. Additionally, the bronchial anastomotic cross-sectional area was significantly better in the internal mammary artery group (84.5 +/- 3.3) as compared with that of the omental (68.4 +/- 8.3), intercostal muscle (66.9 +/- 10.9), or control groups (70.2 +/- 7.6). An internal mammary artery pedicle graft and the presence of dense confluent submucosal vascular ingrowth from any pedicle graft were independently predictive (p less than 0.05) of minimizing bronchial anastomotic narrowing. These data are consistent with previous findings suggesting that omental and intercostal muscle pedicle grafts promote early bronchial revascularization; moreover, the data demonstrate the superiority of an internal mammary artery pedicle graft to provide submucosal vascular ingrowth and to minimize anastomotic stenosis.

Use of a Caval-Atrial Shunt for Resection of a Caval Tumor Thrombus in Renal Cell Carcinoma

Extraction of a tumor thrombus in the vena cava from a renal cell carcinoma is a technically demanding but gratifying procedure. We describe a technique for isolation of the superior vena cava during thrombus extraction using an inferior vena caval to atrial shunt.