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Biomedical subjects

Kalyanam Shivkumar

Publications and source records attributed to Kalyanam Shivkumar.

34 records · Page 2Linked to original sources
PubMed2005

Beyond coronary sinus angiography: the value of coronary arteriography and identification of the pericardiophrenic vein during left ventricular lead placement.

OBJECTIVE: The purpose of this study was to define the role coronary arteriography (venous phase) for improving the success of left ventricular (LV) lead implantation and to define the value of identifying the pericardiophrenic vein for optimal LV lead placement in biventricular (bi-v) device implantation. METHODS: Seventy-seven patients underwent bi-v device implantation between July 2002 and October 2003. If the coronary sinus (CS) could not be accessed, then left coronary arteriography was performed during the same procedure. CS access was guided by venous phase images of the coronary arteriogram. The pericardiophrenic vein was identified by selective cannulation or direct visualization. Patients with Cr > 1.5 had gadolinium used as the contrast agent. RESULTS: Seventy-five successful implants were performed (97%). In seven patients (9%) repeated attempts at retrograde cannulation of the CS failed (attempt time 130 +/- 20 minute, mean +/- SD). In these patients, coronary arteriography helped define the location of the CS, which was subsequently successfully cannulated. In six patients the pericardiophrenic vein was identified either during occlusion venography of the CS (postthoracotomy, veno-venous collaterals, n = 2) or during selective cannulation of the pericardiophrenic vein (using a DAIG Csl catheter, n = 4). The vein was directly visualized in three patients who underwent surgical LV lead implantation. LV leads in all these cases were implanted in areas not overlying the preidentified pericardiophrenic vein. During follow-up, none of these patients had evidence of phrenic nerve stimulation. CONCLUSIONS: Intraoperative left coronary arteriography increases the success of CS cannulation. Identification of the pericardiophrenic vein is a useful method to avoid phrenic nerve stimulation.

Contrast Media↗
PubMed2004

Signal-averaged electrocardiogram in Ebstein's anomaly.

We sought to establish pathogenetic links between electrophysiology, histopathology, and ventricular tachyarrhythmias in patients with Ebstein's anomaly. The atrialized right ventricle (ARV) is the site of mechanically inducible ventricular tachyarrhythmias, but relations between the arrhythmogenic substrate, the type of tachyarrhythmias, and the trigger(s) have not been established. This study comprised 23 patients (10 men and 13 women; aged 18 to 58 years; mean 32 +/- 3) who did not undergo surgery and 6 pre- and postoperative patients with Ebstein's anomaly, diagnosed by transthoracic and transesophageal echocardiography. Twenty-one patients had classic Ebstein's anomaly and 2 had mild forms. Signal-averaged electrocardiograms (SAECGs) identified slow conduction by using 3 time-domain variables calculated by an automated algorithm and inspected visually. Two variables were required to establish the presence of late potentials. SAECGs were repeated in 6 patients after surgical exclusion of the ARV. Five surgical specimens of the ARV and the true right atrium were examined histologically. Mathematic simulations were used to illustrate anchored and unanchored spiral/scroll waves. SAECGs were positive in 21 patients with classic Ebstein's anomaly and were negative postoperatively in the 6 so studied. The ARV was characterized histologically by clusters of cardiomyocytes isolated within a fibrous matrix. We hypothesize that SAECGs identify slow conduction residing in the ARV, and that excitation of this arrhythmogenic substrate provokes spiral/scroll waves that cannot anchor because clusters of cardiomyocytes are isolated within a fibrous matrix. The waves meander erratically as polymorphic ventricular tachycardia or break up into ventricular fibrillation.

Adolescent↗
PubMed2004

The molecular basis of cardiac arrhythmias in patients with cardiomyopathy.

Cardiac arrhythmias are a leading cause of mortality and morbidity in Western society. In some specific instances, these arrhythmias are caused by abnormalities of cardiac ion channels, such as sodium, calcium, and potassium channels, which carry ionic currents and are fundamental determinants of cardiac excitability. Abnormalities of these ion channels are attributed to mutations in the genes encoding the channel protein and cause altered function of channels, which can predispose to arrhythmias. During heart failure, many channels also malfunction because of altered expression, resulting in lethal arrhythmias.

Cardiomyopathy, Dilated↗
PubMed2004

Percutaneous epicardial mapping during ablation of difficult accessory pathways as an alternative to cardiac surgery.

OBJECTIVES: The aim of this study was to define the role of percutaneous epicardial mapping for the ablation of previous failed ablation of accessory pathways. BACKGROUND: Cardiac surgery is the only curative option for failed radiofrequency (RF) catheter ablation of accessory pathway (AP)-mediated tachycardias. We investigated a combined percutaneous epicardial and endocardial approach for failed AP ablations. METHODS: We present our experience in a series of 6 cases (7 APs) with previous failed attempts at catheter ablation (median 2 attempts, range 1-4) and persistent symptomatic tachycardias. Endocardial mapping of the APs was performed using conventional techniques. Sites with local electrograms suggestive of AP location were selected. When initial endocardial mapping was not successful for ablation of the pathway, percutaneous transthoracic pericardial puncture was performed via a subxiphoid approach, and an ablation catheter was positioned at the epicardial aspect of the putative AP location for epicardial-endocardial electrogram comparison. Endocardial RF energy was applied to locations considered appropriate. Epicardial RF applications were delivered when endocardial applications failed. Coronary arteriography was performed to assess the proximity of coronary arteries to the ablation catheter. RESULTS: APs were located in the right free wall (4 patients, 5 APs) and the right (1 patient) and left (1 patient) posteroseptal regions. In all patients, epicardial mapping assisted in identifying successful ablation sites. In 3 patients, the earliest atrial activation during orthodromic tachycardia was present in an epicardial electrogram. Successful AP ablation was achieved with an epicardial RF application in 2 patients, either alone or with simultaneous endocardial-epicardial delivery. In the remaining 4 patients, APs were successfully ablated endocardially after epicardial mapping. These patients represent 18% of all cases referred to our institution for ablation of previously failed accessory pathways (6/32 patients). CONCLUSIONS: A combined endocardial-epicardial approach to mapping and RF ablation can facilitate successful endocardial ablation in most cases. In selected cases, APs can be ablated by epicardial delivery of RF. Epicardial mapping is an effective alternative to cardiac surgery for patients in whom prior attempts at AP ablation have failed.

Adolescent↗
PubMed2004

Catheter ablation of ventricular tachycardia guided by contrast-enhanced cardiac computed tomography.

We describe catheter ablation of recurrent ventricular tachycardia using high-resolution definition of a myocardial infarct scar by contrast-enhanced cardiac computed tomography (CT). Positron emission tomography scanning as well as three-dimensional electroanatomic mapping confirmed the extent of scar prior to ablation. Catheter ablation based on substrate mapping was successful in eliminating the ventricular tachycardia. Detection of scar by cardiac CT has the potential to abbreviate voltage/substrate mapping in the electrophysiology laboratory. To our knowledge, this is the first time myocardial scar was defined by cardiac CT and utilized for defining an ablation strategy for ventricular tachycardia.

Aged↗
PubMed2004

Electrophysiological characterization of cardiac veins in humans.

BACKGROUND: The coronary sinus is a complex structure with a surrounding myocardial coat and muscle bundles that course within it. The purpose of this study was to evaluate the electrical activity of the coronary sinus (CS), great cardiac vein (GCV) and related structures, such as the Vein of Marshall (VOM). METHODS AND RESULTS: Data obtained from adult ( n = 114) and pediatric patients ( n = 16) were analyzed. The width of atrial electrograms (EGMs) within the CS at a basic pacing cycle length of 600 ms was 46 +/- 7.4 ms (mean +/- SD) vs. 29.7 +/- 6.3 ms in the GCV ( p < 0.01). With decremental pacing the width of the EGM within the CS at 300 ms increased to 66.6 +/- 8.5 ms ( p < 0.1 compared to CS EGM at pacing cycle length of 600 ms). The width of the EGM within the GCV increased from 29.7 +/- 6.3 ms at a pacing cycle length of 600 ms to 34.6 +/- 6.0 at 300 ms ( p = NS). There were no significant differences in the atrial EGM width between CS and GCV in the pediatric patients. CONCLUSIONS: We conclude that atrial electrograms are wider in the CS but not in the GCV. This finding can be explained by the presence of a myocardial coat around the CS. The rate response characteristics of the atrial electrograms within the CS are consistent with a lack of tight coupling between muscle bundles and the CS musculature. Further, the absence of such differences in pediatric patients could partly explain relative differences in types of supraventricular arrhythmias seen in different age groups.

Adolescent↗
PubMed2004

Azygos vein lead implantation: a novel adjunctive technique for implantable cardioverter defibrillator placement.

High defibrillation thresholds (DFTs) occasionally are encountered during placement of implantable cardioverter defibrillators (ICDs). There are multiple strategies to lower DFTs in such patients, including reassessment of right ventricular lead position, alteration of the shock waveform, and implantation of subcutaneous arrays. This article describes a novel technique of implanting a high-voltage lead in the azygos vein. This procedure may serve as an adjunctive approach to reduce DFTs. The anatomic location of the azygos vein posterior to the heart provides a suitable shocking vector between the right ventricular electrode, a high-voltage lead placed in the azygos vein, and the ICD can.

Adult↗
PubMed2003

Determination of the upper limit of vulnerability using implantable cardioverter-defibrillator electrograms.

BACKGROUND: The upper limit of vulnerability (ULV) correlates with the defibrillation threshold and can be determined with 1 episode of ventricular fibrillation (VF). To automate the ULV in an implantable cardioverter-defibrillator (ICD), the most vulnerable intervals must be identified from an ICD electrogram rather than the latest-peaking surface T wave (Tpeak). We hypothesized that the recovery time (TR), defined as the maximum derivative (dV/dt) of the T wave of the shock electrogram, correlates with the most vulnerable intervals. METHODS AND RESULTS: We determined ULV, defibrillation threshold, and the most vulnerable intervals in 25 patients at ICD implantation. The ULV was the weakest T-wave shock that did not induce VF. The most vulnerable intervals were the ones associated with the strongest shocks that induced VF. Telemetered shock electrograms were stored on digital tape and differentiated offline to measure TR. Tpeak and TR were highly correlated (Tpeak-TR=-2+/-11 ms; rho=0.80, P<0.001). At least 1 most vulnerable interval timed between -20 ms and +20 ms relative to Tpeak in all patients and between -40 ms and +20 ms relative to TR in 96% of patients. CONCLUSIONS: The recovery time of shock electrograms provides accurate information about global repolarization. TR closely approximates Tpeak. The ULV method may be automated in an ICD by timing T-wave shocks relative to TR.

Aged↗
PubMedDate not supplied

Irreversible intrapulmonary vascular changes after pulmonary vein stenosis complicating catheter ablation for atrial fibrillation.

BACKGROUND: Pulmonary vein stenosis is a recognized complication of catheter ablation of arrhythmias emanating from the pulmonary vein; however, there is little information on secondary effects of pulmonary vein stenosis on lung tissue. METHODS AND RESULTS: A 55-year-old man with a history of paroxysmal atrial fibrillation refractory to antiarrhythmic medication had radiofrequency ablation in April 2003 and July 2003. Although these procedures were successful in resolving the patient's arrhythmia, they were complicated by the development of pulmonary vein stenosis of all four veins and pulmonary hypertension requiring patch annuloplasty of the pulmonary veins in October 2003. The patient was referred to our center for pulmonary vein stent placement in December 2003, June 2004, and August 2004, each time for recurrent hemoptysis. Due to persistent hemoptysis over the next several months, the patient underwent left lower lung lobectomy in September 2005. Microscopic examination of the lung showed marked medial thickening and intimal hyperplasia of large and small pulmonary veins and arteries, as well as focal organizing thrombi in the small arteries. The lung tissue showed extensive hemosiderin deposition indicative of prior hemorrhage. CONCLUSION: Chronic pulmonary vein stenosis after radiofrequency ablation of atrial fibrillation results in irreversible venous and arterial morphologic changes throughout the lung, including areas both close to, and remote from, the site of catheter ablation. Because there are persistent pathological changes remote from the ablation site causing the pulmonary hypertension, stenting the site of ablation to reopen large pulmonary veins may not be effective in treating the pulmonary hypertension.

Atrial Fibrillation↗